safety in lpg design 2000

ExxonMobil

Safety in LPG Design

LHHA(CO) if filled by

Pipeline or by Ship

EBV

Tank Slope 1:100

min. 0.9 m

LPG

PRVLHHA

LI

LHAWater Draw-off to Location

min. 15 m from Fence

Removable Fill

Distance Valve to Fence15 m

Removable Part

to ESS

TIPI

Concrete Wall

First Edition byExxon Company, InternationalFlorham Park, New Jersey

ExxonMobilFairfax, VirginiaExxonMobil Proprietary Information

This manual was produced using Doc-To-Help® Version 4, WexTech Systems, Inc.

Revision History

First Edition - January, 1996Second Edition –October, 1999Third Edition ExxonMobil – March, 2001 now including Mobil EPT 15-T-02 and Mobil SCS Volumes 1 and 2

For future additions, suggestions and changes please contact either:

Detlef Robertz/CentralEurope/ExxonMobil@xom or

Herbert Pui-Shui Ho/HKPRCTWN/ExxonMobil@xom

Safety in LPG Design Contents i

Contents

1 PREFACE 1-11.1 Introduction 1-11.2 Objectives for Safety in LPG 1-2

2 PLANT SITE 2-12.1 Exposures from and to the Site 2-1

2.1.1 Planning Considerations and Criteria 2-12.1.2 Topography and Prevailing Wind 2-22.1.3 Road Access and Traffic Situation 2-2

2.2 LPG Plant Layout 2-22.2.1 Space Requirements 2-32.2.2 Equipment Spacing to Maximize Separation 2-4

2.3 Electrical Equipment Specifications 2-92.3.1 Electrical Area Classification 2-9

2.4 Emergency Shutdown System 2-15

3 BULK STORAGE 3-13.1 Storage in Plants and Industry 3-13.2 Mounded and Above Ground Storage 3-2

3.2.1 Dimensional Sizing of Drums 3-23.2.2 Materials Selection for Tanks 3-33.2.3 Design Basis for Mounded Drums 3-63.2.4 Testing Requirements 3-113.2.5 Horizontal “Bullets” and Spherical Tanks 3-123.2.6 Spill Containment 3-143.2.7 Vacuum Conditions 3-15

3.3 Refrigerated LPG Storage 3-153.4 Overpressure Protection for Tanks 3-16

3.4.1 Contingencies to be Expected 3-163.4.2 Refinery and Upstream Pressure Relief 3-173.4.3 Pressure Relief in Marketing Terminals 3-17

3.5 Emergency Block Valves on Bulk LPG Tanks 3-233.5.1 Tank EBV's in Liquid Service 3-233.5.2 Tank Shutoff Valves in Vapor Service 3-25

3.6 Tank Instrumentation 3-263.6.1 Tank Level Measurement 3-273.6.2 Pressure and Temperature Indicators 3-283.6.3 Grounding Connections for Tanks 3-293.6.4 Product Odorization 3-30

4 PUMPS & COMPRESSORS 4-14.1 Pumps 4-1

4.1.1 Pump Types Commonly Used 4-14.2 Compressors 4-11

4.2.1 Compressor Types Used 4-124.2.2 Compressor Sizing 4-14

ii Contents Safety in LPG Design

5 PIPING AND VALVES 5-15.1 Piping in Plants 5-1

5.1.1 Piping Arrangements 5-15.1.2 Piping Location 5-45.1.3 Piping Integrity 5-45.1.4 Pressure Ratings 5-55.1.5 Pipe Sizing 5-55.1.6 Pipe Connections 5-65.1.7 Small Piping Connections 5-75.1.8 Installation 5-8

5.2 Valves in Piping 5-95.2.1 Valve Integrity 5-95.2.2 Shutoff Valves 5-95.2.3 Backflow Check Valves 5-105.2.4 Thermal Relief Valves 5-105.2.5 Emergency Block Valves for Piping 5-115.2.6 Valve Packings 5-11

6 PRODUCT TRANSFER 6-16.1 Principles of Product Transfer 6-1

6.1.1 Loading or Unloading with Pumps 6-36.1.2 Loading or Unloading with Compressors 6-46.1.3 Using Pumps Versus Compressors 6-56.1.4 Static Electricity in Unloading and Loading 6-66.1.5 Hard Arms 6-66.1.6 Hoses in Product Transfer 6-8

6.2 Loading and Unloading 6-106.2.1 Truck Loading and Unloading 6-106.2.2 Rail Car Loading and Unloading 6-136.2.3 Marine Loading and Discharge 6-156.2.4 Marine Pier Installations 6-156.2.5 Pipeline Dispatch and Receipt 6-21

7 LPG CYLINDERS 7-17.1 Cylinder Purchasing Specifications 7-1

7.1.2 Cylinder Specifications 7-27.2 Cylinder Valve Purchasing Specifications 7-8

7.2.1 Manufacturing Design Standards 7-87.3 Regulator Purchasing Specifications 7-10

7.3.1 Manufacturing Design Standards 7-117.4 Hose Purchasing Specifications 7-13

7.4.1 Hose clips 7-147.5 Cylinder Filling Plant 7-157.6 Cylinder Filling 7-15

7.6.1 Cylinder Processing and Filling 7-167.6.2 Manual Filling System 7-177.6.3 Automated Filling System 7-177.6.4 Integrated Automated Filling Plant 7-227.6.5 Purchasing Guidelines for Filling Plants 7-307.6.6 Third Party Cylinder Filling Plant 7-33

7.7 Cylinder Distribution 7-337.7.1 Distribution Center 7-337.7.2 Dealer and Reseller Cylinder Storage 7-35

8 FIRE PROTECTION 8-18.1 Passive and Active Fire Protection 8-1

8.1.1 Fireproofing, a Passive Fire Protection 8-18.1.2 Fire Resistant Coatings 8-2

Safety in LPG Design Contents iii

8.2 Fire Protection System Design Philosophy 8-78.2.1 Firewater System, an Active Fire Protection 8-88.2.2 Protection Requirements 8-168.2.3 Flammable Gas Detectors 8-198.2.4 Fire Detectors 8-20

9 TRANSPORTATION 9-19.1 Means of Product Movement 9-19.2 Road Bulk Transportation Equipment 9-1

9.2.1 Truck Design and Procurement 9-19.2.2 Basic Design Considerations 9-29.2.3 LPG Truck Discharge System 9-7

9.3 Road Cylinder Transportation 9-119.4 Rail Tank Cars 9-129.5 Marine 9-13

10 CUSTOMER INSTALLATIONS 10-110.1 Cylinder Bank Installations 10-1

10.1.1 Design of Cylinder Banks 10-110.1.2 Installation of Cylinder Banks 10-210.1.3 Vaporization Rate in Cylinders 10-210.1.4 Icing or Sweating on Cylinders. 10-5

10.2 Containers at Customer Sites 10-510.2.1 Spacing and Location of Containers 10-510.2.2 Designing Customer Storage Systems 10-710.2.3 Sizing Of Containers and Vaporization Rates 10-810.2.4 Sizing Containers for Vaporizing Liquid 10-910.2.5 Enforced Vaporization by Means of Vaporizers 10-1210.2.6 Installation of containers 10-1410.2.7 Container Fittings and Piping 10-1710.2.8 Container Valves and Accessories 10-18

11 AUTOMOTIVE LPG 11-111.1 Automotive LPG Stations 11-1

11.1.1 Design of Automotive LPG Equipment 11-1

12 LPG PROPERTIES 12-112.1 Product Properties 12-112.2 LPG Hazards 12-5

13 GLOSSARY OF TERMS 13-1

Safety in LPG Design PREFACE 1-1

1 PREFACE

1.1 IntroductionThe manual is primarily intended for assisting managers and engineers responsible fordesign, construction, or modification of LPG facilities. It should also be useful as aready reference for members of management who have a need to understand LPGequipment and design practices.

The LPG guidelines included in this manual are intended for application to newconstruction or alterations to existing facilities. The manual covers guidelines for thesafe receipt, storage, loading, transport, and unloading of LPG for refining, upstream,and marketing bulk storage, as well as marketing cylinder filling plants and depots. Themanual is not intended to cover refinery onsites, upstream gas plant facilities, oroffshore platforms. Design practices among the functions are quite similar, although ina few cases some differences appear due to the scale of operations in refineries orupstream plants compared with marketing plants. These are noted. When deviationsfrom the guidelines become necessary they should receive safety review and approvalby the country/cluster.

If local regulatory requirements or current country/cluster practices are morerestrictive, however, they will of course supersede the guidelines described herein.Local regulations have to be followed as a minimum.

The manual references EMRE Global Practices (GPs), EMRE Design Practices (DPs)and ExxonMobil Engineering (EMRE) reports. GPs are typically referenced to providedetail on the implementation of design concepts. Within GPs, individual paragraphs areidentified as to their purpose, i.e. safety, operability, reliability, maintainability, etc.Deviation from “safety” paragraphs should receive formal safety review and approval.The lead design engineer would control deviation from “other” paragraphs. DPs arereferenced to provide considerations for design. Their application requires engineeringjudgment and the lead designer should determine when deviations require formal safetyreview. EMRE reports are referenced to provide additional design considerations onspecial topics. The lead design engineer should determine their applicability byreviewing or contacting EMRE.

Industry standards used in this manual include NFPA (National Fire ProtectionAssociation), LPGA (Liquefied Petroleum Gas Association), API (American PetroleumInstitute), NPGA (National Propane Gas Association), and IP (Institute of Petroleum,UK).

The material contained in this manual is considered “Proprietary” and its distributionlimited according to company procedures for safeguarding proprietary companyinformation. If there is a strong business reason to give portions of the material tocustomers or contractors, only the minimum portion containing pertinent informationshall be released.

1-2 PREFACE Safety in LPG Design

Quality Assurance

Whenever possible, equipment for LPG Marketing applications should be purchasedfrom manufacturers who have submitted their product to a recognized governmental orindependent laboratory for analysis, evaluation, and performance testing in LPG service,and have been granted approval as indicated by listing and/or labeling. Organizationsperforming or sponsoring the type of testing recommended include US UnderwritersLaboratories, the UK Board of Trade, Lloyds Underwriters, the German BAM(Bundesanstalt für Materialprüfung) or similar institutions, which are widely recognized.It is desirable to have selected equipment covered by a testing program that providesperiodic quality assurance of the manufacturer that design, materials, and procedures areunchanged from the initial approval. The Underwriters Laboratories listing programincorporates this feature.

Approved LPG equipment will often be available for standard Marketing equipment,e.g. cylinders, cylinder valves, filling equipment, small pumps and seals, and regulators.Equipment for larger scale LPG operations in refining and upstream is often notsubmitted for formal LPG approval, because it is manufactured in accordance withindustry standards for hydrocarbon service, which includes LPG. When equipment hasnot been approved for LPG, its mechanical design and materials of constructionreviewed by the project engineer, with input from specialists when necessary, todetermine suitability for LPG use, and to ensure that the device will functionsatisfactorily for the intended service life.

The conversion of valves and accessories originally designed and fabricated for anotherservice is not recommended. All valves and accessories shall be supplied by themanufacturer as assembled and tested at the factory, without subsequent modifications

1.2 Objectives for Safety in LPGFollowing are objectives to maintain high standards of equipment design and operations.

1. Minimize or eliminate LPG incidents

2. Develop and coordinate inter-functional LPG safety training programs.

3. Monitor regulatory trends.

4. Update manuals at regular intervals.

5. Publish information on lessons learned from incidents that occurred in thecompany or industry.

Procedures for LPG

Inter-functional training programs for LPG safety have been developed and coordinatedthrough the LPG Safety Network.

The LPG design guidelines contained in this manual are based on current ExxonMobiland industry design philosophy and practices, and on the results of company LPG riskassessment programs. Where differences exist between country/cluster design practicesand those presented in this manual, it is suggested that country/cluster managementconsider adopting the practices described herein. ExxonMobil issues this manual to itscountry/clusters for suggested use in design of Liquefied Petroleum Gas (LPG) facilitiesused in Upstream, Refining and Marketing operations. Relevant aspects of safety forLPG design are documented in this third edition (2001) of the “Safety in LPG Design”manual. LPG safety design and operations manuals will be updated on a 3-yearly basis.More urgent updates will be communicated through the LPG Safety Network andthrough the BestNet. Recommended changes to guidelines and practices will bedeveloped as appropriate.

Safety in LPG Design PREFACE 1-3

New directives and standards are coming from legislative bodies and industrialassociations, which every nation is directed to follow. Regulatory developments will becontrolled by following the OIMS systems.

Distribution of industry and company incidents and lessons learned will be done on atimely basis through the LPG Safety Network.

Responsibilities

ExxonMobil LPG Technical Advisors provide guidance and assistance to help plants toimplement procedures and practices described in the LPG manuals and solve theirproblems. The ExxonMobil LPG Advisors are primary contacts for Marketingcountry/cluster LPG issues such as incidents and lessons learned, training needs,suggested revisions to LPG safety manuals. They attend industry LPG meetings,monitor technical and regulatory trends, evaluate changes in industry procedures andpractices for applicability. They communicate to the country/clusters as appropriate.Representatives from Upstream, Refining, Marketing, and Marine will have an influenceon company LPG standards reflected in the “Safety in LPG Design” and “LPG SafeOperations Guidelines.” Ultimate decisions on technical issues will be made by theExxonMobil LPG Technical Advisors and ExxonMobil Research and Engineering.

Verification and Feedback

Yearly verification of SHE performance of LPG operations by the SHE organization.Summary of incidents, lessons learned. Identify areas for system improvement andimplement.

Safety in LPG Design PLANT SITE 2-1

2 PLANT SITE

2.1 Exposures from and to the SiteBefore choosing a plant site it is important to study all relevant facts that may be ofinfluence on the choice. Such items of influence are exposure to and from theneighborhood, topography, prevailing wind direction and the road traffic situation.

It is considered appropriate to locate an LPG plant in an industrial zone. The plants inthe neighborhood may preferably be refineries or storage plants or similar industrieswhere ignition sources are rare or under control. Therefore, neighborhood to any type offacility which incorporates obvious ignition, sources, or which employ hazardousprocessing methods (e.g. storing powerful oxidizing agents), shall be avoided. If knownexposures are more severe, increased clearances may be necessary.

Warning signs “NO SMOKING,” “FLAMMABLE GAS” shall be posted at allLPG handling areas and outside the gate. The locations of the signs shall bedetermined by local conditions, but the lettering shall be large enough to be visible andlegible from each point of transfer.

2.1.1 Planning Considerations and Criteria

The input data required to start the design of an LPG system shall be available from theExxonMobil marketing unit responsible for the proposed facility. This data shallinclude the following:

1. Products to be handled and peak volumes in bulk and in cylinders.

2. Total storage capacity required for each product.

3. Requirements of local government agencies with jurisdiction.

4. Allowances for future expansion.

5. Product sampling requirements.

6. Toxic materials in plant.

7. Site data including limitations or restrictions.

8. Possibility of storage and handling of other petroleum products within thefacility.

9. Evaluation of any surrounding external hazards at the site.

10. Capacity and frequency of each type of LPG delivery to the site from tanktrucks, railroad cars, marine vessels and pipelines.

11. Number of tank truck or railroad tank car unloading positions required.

12. Maximum and minimum flow rates for each type of equipment.

2-2 PLANT SITE Safety in LPG Design

13. Method used to verify quantity of shipment: weight, volumetric measurementor meters.

14. Types of unloading pumps or compressors carried by transporting equipment.

15. Number, size and type of connections on transporting equipment.

16. For cylinder filling, the type, number and layout of scales, and the size,number and type of cylinders to be filled.

17. Cylinder painting, stenciling, washing and testing facility requirements. Ifpossible, this task should be contracted to third party companies.

18. Method of receipt, storage and handling of cylinders: Manual handling orpalletization, forklift, hand truck or other.

2.1.2 Topography and Prevailing Wind

Considering the basic characteristics of LPG vapor, it is desirable to locate a plant in anarea which is free of depressions and contours radiating from the plant which mightconvey vapors to a point of exposure.

In the event of an accidental discharge of product within the plant, LPG tends tovaporize rapidly. Dissipation of vapors below the lower flammable limit developsmore rapidly if the plant site is elevated slightly above the general terrain, or is slightlyinclined. Dissipation of vapors in a flat location will mainly depend on wind or time. Inlow-lying areas vapors may stay trapped despite wind. This potential shall beconsidered in connection with gas leaks.

Any site considered for a marketing plant shall be analyzed with respect to theprevailing wind direction. Prevailing winds may have an influence on potentialexposures. Based on prevailing wind, sites shall, whenever possible be located downwind (meteorological data) of population centers or known ignition sources. Tanks shallalways be located downgrade and downwind from possible ignition sources.

2.1.3 Road Access and Traffic Situation

Any streets adjacent to the plant site shall be analyzed to determine that a safe trafficflow in and out of the plant is possible. The access road shall be of such width thatvehicles could enter and leave the plant without creating a hazardous condition.Consideration shall be given to the traffic conditions on the access road during peaktraffic flow in and out of the plant. Visibility, which is influenced by road curves etc.,may play an important role in these considerations.

2.2 LPG Plant LayoutFollowing are some concepts that govern the layout/plot plan of the bulk LPG storagefacilities.

Bulk LPG Tanks shall be located together to minimize piping and general site size.Before the final location for bulk storage is selected, a site survey shall be conductedand if deemed necessary, soils investigation shall be done. It should be defined whetherthe storage is above or below ground and whether cylindrical or spherical tanks shall beused. These investigations shall provide sufficient data on the bearing capacity,drainage characteristics, estimates of settlement, and remedial measures, if necessary.Future expansion plans shall also be considered. Bulk transports that discharge orreceive product within the plant shall be provided with a clear access through the plant,which can be negotiated without, at any time, reversing the unit. Sufficient space shallbe provided at a loading or unloading location to allow for positioning the transport withminimal chance of collision with other vehicles or fixed objects. Loading or unloading


facilities shall be protected with guardrails or stanchions to prevent damage fromvehicles. Vehicles shall be facing an exit while loading or unloading.

Pipeline or marine loading and discharge operations will utilize the least amount ofland since pipelines need only metering and control equipment and ships need onlyshore-based compressors for the unloading operation. However, a considerable amountof waterfront space shall be allocated for marine berth(s). With product delivered byrail tank car, sufficient space shall be allotted to the rail line and the racks andcompressors for the unloading operation.

Pumps and compressors shall be grouped together and arranged such that the pipingis as simple and direct as possible. Electrical control panels and other supportequipment shall be located in accordance with the electrical area classifications.

Figure 2.1 a: - Example for plant layout in sloped terrain

The Cylinder Filling Plant, with storage area, loading dock and access area, shall belaid out to ensure:

1. Optimum traffic pattern/parking for cylinder transport trucks.

2. Minimum interference between truck and fork lift traffic.

3. Clear separation of filled/empty cylinders.

4. A minimum of necessary cylinder handling. Cylinders should “flow” fromthe empty to filled area.

5. Optimize natural ventilation by positioning the cylinder filling plant such thatnatural air currents will be utilized in the most effective manner.

6. A separate area is designated for cylinders requiring repair or refurbishment.

2.2.1 Space Requirements

Space requirements will normally incorporate the following functions:

1. Gate house and security fence.

2. Administration and Control Building.

3. Bulk product receiving and dispatching areas, including weighbridge.

4. Tank truck loading and unloading area with access roadway.

5. Railroad siding, including loading and unloading area.

6. Tanker or barge loading or unloading facilities.

7. Stenching facilities for odorization of the LPG.


8. Bulk product storage.

9. Cylinder handling and storage (new, empty, filled, scrapped, truck parking).

10. Cylinder filling and inspection processes.

11. Other fuels storage or manufacturing facilities.

12. Pumps and compressors for loading and unloading trucks, rail cars, tankersand barges.

13. Pumps normally used for filling cylinders.

14. Cylinder repair and re-qualification processes (if located in filling plant).

15. Maintenance shop and warehouse.

16. Storage area for reserve supply of cylinders and customer containers.

17. Staff, customer and plant vehicle parking areas.

18. Fire water systems.

19. Firefighting access.

All of the above should be interrelated to the spacing requirements which are discussedbelow. A qualified company outside the filling plant may preferably carry out thecylinder repair and re-qualification process.

Figure 2.1-.b: Filling plant with unloading rack, tanks, pump/compressor house and filling area

2.2.2 Equipment Spacing to Maximize Separation

The most important objective of spacing is to separate risks by zoning. The higher arisk, the larger the spacing. Spacing requirements between tanks will help to limit thespread of fire, should it occur. In case of accidental leakage, spacing betweenequipment and the fence will help to disperse flammable mixtures below lowerflammability limits (LFL) such that ignition by uncontrollable external ignition sources(e.g. passing cars) may be prevented. Another aspect that influences spacing is therequirement for safe access of the operator to perform an emergencyshutdown/activities but also for normal operations and maintenance. Also trafficpatterns for truck and rail loading shall be considered. The safe location of the controlroom and firefighting pumps may be of importance during an emergency.

The equipment spacing requirements detailed below are minimum figures, which ingeneral will satisfy the above objectives. Whenever a special consideration or particularfactors (e.g. plot space available) require deviation from the spacing rules a safetyspecialist shall perform a risk assessment. Additional safety and firefightingequipment requirements may compensate for a lack of spacing. So, if for instance, LPGis stored in vicinity to housing, passive fire protection may be the answer to reducing therisk. This may be achieved by mounded storage of the tanks.


Where sufficient space is available, the ground can be contoured and sloped such thatthe liquid from a potential leak will flow away from the storage tank to a remotelocation. In case of a subsequent fire, this would be desirable since the liquid from theleak would burn at a place away from the tank. Admittedly for Propane and hot climatesthis is not a major mitigation factor since the bulk of the leaking gas will flash right atthe leak. But for Butane and colder climates it may mitigate the situation considerably.

2.2.2.1 Spacing at Refining and Upstream Gas Plants

Spacing of storage and loading and unloading facilities at Refining and Upstream GasPlants shall be in line with spacing requirements documented in the Design Practices DPXV-G, “Equipment Spacing” and GP 9-1-1, “Spacing and Dikes for Storage Vessels andTanks.”

2.2.2.2 Spacing Requirements for Marine Berths

Planning for Marine berths requires considering a number of issues affecting spacing.Generic marine issues such as berth layout, approaches to the berth, dredging etc. mayaffect the location of the berth and spacing requirements regarding other shore-basedfacilities. Information on such issues is available in the Marketing Engineering StandardEE.3M.86 “Marine Facilities, Design, Specification and Evaluation.” If multiple LPGberths are planned, additional spacing considerations between berths shall be taken intoaccount. The minimum spacing criteria for fire and safety considerations is 30 m.However, in most cases, other plant design considerations shall require berth spacinggreater than 30 m. More detailed descriptions of such considerations and additionalcommentary is provided in the ERE report EE.131E.79 “Suggested DesignConsiderations for Refrigerated Liquefied Gas Facilities.” Additional clarifications areprovided in “Clarifications of Recommendations Arising from the ‘Betelgeuse’Incident” (83 EEEL 514 or 83 CMS3 R9). EMRE's Marine Section should be consultedfrom the early stages of the project to ensure that the appropriate issues have beenconsidered regarding berth layout and spacing.

2.2.2.3 Spacing at Marketing Plants

Spacing to the property line for Marketing Plants is consistent with API 2510, asindicated in the table below. Marketing plants may store considerably smaller volumesof LPG than Refineries or Upstream sites.

Individual TankCapacity, m3 8 - 110 < 260 < 340 < 450 < 760 < 3800 > 3800

Spacing toProperty Lines, m 15 20 30 40 60 90 120

Table 2.2.2.3-a: Spacing to property lines

At some locations, where risk exposure is considerably lower than usual the designengineer may deviate from the spacing requirements. A typical example would be amarketing plant on a riverbank surrounded by industrial plants (no housing). Whenadditional storage is required at existing sites, and the spacing guidelines cannot be met,risk assessment techniques may be used to evaluate reduced spacing. As explainedearlier, compensation for reduced spacing may be achieved by adding active/passive fireprotection. The ExxonMobil LPG Technical Advisor or an EMRE Safety Engineershould be consulted when planning to deviate from spacing requirements. The rationalefor deviating shall be documented in the design memorandum.

In addition to property line spacing, Marketing sites have other spacing guidelines notcovered by DP XV-G. Additional guidelines, as well as spacing from DP XV-Gcommonly applied at Marketing plants, are covered by the following table.


Spacing Distances,

in Meters

Pro

per

tyL

ines

Off

ice

Bu

ildin

g

Cyl

ind

erF

illin

g

Lo

adin

g,

Un

load

ing

Sp

her

e

Ho

rizo

nta

lB

ulle

t

Mo

un

ded

Tan

k

Pu

mp

or

Co

mp

ress

or

Sphere Note 1 30 30 30 Note 2 Note 3 Note 6 Note 9

Horizontal Bullet Note 1 30 15 15 Note 3 Note 4 Note 7 Note 10

Mounded Tank Valving 15 15 15 15 Note 3 Note 5 Note 8 5

Mounded Tk. Covered Part 3 3 3 3 Note 6 Note 7 Note 8 3

Truck Loading/Unloading 30 30 30 15 30 15 3 3

Rail Unloading/Loading 15 30 30 15 30 15 3 3

Cylinder Filling 30 30 Note 11 30 30 15 Note 12 5

Firewater Tank or Pump Note 11 Note 11 30 30 30 30 Note 12 30

Table 2.2.2.3-b: Spacing within Marketing LPG bulk storage plant

1. Note 1: Above ground tank spacing from property lines according tothe above Table 2.2.2.3-a: Spacing to property lines.

2. Note 2: ¾ Diameter of larger sphere.

3. Note 3: ¾ Diameter of sphere.

4. Note 4: 1 Diameter of larger bullet (or 1.5 m min.).

5. Note 5: 1 Diameter of bullet.

6. Note 6: At sphere bund wall.

7. Note 7: Next to bullet toe wall.

8. Note 8: Spacing between mounded drums does normally not involveany fire hazard considerations, therefore, the following isrecommended:a. Tanks up to 135 m3 water capacity shall have a minimum

spacing of 1.5 m between the tanks.b. Tanks over 135 m3 water capacity: The site conditions and

the needs for safe installation, testing, maintenance, andremoval shall determine the spacing between adjacenttanks.

9. Note 9: Pumps, compressors, and other equipment (including pipingnot related to LPG tanks) shall be outside bund walls.

10. Note 10: Pump drawing from individual bullet may be outside toe walland minimum 3 m from bullet. Other pumps or compressors5 m.

11. Note 11: No minimum. Provide spacing appropriate for access.

12. Note 12: From drains, vents, and valving or flanges 15 m; fromcovered part of mounded drum 3 m.

For spacing to atmospheric storage of other fuels or refrigerated storage see GP 9-1-1.Spacing of groups or “stacks” of cylinders to the property line is discussed in Chapter7. Dikes spacing to spheres shall be according to GP 9-1-1 “Spacing and Dikes forStorage Vessels and Tanks.” Toe wall spacing to shell of bullet shall be 3 m. Also referto section 3.2.6 “Spill Containment.”


Minimum DistancesFlammable Liquid

Storage TankBullet up to 135 m3 Bullet over 135 m3

Flash Point lowerthan 37 oC

6 m to bund wall 15 m to bund wall

Flash Point from 37to 65 oC. Tank sizeup to 3,000 liters

Safety distances for LPGtank or 3 m to the tank /bund wall, whichever isthe less

6 m to tank, bund wallor diversion wall

Tank size over 3,000liters

3 m to bund wall ordiversion wall and 6 m totank

15 m to tank, bund wallor diversion wall

Table 2.2.2.3-c: Minimum separation distances for LPG horizontal tanks (bullets) from otherflammable liquid storage

Non pressurized hazardous and FlammableStorage Tank Type and Product

Minimum separationdistances

Refrigerated LPG Tank ¾ diameter of the largertank or sphere

Storage Tank with product flashpoint 37 oCor less

1 diameter of the largertank or sphere

Storage Tank with product flashpoint morethan 37 oC

½ diameter of the largertank or sphere

Table 2.2.2.3-d: Minimum separation distances for LPG sphere tanks from other flammable liquidstorage.

LPG tanks shall not be installed within the bunded area for flammable or combustibleliquid storage tanks. The minimum distances of separation between a LPG horizontaltank and a storage tank containing a flammable liquid shall be according to Table2.2.2.3-c. For LPG spherical tank and a tank containing flammable liquid, Table2.2.2.3-d shall be used. Open drains, gullies or ducts located within the tank safetydistances in Tables 2.2.2.3-a and b, carrying water runoff from the ground underneathaboveground LPG tanks shall be provided with an LPG trap or be sealed to prevent LPGliquid and vapor from passing through.

No permanent source of heat shall be located within 1.5 m of a LPG tank. LPG tanksshall not be located directly beneath electrical power cables. LPG tanks shall be locatedsuch that a break in overhead electrical lines shall not cause exposed ends to fall ontoany tank or equipment. No horizontal separation shall be required between anaboveground LPG tank and underground tanks containing flammable or combustibleliquids installed in accordance with NFPA 30.

If, in industrial installations, LPG and oxidizing gases or hydrogen are stored on thesame premises, the following minimum distances shall be observed:

Chlorine LPG 300 mOxygen* (> 0.75 t) LPG (> 1.9 m3) 15 mGaseous Hydrogen* (> 7 kg) LPG (> 1.9 m3) 15 m*see NFPA 58 for smaller capacities


RAILWAY

GATE

OFFICEBUILDING

FIREPUMPS

FIRE

WATERTANK

Propane Loading

SPHERE

Dike

RAIL CARS15 m

Butane Loading

One Way

EMPTYCYLINDERS

FILLEDCYLINDERS

CYLINDERFILLING

min.3 m

MOUNDEDTANK

Distance dependson drum size

Earth Mound

min. 15 m

Dependingon Tank Size

15 m

3/4 SphereDiameter

one

bulle

t dia

met

er

BU

LLE

T

min. 15 m fromLPG bulk storagemin. 30 m from

Sphere or Bullet

min

. 15

m fr

om m

anho

le o

f Mou

nded

Dru

m

min

. 30

m fr

om S

pher

e/B

ulle

t or

Cyl

inde

r fil

ling

30 m30

m

30 m

Pumps or compressors must be outside spill containmentand may be 3 m away from tanks they take suction from, but 5 m from other tanks (like next bullet or next sphere dike)

min

. 15

m

MOUNDEDTANK

BU

LLE

T

Toe Wall

Dep

endi

ngon

Tan

k S

ize

Dep

endi

ngon

Tan

k S

ize

ElectricalInsulation

RemoteImpoundment

Figure 2.2.2: Spacing in marketing LPG bulk plant with cylinder filling

2.2.2.4 Siting of Aboveground Tanks and Equipment

Pressurized LPG tanks shall not be located within buildings, within the spill containmentarea of flammable or combustible liquid storage tanks as defined in NFPA 30, or withinthe spill containment area for refrigerated LPG tanks.

Rotating equipment and pumps taking suction from the LPG tanks shall not be locatedwithin the spill containment area of any storage facility.

Horizontal tanks used to store LPG may be oriented so that their longitudinal axes donot point toward other tanks, process equipment, control rooms, loading or unloadingfacilities, or flammable or combustible liquid storage facilities located in the vicinity ofthe horizontal tank.

Horizontal LPG tanks shall not be stacked one above the other. Horizontal tanks usedto store LPG shall be grouped with no more than six tanks in one group. Where


multiple groups of horizontal LPG tanks are to be provided, a minimum horizontal shell-to-shell distance of 15 m shall separate each group from adjacent groups.

2.3 Electrical Equipment SpecificationsElectrical equipment and wiring shall comply with the specifications of, and be installedin accordance with the requirements of the local electrical codes. For reference onreliability in electrical design, see the related electrical GPs.

2.3.1 Electrical Area Classification

Normal electrical equipment can be considered an ignition source. Therefore, whereflammable liquids, gases or vapors are handled, or stored, special electrical equipmentshall be installed, which normally will not serve as an ignition source. The industry hasproduced standards to differentiate the ignition potential of electrical equipment.Following are the levels of protection:

1. Equipment that will never produce a spark, even if it fails.

2. Equipment that, when operating normally, will not produce a spark, but maydo so if it fails.

3. Equipment that will produce a spark during normal operation.

The likelihood of encountering flammable vapors in plants governs the level ofequipment needed. Plants shall be divided into separate areas according to thelikelihood of flammable LPG vapors being present.

FILLING HOSE

FLAMMABLEVAPORS

FLAMMABLE

Figure 2.3.1-a: Example for Zone 1 area

Based on experience, minimum distance requirements between points of potential gasrelease and electrical installations have been developed. These minimum distancerequirements are defined in both NFPA 497A and API 500. Classifications used in LPGand other Hydrocarbon service are called Zone 0, Zone 1 and Zone 2 distances. Zone 0is an area where an explosive gas atmosphere is continuously present, or present for along period. Definition of Zone 1 and 2 follow below. Different Zones require differentquality electrical installation. Areas that require no special electrical equipment arecalled “Unclassified.” Following are definitions for the electrical classification areas.

Zone 1 areas are defined as locations where ignitable concentrations of flammable gasesor vapors are likely to occur in normal operation. Below grade spaces such as trenches,


pits and sumps are typical Zone 1 areas. This may be by frequent releases or byinfrequent releases or small releases combined with inadequate ventilation. TheExample in Figure 2.3.1-a shows a solvent drum filling area, for LPG it would bearound the filling nozzles.

FLAMMABLE VAPORS

PUMP SEAL LEAK

VAPORIZING LIQUID

Figure 2.3.1-b: Example for Zone 2 area

Zone 2 areas are defined as locations where an ignitable concentration of flammablegases or vapors is not likely to occur in normal operations. If it does occur it will beinfrequent and will exist for a short period. Examples for Zone 2 are areas adjacent toZone 1 (and not separated by a vapor barrier), areas normally prevented from explosivemixtures by positive ventilation, and areas where abnormal operation or equipmentbreakdown might create an explosive mixture.

Figure 2.3.1-c: Example for Unclassified area

Unclassified is defined as locations where there are little or no hazards from flammablegases or vapors under normal or abnormal operating conditions. Plant roads, adequatelyventilated LPG cylinder storage areas, and maintained, adequately ventilated pipingsystems, which may include valves, fittings, meters and flanged or threaded connections(per GP 16-1-1) are examples of unclassified areas.


Following selected example drawings from NPFA 497A showing how the electricalclassifications apply. It is important to notice that they also include the space above thepotential leak source. The hatched areas indicate that in these spaces only certified(Zone 1 or 2) electrical equipment can be installed.

7.5 m

15 m

30 m

0.6 m

7.5 m

7.5 m

BELOW GRADE LOCATIONSUCH AS A SUMP OR TRENCH

SOURCE OFPOTENTIAL LEAK

UNCLASSIFIED

UNCLASSIFIED

UNCLASSIFIEDADDITIONAL ZONE 2 AREAZONE 1 ZONE 2

Figure 2.3.1-d: Electrical classification area around pump seal.

The contour of the envelope roughly approximates the flow that gases may follow incase of leak. It is important to notice that the complete area below a potential leak isconsidered classified. However, if a vent exits through a roof the hemisphere of a 7.5 mradius may be considered Zone 2 area. Pits and trenches, unless ventilated by force,shall be considered as Zone 1 areas. The outer 0.6 m Zone 2 region in the figure aboveis additional area to reflect crawling of heavier-than-air vapors along the ground. Thisarea would normally be included for LPG applications, as explained in NFPA 497A.

7.5 m

15 m

30 m

0.6 m

7.5 m

7.5 m

BELOW GRADE LOCATIONSUCH AS A SUMP OR TRENCH

SOURCE OFPOTENTIALLEAK

UNCLASSIFIED

UNCLASSIFIED

UNCLASSIFIEDADDITIONAL ZONE 2 AREAZONE 1 ZONE 2

Figure 2.3.1-e: Electrical classification area around an elevated source of potential release

Notice that a sump on a pier is a Zone 1 area due to potential collection of vapors. At aPier the Zone two area extends to the water level. Electrical installations are rarelyfound below the pier level but this may be important for small vessel traffic.


The area around the valves of rail cars and trucks is Zone 1 because of frequent makingand breaking of loading and unloading connections. Depending on conditions, a 7.5 mdiameter zone may be required around the pressure relief valve as indicated in the truckdrawing.

7.5 m

15 m

7.5 m

UNCLASSIFIED

UNCLASSIFIEDZONE 1 ZONE 2

15 m

7.5 m

15 m

SUMP

7.5 m

0.6 m

PIER

WATER LEVEL

Figure 2.3.1-f: Electrical classification area around marine unloading facility

2.3.1.1 Electrical Codes

The US National Fire Protection Association Codes #70 (National Electrical Code) and#58 (LP-Gas Code), or UK Institute of Petroleum “Model Code of Safe Practices in thePetroleum Industry,” Parts 1, (Electrical) and 9, (Liquefied Petroleum Gas),supplemented by Health and Safety Executive publications HSG 34, “The Storage ofLPG at Fixed Installations” and HSG 22, and British Standard 5345 are commonly usedas the design basis for electrical systems.

7.5 m1.5 m


Figure 2.3.1-g: Electrical classification area around LPG rail car


.

Truck ESS

EBV

EBV

ElectrostaticBonding Cable

Truck ESS

Truck PRV


1.5 m

7.5 m

7.5 m

Figure 2.3.1-h: Electrical classification area around LPG truck

StandardContinuous

HazardIntermittent

Hazard

Hazard underabnormalconditions

IEC/CENELEC/EUROPEAN Zone 0 Zone 1 Zone 2

NORTHAMERICA

Division 1 Division 2

Table 2.3.1.1-a: Comparison of Area Classification

GAS IEC / CENELEC /EUROPEAN

NORTH AMERICA(CLASS 1)

Acetylene II C A

Hydrogen II C B

Ethylene II B C

Propane/Butane II A D

Table 2.3.1.1-b: Gas Grouping for Area Classification Protection Techniques

2.3.1.2 Electrical Installations

Both European and American practices are acceptable. The requirements for electricalinstallations shall be in accordance with NFPA 70 or equivalent. Current-carrying


conductors shall be made of copper. Electrical wiring shall be installed such that thesystem is free from short circuits and from grounds. All protection devices shall beproperly sized, selected and installed. An overall electrical study for the entire electricalsystem shall be undertaken by qualified electrician or electrical engineer. Internal partsof electrical equipment shall not be damaged or contaminated by foreign materials.There shall be no damaged parts that may adversely affect safe operation or mechanicalstrength of the equipment. Conductors of dissimilar metals shall not be inter-mixed in aterminal or splicing connector where physical contact can occur between the dissimilarconductors.

Live parts of electric equipment shall be designed to guard against accidental contactusing any of the following means:

1. Approved enclosures.

2. Locations in a room or similar enclosure accessible only to qualified persons.

3. Suitable partitions arranged so that only qualified persons will have access tospace within the reach of live parts.

4. Location on platform so elevated and arranged as to exclude unqualifiedpersons.

5. Elevation of 2.5 m or more above the working surface.

Parts of electric equipment which in ordinary operation produces arcs or sparks shall beenclosed or separated and isolated from all combustible material. Circuit breakers forelectrical equipment shall be legibly marked to indicate its purpose.

2.3.1.3 Emergency Shutdown Systems

The emergency shutdown system in a liquid transfer operation shall close all emergencyshutoff valves and stop all pumps when activated. The location of EmergencyShutdown Pushbuttons is described below under “Emergency Shutdown Systems.” Theshutdown buttons shall be RED in color of the Push-to-Activate, Pull-To-Reset type.They shall be clearly marked for the purpose for which it is intended and protectedagainst accidental activation. All emergency shutoff valves shall be provided with bothopen and closed position indicators. All wiring and logic diagrams shall include awritten description of the proposed operation. Each sequence trip and alarm shall bedescribed in detail.

2.3.1.4 Instrumentation

Instrumentation shall meet the requirements of the applicable national codes. Allinstruments, pneumatic or electronic, shall fail to the safest position or lock in placeupon air or power failure. Enclosures and cabling for all instrumentation shall conformto the requirements of the electrical area classification of the area of installation.Instrument installations shall meet all area classifications and code requirements. Allelectronic instrumentation shall be grounded at a single, common point separate fromthe plant ground grid.

Cable and conduit shall be routed in underground trenches where practical. Armoredcable may be installed by direct burial methods. Where underground routing is notpracticable, overhead cabling shall be routed in cable racks. All terminal strips usedshall be of modular construction. Electric terminals shall be of the pressure-plate type,with all “live” parts recessed into the insulated block.

2.3.1.5 Lightning Protection

Aboveground LPG tanks do not require lightning protection for tank integrity.However, it is common practice in refineries and production plants to ground all towersand drums. This is done to protect electronic instrumentation and control systems.Therefore, grounding is recommended when electronic instruments are on the tank, but


is optional if the tank has no electrical instruments or control systems. Grounding rodsshall be provided for tanks supported on non-conductive foundations.

2.3.1.6 Plant Lighting

Adequate lighting is needed for security as well as operations. It shall be provided toilluminate operating facilities such as walkways and essential control valves anddevices. Any loading or unloading facility to be used after daylight hours shall beprovided with adequate lighting, as well as gates within the plant fence area. Thequality of the lighting installations as well as all other electrical installations shallcomply with the Electrical Area Classifications.

Adequate lighting shall be provided for the following:

1. All storage and operating areas for normal operation.

2. To illuminate storage tanks, tanks being loaded, control valves and otherequipment.

3. Facility gates.

In addition, sufficient emergency lighting shall be provided to allow safe operationsduring an emergency. Lighting shall be designed to provide the average maintainedillumination in Table 2.3.1.6.

Location Lux Footcandles

Cylinder inspection and filling 540 50

Cylinder processing plant (general) 320 30

Tank car, tank truck, loading point 320 30

Piers, loading point 110 10

Entrance gate 55 5

Table 2.3.1.6: Average maintained illumination

2.4 Emergency Shutdown SystemThere shall be an Emergency Shutdown System (ESS) by which the facility can beshut down in case of emergency. At the following strategic locations throughout theplant, emergency push-buttons shall be installed which relay a signal to the centralemergency shutdown system.

1. One in a central area which is at least 15 m from LPG tanks.

2. One at each loading or unloading position.

3. One, located 15 m from each loading or unloading position.

The actuating system shall be designed to close valves upon failure of any systemcomponent. More information on Electrical requirements are described under“Electrical Classification” above. When one of these push-buttons is activated thefollowing shall happen:

1. Shutdown power to all product pumps, compressors, and cylinder filling.Rundown streams from processes are not included in this requirement. Theyshall be handled individually based on “fail safe” considerations.


2. Closing of all Emergency Block Valves (EBV) at unloading, loading, tankageand cylinder filling. EBV’s in rundown streams from refinery or gas plantprocess units are not included in this requirement. They shall be closed orkept open individually based on “fail safe” considerations.

3. An audible alarmshall be activated.

4. The power to the firewater system shall be maintained throughout theemergency/alarm.

5. Emergency push buttons at the pier may shut down the pier lines only or theymay be tied into total plant shutdown. This may depend on distance to thepier and on other factors. The necessity shall be determined in a Hazard andOperability Analysis (HAZOP). In any case, the closure of the pier valvesshall result in an alarm at the plant.

6. When the loading/unloading area is part of a refining or upstream site,activation of the ESS shall not necessarily require a shutdown in the processarea. This shall be confirmed during the design.

EBV

E M E R G E N C Y P U S H B U T T O N





EBV

EBV

EBV

EB

V

EB

V

EB

V

EBV

ESS

EQUIPMENTSHUT DOWN

EMERGENCYSHUTDOWNSYSTEM

POWER TOFIRE PUMPNOTINTERRUPTED

FIRE WATER

MOUNDED DRUMS SPHERE

BULLETS

RAIL CAR

TRUCKS

CYLINDER FILLING

OFFICE

ALARM

MARINE PIER EB

VE

BV

SHORE



Figure: 2.4: Plant Emergency Shutdown System (ESS). Only control system shown.

Safety in LPG Design BULK STORAGE 3-1

3 BULK STORAGE

3.1 Storage in Plants and IndustryThis chapter is intended to provide general technical guidance to engineers who areresponsible for the design and installation of bulk tanks for Liquefied PetroleumGas (LPG). The guidelines are intended to assist engineers in the development oftechnical specifications, which meet company and industry standards for design,fabrication, installation, and testing of such facilities. These specifications aim tomaximize the integrity and safety of these facilities. Achieving this objective isdependent upon using design concepts, which are proven to be safe and conform to goodoperating and maintenance practices throughout the operating life of such facilities. Indeveloping these specifications, designers shall also follow Global Practices (GP's),Design Practices (DP's) specified in this section, and local regulations.

This guide tries to use consistent wording for LPG storage. “Tanks,” “mounded drums,”“spheres” and “bullets,” are used for bulk storage at company plants or industry.“Vessels” means ships and barges only. Note that the GP's, DP's and other codes do use“vessel” for refining drums and towers. “Containers” are used in small bulk anddomestic use. “Cylinders” (also often called “bottles”) are used for small portable LPGcontainment.

If LPG tanks for commercial, utility, or industrial customers are as large as plant bulkLPG tanks they shall be designed to the same principles. Typically commercialconsumers or domestic users require containers. Such containers may be designedaccording to requirements in the chapter “Customer Storage” of this Guide.

For all new designs or design modifications in LPG storage service, a review of allapplicable local regulations, codes, standards, practices and operating permits is needed.Major pressure tank manufacturers have developed standard designs for different tankcapacities, permitting the purchaser to specify only the code required at the proposedplant site, and the tank openings and fittings required. Standardization can providesubstantial savings over development of an individual design. However, the standardshall meet all the requirements of the GPs specified in this section.

For new designs the use of “mounded drums” for pressure storage is required for somecountries (Europe). These are horizontal tanks placed on above ground foundations oron sand beds but thereafter completely covered by an earth mound. This type of storageis inherently safer since its passive fire protection makes it not vulnerable to externalfires.

The most frequent tank types used in the past and still in use in many countries today arethe horizontal cylindrical (“bullet”) tank and the sphere. These are above groundtanks on concrete foundations. The horizontal “bullet” tank was the most commondesign in the past for tanks sized between 28 and 282 m3. For larger capacities, often

3-2 BULK STORAGE Safety in LPG Design

the most economic solution was the spherical tank. Depending on location and exposurein some cases it may still be appropriate to use this approach for new designs, however,more and more regulations ask now for retroactive passive fire protection byfireproofing.

Vertical “bullet” type tanks have also been installed by industry. They may have theirmerits when spacing is tight, however, from a safety and firefighting standpoint this isan undesirable configuration and shall be avoided.

The following International Codes may be applicable to the design of pressurized LPGtanks:

1. The United States American Society of Mechanical Engineers, “ASME Boilerand Pressure Vessel Code, Section VIII” Section VIII is subdivided intoDivision 1 “Unfired Pressure Vessels” and Division 2 “Rules for Constructionof Pressure Vessels.” To be more economical, LPG horizontal tanks shall bedesigned and fabricated according to ASME VIII Division 1 while LPGsphere tanks shall be designed and fabricated according to ASME VIIIDivision 2.

2. API STD 2510 and NFPA 58.

3. BS 5500 Specification for Unfired Vessels.

4. BS 1501 Steels for Fired and Unfired Pressure vessels - Plates, or Equivalent.

5. BS 1502 Specifications for Steels for Fired and Unfired Pressure vessels -Sections and Bars.

6. BS 1503 Specifications for Steel Forgings (including semi-finished forgedproducts) for Pressure Purposes.

7. Finnish Standards (SFS) 3205, 3339, 3340, 3341, and 3342. FinnishGovernment Statues 98/73, 636/77, 257/84, 258/84, 312/79, and 1106/81.

8. Japan High Pressure Gas Law (HPGL). Japan Industrial Standards (JIS).

9. Australian Pressure Vessel Code AS 1210.

3.2 Mounded and Above Ground StorageThe guidelines and technical considerations discussed below refer to facilities, whichutilize large horizontal mounded drums for storing LPG. Storage in aboveground tankspresents the risk of a BLEVE. Storage of LPG in mounded drums avoids the risk ofexternal fire exposure. Mounded drums are long horizontal cylindrical tanks, withdished heads, which are installed above grade level and covered completely with sandbed fill and general fill material. The mounding of drums permits reduced spacing whencompared to the space needed for spheres/bullets, which is mandated by regulatoryrequirements.

As of 1993 there are several mounded drum installations in company Refining andMarketing facilities in Europe and the Asia Pacific region. These tanks have been usedto store LPG since 1982-83. Operating experience with the installations during the yearshas been good.

3.2.1 Dimensional Sizing of Drums

The specific dimensions for the drums are based on LPG storage requirements, availablespace on site, safety considerations, spacing from buildings, facilities, and otherequipment, orientation, and the costs associated with fabrication, transport andinstallation. The capacities of the drums should be based on planned sales. However,shipment parcel size, transport delays, seasonal effects, future business outlook or otherfactors may have an influence on the capacity.


Mounded drum sizes vary substantially in diameter and tangent length. The drumsizes that are currently in use have diameters in the 4 to 6.5 meter range and tangentlengths of 34 to 88 meters. The diameter and length chosen are dependent upontransportation and site spacing. In addition, considerations such as field assembly andfabrication of drum sections should be used to optimize LPG storage and inventoryneeds at specific installations.

LHHA(CO) if filled byPipeline or by Ship

EBVTank Slope 1:100

min. 0.9 m

LPG

LPG

Fill

ing

PRVLHHA LI

LHAWater Draw-off to Locationmin. 15 m from Fence

LPG

Vap

or R

etur

n

Removable Fill

Distance PRV to Fence15 m

Removable Part with Sleeve

to ESS

TIPI

Concrete Wall

Figure 3.2.1-a: Typical LPG mounded drum

Tank Slope 1:100

PITI

min. 0.9 m

PRV

LHHA

LILHA

Water Draw-off to Locationmin. 15 m from Fence

Distance PRV to Fence 15 m

to ESS

Sub

mer

ged

Pum

pDistance to Fence 3 m

LHHA(CO) if filled byPipeline or by Ship

Figure 3.2.1-b: Mounded drum, spacing alternative with submerged pump

In general, it is preferable to have the drums fabricated in the manufacturer shop andtransported to site. However, due to the large sizes involved, transportation, site accessand off-loading at the plant usually dictate the feasibility of shop manufacture or theneed for site assembly of major drum sections. Recent LPG mounded drum installationshave used both shop fabrication and field construction practices.

3.2.2 Materials Selection for Tanks

All materials of construction shall meet the requirements of Section II of ASME “Boilerand Pressure Vessel Code”, or equivalent national code. Low melting point materials ofconstruction such as aluminum and brass shall not be used for LPG storage drums. It isrecommended that the drum materials consist of fully killed, grain refined andnormalized carbon steel plates and forgings, with adequate mechanical strength andtoughness properties for the storage of LPG. The presence of H2S in has led to wet H2Scracking problems associated with hard welds (> 225 Brinell Hardness). The tendencyfor in service cracking increases as the H2S concentration and strength of the materialincreases. H2S is more of a problem in refining and less in marketing where H2S


contents by specification is in the order of magnitude of 1 ppm. Minimum specifiedtensile strength of the tank steel historically has been below 483 MPa. However, withmore recent technology development higher strength steel is used to keep the thicknessof spheres below 38 mm, so PWHT can be waived per ASME Code. Experience showsthat if a proper procedure is taken (e.g. pre-heating 90-150 ºC), high strength steel canprovide satisfactory service. The amount of H2S in the product to be stored is a veryimportant factor to determine metallurgic characteristics of the material of construction.Steel specifications shall include chemistry control per GP 9-2-1, and requirements forimpact properties at the Critical Exposure Temperature (CET), and heat treatmentper GP 5-1-1. Impact Requirement for Materials shall follow GP 18-10-1 "AdditionalRequirements for Materials." Additional information which may be useful to thedesigner is available from GP 18-7-1 “Welding Procedures,” GP 5-3-1 “HydrostaticTesting of Vessel,” and GP 5-2-1 “Internals for Towers & Drums.”

Material of construction for the pressure parts shall comply with ASME Sec II DAppendix 5. Alternative materials equivalent to the ASME Code material specificationmay be used. However, alternative materials shall be provided with the following toEMRE for approval:

1. Nomenclature and complete chemical and physical properties of the proposedmaterial stated along with ASME equivalent. Any additional requirementnecessary for equivalence shall be stated.

2. Where necessary to demonstrate the equivalence of alternative material, testspecimens shall be provided for Charpy V-Notch testing according toapplicable ASME material specification.

3. Quenched and tempered steel is limited to a maximum tensile strength of 690Mpa and an actual yield-to-tensile ratio of < 0.85.

The following shall NOT be used as material of construction for pressure parts:

1. SA36, SA283 and other structural grade steel.

2. Steel casting.

3. Low melting point materials such as aluminum and brass.

3.2.2.1 Minimum and Maximum Design Temperature

The principal purpose for specifying impact requirements is to ensure that a catastrophicbrittle fracture of the drum will not occur during hydrotesting, start-up, shutdown, andnormal operations throughout its service life. Impact requirements are based on theCritical Exposure Temperature (CET, also “Minimum Design Temperature”),metal thickness of the drum component, and the material specification selected.

The CET for a LPG pressurized storage drum or sphere shall be based on the lower ofthe following:

1. Lowest one-day mean temperature. This would account for filling the drumor sphere up to the safety valve pressure limit on the coldest day.

2. The temperature equivalent to 25% of the design pressure on the vaporpressure curve for the material to be stored.

The minimum design temperature shall be the minimum metal temperature expected inservice, taking into consideration ambient temperature and auto-refrigeration of thestored product when it flashes to atmospheric pressure. For storing Propane, thistemperature will be –42 °C. In no case shall the minimum design temperature be higherthan –18 oC. In many situations, the owner prefers to set the minimum designtemperature at the lowest possible temperature due to depressurizing the LPG toatmospheric pressure (–42 °C). This is almost always more conservative than thecriteria provided above. It adds an extra safety margin for protection against brittlefracture and is recommended. Using modern carbon steels, this should not significantlyadd to the cost for the drum, bullet or sphere.


3.2.2.2 Post-Weld Heat Treatment

For aboveground bullets with a plate thickness below 38 mm Post Weld Heat Treatment(PWHT) is not required. However, Post-Weld Heat Treatment is recommended formounded drums due to service considerations. These requirements are independent ofPWHT that may be required from Code considerations of plate thickness, and materialspecification. The preferred method of PWHT for shop fabricated drums is to heat treatthe entire drum or major sections of the drum in a heat treating furnace. This minimizesthe thermal stresses, which can be introduced by local PWHT, which typically involvesbanding the weld seams with electric resistance heating jackets. If this capability is notavailable in the shop or if PWHT in the field becomes necessary, then local Post-WeldHeat Treatment of the individual seams may be done, subject to careful control oftemperature and temperature gradients.

3.2.2.3 Materials Specifications

The recommended materials specifications for bullets and mounded drums are identicalto ASTM Specifications as follows:

SA 516 Grade 70 normalized for the shell and headsSA 333 Grade 1 or 6 for nozzlesSA 350 Grade LF2 for flanges & fittingsSA 352 Grade LCB for fittingsSA 334 Grade 1 or 6 for tubing

Substitute Materials specifications may be made provided they meet with therequirements in GP 18-1-1. Materials not covered in GP 18-1-1 should be evaluated ona case by case basis.

3.2.2.4 External Corrosion Protection

The earth mounds used on mounded LPG Drums increase the potential for soils inducedcorrosion and holing through. In addition, the design does not permit on streamthickness measurements and/or visual inspection of the drum surface. Shop fabricationis preferred when drum size permits. Any damage during transport to the coatings onshop fabricated drum shall be repaired. It is extremely important, therefore, to considerthe following:

1. Develop an earthwork specification for the mound. Specify sand bed fills,general fills, and acceptance tests, in accordance with ASTM Standards andGlobal Practice GP 4-9-1.

2. Provide an adequate corrosion resistant coating on the external surface ofthe drum per GP 19-1-1. Shop-applied coatings are preferred, but fieldapplications are also acceptable. Irrespective of type and application methodof coatings, a holiday test on the coating shall be carried out immediatelyprior to back-filling on site. The following specification is the normalrequirement:

Surface Preparation: Abrasive Blast Clean toSSPC SP-10 Near White

1st Field Coat: Coal Tar Epoxy @ 6-8 mils DFT

2nd Field Coat: Coal Tar Epoxy @ 6-8 mils DFT3. Install a cathodic protection system utilizing sacrificial anodes. Permanent

reference electrodes shall be buried along with the drum at each end of thedrum and above and beneath the drum at its midpoint.

4. Requirements for a cathodic protection system are a twenty-year life and amaximum exposed steel surface of 10%. Insulating flanges shall separatepermanent lines connected to plant piping from this cathodic protection


system. The cathodic system may be used to protect short runs of buried pipeprovided the pipe coating is equal or better than the tank coating.

5. Any special plant refinery/production applications where the LPG is expectedto contain wet H2S, shall have the drums lined internally.

The exterior surface of aboveground tanks, including the steel supports, shall be gritblasted to SSPC SP-10 standard or chemically treated and adequately painted.

After grit blasting horizontal LPG storage bullets and LPG sphere tanks, shall bepainted with a primer coat of alkyd zinc phosphate (75 microns dry film thickness),build-coat of alkyd micaceous iron oxide (50 microns dry film thickness) and topcoat ofwhite alkyd enamel (30 microns dry film thickness).

1. Sphere legs shall be fireproofed and left unpainted

2. Bases and saddles of bullets that are concreted shall not be painted.

3. If bases and saddles on bullets have exposed metal, they shall be painted withsame primer coat, build-coat and finished with topcoat.

The exterior of aboveground LPG tanks shall be inspected every 2 years. Repaintingshall be carried where necessary.

3.2.3 Design Basis for Mounded Drums

The mechanical design of large mounded drums is complex, due to its moundedconfiguration, internal pressure, nozzle geometry and piping loads, type of support,foundation pad design and soils settlement characteristics. In addition, if these facilitiesare located in earthquake zones, the seismic loads substantially increase the complexityof mechanical design considerations.

Most national codes entrust the responsibility to users for defining and specifying theloading mentioned above. Therefore, it is recommended that users develop MechanicalSpecifications (MSpec) for these drums and ensure that all pertinent design criteria andloads are specified.

The following guidelines are intended to assist users when developing MSpecs formounded drums.

3.2.3.1 Design Conditions for LPG Drums

Design conditions for LPG drums should preferably be based on Propane storage. Thiswill allow the flexibility to switch to Propane and will provide protection againstinadvertent loading of Propane to a lower design pressure drum. Based on localregulations in several countries, the minimum design pressure is specified as 17.2 bargauge with a corresponding design temperature of 55 °C. Under design conditions, 1.6mm corrosion allowance shall be added to the design thickness of a drum. In addition,external pressure of 1 bar gauge is used to allow for the soil pressure from the earthmound. In the absence of local regulations, the maximum design temperature shall betaken as the highest ambient temperature that has been recorded over the last 10 years atthe nearest meteorological station. In no case shall this temperature be lower than 38°C.

3.2.3.2 Design Codes Applied

Most nationally recognized Codes can be used for the design of mounded drums.However, design, fabrication, inspection, and testing requirements shall be based, as aminimum, on the requirements of Global Practice 5-1-1. Design and fabricationinspection of LPG tanks shall be carried out by an internationally recognized and EMREEngineering approved third party inspection agency.


3.2.3.3 Permanent Identification is Needed

For continuous reference, a non corrosive identification plate shall be fixed to the drumin a suitable and clearly visible location. It shall be stamped with the followinginformation as a minimum:

Drum Serial Number:Owner’s Name:Designer’s Name:Design Code:Manufacturer’s Name:

Design Pressure, min./max.:Design Temperature, min/max:Product Stored:Water Capacity in volume units:Date of test and test pressure:

3.2.3.4 Earth Mound Design

The following supplementary requirements shall apply to mounded drums:

1. Partial mounding is not recommended. Partial mounding continues to havethe design considerations of storage in aboveground bullets so that little ornothing is gained.

2. The depth of the mound over all surfaces of the drum shell shall be aminimum of 0.9 m. The mound cover shall include the heads of the drums,which shall not be exposed.

3. The backfill used for mounding shall consist of washed sand totally free ofrocks or abrasive materials likely to damage the drum coating. The moundsshall have good stabilization to prevent erosion by firewater or heavy rain.Furthermore, it shall be capable of withstanding prolonged heat radiation orjet flame impingement. This is important since the pressure relief valves onsuch drums are not designed to provide protection against heat input byexternal fire. Therefore, if the drum is being uncovered later, e.g. forexternal inspection, LPG shall be taken out of the drum before it isuncovered. If a drum has to be removed and the adjacent drum is still filledwith LPG the side of the filled drum shall still be covered by a mound of0.9 m thickness.

3.2.3.5 Nozzles on LPG Drums

As a matter of principle the number of nozzles on mounded drums shall be kept to thenecessary minimum. This pertains in particular to the lower part of the drum.Following nozzles are considered necessary:

1. Pressure relief valve (PRV) connection to the vapor space.

2. Water draw-off connection via the top (similar to GP 9-2-1, para. 9.5).

3. Connection for the level indicator with high level alarm.

4. Connection for the independent high level alarm.

5. Connection for the fixed level gauge.

6. Filling connection at the top of the drum.

7. Withdrawal connection at the top or bottom of the drum.

8. Vapor return connection at the top of the drum.

9. Vent connection to atmosphere.

10. Connection for the temperature indicator.

11. Pressure indicator connection to the vapor space.

Careful engineering may permit the combination of some of the above fittings toreduce the number of nozzles on the drum. The preferred location for nozzles is at themanhole (see below). All nozzles on new drums are preferred to be flanged and notsmaller than 50 mm. This type of connection presents adequate integrity against


mechanical damage or leak during fire. Fittings on underground or mounded tanks shallpreferably be accessible from above ground level.

As a matter of principle nozzles on above ground drums are preferably located in thevapor phase section, however, those necessary for liquid withdrawal shall be at thebottom. All tank nozzles’ connections and nozzles’ flange joints shall be welded.Flanged joints on tanks (and pipelines) shall be designed based on the relationship ofpressure limits against temperature of carbon steel. The material class shall not beinferior to that based on the pressure limit at the design temperature. Gaskets forflanged joints shall be resistant to liquid LPG and shall be made of metal or othersuitable material confined in metal having melting point over 816 °C. Gaskets of naturalrubber or bonded with natural rubber shall not be used.

Figure 3.2.3.5-a: Submerged pump

The following shall be considered when designing nozzles on LPG drums. Therequirements below are intended to address the mechanical and structural designconsiderations of nozzles on LPG mounded drums. They are not intended to cover theinstrumentation, controls and alarms that are recommended from a safety and operabilitystandpoint.

1. All nozzles, with the exception of the pump suction, shall be installed at thetop of the drum. If the drum is located in an earthquake zone, the bottomsuction design shall be a last resort and requires additional assessments forpossible structural failure, corrosion and leakage. An access chamber shallpermit inspection of the bottom suction nozzle for the pump. The accesschamber may be filled with sand and closed by a cover, which can beremoved to permit inspection, with the drum in service.

2. Installations where the suction line for an external pump enters through thetop shall be avoided. Even though a compressor may permit continuousvapor return, often NPSH problems are encountered. Solar radiation maycause vapor lock in the line and it may be impossible to empty the drumbelow a certain level.


3. Since pumps have become highly reliable, the submerged pump is anelegant solution for locating the pump suction nozzle on the top of the drum.A bottom shutoff valve permits removal of the pump while the drum is filled.

4. Shell penetrations between bullet supports shall be avoided. They are moredifficult to access in mounded drums. When the tank is above ground, theyare difficult to reach with cooling water in the event of a fire.

5. It is recommended that drum larger than 56 m3 or exceeding 2 m diameter beprovided with a manhole of not less than 610 mm. Manholes on moundeddrums must be located at the top of the drum in form of an extended nozzleand shall be protected from direct involvement in a fire by covering theopening with a removable insulated lid. A manhole may be positioned belowthe mound rim however, in such cases it shall be adequately protected fromcorrosion by providing a steel skirt with cover. The skirt shall be attached ata level below the flange ensuring that the nuts and bolts are not buried insidethe mound. In drum 56 m3 or smaller volumetric capacity, provision of amanhole is optional unless a need for cleaning is anticipated, or required bylocal regulations. The manhole shall be located to facilitate cross ventilationwith the tank nozzles. It is suggested to locate nozzles and connections forinstrumentation, PRV and other on the manhole in order to reduce thepenetrations to the tank shell and to facilitate later changes should they benecessary. However, it should be checked whether the code is not restrictiveon nozzles on manholes.

Figure 3.2.3.5-b: Two-plane gusset

6. The nozzle shall be of fully integrally reinforced and shall not permit the useof reinforcement pads. All nozzles shall be flanged and valved. The flangedjoint shall not be buried inside the mound.

7. Nozzles shall be adequately spaced to ensure that localized stresses wouldsatisfy the criteria of ASME Section VIII and GP 5-1-1 and GP 9-2-1.

8. If the drums are frequently filled and emptied, cyclic loading effects shall beconsidered in the nozzle attachment design (See GP 5-1-1).

9. The nozzle to shell design shall be adequate to accommodate external pipingloads, as appropriate.

10. The following minimum nozzle wall thickness shall be used:

Nominal Nozzle Size Pipe Schedule or Thickness< 50 mm Schedule 80 or 160

75-150 mm Schedule 80> 200 mm 12,5 mm

11. All nozzles 50 mm or smaller shall be gusseted in two planes in accordancewith GP 3-18-1.

12. Sampling connections may be provided on piping to tanks. Adequategussetting of small connections and piping in sampling lines shall be provided


to minimize vulnerability to mechanical damage. The inlet piping tosampling connections shall be double valved. For above ground drums,sample locations shall not be under the drum. Connections shall be orientedso that the purge vapors do not engulf the operator or approach an ignitionsource. Ideally the purge shall be discharged into a closed system (blowdownin refining). Consider the addition of a restriction orifice (< 2 mm) externalto the sampling valve.

13. Appropriate startup and shutdown connections shall be provided forcommissioning storage drums and taking them out of service. Pressure drumsmay be purged by water filling, with a 50 mm vent connection to remove airdisplaced as the water rises. A 50 mm vapor connection to an adjacent drumin the same service, where available, allows vapor to be drawn in when thewater is drained. The same connection can be used for taking the drum out ofservice. When water is injected, the residual liquid and vapor is displacedover the top into another drum.

3.2.3.6 Drum Shell Design1. The non-uniform external loads transmitted to the drum shell, by the earth

mounds, should be analyzed using Finite Element Analysis (FEA) methods.The FEA stresses should comply with ASME Section VIII Div 2. In addition,a theoretical safety factor of 3.0, for buckling design, should be used asacceptance criteria for minimum shell plate thickness. Review with the fixedequipment specialists in EMRE or EMPRCo may determine when FEA maynot be required.

2. When calculating shell thickness due to internal pressure no credit shall betaken for the restraint provided by the earth mound on the drum shell.Corrosion allowance as per section “Design Conditions for LPG Drums”above.

3. Stiffeners, used on the drum shell shall be attached to the internal surface.Design calculations and details as well as fabrication and NDE (NonDestructive Examination) requirements shall ensure that shear and lamellartearing does not occur (see also ASME Section V “Non-destructiveExamination”).

3.2.3.7 Drum Support and Foundation Design

The recommended type of supports for mounded drums is as follows:

1. For locations, which are subjected to earthquake forces, mounded drumsshall be located on sand beds. Saddle supports are not recommended due tothe increased risk of failure from liquid sloshing and dynamic forces during aseismic event.

2. For other locations, saddle supports on rigid slabs supported on piledfoundations are permissible. However, the mounded drum shall beinvestigated for buckling, local circumferential bending and shear stresses perGP 5-1-1.

3. In addition, reinforced concrete retaining walls have been used to confine theearth mound. Reinforced concrete walls shall have adequate drainage and theconcrete shall not touch the drum or it can cause accelerated corrosion. Seealso GP 4-9-1 “Site Preparation/Earthwork.”

It is recommended that soils investigation and assessments be completed prior todetermining the most suitable type of foundation. The primary objective of theseinvestigations should be to reduce to an absolute minimum the potential for differentialsettlement. The foundation design shall be based on the weight of the drum full ofwater (needed for pressure test).

If these settlements are not kept to a practical minimum, they may introduceunacceptably high stresses at the drum support locations and increase the risk of in-


service failures. The sensitivity to such settlements is due to the large length to diameterratios and the relatively thin shells in these drums. Also the piping connecting to thedrum must be kept free floating and not embedded into concrete or other fixations. It isimportant that connecting piping is not subjected to any stress from earth movement etc.

In view of the above considerations, a maximum differential settlement of 25 mm on a16.5 m long drum has been used at one facility.

Where groundwater or possible flooding makes it advisable, anchorage shall be providedto prevent flotation. Underground pipes and services, such as steam, water, electricityand sewer, shall be at least 1.5 m horizontally from the mounded tank. Above groundhorizontal LPG tanks of more than 7.6 m3 water capacity shall be provided withstructural steel saddles designed to be mounted on flat-topped concrete foundations bymeans of anchor bolts or other adequate devices. Lifting lugs for LPG horizontal tank,where provided, shall be designed for taking 1.5 times of the total weight of an emptytank. LPG horizontal tanks’ supports shall be of reinforced concrete, masonry orfireproofed structural steelworks. Design of the supports and foundations shall take intoconsideration:

1. Ground conditions, including allowable bearing pressure and differentialsettlement.

2. Possibility of flotation.

3. Expansion and contraction of the tank shell.

4. The greatest combination of static loading due to weight of the tank, itscontents, weight of water used for testing, wind loading, vibration, thermaleffects and seismic conditions.

3.2.4 Testing Requirements

NDE and testing of LPG horizontal tanks shall be per ASME Code Section VIII,Division 1.

For a tank which has a wall thickness of:

More than 38 mm, the minimum Non-Destructive Examination (NDE) shall be per thefollowing sequence:

1. 100% X-ray on all seams.

2. Post Weld Heat Treatment (PWHT). Hardness test after PWHT shall not bemore than 225 HB unless waived by EMRE Engineering.

3. 100% ultrasonic test on all seams.

4. 100% Magnetic Particle Test (MT) on all seams.

5. Hydrostatic test at 1.3 times of the design pressure. (The 1999 ASMESection VIII, Div.1 specify 1.3 times of MAWP as Hydrostatic testingpressure, since ASME has lowered the safety factor for materials from 4 to3.5. For any alteration of a tank built prior to 1999, EMRE Engineering shallbe consulted.) Also refer to GP 5-3-1 "Pressure Testing of Unfired PressureVessels", which has a clearer description for hydrostatic testing. It states: Inthe hydrostatic test condition, the maximum membrane stress in the tank inthe un-corroded or corroded condition shall not exceed 90% of the specifiedminimum yield strength for ferritic steels, nor 100% of the specifiedminimum yield strength for austenitic steels or non-ferrous materials.

6. 100% MT on all seams.

Between 32 mm to 38 mm, the minimum NDE shall be per the following sequence:


1. If a service condition permits (e.g. H2S concentration under 50 ppm), PWHTcan be waived provided that the Metal is preheated prior to welding.Otherwise, follow the procedures as above.


3. Hydrostatic test at 1.3 times of the design pressure.


Less than 32 mm, the minimum NDE shall be per the following sequence:

1. If a service condition permits (e.g. H2S concentration under 50 ppm), PWHTcan be waived. Otherwise, follow the procedures as above.




NDE and testing of LPG sphere tanks shall be per ASME Code Section VIII, Division2. For a tank which has a wall thickness of:

More than 38 mm, the minimum Non-Destructive Examination (NDE) shall be per thefollowing sequence:

1. 100% X-ray on all seams

2. Post Weld Heat Treatment (PWHT). Hardness test after PWHT shall not bemore than 225 HB unless waived by EMRE Engineering.

3. 100% ultrasonic test on all seams.

4. 100% Magnetic Particle Test (MT) on all seams.



Between 32 mm to 38 mm, the minimum NDE shall be per the following sequence:

1. If a service condition permits (e.g. H2S concentration under 50 ppm), PWHTcan be waived provided that the Material is preheated prior to welding.Otherwise, follow the procedures as above.




Less than 32 mm, the minimum NDE shall be per the following sequence:

1. If a service condition permits (e.g. H2S concentration under 50 ppm), PWHTcan be waived. Otherwise, follow the procedures as above.




Documentation from fabricator shall include MDR (manufacturer's data report) and alltest recordings according to ASME VIII requirement.

3.2.5 Horizontal “Bullets” and Spherical Tanks

Design procedures for horizontal “bullet” tanks and spheres are similar to thosedescribed above for mounded drums except those items that are specific to moundeddrums. All connections shall be flanged. Existing screw type connections in olderMarketing tanks need not be retrofitted to flange connections. Older Marketing bulletsalso may have 3 meters from the edge of the bullet to the water drain discharge point


compared with the latest 4.5 meter recommendation in DP XXII-C. Existing drainpoints do not need to be retrofitted.

For aboveground bullets the bottom nozzles should be positioned at the two ends and notbetween foundations. This is to facilitate access of valves and better firewater coverageif needed. If possible the bottom nozzles may be reduced in favor of top nozzles. Thismay avoid the potential for liquid leaks. Top spray filling is desired for bullets andspheres since it lowers the pressure during filling. Typical sphere and bullet designs areshown in Figure “Typical horizontal bullet tank” and Figure “Typical spherical tank.”Tanks used in loading and unloading service would normally have a vapor balancingline, which is not shown in these figures.

3

LHA

(INDEPENDENT)

P I

CS

O

BLEED (GUSSETED)

DRAIN WITH ELL

SAFETYVALVE

7

PI

3

1PLATFORM ACCESSVIA LADDERS

7

INSTRUMENTS

1 3

(IF LARGE BULLET)

4

OUTSIDETOE WALL

EBV(D)�(FIREPROOFED OR�FIRE SAFE ACTUATOR)

SAMPLE CONNECTION

H

TO SEWER ORDRAINAGESYSTEM

2

HYDRANTS(PREFERABLYWITH MONITORS)

4

TOE WALL

2

WATER

CATCHBASIN

2

THROTTLING 5

30 m

MIN.

FILL

WATER FLOOD

LHA AND LHHA FOR �ALL BULLETS �LHCO IF FILLED BY RUNDOWN, PIPELINE OR SHIP.

5

5DRAW-OFF

NC

1

2

3

4

5

6

7

GP9-1-1

GP15-1-3

GP3-2-3

GP3-5-1

GP14-3-1

GP3-2-4

DPM XV-J

REFERENCES

GENERAL

GP9-2-1

GP9-2-1

NO GAGEGLASSES

SUPPORTS FIREPROOFED

FIRE-SAFEQUICK CLOSING 5

NON-FREEZE DRAIN(IF COLD CLIMATE) 1

6

NOTES:

1 IF POSSIBLE ALL CONNECTIONS SHOULD BEAT ONE END OF VESSEL AND THE CATCHBASIN SHOULD BE LOCATED NEARBY.

1 5

FILL & DISCHARGE

SLOPE SLOPE

SLOPE

GROUNDED

DR, 3/2001

LI

PdI

LHA

PI

4 m

MIN.

RELIABLE GAUGE

BULLET IN OPERATIONMAINTAINABLE WITH

Figure 3.2.5-a: Typical horizontal bullet tank (from DP XXII-C)

2

TO SEWER ORDRAINAGESYSTEM

2

2 OR MORE FIRE HYDRANTS(PREFERARLY WITH MONITORS)

4

COATED OR SLEEVED

5

H

NC

1

2

3

4

5

6

7

8

GP9-2-1

GP9-1-1

GP15-1-3

GP3-2-3

GP3-5-1

GP14-3-1

GP4-2-1

GP3-2-4

GP9-2-1

DPM XV-J

REFERENCES

GENERAL

TYPICAL AREA LAYOUT

LHA IF FILLED BY RUNDOWN,

PIPELINE, OR SHIP3

NO GAGE

GLASSES

STAIRWAY &PLATFORM

1 7

(IN

DE

PA

ND

EN

T)

CSOPI

3

1

LHA

DELUGESYSTEM

4INSTRUMENTS

1 3

PdILI

4

FILL &DISCHARGE 5 1 CATCH

BASIN

2

2

SUPPORTSFIREPROOFED

DIKE

WATER DELUGEINSTRUCTION SIGN

4

SUCTIONCONNECTION

1

TI1

3

4 m MIN

5

SAMPLECONNECTION

FIRE-SAFEQUICK CLOSING

THROTTLING

1 6

5

5

1

WATER DRAW-OFF

NON-FREEZE DRAIN(IF IN COLD CLIMATE) 1

WATER

4OUTSIDEDIKED AREA

5

MIN 30 m

OR FIRE-SAFE ACTUATOR)

5

EBV(D) (FIREPROOFED

FLOOD

FILL

GREATER OF 30 m OR ONE DIAMETER

RELIABLE GAGEMAINTAINABLE WITHSPHERE IN OPERATION BLEED (GUSSETED)

DRAIN WITH ELL

SAFETYVALVE 8

GROUNDED

1

SLOPE

2

SLOPE

DR 1999

FIREWATERSPRAY SYSTEMBELOW SPHERE

Figure 3.2.5-b: Typical spherical tanks (from DP XXII-C)

Note: GP 15-1-3 referenced in the both figures further refers to GP 9-7-1 for details oninstalling level devices. GP 9-7-1 shows welding to an atmospheric tank. Welding shallnot be done to pressure tanks and an alternate means of level device support isnecessary.


Aboveground pressurized LPG tanks need certain considerations as to siting andlocation. These are explained under section 2.2.2.4 “Siting of Aboveground Tanks andEquipment.” Horizontal bullets and spheres are more vulnerable to fire exposure thanmounded drums. Therefore, codes recommend installation of some kind of fixed fireprotection. Depending on risk, fire resistant coatings may be needed for bullets andspheres that are normally equipped with fixed water spray or water deluge systems.These requirements are discussed in depth in Chapter 8 under “Firewater Sprays,”“Firewater Deluge for Spheres,” and “Fire Resistant Coatings.” Storage at refineries andUpstream Gas Plants shall be provided with water flooding facilities to inject water anddisplace LPG in the lower parts of tanks, in the event of a tank leak.

Spheres shall be built in accordance with GP 9-2-1. They are normally equipped withtop and bottom manholes. The filling and withdrawal connections for spheres arenormally at the bottom. LPG Sphere tanks shall be provided with steel support columnsand wind (earthquake) girders. Columns shall be mounted on concrete foundation withanchor bolts. The columns shall be fireproofed from ground level to intersection of thesupport with the tank shell (see also drawing in Chapter 8).

3.2.6 Spill Containment

Spill containment shall be considered for all locations and shall be provided in locationsin which either of the following would result in a significant hazard to important nearbyfacilities, nearby properties, or public areas, per API 2510:

1. The physical properties of the stored LPG make it likely that liquid materialwill collect on the ground. The more hydrocarbons like Butane (or Pentane)is contained in the LPG the more it will spill as a liquid.

2. Climatic conditions during portions of the year make it likely that liquid LPGwill collect on the ground.

The ground beneath aboveground LPG tanks shall be of impervious construction andgraded to be sloping away from the tanks at minimum 1 percent gradient, to drain anyliquid spills to a safe area away from the tanks and piping. Diversion kerbs with aheight not exceeding 380 mm to avoid formation of gas traps may be permitted ifnecessary for directing possible spillage away from bullet tanks.

If spill containment is to be provided, it shall be either remote impoundment or diking ofthe area surrounding the spherical tank. If diking around the tank is to be used forspill containment, the diked area shall be designed according to GP 9-1-1.

Remote impoundment collects any spill at a location away from the tank. This may beof significant importance shall the vaporizing LPG ignite during the spill. However,installation of remote impoundment may need more land. In any case, all materials forcomponents of spill containment shall be capable of withstanding the effects of athermal shock associated with spilling LPG. Furthermore, spill containment shall allowfor adequate venting of the vapor generated during an LPG spill.

If remote impoundment is to be used for spill containment, the remote impoundmentfacility shall be designed as follows:

1. Grading of the area under and surrounding the tanks shall direct any leaks orspills to the remote impoundment area. Grading shall be at a minimum of1 percent slope.

2. Walls, dikes, trenches, or channels may be used to assist in draining the area.

3. The remote impoundment area shall be located at least 15 m from the tanksdraining to it and from any piping or other equipment.

4. The holdup of the remote impoundment area shall be not less than 25 percentof the volume of the largest tank draining to it. If the material stored in the


tank has a vapor pressure less than 690 kPa at 38 °C, the holdup for theremote impoundment facility shall be not less than 50 percent of the volumeof the largest tank draining to it. Larger holdups shall be provided in theremote impoundment facility at locations where the expected vaporization isless than that specified above because of climatic conditions or the physicalproperties of the material.

5. The electrical classification is to be the same as a diked area.

Whether spill containment is provided or not, the ground under and surrounding a tankused to store LPG shall be graded to drain any spills to a safer area away from the tank.The drainage system shall be designed to prevent liquid spilled from one tank fromflowing under any other tank. The spill drainage area shall not contain equipment likepumps or LPG piping not associated with the tank.

3.2.7 Vacuum Conditions

An additional design consideration shall be addressed where commercial Butanes arestored in cold climates in horizontal “bullet” tanks and spheres. If the temperature ofthe stored liquid can fall below boiling point of Butane (approximately –7 °C, for thetypical commercial Butane/Butene mixture and 0 °C for pure normal Butane), thepressure in the tank can drop below atmospheric pressure. There are several options tohandle this low pressure situation.

1. The tank can be designed to withstand the maximum degree of partialvacuum possible by increasing wall thickness or adding stiffening rings. Ifan adequate margin of safety is provided, this is a satisfactory solution,because it requires no operational control.

2. Pressure can be maintained by bleeding vapor from nearby Propane tanksor 50 kg cylinders.

3. Provision can be made to heat the liquid by means of hot gas return from anexternal vaporizer, thereby maintaining positive pressure.

4. The supplying refiner can be asked to raise the vapor pressure of the Butaneduring periods when cold weather can be anticipated by increasing thePropane/Propylene content.

5. Vacuum breakers may be installed. However, this is discouraged andshould be considered only if no other solution can be implemented since theyinvolve uncontrolled introduction of air into the system, and may createpotential operating and safety problems.

It is always best to design the system such that it can withstand full vacuum. All otherdesign options should be evaluated using risk assessment techniques.

In an emergency case, inert gas (Nitrogen) may be injected to maintain pressure. Partialpressure effects and associated lifting of the pressure relief valves may be encountered.Therefore, extreme care shall be required when embarking on such activities.

The proposals are ranked by preference. Options 2), 3), 4), and 5) require control andalarm instrumentation, and are subject to operator error and maintenance deficiencies.

3.3 Refrigerated LPG StorageUsing refrigerated storage (–50 °C for Propane) normally accommodates large capacityrequirements. This type of storage involves a thermally insulated tank operated atapproximately atmospheric pressure. Additionally, a cooling system involving pumps,compressors and exchangers as well as an emergency blowdown system (flare) are


needed. Details on refrigerated storage are not outlined in this Guide. For design,reference shall be made to EMRE Design Practices, GP 9-6-1 and NFPA 58 Section 9.

3.4 Overpressure Protection for TanksThis chapter discusses overpressure protection for LPG tanks, the different types ofPressure Relief Valves (PRV) used, the procedure on how to size them, the principlesof installation and the testing frequency.

Prevention of loss of containment is by far the most important concept during thedesign of a pressure system. Overpressuring a system has the potential for loss ofcontainment. Therefore, it is important to incorporate adequate facilities to preventoverpressuring LPG systems.

3.4.1 Contingencies to be Expected

A “contingency” is a normal or abnormal event during plant operation that could lead tooverpressuring. The magnitude of the contingency will have a direct impact on sizingthe pressure relief system. Following is a description of common contingencies thatmay affect LPG storage:

1. Tank exposure to external heat in the form of impinging fire or heatradiation from an adjacent fire will lead to boiling and subsequent pressureincrease.

2. Overfilling to liquid full can cause overpressure.

3. Thermal expansion of the liquid can cause overpressure. If a tank is filledwith cold product and filling has exceeded 85% and the tank is exposed toexternal heat (sun) its contents will expand and may exceed 100% of tankvolume.

4. Introduction of Propane into a Butane tank, which has been designed onlyfor Butane, could cause overpressure.

5. Improper commissioning (air freeing) of a tank may lead to high pressurebecause of presence of non-condensables (inert gas, Nitrogen).

Bullets and spheres exposed to external heat normally will produce the largest reliefrequirements. Therefore, this will dominate sizing of the valve. This is not true formounded drums.

Avoiding loss of containment by overpressure can be accomplished in two ways. First,a pressure relief device protects the system. A Pressure Relief Valve (PRV) is the mostcost effective solution to protect the system. Typical PRVs in LPG service are springloaded valves that are designed to open automatically if the set pressure (tank designpressure) is reached. Second, the system could be designed for a pressure considerablyabove the operating pressure. The cost for this in most cases would be considerablyhigher than that of a normal tank, yet, in some countries such designs are required fortanks in transportation services. The draw-back here is that in case of truck overfillingthere is no protection against thermal expansion pressure increase. The latter designmethod shall only be used where local codes prohibit Pressure Relief Valves.

It should be noted that during fire impingement on a tank, the containment couldultimately be lost due to excessive metal temperatures causing a Boiling LiquidExpanding Vapor Explosion (BLEVE). Overpressure protection cannot prevent aBLEVE since red-hot tank walls will fail at pressures far below the design pressure ofthe tank. The best way to prevent this kind of failure is by providing passive fireprotection by mounding the tank. Fireproofing combined with firewater protectionmost likely may prevent a BLEVE, however, if the firewater fails during a prolonged


fire the tank may fail since fireproofing is only good for a limited duration of fireexposure.

3.4.2 Refinery and Upstream Pressure Relief

Pressure relief requirements for LPG storage and loading/unloading facilities atRefineries and Upstream Gas Plants are described in Design Practices Section XV-C.To prevent liquid discharge and undersizing of PRVs the ERE report EE.28E.90 “SizingPressure Relief Valves in Flashing and Two Phase Service, An Alternative Procedure”shall be followed. Furthermore, API RP 520 “Design and Installation of PressureRelieving Systems,” as well as API RP 521 “Guide for Pressure Relieving andDepressuring Systems” apply. Refineries and Upstream facilities typically useconventional pressure relief valves. The typical pressure relief valve in Marketing is theaxial flow valve described below.

Figure 3.4.2: Conventional pressure relief valve

3.4.3 Pressure Relief in Marketing Terminals

Sizing of pressure relief valves is governed by codes. If local codes are more stringentthan those discussed below, they shall apply. Tanks for bulk storage have typically been


designed according to the American Society of Mechanical Engineers (ASME) Boilerand Pressure Vessel Code Section VIII. This code also covers requirements foroverpressure protection and relief devices. In addition, the Compressed GasAssociation (CGA) has applicable provisions in their three pamphlets on PressureRelief Device Standards S-1.1, S-1.2, and S-1.3. National Fire Protection Association(NFPA) has included the CGA provisions in NFPA 58, Appendix E and in NFPA 59,Chapter 9. Capacity requirements for pressure relief valves on above ground, non-refrigerated ASME tanks (bullets, spheres) shall be in accordance with the applicableprovisions in these standards. Following are the details on the sizing of PRVs forbullets, spheres and for mounded drums.

Figure 3.4.3-a: Large pressure relief valves on marketing sphere

The set pressure of a pressure relief valve shall be equal to or less than the designpressure of the tank. Historically this was not always the case. Tanks built before 1950


had different settings, which can be taken from NFPA 58. The CGA pamphlets alsomention the “start to discharge pressure” which is the pressure at which the PRV showsthe first signs of leakage. This is typically at about 90% of the set pressure but is onlyrelevant for judging the quality of PRV maintenance. The flow rating pressure (atwhich the capacity of the pressure relief valve is determined) is 121% of the set pressurewhen the valve is sized for the fire contingency only. The reseating pressure (at whichthe PRV closes again) shall be 7% below set pressure.

Figure 3.4.3-b: Multi-port pressure relief valve

Flow rating requirements are determined as follows. As already stated earlier forbullets and spheres the largest relief requirement originates from external heat exposurecaused by fire. For these tanks the heat input will be related to the size of the tank andits total surface area.

1. For tanks below 186 m2 total surface area the adequate rate of discharge incubic meters per minute of air at 121% of the set pressure is presented inTable 3.4.3 “Flow Requirements for Pressure Relief Valves for Tanks.”

2. If the tank surface area is larger than 186 m2 the adequate rate of dischargein cubic meters per minute of air at 121% of the set pressure is determined bythe formula:

PRV Flow Rate (m3/min., Air) = 10.66 x A 0.82

Where A = Total outside surface area of the tank in m2.


A simplified method for calculating the surface of tanks is outlinedbelow.

The surface area is the total outside surface area of the tank in square meters. Thetank surface area can be calculated by using one of the following simplified calculatingformulas:

1. Cylindrical tank with hemispherical heads:

Area = Over-all length x outside diameter x π.

2. Cylindrical tank with other than hemispherical heads:

Area = (Over-all length + 0.3 outside diameter) x outside diameter xπ. Note that this formula is not exact, but results will be within thelimits of practical accuracy for the sole purpose of sizing relief valves.

3. Spherical tank:

Area = Outside diameter squared x π.

Figure 3.4.3-c: Internal and external pressure relief valves used in marketing facilities

It should be borne in mind that it is important to choose the valve(s) to match the flowrating as close as possible. The appropriate choice of valve orifice size (or the sum oforifices if more than one valve is used) will result in slight oversizing. Undersizingcould lead to overpressure; however, grossly oversizing could lead to valve“chattering” (a rapid succession of opening and closing the valve) and self destructionof the PRV. If a multi-port manifold is used, one valve shall be spare, the other(s)good for a total 100% of the required relieving rate.

3.4.3.1 Pressure Relief on Mounded Drums

Mounded drums shall be protected against overpressure as follows. The larger of thetwo figures shall be used to determine the flow rate for PRVs on mounded drums.

1. Determine the required PRV flow capacity by considering the maximum flowcaused by overfilling, high vapor pressure (if Butane is stored), impropercommissioning (air freeing), or inert accumulation (Nitrogen). Since in all


of the above cases the filling process will cause overpressure, the pumpingcapacity shall be checked when determining the PRV size.

2. The codes propose the following simplified orifice sizing approach toestimate fire loads. Calculate the surface area of the mounded drum. If themounded drum surface is less than 186 m2 establish 30% of thecorresponding flow rate in Table 3.4.3 “Flow Requirements for PressureRelief Valves for Tanks.” If the tank surface exceeds 186 m2, calculate 30%of PRV Flow Rate (m3/min, Air) = 10.66 x A 0.82. Check whether thisfigure is larger than the pumping capacity mentioned above.

Since mounded drums are completely covered by an earth mound they will not besubject to direct radiation from external fire and PRVs are not sized for this contingency.If the tank has to be uncovered for maintenance (See LPG Safe Operations Guide) orother reason, LPG shall first be completely removed from the tank. Otherwise, shoulda fire occur during maintenance the tank would not be protected against thiscontingency. Likewise, during first commissioning the tank shall be mounded beforefilling.

SurfaceArea

Air FlowRate

SurfaceArea

Air FlowRate

SurfaceArea

Air FlowRate

SurfaceArea

Air FlowRate

m2 m3/min m2 m3/min m2 m3/min m2 m3/min

>1.86 17.57 12.07 82.12 26.01 154.30 83.61 401.80

2.32 21.27 12.54 84.67 26.94 158.90 88.26 419.90

2.79 24.69 13.00 87.22 27.87 163.10 92.90 438.00

3.25 28.03 13.47 89.77 28.80 167.60 97.55 455.90

3.72 31.15 13.94 92.32 29.73 172.10 102.19 473.50

4.18 34.55 14.40 94.87 30.66 176.40 106.84 491.30

4.65 37.66 14.86 97.42 31.59 180.90 111.48 508.60

5.11 40.49 15.33 99.96 32.52 185.20 116.13 525.80

5.57 43.61 15.79 102.50 33.45 189.40 120.77 543.10

6.04 46.44 16.26 104.80 34.37 193.70 125.42 560.10

6.50 49.56 16.72 107.30 35.30 198.20 130.06 577.10

6.97 52.39 17.19 109.90 36.23 202.50 134.71 594.10

7.43 55.22 17.65 112.10 37.16 206.70 139.35 610.80

7.90 58.05 18.12 114.70 41.80 227.70 144.00 627.50

8.36 60.88 18.58 116.90 46.45 248.00 148.65 643.90

8.83 63.43 19.51 121.80 51.09 268.20 153.29 660.30

9.29 66.26 20.44 126.60 55.74 287.90 157.93 676.80

9.76 69.09 21.37 131.10 60.39 307.50 162.58 692.90

10.22 71.64 22.30 135.90 65.03 327.00 167.23 709.30

10.68 74.48 23.22 140.50 69.68 346.00 171.87 725.50

11.15 77.02 24.15 145.30 74.32 364.70 181.16 757.50

11.61 79.57 25.08 149.80 78.97 383.40 185.81 773.30

Table 3.4.3: Flow requirements for pressure relief valves for tanks (below 186 m2)

NOTE: The required flow capacity is in cubic meters per minute of air at standardconditions, 15.6 °C and atmospheric pressure. For intermediate values of surface area,the rate of discharge may be interpolated.

3.4.3.2 Installation of Pressure Relief Valves

All pressure relief valves shall bear a substantial non-corrosive metal identificationplate giving, at a minimum, the manufacturer's name, code under which fabricated,set pressure and orifice size.


The total required relief valve capacity can be covered by multiple pressure relief valves.These may be installed with a manifold that includes provision for selectively closingoff any particular relief valve to permit removal for inspection while the remaining reliefvalves provide the discharge capacity required for the tank.

Pressure relief valves shall be located on top of the tank in direct flow connection to thevapor space such that the frictional pressure drop between tank and PRV nozzleunder full flow conditions (at rated capacity of the PRV) does not exceed 3% of thePRV set pressure. Long or narrow piping connections between the tank and the PRVare not allowed because this could result in excessive pressure drop and the associateddifficulties (inadequate relief and “chattering”).

Regulations concerning valving between tank and PRVs allow for the followingoptions:

1. Install pressure relief valves without block valves.

2. Provide excess relief capacity with multi-port arrangement valves, interlockedvalves, or sealed (CSO = Car Sealed Open) block valves. Isolating one valveshall not result in reducing the capacity below required relieving capacity.

3. Install pressure relief valve with CSO block valve and warehoused spare.PRV can be removed and replaced under carefully managed procedure whichminimize time without PRV and control operations and pressure during thattime.

In the first case, the tank has to be emptied for testing and maintaining the PRV. Thelatter cases permit removal with the tank in operation. CSO valves may not be permittedby some local codes.

If CSO gate valves are installed upstream or downstream in piping associated with aPRV their stems shall be oriented horizontally or upside down. This is to prevent thegate from dropping by gravity, should it detach from the stem.

Pressure relief valve discharges on tanks having volumetric capacity of 10 m3 or largershall be discharged via a vertical vent stack extending above the heads of personnelwho could be on the PRV platform (minimum of 2.1 m typical in Marketing and 3 m inRefining and not less than 3.0 m above ground level.) into open air or closed flaresystems if so required by authorities. The discharge vent or header shall be sized suchthat at full flow the pressure drop does not exceed 10% of the PRV set pressure.Discharges shall not be allowed to enter enclosed spaces. The vent shall be piped toprevent impingement of escaping gas on the tank, nearby tanks, operating pipelines andequipment. Vents shall be protected against mechanical impact and be designed tohandle any thrust during PRV discharge. Vent systems where several vents dischargeinto a header are not permitted since the discharge velocity at the end of the vent systemmay be so low that proper dispersion of the vapors is not guaranteed.

Drilling a 20 mm weep hole in the vent line low point shall prevent accumulation ofliquid or condensate. If vapor exiting the weep hole would impinge on the tank or otherequipment, an elbow or deflector plate may be used to redirect flow. Small diameterdischarge lines (typically Marketing) could have their mechanical integritycompromised by a 20 mm hole. For these small lines a loose fitting plastic rain cap atthe top of the vent may be combined with a smaller weep hole.

3.4.3.3 Pressure Relief Valve Testing Requirements

Pressure relief valves in LPG service normally operate in a clean, non-corrosiveenvironment. Pressure relief valves in LPG service have shown a good reliability overthe years. However, since no mechanical device can be expected to remain in operativecondition indefinitely it is recommended to test or replace PRVs on LPG bulk storagewithin a 5 year interval. Local regulations, if more stringent, may overrule this


interval. Testing of PRVs requires special procedures and equipment, manufacturer’sadvice shall be obtained if testing is to be carried out at plant.

3.5 Emergency Block Valves on Bulk LPG TanksEmergency Block Valves (EBV) are provided to stop LPG liquid flow from the tank topotential downstream emergencies. EBVs permit quick control of hazardous situationsby stopping leaks at pump seals, at hose ruptures, or at fires. EBVs are recommended tobe metal gate or plug valves or high performance ball or butterfly valves with metalseats (not soft seats). They shall meet the requirements of GP 3-12-1 and DesignPractices Section XV-F. Soft-seated valves NPS 4 and smaller meeting GP 3-12-1 maybe used. Soft-seated valves over NPS 4 shall not be used as EBVs. They may be usedin non-EBV service provided they meet the fire-safe requirements of API 607 and GP 3-14-1.

EBV shall be of approved make and shall incorporate all the following means of closing:

1. Local manual shutoff.

2. Remote-operated manual shutoff. Remote activation device or pushbuttonshall be accessible during an emergency

Valves which are sandwiched between 2 flanges by long, exposed bolts shall not beused. EBV's may be either automatic/remote operation or manual operation as definedbelow. In Upstream and Refining typically EBV's may be fitted externally between tankflange and piping. For Marketing EBV's are often installed internally upstream of theoutlet flange. More details on Emergency Block Valves can be found in ERE reportsEE.27E.84, “Guidelines for Selection and Installation of Emergency Block Valves” andEE.44E.94, “Possible Risk Reduction Design Items for Above Ground Pressurized LPGStorage.”

3.5.1 Tank EBV's in Liquid Service

All liquid phase inlet and outlet connections on the tank larger than 25 mm diametershall have an EBV and an additional manual shutoff valve located as close as practicableto the tank. The EBV may be installed inside tank (manual or automatic remotehydraulic operation). Externally installed EBVs to the liquid phase shall either close byremote operation or automatically. Remote operated valves may be either fail safe ortheir actuators and energizing lines fireproofed. Connections to the liquid phasebelow 25 mm may only have two manual block valves.

Automatic fail safe valves close upon failure of motive energy or control signal. Theirmotive energy supply shall be designed to fail (melt) in the event of a fire. Remoteoperation non fail safe valves (gate or quarter turn) usually rely on an electrical orhydraulic actuator. In order to function, these valves need to be energized during apotential fire. Therefore, signal and electric cables (or hydraulic ducts) as well asactuators shall be fireproofed in order to function during the first 15 minutes of anemergency. The 15 minutes are based on API 2510 and on the assumption that within15 minutes of a fire developing appropriate action has been taken. Normally refinerieshave fireproofed valves and new Marketing installations have fail safe valves. Thecontrol system shall be arranged so that these valves can be closed individually and canalso all be closed simultaneously by an emergency shutdown system that shuts down allLPG pumps and compressors at the facility as well. See also Chapter 2, “EmergencyShutdown system.” Means of remote actuation of EBV may be pneumatic, hydraulic,electrical or mechanical. The actuation point shall be in a safe location outside theimmediate risk area, at least 15 m away from an aboveground tank or the valve assemblyon an underground or mounded tank. Signage shall be installed at the actuation point toindicate its location and mode of operation.


Manual shutoff valves installed close to the tank shall be capable of an adequate sealunder fire conditions as specified in the 30 minutes fire test in API 607 or equivalent.

3.5.1.1 External Shutoff Valve

Remote operated external shutoff valves installed immediately at the first flange of thetank are the preferred option to provide emergency blocking capability. Springactuated quarter turn ball valves (NPS 4 or less) with electric, hydraulic or pneumaticspring release is an adequate choice to perform fail safe operation. The signal lines tooperate the valve shall be either of plastic or low melting point metal. Should a firedevelop in the vicinity of the tank, these lines should fail and the valve would closeautomatically. Tying the valve into the plant Emergency Shutdown System (ESS)provides remote shutdown capability.

Figure 3.5.1.2-a: Internal excess flow shutoff valve

3.5.1.2 Internal Excess Flow Shutoff Valve

Another option for the remote operated tank emergency block valve is an “internalexcess flow shutoff valve.” It is located inside at the bottom of the tank and kept openby a hydraulic system. The signal lines to operate the valve shall be either of plastic orlow melting point metal. In case of fire close to the tank these lines fail and the valvesclose automatically. Tying a depressuring valve into the plant Emergency ShutdownSystem (ESS) provides remote shutdown capability. However, such valves are onlyavailable for sizes up to 100 mm. Larger internal valves without excess flow shutoffhave been installed in the past and may continue to be used.

Selecting the closing flow rate of an excess flow valve involves an analysis of the flowcharacteristics of the complete piping system. If the closing flow rate happens to beconsiderably above the flow that could be obtained by rupture of downstreampiping/hose the valve will not close automatically. The valve shall be mounted in thecorrect direction. Furthermore, installation shall be such that adequate clearance isprovided around the inlet ports of the valve, otherwise the pressure conditions duringnormal flow may be equal to excess flow conditions and the valve would close undernormal operating conditions. Excess flow valves shall have a rated closing flow about50% greater than the expected design flow rate. All liquid and vapor withdrawal


connections on the tank (except for the pressure relief valve connection or where theeffective opening into the tank is smaller than 1.4 mm diameter) shall have a positiveshutoff valve located as close as practicable to the tank, in combination with an excessflow valve installed on the tanks’ withdrawal nozzles.

Figure 3.5.1.2-b: Internal excess flow shutoff valve operation

The effectiveness in the event of a line/hose break of an excess flow valve is limited bycertain conditions. It can only be maintained when the tank is taken out of service. Thevalve may not close automatically if:

1. Piping system restrictions (due to pipe length, branches, reduction in pipesize or number of valves) decrease the flow rate to less than the valve'sclosing flow.

2. The break or damage to the downstream line is not large enough to createenough differential pressure across the valve to close it.

3. A shutoff valve in the line is only partially open and will not allow enoughflow to close the excess flow valve.

4. LPG pressure upstream of the excess flow valve, particularly due to lowtemperature, is not high enough to produce a closing flow rate.

5. Foreign matter (such as welding slag, scale or sludge) is lodged in the valveand prevents closing.

Figure 3.5.1.3: Quarter turn ball valves

3.5.1.3 Manual Back-up Valve

All automatic or remote operated EBVs shall be provided with a second, manuallyoperated isolation block valve. This double block is provided as a backup formalfunction of the automatic or remote operated valve and to ensure additional shutoffin case of leak. The best choice is a quick closing quarter turn ball valve, which shallmeet the requirements of GP 3-14-1.

3.5.2 Tank Shutoff Valves in Vapor Service

Vapor return lines and other tank connections to the vapor phase shall have two manualisolation valves. Any ball valve shall meet the requirements of GP 3-14-1.


3.6 Tank InstrumentationThe following LPG tank instrumentation is needed to satisfy the basic needs for safeoperation of LPG bulk storage:

1. Tank level measurement shall be based on risk of overfill considerations.Tanks receiving rundown streams from processes or pipelines or shipunloading shall be equipped with two independent level gauges and a highlevel alarm. Tanks receiving smaller parcels like road bulk trucks or singlerail cars may need only one level gauge.

2. Independent level high-high alarm (LHHA) for continuous rundown and largeparcel receipt. If tank is filled by ship or pipeline the LHHA may also act as aCut Off (LHHA(CO)) on the tank inlet valve.

3. Pressure indicator.

4. Temperature indicator.

Figure 3.6: Typical connections for LPG sphere tank

Legend:

1. Inlet Nozzle 7. Bottom Manhole2. Outlet Nozzle 8. Top Pressure Gauge Connection3. Pressure Relief Valve Nozzle 9. Top Level Indicator Connection4. Atmospheric Vent 10. Bottom Level Indicator Connection (DP Cell)5. Drain Nozzle 11. Top and Bottom Temp. Indicator Connect.6. Top Manhole 12. Level Gauge Connection


The level high alarm and the independent level high-high alarm need an audible alarm atthe control room and, if the control room is not permanently manned, also a localaudible alarm. There shall be a local read-out for the tank level gauge, the pressuregauge, and the temperature indicator, however, the design engineer may decide to haveadditional remote read-outs at the control room. The alarm instrumentation shall bedesigned and installed so that the alarms can be tested without taking the tank out ofservice. In addition, an appraisal of the measurement needs of the particular locationmay reveal the need for more instrumentation depending on automatic stock control,custody transfer etc. Instrumentation shall be replaceable without taking the tank out ofservice.

Level and flow indicators with glass components shall not be used, because the glass issubject to breakage from fire, mechanical damage, or improper assembly.

Figure 3.6.1: Radar gauge (Saab)

3.6.1 Tank Level Measurement

New or renovated installations may be equipped with radar type tank levelmeasurement. This technology developed recently and has proven to be reliable. It issuitable for complete custody transfer automation with control from remote locations. Ithas no moving parts and is easy to be repaired with the tank in operation.

The previous type of tank level measurement was the servo gauge. Servo-gaugetechnology also offers high measurement precision but has moving parts and thereforeneeds more maintenance Servo gauges employ a small displacer, rather than a float,attached to a tape that passes over a measuring drum. A shaft to a servo motor (or“stepping motor” that continuously balances the downward force of the barely immerseddisplacer and its tape against a stress transducer connects the measuring drum. This


balanced system completely eliminates measurement error due to tape weight variationsor tape system friction.

The Magnetic Gauge may often be a solution to low cost installations in bullet tanks. Itconsists of a gauge constructed with a float inside the tank resting on the liquid surfacewhich transmits its position through suitable leverage to a pointer and dial outside thetank indicating the liquid level. The motion is transmitted magnetically through anonmagnetic plate and, since no venting of LPG is required, the magnetic gauge is arecommended type. However, it cannot be used for Custody Transfer of product.

Early installations have used dip-tubes, fixed level gauges or rotary gauges for levelindication. The fixed maximum liquid level gauge shall have the liquid level determinedon the maximum permitted filling limit when the liquid is at 4 °C for aboveground tanksor at 10 °C for underground or mounded tanks. Though outdated, they may still servetheir purpose especially as a back-up indication for the radar or servo gauges. If such avent type gauge is the only level control, a more modern level measurement system maybe warranted.

Float and tape gauges have been frequently installed in LPG sphere tanks. However,reliability has not been satisfactory. Their precision is limited by two factors inherentin their design: friction in the tape guides and pulleys, and varying weight of the tapeitself as product level changes in the tank. Therefore, installation is no longerrecommended.

3.6.1.1 Level High Alarms

Up to two level high alarms may be provided for LPG bulk tanks. The first alarm(Level High Alarm, LHA) can be integrated into the level gauge system. If there is acomputerized level measurement system the first alarm may be an integrated softwarealarm. The second alarm (Level High-High Alarm, LHHA) shall be entirelyindependent. It shall be installed for continuous rundown or large parcel receipt. Itshall be hard wired, fail safe (i.e. self checking with failure indication) and shallcontinue working when the level gauge and/or the first alarm fails. If the alarms are notfail safe the system shall be tested frequently. The first alarm shall be set just above the85% level, the second shall be set as close as possible above the first. If the plant issupplied by pipeline or tanker large volumes come into the tanks at high velocity.Therefore, the level high-high alarm shall also act as a cut off (LHHA(CO)) on thesupply line.

Alarm systems shall be tested quarterly with the option to change if there is adocumented good history, but not less than annual. Therefore, installation of a highlevel alarm system shall provide for complete testing of all mechanical and electronicsystem components without depressuring the LPG tank. The system shall be configuredto actuate the alarm when the electrical power circuit is de-energized, thus assuringprotection in the event of an undetected power supply failure. This latter feature shallnecessitate battery back-up for the alarm system. For horizontal pressure tanks apackless ball float in an external chamber, actuating a micro switch outside the chamber,is the preferred option. This typical design, explained in Section XII-C of DesignPractices, permits maintenance and testing without depressuring the LPG tank, butrequires two 38 mm valved connections on 609 mm centers for installation. A similar,but more complex installation, also described in Section XII-C, could be made using arefinery type displacer level measuring device.

3.6.2 Pressure and Temperature Indicators

A pressure indicator shall be installed on a 13 mm valved fitting to the 50 mmconnection at the top of the tank. The indicator shall be a high quality instrumentdesigned to permit test bench re-calibration, and shall be capable of accurately reading


pressures up to 120 percent of the pressure relief valve setting. There shall be a 50 mmblock valve on the tank nozzle and a 13 mm quarter turn valve as a second block valve.

The tank shall be equipped with a stainless steel thermowell, and a precision liquidfilled dial thermometer capable of accurately reading all expected tank operatingtemperatures. This requirement is not eliminated by provision of resistance temperaturedetectors or thermocouples. The independent thermowell and thermometer are stillrequired as a quick verification check on accuracy of the electrical/electronic devices.The liquid filled dial thermometer is recommended as it can easily be removed forcheck-calibration or for storage in a secure place when not in use. Flanges shall attachthermowells since this arrangement cannot result in erroneous unscrewing of the wholeattachment.

Figure 3.6.2-a: Pressure and temperature indicators

ThermowellTank Shell

Temperature

Indicator

Pressure

Indicator

DoubleBlock

Valves

Figure 3.6.2-b: Pressure indicator (PI) and temperature indicator (TI)

3.6.3 Grounding Connections for Tanks

Each tank shall be grounded to earth from at least two points. It shall be designed todissipate lightning strokes, which may affect the instrumentation. Copper tape, 25 mmby 3 mm shall be used for this connection and each grounding point shall be taken to aseparate electrode. The ground electrode (ground rod) may be a 16 mm diameterextensible type copper rod with a minimum length of 2.4 m. In areas where the water


table is low, the rod may have to be longer to reach the moisture in the ground. Theseelectrical connections shall be checked and tested on an annual basis. Therefore, theconnections shall be accessible. Some local regulations require grounding on all tanksabove a minimum size. Equipment using cathodic protection shall not be grounded.Cathodic protection shall comply with GP 19-5-1.

3.6.4 Product Odorization

LPG product, which is provided for sale for combustion use, shall be odorized.Odorization systems are offered as package units by companies like Williams,(Valencia, Ca. USA) and Lewa (Leonberg, Germany). They are fully integrated,electro-pneumatically operated and may have one or two injection pumps. They may becontrolled from either the digital or analog output signal from measuring equipment inthe gas line. A standby solid state repeat cycle timer may permit manual operation andstroke rate adjustment in the event the flow signal is temporarily lost or disconnected formaintenance. The odorant may be delivered in ordinary 200 liter drums and pumpedover into a storage tank, or a dedicated stainless steel drum may be filled at themanufacturer site and transported to the plant.

Figure 3.6.4: Odorization systems by Williams and Lewa

Safety in LPG Design PUMPS & COMPRESSORS 4-1

4 PUMPS & COMPRESSORS

4.1 Pumps

4.1.1 Pump Types Commonly Used

There are two fundamental types of pumps used for any service including LPG.These are the positive displacement pump or “PD” pump and the centrifugalpump. Positive displacement pumps have internal gears, vanes or othergeometry's which enclose discrete volumes of liquid at the suction and transportthem to the discharge. Positive displacement pumps do not in themselves generatepressure but simply move the fluid to the discharge where it assumes the backpressure in the piping.

In a centrifugal pump, the liquid enters an impeller and is accelerated to a highvelocity. Upon exiting the impeller the fluid is slowed down in the pump diffuserand the energy imparted in the form of velocity is changed to pressure.

Pump Flow

PositiveDisplacementPump Curve

Centrifugal Pump Curve

Pum

p H

ead

Figure 4.1.1: Pump characteristic curves

4-2 PUMPS & COMPRESSORS Safety in LPG Design

Positive displacement pumps are virtually insensitive to the type of fluid beingpumped, the fluid viscosity and fluid density. They deliver essentially the sameflow rate regardless of the fluid or pressure in the discharge. Centrifugal pumpson the other hand are very sensitive to the type of fluid (density) and the pressuredeveloped is a function of both the density and flow rate. The figure above showsthe characteristic flow curves for both types of pumps.

4.1.1.1 Rotary Shaft Positive Displacement Pumps

The type of positive displacement pump normally used in LPG service is a rotaryshaft positive displacement pump (see the Design Practices, Section X-F,“Positive Displacement Pumps” for a complete description of all positivedisplacement pump types).

Figure 4.1.1.1-a: Multiple gear pump

Figure 4.1.1.1-b: Internal gear "Crescent" pump

The design and installation of positive displacement pumps for most operatingplants are governed by American Petroleum Institute API 676, “PositiveDisplacement Pumps, Rotary Shaft;” GP 10-2-2; and Design Practices Section X,“Pumps.” The reader may wish to review these documents to determineapplicable features dependent on the particular installation. See also GP 10-1-1


“Centrifugal Pumps.” The following API codes may apply: API 610 “CentrifugalPumps for Petroleum, Heavy Duty Chemical and Gas Industry Series.” ASMEB73.1M “Horizontal End Suction Centrifugal Pumps,” ANSI B73.2M “VerticalIn-Line Centrifugal Pumps.”

The figures here show two different types of internal gear pumps, one with severalgears and one with only two gears, also called a Crescent pump. In these pumpsfluid is trapped between the teeth of the gear and casing and transported to thedischarge.

The figure below shows a sliding vane pump. Fluid is trapped between the vanesand the casing and transported to the discharge. The benefit of the sliding vanepump is that as wear occurs, the vanes simply move out automaticallycompensating. In both of these pump types, a single shaft penetrates the pressurecasing and shall be sealed to keep the LPG in the pump. See the section on “ShaftSealing” below, for additional details.

Figure 4.1.1.1-c: Vane pump

The advantages of positive displacement or “PD” pumps include:

1. PD pumps are capable of handling some vaporization in the suction.

2. PD pumps can tolerate more change in the net positive suction headavailable (NPSHa) and are self priming.

3. PD pumps are generally smaller and operate at lower speed thancentrifugal pumps making them ideal for mounting on road transportand taking power from an engine power take off (PTO).

4. PD pumps have higher efficiency than centrifugal pumps (dependent onthe viscosity of the fluid).

5. The pumping direction is reversible by reversing the direction ofrotation.

The disadvantages of PD pumps include:

1. Higher maintenance costs due to actual rubbing of the internal partscausing wear.


2. Potentially higher cost due to the need for special low speed motor orgear.

3. Not suitable for continuous operation over many weeks of duration.

4. Requires a pressure relief valve on the discharge.

Pressure relief valves are always required in the discharge of PD pumps becausethe pump simply pushes the fluid into the discharge line. If the discharge isblocked, the pump will continue to push the fluid until either there is insufficientpower to turn the pump or the pump casing or piping breaks. Pressure reliefvalves shall be sized for the maximum pump capacity and there shall not be anyvalves in the line between the pump discharge and relief valve. See DesignPractices Section XV-C, Safety in Plant Design, “Pressure Relief” for a completedescription of relief valve sizing and installation.

Figure 4.1.1.2-a: Centrifugal pump operation

Figure 4.1.1.2-b: Multi-stage centrifugal pump

4.1.1.2 Centrifugal Pumps

The figure below shows a cross section of a centrifugal pump. Inside thestationary casing (C), turns the shaft (A) to which the rotating impeller (B) isattached. The blades of the impeller accelerate the liquid inside the impeller andpush it to the impeller outside diameter at high speed. This action creates a lowerpressure at the impeller eye or inlet (D) thus drawing more fluid into the impeller.The high velocity fluid at the impeller exit is slowed within the casing thatconverts the velocity energy to head or pressure before the fluid exits the casing at(E). More information about the many styles of centrifugal pumps can be found inthe Design Practices, Section X: “Pumps.”


As previously stated, the head or pressure developed by a centrifugal pump varieswith flow. To match the required flow and pressure, centrifugal pumps can bedesigned with different width and diameter impellers, different speeds, and byproviding multiple impellers on one shaft as shown on the figure below.

Figure 4.1.1.2-c: Tank mounted submersible pump

The design and installation of centrifugal pumps for typical operating plants aregoverned by API 610, “Centrifugal Pumps for Petroleum, Heavy Duty Chemicaland Gas Industry Service,” GP 10-1-1, “Centrifugal Pumps” and for less severeduties, ANSI B.73. Unlike PD pumps, centrifugal pumps develop their ownpressure and the maximum pressure they can develop is at zero flow. Therefore,the pump casing and downstream equipment are usually designed accounting forthe maximum pressure and a relief valve is not normally provided in thedischarge.

The advantages of centrifugal pumps include:

1. Can provide very high flow rates economically.

2. Lower maintenance cost (no rubbing parts).

3. Lower installation cost on a cost per unit capacity basis.

4. Wide discharge pressure and flow range.

The disadvantages of centrifugal pumps include:

1. Lower efficiency, especially at lower flow rates.

2. Need to be primed.

3. Not tolerant of vapor in the suction.

4. More sensitive to inlet system problems and NPSH.


4.1.1.3 Minimizing Pump Cavitation and Vaporization

Pumping systems and the choice and location of pumps shall be based on anassessment of the Net Positive Suction Head (NPSH) required at the pump withthe aim of minimizing the likelihood of pump cavitation and vaporizationoccurring in the pump's suction system.

NPSH or Net Positive Suction Head, is the amount of energy available at theinlet of a pump above the total energy at which the fluid will vaporize. All pumpshave a Net Positive Suction Head requirement or NPSHr expressed in feet ormeters of water.

The suction system that the pump is connected to has an available NPSH orNPSHa. The available NPSH must always exceed the required NPSH or vaporbubbles will form at the inlet to the pump. These bubbles form at the impeller eyeand then implode within the impeller in a process called cavitation. Cavitation isdamaging to the pump and will eventually cause failure.

In addition to adequate NPSH, the inlet line to the centrifugal pump shall be freeof vapor bubbles and shall be completely filled with liquid: There shall not be anyhigh point in the suction line where vapor can collect and restrict the flow. Avapor return line to the supplying LPG tank will help to reduce vaporization in thesuction line. Heat reflective paint, shading from the sun or similar arrangementsto reduce the temperature of the product in the suction system may be helpful toprevent vaporization.

Vaporization of liquid LPG can also be reduced by providing sufficient static headon each restrictive piping device to cancel out the pressure drop of each device. A1370 mm column of LPG creates about 6.9 kPa (0.069 bar g) of static pressure.

Suction line and NPSH problems usually occur in centrifugal pumps for thefollowing reasons:

1. Suction line is too long or too small or both. Suction lines are typicallyat least one size larger than the flange of the pump to which they areconnected.

2. Too many bends, valves or fittings in the suction line.

3. Too high a flow rate causing increased pipe friction and inability tovaporize fluid in the suction tank to accommodate the drop in liquidlevel. A guideline to help control liquid LPG boiling is that no morethan 2 - 3 percent of the total tank volume shall be removed per minute.For underground tanks, it is even less: 1 - 2 percent..

4. Pump installed on a level that is higher than the tank minimumoperating level.

5. Suction line has high points between the pump and tank. Typically thesuction line shall slope upwards continuously from the pump back tothe tank.

6. LPG temperature higher than normal.

7. Debris or obstructions (such as valves not fully open) in suction line.This may include strainers or filters.

Taking these factors into account leads to the design criteria that the pressure dropin the suction line shall not exceed 0.07 to 0.14 bar. Complete information onpump NPSHa calculation can be found in the Design Practices Section X-D,“NPSH” and other Design Practice Sections on sizing lines for pressure drop,Section XIV, “Fluid Flow.”

One method to resolve NPSH and suction line concerns is to use a tank mountedsubmersible pump as shown in the figure above. Here, the pump is installed in a


pipe or barrel inside the tank with a ball valve on the barrel bottom. Formaintenance, the ball valve is closed and the barrel is de-pressurized.

4.1.1.4 Selecting Pump Type and Pump Features

Selection of the correct pump type is the key to a reliable, low cost installation.The following guides shall be used when selecting the pump type.

For most LPG transfer applications which are not in continuous service and wherehighly variable suction conditions exist, where maximum evacuation of the tank isdesired, where pumps are motor transport mounted and power take-off driven, apositive displacement pump shall be used. The sliding vane pump is preferredover a gear pump since it operates at higher speed (more compatible with availabledrivers) and is self compensating for wear when the correct vane and casingmaterials are chosen. The sliding vane type pumps are mostly used in cylinderfilling and loading/unloading applications with capacities up to 80 m3/h andpressure differential of 1.4 – 5.5 bar. The regenerative turbine type pump is veryreliable in cylinder filling applications where filling rates are up to 8 m3/h andpressure differentials up to 10 bar. The low NPSH vertical turbine canned typecentrifugal pumps are used in loading/unloading marine tanks or in applicationswhere the flow rates are higher than 80 m3/h.

Figure 4.1.1.4: Regenerative turbine pump

For LPG services, which are continuous, 24 hour a day, seven days a week,involve large flow rates (typically over 12 m3/h), have relatively constant inletconditions or are outside the range of commercially offered vane pumps, acentrifugal pump shall be selected.

For additional information on selecting pumps for any general service, see DesignPractices Section X, “Pumps.”


Pumps used in LPG service shall have the following minimum features:

1. Pumps shall be designed for LPG service. The characteristics of LPGrequire that all shaft and stem seals, set disks and other resilient parts beof materials that are impervious to the action of both LPG vapor andliquid.

2. Steel is the best choice of material for pressure containing parts of LPGpumps. However, some manufacturers produce pumps in ductile irondue to limited market demand on steel. Ductile iron would be thesecond choice. Cast iron is not allowed.

3. All pumps shall have proven experience in LPG service at or near theconditions of the service they will be used in. See GP 10-1-1 for theexperience clause required.

4. Positive displacement pumps shall have a relief valve in the dischargepiping. Integral relief valves in the pump are not considered areplacement for PRVs.

5. Centrifugal pumps shall be self venting or incorporate a ventconnection.

6. All pumps shall have a mechanical seal (proven LPG service), notpacking. More information DP X- G.

7. O-rings shall be of a fluorelastomer material such as viton.

8. Consideration shall be given to the non-lubricating characteristic ofLPG product when selecting pump for LPG service.

9. Pumps shall be selected and installed with sufficient net positive suctionhead (NPSH) to avoid cavitation under both normal operatingconditions.

10. Suction and discharge piping systems shall be sized to accommodatethe maximum design flow rate of the pump and the related pressurelosses.

11. Check valve shall be installed on the discharge side of all centrifugalpumps.

12. Where positive displacement pumps are used, a suitably sized pressurebypass system shall be installed. The product shall be re-circulated tothe pump suction line at least 5 m ahead of the pump suction.

13. Pumps capable of producing pressure high enough to damage anycomponent on the discharge side shall be equipped with a suitable reliefdevice that discharges to a safe location. This device shall be locatedupstream of the of the first block valve.

14. Electric motors shall be Class I, Division 2, Group D or equivalent.Motor enclosure shall be flameproof. Other electrical equipment shallbe approved for operation in the hazardous area in which they arelocated. All equipment located in the open shall be weatherproof.

4.1.1.5 Pump Sizing

Pumps shall be sized to suit the maximum operational flow rates and pressuresrequired. Pumps, compressors and piping systems shall have a loading rate sizedaccording to the size of the tank being filled. Adequate controls shall be providedto prevent tanks from being filled beyond their maximum liquid level.

A loading rate of 11.5.- 23 m3/h shall prove satisfactory for tank truck units up toa capacity of 9500 liters. A loading rate of 23 - 46 m3/h shall be required for38,000 liter units. In larger terminals, consideration shall be given to loading ratesof 68 - 114 m3/h to reduce the number of loading positions required.

See Table 4.1.1.4 for typical pump flow rates and pressure differentials.


Flow Rate Pressure Differential

Pump Sizing m3/h kPa

Rail car or truck unloading

With vapor return 23–34 340–520

Without vapor return 7–11 520–860

Loading delivery tank truck

With vapor return 23–34 340–520

Without vapor return 7–11 520–860

Cylinder filling 3–11 410–860

Table 4.1.1.4: Typical Pump Flow Rates and Pressure Differentials

4.1.1.6 Shaft Sealing

Whether the pump is a rotary shaft PD pump or centrifugal, the shaft mustincorporate some kind of device to keep the LPG in the pump. The characteristicsof LPG require that all shaft and stem seals, set disks and other resilient parts be ofmaterials that are impervious to the action of both LPG vapor and liquid. Mostpumps of current design will use a face contact mechanical seal consisting of acarbon ring and a silicon carbide or tungsten carbide ring. Either of the rings mayrotate or is stationary depending on the pump vendor's design.

The primary concern in sealing LPG is to ensure that there is a back-up device,which will limit the release of product in the event of primary seal failure. Currentpractice for onsite units and operating plants is to utilize a single mechanical sealwith a contacting, dry running back up seal, which takes over in the event ofprimary seal failure. There is also a pressure switch connected to the area betweenthe primary and back up seal to alarm a rise in pressure. Note: Due to a largepopulation of high pressure pump applications, Upstream requires at least tandemseals in all hydrocarbon applications, including LPG.

Complete details for selection of seals, seal types and seal arrangements can befound in the “ERE Pump Sealing Technology Manual,” No. TMEE-23 and in theDesign Practices section X - G.

4.1.1.7 Pump Pressure Control Valve

Where positive displacement pumps are used or pumps run at intermittent servicefor long intervals at shutoff conditions (e.g., topping off transports, fillingcylinders), a suitably sized pressure bypass system shall be installed. In suchconditions a pressure control valve shall return the product to the tank. This isimportant since just returning the product to the suction side or relying on theinternal pressure relief valve will result in rapid heat up, loss of suction andpotentially in damage to the pump. Spring loaded valves can be used to controlthe pressure, however they are not as good as the “Camflex” valves, which havesmooth flow characteristics. The Pressure Relief Valve shall not serve as apressure control valve since this will result in chattering, vibration and destructionof the pressure relief valve.


4.1.1.8 Strainers

Temporary strainers are used to protect a pump or compressor during the startupof new equipment. The piping layout shall permit insertion and removal of thestrainer without disturbing equipment alignment. Fittings such as tees, Ys, orspool pieces may be used for this purpose. The manufacturer of the equipmentbeing protected should be consulted concerning the size and type of strainer orfilter required.

A permanent strainer or filter may be needed to protect a meter or other sensitiveequipment. Its design and location shall permit cleaning without removing thestrainer body or draining long sections of line. Block valves and bypasses shall beprovided for this purpose. Connections larger than 50 mm diameter shall beflanged.

4.1.1.9 Pump Installation Requirements

Regardless of the pump type selected, the pump installation shall incorporate thefollowing items to help ensure safety and reliability:

1. The pump shall be located outside the LPG tank drainage and impoundarea in a freely ventilated space. Pumps shall not be positionedunderneath LPG tanks or containers. Drainage shall be provided toprevent liquid accumulation around a pump and to drain a spill to asafer area to minimize exposure to other pumps and piping.

2. The pump suction line shall be as short and large as possible with aminimum of bends, fittings and other obstructions. The suction lineshall slope up continuously from the pump to the tank with no highpoints or vertical U-bends than can trap vapor. Typical installationdetails for piping at a pump can be found in GP 3-3-2, “Suction andDischarge Piping for Centrifugal Pumps.”

3. Suction and discharge piping shall have flexibility and shall be properlyaligned to the pump in order not to exert excess forces on the pump.Incorporation of one or two horizontal ninety degree bends in thesuction and discharge near the pump will impart flexibility to minimizethermal stresses as ambient temperature changes. However, the bestmethod is to have a piping flexibility analysis done and compare theresults to the allowable flange stresses from the pump vendor.Additional requirements and information on piping installation can befound in GP 3-7-1, “Piping Flexibility and Support;” GP 3-18-1,“Piping Fabrication;” and GP 3-19-1, “Piping Erection and Testing.”

4. When a stationary pump is installed it shall be bolted and grouted to asubstantial concrete foundation and steel base plate. The pump shallalso be level and the driver aligned to the pump within themanufacturer's tolerances. Pump installation information can be foundin the pump and driver's manual from the vendor and in the API 686“Recommended Practices for Machinery Installation and InstallationDesign.”

5. Standard valving around the pump shall be as follows:

+ Remote and automatic shutdown valve at the tank outlet.

+ Manual block valve at the pump suction.

+ Manual block valve at the pump discharge.

+ Check valve in the pump discharge just inside the block valve.

+ A valved connection on the discharge within the check valve fora pressure gauge. The connection shall be seal welded and twoplane gusseted.


6. If the pump will be operated for any period of time below the minimumallowable flow from the vendor or at shutoff (such as in topping offtransports, filling cylinders, etc.) then a pressure controlled recyclesystem shall be installed (see Pump Pressure Control Valve). Thiswould be in addition to the relief valve on a positive displacementpump.

7. Suction and discharge piping systems shall be sized to accommodatethe maximum design flow rate of the pump and the related pressurelosses. If high transfer rates (above approximately 2.5% of tank volumeper minute) must be achieved, provision shall be made to supplyadditional vapor to the tank. The vapor pressure within the tank beingemptied may become sufficiently depressed during high flow rates tocause loss of suction to the pump. A vapor return line from the tank orvehicle being filled automatically eliminates this problem.Withdrawing liquid from two or more tanks at the same time may alsoeliminate this situation. A tank with fireproofing, which retards heattransfer from the surroundings, may also need supplemental vapor atmedium rates.

8. A pressure relief valve shall be installed on the discharge of all positivedisplacement pumps. The valve shall be located in the piping beforethe check valve and discharge block valve. The relief valve shall besized for the maximum pump flow rate. Since such relief valves releaseLPG in the liquid phase, the discharge piping of the valve shall bedirected back to the LPG tank.

9. If the LPG is stored below the freezing point of water, specialprovisions for the pump, seal, piping and installation are required.These include such items at special pump materials to withstand theCritical Exposure Temperature, special seal designs to avoid hang upfrom icing, and special connections to allow chill down of the pumpprior to starting. For such services contact EMRE for specialrequirements.

10. Pump discharge piping shall be securely anchored as close as practicalto prevent system vibrations from acting directly on the pump.

11. The pumps shall be provided with the following operational and safetyfeature: A local start-stop pushbutton shall be installed in the vicinity ofthe pump. A remote Emergency Shutdown System (ESS) pushbuttonshall be provided in a safe location in case the local start-stoppushbutton is not accessible because of fire or vapor cloud. Pump shallbe interlocked to stop when any Emergency Shutdown (ESS)pushbutton is activated if such a system is provided.

12. LPG pump shall be provided with block valves to isolate the pump fromLPG source. The block valves shall be installed on both suction anddischarge piping lines. They shall be located within 3 m from the pumpflanges.

4.2 CompressorsIn transfer operations, compressors are used to create a pressure differentialbetween two drums causing a flow of liquid from the drum at higher pressure.Compressors are also employed to transfer residual vapor from supplying drumsand other facilities in transport and maintenance operations. When designing acompressor system, consideration shall be given to the principal safety requirements ofselecting a compressor that is fit for the purpose of handling LPG vapor in thespecified conditions of service and that the system prevents liquid entering thecompressor.


Transfer of product by compressor is usually less economic compared to pumping.However, sometimes it is the best or only available method. Compressors areused for the following two purposes:

1. To transfer liquid product by aspirating LPG (taking compressorsuction) from the tank to be filled and discharging into the tank to beemptied. The pressure differential thus created will cause liquid to flowinto the tank to be filled. This transfer method is used to unload railcars, trucks and marine vessels since it will completely empty the tankwithout harming the equipment making the transfer.

2. To evacuate tanks. This may be done for economic reasons whenreceiving product by rail or for maintenance when a tank (or container)or cylinder has to be taken out of service.

.

Figure 4.2.1-a: Reciprocating compressor (Corken)

4.2.1 Compressor Types Used

Reciprocating, single stage, air cooled piston type compressors are mostfrequently used in LPG plants. These operate at low compression ratio. They areused to create pressure differentials between tanks to transfer liquids. Generallythey are small skid-mounted units. The exception may be larger reciprocatingcompressors used to off-load large ships. Various cylinder configurations(vertical, horizontal, 2 stage etc.) are used, depending on the flow rate anddifferential pressure required. There are also several different methods for powertransmission but belt drive is the most common. All belts drives shall complywith GP 10-11-1 para. 5.9 (static conductive belts). A typical reciprocatingcompressor is shown below. In Marketing operations centrifugal compressors are


not normally justified unless very large amounts of gas and liquid must betransferred and they are not covered in the requirements below.

4.2.1.1 Design Requirements for Compressors

Compressor shall be designed for LPG service. The characteristics of LPG requirethat all parts be made of materials that are impervious to the action of both LPGvapor and liquid. Compressors shall be equipped with a device to preventexcessive pressure in the delivery system. The design of the compressor shalllimit or exclude lubricating oil contamination of LPG vapor. Compressor shall besized within the maximum flow rating of the excess flow valves, if available, onthe incoming supply tanks.

Size, configuration and speed of compressors shall be selected on the basis of themaximum operational flow rate and pressure required. Electric motors shall beClass I, Division 2, Group D or equivalent. Motor enclosure shall be flameproof.Other electrical equipment shall be approved for operation in the hazardous area inwhich they are located. In addition to the electrical area classification, allequipment located in the open shall be weatherproof

Figure 4.2.1-b: Typical reciprocating compressor package (Corken)

For reference, larger reciprocating compressors intended for services in refineriesand chemical plants are governed by API 618, “Reciprocating Compressors forGeneral Refinery Services” GP 10-4-1, “Reciprocating Process Compressors; andfor less severe installations,” API 11P, “Specification for Packaged ReciprocatingCompressors for Oil and Gas Production Services.”

Small compressors intended for LPG transfer service shall have the features listedbelow as a minimum:

1. Compressors shall have proven experience in LPG at or near theconditions for which they will be installed. See GP 10-4-1 forexperience requirements.

2. Reciprocating compressors may be of the lubricated (where some oil isinjected into the cylinder to lubricate and seal the piston rings) or non-lubricated type. When the compressor is lubricated, some means shallbe provided in the discharge to remove the excess oil from the vaporstream. Filters and/or centrifugal traps may do this. Non-lubricatedcompressors and compressors specially designed for LPG applicationsdo not require oil removal facilities.


3. Some means (control) shall be provided to limit the suction pressure tothe maximum for which the compressor is designed, otherwise, thedriver will be overloaded. In addition, compressors shall have at leastone high pressure cut-off switch on the discharge side or similar deviceto prevent excessive pressure in the delivery system.

4. The compressor shall have a high temperature alarm to signal that thepressure differential becomes too high. As an alternate, temperatureindication on the discharge or differential pressure alarm may be used.As the compression ratio of a compressor increases, the dischargetemperature also increases which can then damage the compressor.

5. Traditionally, most reciprocating compressors (for LPG and otherhydrocarbons) have been manufactured with cast iron cylinders. Infact, current standards by API allow cast iron up to 69 bar gauge.However, if steel or ductile iron equipment can be obtained, it is thepreferable material choice.

4.2.2 Compressor Sizing

Size, configuration and speed of compressors shall be selected on the basis of themaximum operational flow rates and pressures required. Compressors shall besized within the maximum flow rating of the excess-flow valves installed on theincoming supply tanks when used for unloading shipments and on the plant's LPGtanks when used for loading shipments. When a compressor is used fortransferring liquid LPG in this manner, the liquid transfer rate is less than thevapor displacement of the compressor. The compressor manufacturer shall beconsulted to obtain the expected transfer rate under the plant operating conditions.Typical compressor volume flows and pressure differentials for operations in anLPG marketing terminal are as follows:

Volume Differential Pressure

25–340 std m3/h 70–140 kPa

Table 4.2.2: Compressor Volume Flows and Pressure Differentials Flow Rate: std m3/hat 15.6 °C and 101.325 kPa

4.2.2.1 Compressor Installation Requirements

Compressors shall be installed in a freely ventilated location. The compressorshall be securely mounted on a suitable foundation or base plate in accordancewith the compressor manufacturer’s recommendations. The compressor casingshall not be subjected to excessive strains transmitted to it by the suction anddischarge piping. Compressor piping shall be suitably braced to minimizevibration Properly sized knock out pots, fabricated to appropriate pressure vesselcode, shall be installed on the inlet of the compressor to prevent liquid fromentering the compressor.

On each knock out drum, a high level shutdown system is required so that if toomuch liquid accumulates in the drum, the compressor will automatically shutdownbefore liquid carry over to the compressor occurs. Check valve shall be installedon the discharge side of all centrifugal compressors. Strainers shall be installed onthe suction piping. The strainer element shall be designed and installed so that itcan be serviced.

The compressor shall be provided with the following operational and safetyfeatures:


1. A local start-stop pushbutton shall be installed in the vicinity of thecompressor.

2. A remote Emergency Shutdown (ESS) pushbutton shall be provided ina safe location in case the local start-stop pushbutton is not accessiblebecause of fire or vapor cloud.

Compressor shall be interlock to stop when any Emergency Shutdown System(ESS) pushbutton is activated if such a system is provided.

Figure 4.2.2: Knock-out drums (liquid traps)

Positive displacement compressors shall be equipped with suction and dischargeshutoff valves. A blowdown valve which relieves the trapped pressure when thecompressor is shut down shall be provided. Automatic blowdown valve isacceptable. Each positive displacement compressor shall be equipped with apressure-relieving device on the discharge side discharging to a safe location.

Following are installation requirements for compressors in LPG bulk plantservice:

1. Compressors shall not be positioned underneath LPG tanks. They shallbe located outside LPG drainage and impound areas and in accordancewith the spacing requirements defined in the section of this guideentitled “Equipment Spacing to Maximize Separation” in Chapter 2.

2. The compressor shall be bolted and grouted to a substantial concretefoundation in accordance with compressor manufacturer'srecommendations. Often the compressor and auxiliary equipment aresupplied on a steel frame, which is then bolted and grouted to thefoundation. The proper procedures to mount, level, install and shim thecompressor can be found in the API 686 “Recommended Practices forMachinery Installation and Installation Design.” Pipework to thecompressor shall be fitted and supported in accordance with themanufacturer's recommendations so as not to subject compressorcomponents to excessive stress.

3. On the suction side of the compressor appropriate means shall beprovided to prevent liquid phase of LPG from entering the compressor.


This is typically done by installing a suction knock out drum (liquidtrap) with a high level shut down to stop the compressor driver. Trapsshall be fabricated to an approved pressure vessel code and in addition,equipped with an independent liquid level alarm switch and a liquid drainconnection. For small compressors a knock out drum with a float toclose the inlet line to the compressor may be provided. When the inletvalve is closed the compressor should trip, e.g. on high current or lowsuction pressure, prior to pulling vacuum.

4. Reciprocating compressors, since they are positive displacementmachines, require a pressure relief valve on the discharge line. Thereshall be no valves in the line between the compressor outlet and reliefvalve. The pressure relief valve shall be sized for the maximum flow ofthe compressor. The valve may be routed to an appropriate, safelocation.

5. Standard valving on the inlet and outlet of a compressor is as follows:+ Remote and automatic shutdown valve at the tank inlet and

outlet.+ Manual block valve at the compressor suction.+ Manual block valve at the compressor discharge.+ A valved connection on the discharge for a pressure gauge. This

connection shall be two plane gusseted and seal welded inaccordance with GP 3-18-1.

+ An optional four way valve to automatically reverse the suctionand discharge when the compressor is to be used for bothloading and unloading.

6. Suction and discharge piping shall be fabricated so that they exertminimum stress on the compressor. Guidelines for piping fit up can befound in GP 3-19-1. Incorporation of one or two horizontal ninetydegree bends near the compressor may provide adequate flexibility buta piping stress analysis will reveal any significant problems. Suctionpiping shall also be designed without low points and pockets to trapliquids. For reference, GP 3-3-4 provides requirements forreciprocating compressor suction and discharge piping. Pipework forthe transfer of liquid LPG shall be sized so the overall pressure drop inthe system does not result in excessive condensation. Experience intypical LPG installations indicates that this pressure drop is generallynot in excess of 200 kPa. Install suction and discharge lines so that anycondensate that may form in the piping system does not drain into thecompressor. Isolating valves shall be installed on either side of thecompressor to permit its removal or maintenance while minimizing thevolume of LPG vented to atmosphere.

7. In cold climates compressor suction lines in Butane service shall bespecially reviewed to ensure condensed vapor cannot collect in thesuction line. Sloping the line continuously back to the tank andavoiding low points may do this.

Safety in LPG Design PIPING AND VALVES 5-1

5 PIPING AND VALVES

5.1 Piping in PlantsThis chapter discusses piping in plants. It highlights that piping shall run above groundwhenever possible, clarifies choice of piping materials and briefly explains pressure andtemperature ratings for piping. All metallic LPG piping shall be designed according toASME B31.3 “Chemical Plant and Refinery Piping” and shall meet the requirements ofthe appropriate Global Practices (GPs) noted in this chapter. All Pipelines shall belabeled to indicate contents and function. Country language must be used. Pipingarrangements for customer installations and automotive LPG can be found in therespective Chapters 10 and 11.

5.1.1 Piping Arrangements

5.1.1.1 Small LPG Plant

Figure 5.1.1.1 shows a small LPG plant with a truck unloading facility and cylinderfilling. This figure shows the pump installation in the plant for unloading trucks. Acompressor is preferred for unloading a tank car when a flooded suction is not availableor when vapor recovery from the tank car is required. The pump supplying the cylinderfilling operation requires a liquid bypass line with a back-pressure regulator because ofthe intermittent duty of the filling operations. Internal excess-flow valves and internalback-flow check valves are preferred on horizontal LPG tanks to prevent a major release onaccidental breakage of external piping or fittings. When external valves are used, they shallbe installed so that any undue strain beyond their limits will not cause breakage between thetank and the valves. The liquid volume between the block valve at the unloading vehicle andthe block valve of the plant must be minimized.

Figure 5.1.1.1: Small LPG Plant–Truck Unloading and Cylinder Filling Using a Pump

5-2 PIPING AND VALVES Safety in LPG Design

Description

(A) Use self-sealing couplings and rigid steel pipe/swing joint connections totruck or tank car.

(B) Equip vent line valves at unloading connections with spring-loadedactuators that must be manually held open.

(C) The emergency fail-safe shutdown system that closes valves must also stopthe pumps. Valves are not required at unloading point when receipt lineshold less than 0.05 m3 (50 l) of product.

(D) If pump bypass is not required, valve after pump may be eliminated forshort discharge lines.

(E) Piping at unloading point must be securely anchored to prevent pipingdamage from vehicles that pull away while connected.

Notes:

1. ASME tanks of 8 m3 or less capacity shall have no more than two pluggedopenings (typical in all installations).

2. Only liquid lines shall have thermal relief valves between all shutoff valves.

5.1.1.2 Small Plant with Rail Supply

A small LPG plant with truck or rail car supply and cylinder and truck filling facilities isshown in Figure: 5.1.1.2. This figure illustrates the piping arrangement required when acompressor is used for unloading tank trucks or tank cars. Although a compressor canbe used for truck loading, a pump is more common because it permits loading withoutthe use of vapor return from the truck. . The liquid volume between the block valve at theunloading vehicle and the block valve of the plant must be minimized.

Figure 5.1.1.2: Small LPG Plant–Truck or Rail Supply, Compressor Unloading, Cylinder and TruckFilling


Description

(A) Use self-sealing couplings and rigid steel pipe/swing joint connections to truckor tank car.

(B) Equip vent line valves at unloading connections with spring-loaded actuatorsthat must be manually held open.

(C) The emergency fail-safe shutdown system that closes valves must also stop thepumps and compressor. Valves are not required at loading point when receiptlines hold less than 0.05 m3 (50 l) of product.

(D) Flow reversal four-way valve.

Piping at loading/unloading points must be securely anchored to prevent damage fromvehicles that pull away while connected.

NOTE: Only liquid lines shall have thermal relief valves between all shutoff valves.

5.1.1.3 Multi-tank Installation

Figure 5.1.1.3 a shows a multi-bullet installation for cylinder and truck filling. Whenseveral LPG tanks are installed to meet the storage requirements, they shall bemanifolded in groups to provide operating flexibility. The maximum number of tanksallowed in any one group shall comply with the limitations as stated in NFPA 58. . Theliquid volume between the block valve at the unloading vehicle and the block valve of theplant must be minimized.

Figure 5.1.1.3: Multi-tank Installation


Description

(A) Use self-sealing couplings and rigid steel pipe/swing joint connections to truckor tank car.

(B) Equip vent line valves at unloading connections with spring-loaded actuatorsthat must be manually held open.

(C) The emergency fail-safe shutdown system that closes valves must also stop thepumps. Valves are not required at loading point when receipt lines hold lessthan 0.05 m3 (50 l) of product.

(D) Piping at loading/unloading points must be securely anchored to preventdamage from vehicles that pull away while connected.

NOTE: Only liquid lines shall have thermal relief valves between all shutoff valves.

5.1.2 Piping Location

Piping shall be located above ground and adequately supported and secured.Installations shall incorporate sufficient flexibility to withstand thermal expansion orcontraction, movement or settling of tanks, pumps, compressors, etc. Suction lines fromtanks or unloading racks to pumps shall slope continuously down from the tank outletor rack to the pump suction. For reference also see GP 3-7-1, “Piping Layout,Flexibility and Supports.”

Where piping is installed under a driveway, underground installation shall be within aconduit of sufficient size to accommodate the pipeline and the pipe shall have aprotective coating. The protective coating shall be suitable to withstand corrosion andshall extend at least 150 mm beyond the ends of the conduit. Both ends of the conduitshall be open to atmosphere.

5.1.3 Piping Integrity

LPG poses a higher risk than many liquid hydrocarbons because at atmospheric pressureit vaporizes readily and may develop large vapor clouds. All components of the pipingsystem shall be able to withstand internal temperatures and pressures, plus externalcorrosion and mechanical stresses. They also need a high degree of fire resistance. Forreference, also see GP 3-18-1 “Piping Fabrication” and GP 3-19-1 “Piping Erection andTesting.”

Piping shall conform to the provisions of ASME B31.3 or other appropriate nationalstandard. Piping shall also meet the provisions of GP 3-10-1 “Piping Selection andDesign Criteria”. Although ASME B31.3 allows construction of pipelines to meet onlyB31.4, within the plant site any pipeline shall meet the more stringent requirements ofB31.3. All welding at metallic piping shall be in accordance with the ASME Boiler andPressure Vessel Code Section IX.

Piping LPG service shall be selected from the following options:

Seamless pipe meeting the requirements of ASTM A106, API 5L or approved equal.The use of non seamless pipes shall be approved by the LPG Technical Advisor.

Electric fusion welded pipe (submerged arc or gas metal arc) meeting the requirementsof API 5L or approved equal.

Electric resistance welded pipe meeting the requirements of API 5L and the followingsupplementary limitations and/or requirements:


1. Grade A25 shall not be used.

2. Minimum pipe size shall be 19 mm.

3. If the percent carbon exceeds 0.23, the Carbon Equivalent (per API 5L) shallnot exceed 0.43%.

4. Pipe shall be normalized and tempered.

5. The pipe mill shall be audited or shall provide quality control data that isacceptable to the owner’s engineer.

Note: Upstream allows only seamless pipe in all applications, including LPG.

Carbon steel and Stainless steel are satisfactory for LPG piping components; but castiron, wrought iron, brass and copper shall not be used. Aluminum has limitedapplication for refrigerated LPG in low pressure services.

0100200300400500600700800

-50 0 50 100 150 200 250 300 350 400

Temperature, C

Pre

ssu

re, p

sig class 300 #

class 150 #

Figure 5.1.4: Graph of Pressure Limits Vs Temperature for A106 Carbon Steel

5.1.4 Pressure Ratings

It is suggested that all piping be designed for Propane, with a minimum workingpressure of 17 bar gauge, even where only Butane or a Propane/Butane mixture isexpected to be handled. This provides for flexibility if Propane operation is required ata later date. This requires a minimum flange rating of ASME Class 150. For pipingwithin a plant, minimum wall thickness is as follows:

50 mm and smaller: Schd. 80 (Extra strong)above 50 mm: Schd. 40 (Standard)

Higher flange and pipe ratings may be required for piping connected to high pressuresources, such as reciprocating pumps or cross-country pipelines. In such cases, unless apressure relief valve sufficient in size to relieve the maximum flow from the supplysource provides protection, the rating shall be at least equal to that of the supply piping.Where fluid surges may occur due to rapid valve closing, pump starting etc., a surgeanalysis shall be performed.

5.1.5 Pipe Sizing

Piping system shall be designed to meet the highest operating pressure at the expectedoperating temperature. Pipe sizing for lines shorter than 30 m can usually be determinedby the sizes of connections on transfer pumps and compressors. There is little economicincentive for minimizing diameter at these sizes.


Pressure drop (Friction Loss) calculations are needed for longer lines, where pump orcompressor suction conditions are suspected to be marginal, and where flow fromseveral sources joins in a manifold. The designer shall refer to Design Practices SectionXIV for liquid and vapor flow, and Section XV-C for pressure relief valve inlet anddischarge lines. Some valve and fitting manufacturers also publish guides for fluid flowcalculations.

Examples of situations where pressure drop shall be calculated include:

1. Pump suction lines (including internal isolation valve, when present). Wherea line size larger than the pump connection is found to be necessary, aneccentric reducer shall be installed, flat side up to prevent collection of vaporin the suction line.

2. Lines containing excess flow valves, to assure that cumulative pressure dropwould not limit flow in the event of a break to a rate, which prevents theexcess flow device from functioning.

3. Liquid or vapor manifolds or headers.

4. Long lines, such as to or from marine piers.

5. Pressure relief valve inlet and discharge lines.

0.1

1

10

100 1000 10000

Flow, l /min

25 32 38 51 64 76 102

152

mm pipe diameter

Figure 5.1.5: Pipe friction loss for Propane (for Butane multiply by 1.15)

5.1.6 Pipe Connections

Threaded fittings shall be forged steel while butt-welding fittings shall be seamless steelor equivalent material. Cast iron fittings (elbows, tees, couplings, unions, flanges, andplugs) shall not be used. Pipe joints in steel shall be screwed or welded.

Following are requirements for joints and connections used for piping in bulk storage:

1. Threaded and socket welded joints are limited to pipe sizes 50 mm andsmaller per GP 3-10-1. (Note: Upstream allows threaded and socket weldedjoints only up to 37 mm). Larger piping can be butt welded or flanged;welded joints shall be used whenever possible, and flanged or threaded


joints shall be minimized. Packed-sleeve and resilient-sealed couplingsshall not be used.

2. Flanges shall be weld neck, raised face, per ASME B16.5 or equivalent.Gaskets shall be the self-centering or confined type. Stud bolts shall be used,threaded full length with continuous threads. Flanges, gaskets, bolting andfittings shall meet the requirements of GP 3-16-1, except that slip-on flangesshall not be used for LPG.

3. Pipe bends may be used instead of welding elbows. The centerline bendradius shall be at least 3 times nominal pipe diameter. Bends shall meet therequirements of GP 3-18-1.

4. Flexible bellows type connectors are more vulnerable to mechanical damagethan steel pipe and are very difficult to inspect. Therefore, all efforts shall bemade to avoid installation of flexible bellows connections. In most situations,multiple welded bends can provide required flexibility without loss ofstructural integrity. Where flexible connectors (bellows) are used, they shallbe stainless steel Type 321 or 316L, with the flexible inner hose covered by abraided wire jacket. Working pressure shall be at least 17.25 bar gauge andburst pressure no less than 69 bar gauge. The connector shall be fabricated asa unit with end fittings for attachment to the piping system. If theconnections are flanged, one end shall have a floating flange to avoidtwisting. Overall length of a flexible connector shall not exceed 1 m; this issufficient for an offset up to 50 mm. This type of flexible connector shall notbe used in locations where it can come in contact with water, which containsChlorides.

5. Gaskets shall be suitable to protect against leakage during fire. SeeGP 3-16-1, “Flanges, Gaskets, Bolting, and Fittings” for specific details.

Pipe unions shall not be used except on cylinder filling carrousels, pump sealconnections or similar connections that need dismantling for maintenance and which canbe reliably blocked off. Unions shall be of forged steel with a working pressure of atleast 207 bar gauge, and shall have ground metal-to-metal seats. Gasket unions shall notbe used.

The designer may consider upgrading to stainless bolts on carbon steel flanges atlocations with severely corrosive atmospheres. This will limit the spread of corrosioninto the flange itself.

5.1.7 Small Piping Connections

Piping 50 mm and smaller has less mechanical strength than larger sizes, and less wallthickness to withstand external corrosion, so additional reinforcement of connections isneeded.

1. Branch connection 50 mm and smaller shall meet the requirements ofGP 3-18-1.

2. Threaded connections shall be seal welded in accordance with GP 3-18-1.

3. In addition, small connections in vibrating service and where vulnerable tomechanical damage shall be gussetted as required by GP 3-18-1.

4. An emergency block valve (manual) shall be installed in each small pipingtake-off connection (instrument lines etc.), located as close to the tank or lineas possible, with no elbows between the connection and valve. Connectionsto piping shall be 13 mm or larger. Connections to the bottom of tanks shallbe minimized. Tubing downstream of the emergency block valve shall bestainless steel, and in accordance with GP 3-6-1.

5. Liquid drawoff piping (sampling piping) leading to the atmosphere, or to anopen tank, shall be double valved if the tank contains stocks which can auto-refrigerate. The valve next to the shell shall be a quick action type, such as a


metal-seated plug valve. The second valve, for flow control, shall be of atype suitable for partially open operation.

6. Water drawoff piping shall discharge at a point not less than 4.5 m from theperipheral boundary of the LPG tank. The discharge shall be so located thatany flammable spillage will drain away from the tank.

5.1.8 Installation

All metallic LPG piping shall be installed in accordance with ASME B31.3. Allwelding of metallic piping shall be in accordance with ASME Boiler & Pressure VesselCode, Section IX.

Aboveground piping shall be supported and protected against physical damage. Toprevent corrosion under supported un-insulated pipes, pipe supports and pipe sleepersshall be designed with steel standoffs (19 mm diameter minimum), such as steel rodswelded to the top of support to raise the pipes above possible water/liquid pool that mayencourage corrosion (Figure 5.1.8).

Underground piping shall be avoided, however, when there is no other alternative andpiping is beneath driveways, roads, or streets, possible damage by vehicles shall betaken into account. Underground metallic piping shall be protected against corrosion aswarranted by soil conditions. Depending on conditions and risk involved somecountry/clusters have chosen to install double wall stainless steel flexible piping withleak detection. LPG piping shall not be used as a grounding electrode. LPG piping thatcrosses an open drain where it may contain flammable product (spill in a fuels terminal)shall be protected or fireproofed against any flash fire. Interconnecting piping betweentanks and tanks accessories shall be installed to permit flexibility (possible vertical andhorizontal movement) due to tanks foundation settlement and tanks expansion. Flexibleconnectors between tanks and piping system are prohibited, however, they are permittedwhere local codes require them for earthquake protection.

Figure 5.1.8: Typical pipe sleeper with steel rod standoff

Metallic pipe joints shall be threaded, flanged or welded using pipe and fittings. Whenjoints are threaded or threaded and back welded the following applies:

1. For LPG at pressures in excess of 865 kPa or for LPG liquid the pipe andnipples shall be schedule 80.

2. For LPG vapor at pressures of 865 kPa or less, the pipe and nipples shall beschedule 40 or heavier.


The fittings or flanges shall be suitable for the service for which they are to be used.Gaskets used to retain LPG in flanged connections in piping shall be made of metal orother suitable material confined in metal having melting point over 816 °C.

The outlet of a differential pressure valve in a pumping system shall be piped back to thepump suction line at a point at least 5 m ahead of pump suction. All drain sets orisolation leading directly to atmosphere shall be double block using one ball and oneglobe valve. The globe valve shall be located at the end closer to the atmosphere. Theminimum distance between the valves shall be 600 mm. All drains and vents shall beclosed and capped or plugged when not in use.

After assembly, piping systems (including hoses) shall be tested and proven free ofleaks at not less than 1.3 times the design pressure or maximum operating pressurewhichever is higher. The results of the tests shall be documented. LPG leak tests shallnever be made with an open flame.

5.2 Valves in Piping

5.2.1 Valve Integrity

All pressure containing metal parts of valves in plants or terminals shall bemanufactured in forged or cast carbon steel or stainless steel. All materials use,including valve seat discs, packing, seals, and diaphragms, shall be resistant to the actionof LPG under service conditions. Soft-seated valves shall meet API-607 conditions as“fire-safe.” Cast iron or brass valves shall not be used, with the exception that thatvalves and instruments on LPG cylinders and containers (small tanks) may be made ofbrass.

For reference also see GP 3-12-1 “Valve Selection Criteria.” The following valve typesshall be provided in accordance with API STD 2510. Valve used at pressure higher thanLPG tank pressure shall be suitable for working pressure of at least 4,830 kPa. Valvesto be used with liquid LPG, or with vapor LPG at pressures in excess of 865 kPa, shallbe suitable for a working pressure of at least 1,725 kPa.

Shut-off valves in LPG service shall provide positive bubble-tight shutoff. Toaccomplish this, it is usually necessary to employ resilient seating materials. However,resilient materials are inherently susceptible to damage during a fire. All resilient seatedvalves, other than modified API STD 600 and API STD 602 gate valves shall meet the30 minutes fire test specified in API STD 607 or equivalent standard. Ball valves withdouble-sealing feature shall be used. Valve bodies shall be forged or cast carbon steel.Gate and globe valves shall be made to API valve standards or equivalent.

5.2.2 Shutoff Valves

The shutoff valve considered most dependable in LPG service is the valve manufacturedby the Orbit Valve Company. If a quick-operating valve is needed, the Maxon-Okadeeand Everlasting metal-to-metal seated disk valves are acceptable.

Other suitable shutoff valves are Stockham Wedgeplug (with a resilient insert in theplug), General Twin Seal, fire-safe ball valves by Neles-Jamesbury and McCanna, fire-safe butterfly valves by Neles-Jamesbury, McCanna, Posi-Seal and Flowseal.

Ball valves with a double-sealing feature are recommended for LPG service. Thisfeature provides a leakproof shutoff when pressure is applied in either direction. Thetype of ball valves that effect positive shutoff in only one direction are not suitable.


Gate and globe valves shall be made to API valve standards. Most NPS 3 (NPS =Nominal Pipe Size, inches) and larger gate and globe valves shall be purchased toinclude resilient seating materials in the disk or gate, thereby providing tight shutoff.

5.2.3 Backflow Check Valves

Backflow check valves perform an extremely important safety function in tank openingsand in pipelines intended for flow in one direction only. All filling or liquid-return tankconnections designed for flow into the tank only shall be fitted with backflow checkvalves. Some of these valves are for tank installation only; others can be used either intanks or in pipelines. The type most commonly used in larger transfer piping is theswing check, which has relatively little pressure drop. Poppet, lift, and ball type checkvalves in smaller sizes are used for truck, customer tank, and cylinder fillingapplications. They are smaller and less expensive, but have more pressure drop. Valvesshall meet the requirements of GP 3-14-2. Backflow check valves are required indischarge lines of pumps and compressors. The check valves shall be installed with apositive shut off valve immediately adjacent to the anchor point and on the plant side ofthe anchor point. They are also recommended in dedicated loading or unloading linesfor vapor and liquid, especially in piping from marine berths to shore tankage, wherepiping is designed for flow only in one direction. In marine applications, check valvesshall be positioned in such that they will not present problems when the Cargo TransferEquipment is being de-pressurized under normal operating conditions. Soft-seatedcheck valves have the advantage of a relatively tight shutoff, and would minimizerelease of product in case of a hose or connection failure.

Figure 5.2.3: Double back check valve and swing check valve

Backflow check valves restrict flow but may not provide positive shutoff. EmergencyBlock Valves are required if it is necessary to stop flow reliably. For maintenancepurposes blinds shall be provided for leak tight shutoff.

5.2.4 Thermal Relief Valves

Thermal relief valves (hydrostatic relief valves) are designed for installation in anyportion of a piping system, or in any equipment in which liquid may become entrappedby shutoff valves at both ends, become heated, expand and develop overpressure. Theliquid expansion factor of LPG is twelve times higher than that of water and twice thatof gasoline. To protect piping, the set pressure shall be no higher than the lower of120% of the piping design pressure or system test pressure. This takes advantage ofASME exclusion for thermal relief valves, which protect only blocked in piping.

Thermal relief valves are attached directly to piping and manifolds and may be exposedto mechanical damage. Their location shall therefore be carefully selected and adequate


protection shall be provided where necessary. The thermal relief valves shall beinstalled as close as possible to the piping being protected. The piping connection shallbe 19 mm along with a quarter turn 19 mm Car Sealed Open (CSO) valve. This willpermit maintenance of the PRV without taking the piping system out of service. Wherepermitted, the discharge of the thermal relief valves may be directed to atmosphere butshall be covered by a plastic cap to prevent ingress of rain. Discharge shall be directedso that it does not impinge on adjacent pipework or equipment. When the discharge of athermal relief valve goes to atmosphere and might cause a hazardous condition, the ventoutlet may be fitted with pipe, extended to a safe area and sized so that the free vent areaof the valve is not reduced. The vent outlet shall be at least 15 m away from all firedequipment. A daily walk-by tightness check by the operator is recommended. Atmarketing terminals, odorized LPG is likely to aid in leak detection during thisinspection.

Internal valves specified for LPG tanks will relieve pressure from thermal expansion inthe attached line into the tank. If the auxiliary manual shutoff valve downstream of theinternal tank valve is Car Sealed Open (CSO) in normal operation, lines connectingdirectly with an internal valve do not require a thermal expansion relief valve.

It is recommended to test or replace PRVs in thermal relief service within a 5 yearinterval.

5.2.5 Emergency Block Valves for Piping

For automatic shutoff design of the Emergency Block Valves (EBV), the actuatingsystem shall close valves upon failure of any system component (i.e. also known as fail-close FC) Emergency Block Valves, described in Chapter 3, are provided at strategiclocations to stop LPG flow to potential downstream emergencies.

EBV's in Marketing plants are required for the following services:

1. Tank connections.

2. Transfer Points.

3. Rotating Equipment.

4. Cylinder Filling Shed.

The preferred choice for automated Emergency Block Valves in Marketing plants arespring actuated quarter turn ball valves with electric, hydraulic or pneumatic springrelease as described under “Emergency Block Valves on Bulk LPG Tanks” in Chapter 3.

5.2.6 Valve Packings

The valve stem packings used in LPG service shall be capable of meeting the followingrequirements:

1. Minimize LPG emissions to the atmosphere during normal operations forenvironmental and safety (fire) reasons, and

2. Be fire-safe, especially when used in block valves, to hinder LPG escapingfrom the valve stem during a fire.

5.2.6.1 Block Valve Packings

Global Practice GP 3-12-8 specifies the packing systems that shall be used in blockvalves to meet the above requirements. For LPG service all-graphite ring packings(Type 1) shall be used. The individual packing rings, that will perform the sealingfunction, shall consist of flexible graphite with 1120 kg/m3 nominal density ( Style B2).


The end wiper rings shall consist of interlaced braided graphite filament or solid 1600kg/m3 minimum density compound carbon rings (Style A).

Graphite die-formed rings, braided rings, and bushings shall have a minimum carboncontent of 95%. Bushings shall be used only to take up excess packing chamber depth.The packing rings shall have an active zinc, or a passive barium molybdate, or a passivephosphorus based corrosion inhibitor. Separate zinc washers between packing ringsshall not be used.

Five-ring packing sets shall be used on API 600 and ASME B16.34 gate valves andother rising stem valves. Four-ring packings shall be used with API 602 valves and onall quarter turn valves (ball, plug and butterfly types) except that for quarter turn valvesNPS 1 and smaller, the wiper rings may be eliminated.

Live-loaded glands (using disk or coil springs installed on the gland stud bolts, on thegland itself, or in the stuffing box) are not recommended. Stuffing box clearances,procedures for environmental emissions testing of the valves, and other block valvepacking information may be found in GP 3-12-8. Additional pertinent information maybe found in the ERE report EE.34E.93 “Low Emission Block Valve Packing GuidelinesUpdated” and report EE.58E.94 “Valve Packing Fire Tests Reinforce RecommendationsNot to Use All-Braided Packings.”

5.2.6.2 Control Valve Packings

Graphite packing may also be used for control valves but is not necessary, since controlvalves do not have to be fire-safe in most cases. Graphite may result in higher stemfriction, which in turn may create problems for the control valve actuator motor. Thisgenerally happens when graphite is used in a control valve that originally had anelastomer/plastic packing. In such cases, the valve stem actuator shall be tested with thegraphite packing installed before the valve is placed in service.

For new valves, the actuators are sized for the appropriate friction loads, so there shallnot be any problems using graphite packing. Most major control valve manufacturersare providing their own proprietary packings, which have already been tested, foremissions and friction. See ERE report EE.84E.93 “New ‘Low-Emission’ ControlValve Packings Successfully Demonstrated In Plant Performance” for additional detailson control valve packings.

Safety in LPG Design PRODUCT TRANSFER 6-1

6 PRODUCT TRANSFER

6.1 Principles of Product TransferThis section describes design requirements for equipment used to receive bulk productinto an LPG plant and ship it to customers. Components of product transfer within theplant is described in Chapters: PUMPS AND COMPRESSORS as well as PIPING ANDVALVES. This Chapter discusses: principles of product transfer, static electricity inloading and unloading operations, hoses in product transfer, loading and unloading fortrucks, rail cars and marine vessels. Also pipeline dispatch and receipt facilities arediscussed.

New piping transfer systems shall be designed for Propane vapor pressure. Thedifference in cost, compared with Butane conditions, is not significant. However, if at alater date a Butane system would be changed to Propane service this could only be doneat high cost.

Unloading systems can use compressors, pumps or a combination of the two. Pumpdesign ratings shall depend on type of product, desired pumping volume, resistance inliquid line and availability of vapor return line. When a pump alone is used, vaporscannot be recovered from shipment tanks.

Vapor

LiquidFlow Indicator

Pump

Figure 6.1-a: Pumping liquid from one tank to another

In most design cases, two options are available to provide equipment for the tank fillingoperations, plant receiving and transport loading.

1. Product can be pumped into the bottom of the receiving tank with vaporreturned to the source tank via a vapor balance line, or

6-2 PRODUCT TRANSFER Safety in LPG Design

2. Product can be sprayed into the receiving tank vapor space (usually through alongitudinal perforated pipe) and depend on cooling and absorption of thevapor to accommodate the liquid volume transferred.

Both methods have advantages and disadvantages:

1. Vapor balanced bottom loading can be accomplished with lower pump headpressure, and consequently, consumes less energy. It provides positiveassurance that the receiving tank will not be overpressured as long as itsvolumetric liquid capacity is not exceeded. However, it requires a vaporbalance line with valving and connection fittings and exposes the operator tomaking and breaking twice as many temporary connections to thetransportation tank as is needed for spray filling. Another disadvantage ofvapor balanced bottom loading is for custody transfer using meter. Onaverage a quantity (2 - 3%) of vapor is returned to the delivering tank whichcreates stock accountability problems.

2. Spray filling makes use of the condensation of the LPG vapors and requiresonly a single discharge piping system, however, it usually requires a higherhead transfer pump (consuming more energy) to compress the receiving tankvapor space. Due to higher pressures, loading rates are reduced comparedwith using a vapor return line. Depending on ambient temperature, productvapor pressure, and receiving tank pressure rating, it may be necessary toreduce the transfer rate to avoid lifting pressure relief valves on the receivingtank. It is difficult to predict precisely the results in limiting pressure. Ingeneral, the pressure increase using spray filling is approximately 25 percentof the increase caused by filling into the liquid space without vapor return.For example, if a product has a vapor pressure of approximately 1000 kPa andis filling into the liquid space without vapor return, the terminal pressure mayincrease by approximately 700 kPa. However, if the spray filling method isused, the terminal pressure increase would be about 175 kPa.

Vapor

Liquid

Flow Indicator

Compressor

Figure 6.1-b: Transfer by displacement through compressed vapors

In order to select the most desirable mode of tank filling, the designer shall consider allof the factors listed above and weigh their relative importance in each individual case.The only normal exceptions shall be:

1. Receiving from a product pipeline, where there is no place to return vapor,and spray filling into the vapor space is the only option available, and

2. Receiving into a refrigerated tank, which has an integral vapor handlingsystem. The tank shall still be equipped with a jet mixing nozzle to avoidpotentially hazardous product “rollover” when the receipt temperature issignificantly above inventory temperature.


6.1.1 Loading or Unloading with Pumps

Pumping systems designed for the discharge of LPG from plant storage into anothertank are closed systems with no venting to the atmosphere.

1. If the two tanks contain liquid product before pumping is started, the pressureshall be approximately the same in both tanks.

2. If there is no vapor line connection between the two tanks, the pressure in thereceiving tank increases during the product transfer.

3. With an increase in pressure, some vapors in the tank change to liquid bycondensation.

Figure 6.1-c: Pumping with vapor balance line

Figure 6.1-d: Pumping without vapor balance line


The rate at which vapor changes to liquid is determined by the following:

1. The differential between the pump discharge pressure and the normal vaporpressure of the product.

2. The temperature of the liquid in the tank.

3. The surface area of the liquid.

When the liquid enters from the top of the tank and is sprayed into the vapor space, thetotal surface area of the liquid is increased and less differential pressure is needed.

The most important factor in the design and installation of LPG pumping transfersystems is to keep LPG from vaporizing in the suction system.

1. LPG is usually stored at the product vapor pressure and this makes producttransferring more difficult.

2. When internal pressure is reduced due to product volume removal by thepump, LPG vaporizes to maintain its temperature-pressure balance. Thevapor bubbles are formed at the tank wall because it is warmer and thereforebubbles at the bottom of the tank that are in close vicinity of the pump suctiontravel easily to the pump. In addition, vapor bubbles may be formed in thesuction line due to higher velocity and lower pressure.

3. Excessive entrained vapor at the suction of the pump could eventuallydamage it.

Design features for avoiding low pressure and vapor bubbles in pump suction systemsare discussed in section “Minimizing Pump Cavitation and Vaporization” in Chapter 4.

A vapor-equalizing line installed between the two tanks will greatly reduce thedifferential pressure requirements for the pump and, therefore, shall be used whereverpossible. With such a line, the differential pressure will be the total flow resistancethrough the pipes and fittings of the liquid line, plus the resistance in the vapor lines.This shall not exceed 275 kPa. When the equalizing line is used, a quantity of vapor istransferred from the receiving tank during the pumping operation.

6.1.2 Loading or Unloading with Compressors

Vapor compressors are often used to transfer liquid LPG by withdrawing vapor from acontainer being filled, increasing the pressure through the compressor and dischargingthe vapor into the supply tank.

1. The increased pressure in the supply tank and the decreased pressure in thereceiving container provide the differential pressure needed to force liquidthrough a pipeline from one tank to the other.

2. The differential pressure is normally 70–140 kPa.

Vapor compressors offer an advantage in that the remaining vapor can be removed afterthe liquid transfer has been completed. If the product is Propane, the savings can besubstantial, since 900 kg of product is contained in vapor in a 38 m3 tank at a pressure of1000 kPa. Approximately 75 percent of it is economically recoverable.

6.1.2.1 Removing Vapor

To remove the vapor, the liquid line is closed and the pipe connections at thecompressor are reversed, so the vapor is drawn from the supply tank and discharged intothe receiving tank. This is usually accomplished automatically through a four-way valvesupplied by the compressor manufacturer. As previously described, vapors will be moreeasily converted to liquid if the liquid surface area can be increased. This isaccomplished by discharging vapors into the bottom of the receiving tank so they will


bubble up through the liquid and get cooled to minimize pressure increase. See Figure6.1.2.1 for an illustration of a compressor transfer with a four way valve arrangement.

Figure 6.1.2.1: Transferring with a Compressor-Liquid Transfer (Top) and Vapor Recovery (Bottom)

6.1.3 Using Pumps Versus Compressors

The major criteria for choosing between pumps and compressors for loading/unloadingoperations are as follows:

Use compressors when:

1. Liquid cannot be gravity fed to an unloading pump (negative suction head).

2. Vapor recovery is required.

3. A plant has only one transfer device.

Use pumps when:

1. Flooded gravity fed suction is available.

2. Vapor recovery is not required.

3. Differential pressures above 2 bar gauge (200 kPa) are required.


4. Liquid is to be metered.

5. A lower initial the cost is desired.

There are cases where a pump/compressor combination is required. This case is verycommon where distances between shore LPG tanks and marine LPG tankers are verylong. This combination helps to reduce the total head of a tanker pumping system byeliminating the pressure drop of the return vapor line from the LPG tank to the ship.The pressure drop is eliminated from the ship's pumps by installing a compressor to doonly the vapor transfer from one tank to another. This way the pumps only need enoughhead to overcome the pressure drop through the liquid line.

6.1.4 Static Electricity in Unloading and Loading

Static electricity can be a hazard during loading/unloading procedures since, whenbreaking connections, a spark could lead to LPG vapor ignition and fire.

Loading/unloading rack structures shall be grounded to earth from at least two points.In addition, there shall be bonds between piping and the rack supports. The objectiveis to keep all metal parts at the same electrical potential. Copper tape, 25 mm by 3 mmshall be used for this connection and each grounding point shall be taken to a separateelectrode. One ground electrode (ground rod) example is a 16 mm diameter extensibletype copper rod with a minimum length of 2.4 m. The resistance of these groundcircuits shall be tested on an annual basis.

All flanged connections on piping, valves, etc. can be considered to be conductiveconnections. In some countries an additional copper tape link across the flange isrequired. However, this does not increase conductivity above the flange/bolt/flangeconnection, in fact it creates the risk of element corrosion since copper and iron havedifferent electrolytic potentials. In addition, copper bonding straps can also causeuneven bolt tensioning. Therefore, such copper tape connections are not recommended.

For road delivery vehicles normally the grounding wire is permanently attached to thetruck and for loading/unloading a spring-loaded “alligator” clamp at the end of thegrounding wire shall be connected to a dedicated bare steel grounding lug at theloading rack or the customer tank respectively. It is preferred that the loading rackgrounding system is permissive i.e. the loading pump will only start if the groundingconnection is made and properly working.

Grounding and bonding to discharge static electricity and stray currents shall beprovided at the loading rack. Grounding systems composed of a Scully Biclops withGround HOG is acceptable. Lightning protection or grounding rods shall be provided atthe loading rack structure to protect personnel, piping and equipment on non-conductivefoundations. All electrical installations and equipment shall conform to the provisionsof NFPA 70. The area classification for the loading rack shall be Class 1 Division 2 0.9m from point of connection of filling in all direction and up to 0.45 m above groundwithin 3.3 m radius from point of connection. The electrical fittings shall be explosionproof. In addition to the electrical area classification, all equipment located in the openshall be weatherproof. The electrical and instrumentation of the weighing bridge shallcomply with area classification of the installed area. If installed at loading andunloading rack, the area classification shall be of Class 1 Division 2.

6.1.5 Hard Arms

A hard arm (also flexible arm, rigid steel pipe with swivel joints) is required to connect arail car or tank truck to the plant storage system. Hard arms are preferred to hoses forthis service. When a dry break connector is used, the bleeder vent is unnecessary fordaily operations but shall be installed for maintenance purposes. For sizes 50 mm andlarger, rigid steel pipe with swivel joints and counterbalances are recommended. When


self-sealing couplings or valves are mounted on the end of loading arms, the loading armmanufacturer shall provide for this added weight in the counterbalance design incompliance with the requirements of NFPA 77.

Hard arm connections shall withstand a test pressure of 1.5 times the design pressure ofthe system. Hard arms shall be designed and fabricated from materials compatible withLPG, both liquid and vapor form. They shall also have adequate strength and durabilityto withstand the pressures, stress, and exposures to which they may be subjected andshall be designed to maintain sound mechanical and structural integrity. They shall besupported in such a manner as to prevent personnel injury and prevent damages orexcessive wear.

When hard arms are attached to the piping, the end of the piping shall be secured to aconcrete anchor or equivalent device capable of withstanding any forces that may beapplied by the movement of a vehicle while the arm is attached. The anchor for theabove application shall be capable of withstanding at least twice the maximum load thatcould be applied by the arms singly or in combination. A designated weak joint(breakaway) shall be built into the piping system to ensure that break-off is at a plannedlocation if a vehicle pulls away while connected. Self-sealing dry break couplings shallbe provided to prevent uncontrolled discharge of LPG to the surrounding. The pipingupstream of the anchor shall have sufficient flexibility to permit adequate thermalmovement. Thermal relief valves shall be installed to protect against liquid expansionpressure buildup in the hard arms.

Figure 6.1.5: LPG truck loading through hard arm

Provision shall be provided to depressurize the loading arm to a safe location afterloading or unloading is completed. In some installations the contents of the liquid linecan be shifted into the vapor system or blowdown system. However, if this is notpossible, the amount of liquid to be vented to atmosphere must be kept to an absoluteminimum. This can be achieved by either using dry break couplings (see below) or byinstalling block valves at the transfer point as close as possible to each other. The liquidand vapor contained between the block valves shall be vented into a vertical pipe intothe atmosphere. This pipe may be installed at the truck or at the plant. Vent pipes(5 mm) at trucks are typically installed at the truck nozzle and end at a point above the


tank. Vent pipes at plants may be larger and usually end at higher elevation in an openarea. The vent exit point shall not be in the vicinity of air intakes or fired equipment.

6.1.6 Hoses in Product Transfer

Hoses shall be used where no other method of product transfer is practical, such as onhose reels on small bulk delivery trucks. Hoses shall comply with applicablestandards (BS 4089 Hose Standards NFPA77), be designed and certified specificallyfor LPG (in liquid and vapor phase) and the materials used in fabrication shall also becertified resistant to the action of LPG and shall be corrosion resistant. Hoses shall bemarked “LPG” at intervals no more than 3 m. Hoses designed to BS 4089 shall have amaximum working pressure of 25 bar gauge and a minimum burst pressure of 100 bargauge. (Hoses certified to comply with IMO code will have a maximum workingpressure of 20 bar gauge and a minimum burst pressure of 100 bar gauge.) Hoses shallbe hydro-tested to 1.5 times maximum working pressure. Hose connections andstainless steel hose reinforcement shall be electrically continuous. Wire braid used forreinforcement shall be made from corrosion resistant material such as stainless steel.Reinforcing wire within LPG loading hoses shall be in electrical contact with the endcouplings on the hoses to minimize the risk of an electrostatic charge collecting on anelectrically isolated wire within the hoses or on the exterior of the hoses. Intermediatejoints or couplings in a nonconductive hose shall not be permitted because they canaccumulate a charge sufficiently great to spark to an adjacent conductive object.

A shutoff valve at the discharge end of the hose shall be provided to minimize vaporescape when the hose is disconnected after product transfer. When not in use, hosesshall be placed on reels or in trays designed to prevent any kinking, torsion etc. toprevent any physical damage. Particular attention shall be given to potentially damagingice formation on the corrugations of metallic hose.

When hoses are used for unloading, bleeder vent valves (connected to a vent stack) arerequired to depressurize the hoses when they are not in use. Hoses can be equipped withAcme screw thread (or equivalent) fittings and capped with a relieving device that willrelease any pressure in the hose before threads are disengaged. This relieving device istypically vented to atmosphere away from the person loading the tank.

Plants using hoses shall keep a Hose Tracking Program in place. Following are therequirements that should be part of a Hose Tracking Program.

1. There shall be a list showing all hoses used in the plant. The information oneach hose shall contain: unique hose number, purchase date, qualitycertificate, testing conditions, testing schedule, last test date, re-test date,expected hose retirement date.

2. A unique hose number, the last pressure test date and re-test date, shallidentify each individual hose in the field. This is to facilitate control.

3. Operators shall receive training that informs them how to prevent and todetect hose damage.

More information on hoses used for marine services can be found under “MarineCargo Dock Hose.” later in this chapter.

The design criteria for hoses and connections used for transferring LPG liquid or vaporservice at pressures in excess of 35 kPa shall be the following. TruckLoading/Unloading Hoses shall be designed as follows: Working pressure of 2,032 kPaand a Bursting pressure of 10,160 kPa. Hose assemblies shall be designed to withstanda pressure not less than twice the working pressure, 4,830 kPa.

Unloading facilities should be designed such that the liquid in a hose can be drained intothe vapor system. Liquid contents of hoses shall not be vented to atmosphere. If hosescannot be drained, they may be kept under liquid, blocked off at both sides with a


Thermal Relief Valve at one end to protect the hose against excess pressure. The setpressure of the TRV shall be in accordance with the hose manufacturer’s specifications.Venting of the liquid at the transfer point (between truck and hose block valve) shall beperformed as described in the previous section “Hard Arms.” The hose length shall bekept as short as possible.

Hoses shall be supported in such a manner as to prevent personnel injury and preventdamages or excessive wear. When hoses are attached to the piping, the end of thepiping shall be secured to a concrete anchor or equivalent device capable ofwithstanding any forces that may be applied by the movement of a vehicle while thehose is attached. The anchor for the above application shall be capable of withstandingat least twice the maximum load that could be applied by the arms or hoses singly or incombination. A designated weak point (break-away) shall be built into the pipingsystem to ensure that break-off is at a planned location if a vehicle pulls away whileconnected. A self-sealing dry break connector shall be provided to prevent uncontrolleddischarge of LPG. The piping upstream of the anchor shall have sufficient flexibility topermit adequate thermal movement.

Figure 6.1.6: In case of rupture “Smart Hose” is automatically closed at both ends.

A recent development in hose technology is the “Smart Hose.” by Smart HoseTechnologies. This hose has considerable safety features included in its design. Smart-Hose will automatically close at both ends if the hose ruptures or if the truck drivesaway without uncoupling the hose.

Valve plungers, wedges or flappers installed at both ends of the hose, accomplishclosure. During normal operation they are kept open by a coated cable incorporated


within the hose bore. This cable acts as a compression spring providing thrust in thedirection of both ends of the hose, holding the valves open. Should this thrust beeliminated due to coupling ejection, hose stretching or hose separation, the valves arereleased and instantly seat, stopping flow in both directions.

6.2 Loading and Unloading

6.2.1 Truck Loading and Unloading

This section of minimum standards covers the truck loading and unloading facilitieswithin ExxonMobil’s fence at a terminal.

The quantity of shipments may be determined by the weight of the shipping vehicle orby liquid level readings on both shipping and terminal LPG tanks before and afterproduct transfer. Meters are not normally installed in loading or unloading systems.

LOCALEMERGENCY PUSH BUTTON

EBV's Operated byPlant EmergencyShutdown System (ESS)

Truck ESS Truck

ESS

Truck InternalEBVs

EBV

EBV

Break AwayCouplings

ElectrostaticBonding Cable

Figure 6.2.1-a: Mini-bulk truck loading

The loading rack shall be designed such that when the truck is parked for unloading orloading, it shall be able to move away from loading rack to a safe location in anemergency without backing up. The loading rack should not be located in an areadirectly along the longitudinal axis of the horizontal LPG bullets. The loading rack shallhave a concreted paved mat. The concrete mat shall be designed so that the entire truckwill be within the mat during loading and unloading. The concrete mat shall be pitchedso that spills will run to LPG trap. The loading/unloading equipment and supportstructures in the loading rack shall be protected with guard rails or stanchions to preventdamage from vehicles.

Emergency shutdown pushbuttons to activate the Emergency Shutdown System shallbe installed at an easily accessible area at the loading rack and at a safe remote locationat least 15 m from any hazard. This maybe the pushbutton at the filling plant or other.The emergency shutdown pushbutton shall activate an audible alarm of at least 100 Dbinstalled at the loading rack and to shut the flow of LPG.

The structure shall be designed to provide structural support for loading equipment andlighting. The structure shall also provide weather protection for the driver, product and


equipment. The structure shall not have any sides or any restrictions that will inhibitventilation through the structure. All structural materials installed shall be of non-combustible material. The structure shall have lighting suitable for daytime andnighttime operation. Lighting shall be an minimum of 100 lux measured at the loadingconnection. Lighting enclosure shall be flameproof type.

Figure 6.2.1-b: Principle of the breakaway coupling (Alpha Process Control)

Figure 6.2.1-c: Drybreak coupling (Alpha Process Control)

The unloading systems can use compressors or pumps or a combination of both.Compressors and pumps shall comply with the requirements in Chapter 4. The fixedpiping shall be constructed of steel. No other material is acceptable. Vapor return linesshall have check-valves installed to prevent backflow.

When flexible arms or hoses are attached to the piping, the end of the piping shall besecured to a concrete anchor or equivalent device capable of withstanding any forcesthat may be applied by movement of a vehicle while the arm or hose is attached. Theanchor shall be capable of withstanding at least twice the maximum load that could beapplied by the arms or hoses singly or in combination. A designated weak point shall bebuilt into the piping system to ensure that break-off is at a planned location if a vehicle


pulls away while connected. The piping upstream of the anchor shall have sufficientflexibility to permit adequate thermal movement.

New or revamped truck loading and unloading points shall be equipped with swivelhard arms and break-away connections for liquid and vapor return lines. It is highlyimportant to install these couplings exactly as prescribed by the manufacturer. If, afterinstallation, the pull-away force cannot be applied as intended, the coupling may notwork. In special cases where a variety of customer trucks are loaded, the additional useof hoses may be necessary to accommodate the diversity of connection points. Hardarm material shall be Schedule 80 Seamless Steel - ASTM Specification A-106, GradeB.

Figure 6.2.1.1-a: Rotary gauge dial

The liquid lines shall be equipped with dry break couplings. Vapor and liquid linesshall be equipped with automatic, fail safe (thermal/fire actuation) emergency blockvalves (EBV), and a local as well as a remote (accessible during emergency) actuationsystem to activate the emergency shutdown. The EBV shall be installed in thetransfer pipe within 6 meters of the hose connection or loading arm, per NFPA 58.Furthermore, there shall be an interlock system, which can prevent the truck from beingmoved while hard arms (or hoses in older plants) are still connected.

The piping system shall be designed to accommodate maximum forces originating froma truck drive-away rupturing the break-away connections. If this cannot be achieved, abulkhead with an adequate foundation shall be installed which shall be designed towithstand 65 kN. If the EBV is located at the rack it shall fail safe under fireconditions. Actuation of the valves may be automatic by fusible element, which meltsat 120 °C and is 1.5 m at maximum away from the loading connection. In addition tothe EBV a manual quarter turn valve shall be provided at the connection between thepiping and the hard arm. The loading rack area shall be protected against accidentalcrash by trucks. An electrostatic grounding (earthing) point shall be provided ateach loading and unloading location. A permissive grounding (earthing) system ispreferred for road vehicles at each loading rack. This shall ensure that the loading pumpshall only work as long as the grounding contact is intact.


Locations that use hoses instead of hard arms for product transfer will also need theitems discussed above. If no dry break couplings are provided, a purging system andgood natural ventilation shall be present.

Normally unloading of trucks is achieved by using their own pumps. A pump in theplant could also unload trucks if the requirements for Net Positive Suction Head (seeNPSH in Chapter 4) for the particular pump can be satisfied. This may be the case if thetruck can be placed close to and elevated above the pump in question.

Figure 6.2.1.1-b: Rotary gauge tube

Hose connections for bulk transfer shall be designed such that they can be emptied ofliquid after loading. They may be left under vapor phase. Hoses on reels of mini-bulktrucks are an exception because they are constantly connected on the truck side andtherefore provided with a thermal relief valve. Hard arms maybe left under liquid,however they need thermal expansion protection.

6.2.1.1 Truck Tank Level Measurement

All truck tanks shall be equipped with rotary gauges. A rotary gauge is a variable liquidlevel gauge consisting of a small positive shutoff valve located at the outer end of a tube,the bent inner end of which communicates with the tank interior. The tube is installed ina fitting designed so that the tube can be rotated with a pointer on the outside to indicatethe relative position of the bent inlet end. The length of the tube and the configurationto which it is bent is suitable for the range of liquid levels to be gauged. By a suitableoutside scale, the level in the tank at which the inner end begins to receive liquid can bedetermined by the pointer position on the scale at which a liquid-vapor mixture isobserved to be discharged from the valve. The more modern version of this device, the“Magnetel” may also be used.

6.2.2 Rail Car Loading and Unloading

Rail tank car loading racks shall be designed to meet all local regulations and shall be inaccordance with railroad and industry standards. Layout shall provide optimum ease inpositioning tank cars. In some countries, regulatory practices allow loading/unloading atrain where all cars are coupled together. Other countries require uncoupling andkeeping a minimum distance between the cars. A vertical clearance from the track ofnot less than 6.7 meters and a horizontal clearance from center of track to loading rack


edge of not less than 2.6 meters shall be maintained. The loading spots shall be leveland on a straight section of track.

New or renovated loading racks shall be equipped with swivel hard arms for liquid andvapor connections. Hard arm material shall be Schedule 80 Seamless Steel - ASTMSpecification A-106, Grade B. Liquid connections shall have an emergency release aswell as dry break couplings. An alternative would be a purging system for thecoupling. There shall be one fail safe, remote operated emergency block valve (EBV)in the liquid and vapor lines to the plant tanks. The EBV shall be installed in thetransfer pipe within 6 meters of the hose connection or loading arm, per NFPA 58. Theindividual lines to each rail car shall be provided with manual shut-off valves.

L O C A LE M E R G E N C Y P U S H B U T T O N

Liquid

Vapor

TERMINAL ESS

Meltingin Fire

Rail Car EBVs

EBV

EBV

Releasingwhen Moving

Manual ESSon Both Sides

Rail Car ESS

More Rail Cars

Adequate GroundingThrough Rails

Figure 6.2.2: Emergency block valves in rail car unloading

National codes normally require that each rail car shall be equipped with an internalshut-off valve. Ideal loading rack designs incorporate the ability to close all rail carshutoff valves from the loading rack or the plant emergency shutdown system (ESS).However, this requires a special rail car design. As a minimum the individual rail car-shut-off valve shall be operable at the hard arm and also operate if accident or errormoves the rail car. Push-buttons to operate the ESS shall be located at strategic points,which provide ready access to operators.

Where hoses are used, valves and connections are necessary between the hose headersand a vent system to allow draining the loading hose after completing loading but beforedisconnecting the hose from the car. Many rail tank cars are equipped with non-conductive bearings and non-conductive wear pads located between the rail car and thechassis. As a result, the resistance from the tank car compartment to ground through therails may not be low enough to prevent the accumulation of an electrostatic charge onthe tank car body. Therefore, bonding of the tank car body to the fill system piping isnecessary for protection against static accumulation. In addition, because of thepossibility of stray currents and to prevent an ignition hazard as a result of such currents,loading lines shall be bonded to the rails.

The two rails of the siding shall be permanently bonded to the metal loading rack. Theunloading rail spur shall be insulated from the main track to guard against stray currents,which might cause a spark. Often the insulation point is at the spur entering the site asshown in Figure “Spacing in marketing LPG bulk plant with cylinder filling” in Chapter2.


Normally a reciprocating compressor shall be provided for unloading rail tank cars.The compressor shall be sized to provide the desired volumetric liquid unloading rate bypressurization of the rail car vapor space(s). Manifolding shall be provided to allowsubsequent exhausting of LPG vapor from the car(s), discharging to the bottom of theLPG tank into the liquid. It is desirable to unload rail tank cars at such a rate that theoperation can be completed by one individual during a normal working period. Theunloading rate will be affected by the size of the tank car and the compressor capacityavailable. If unloading has to be finished in shorter time unloading pumps may beused. If a manifold system is used to unload cars simultaneously, check valves shall beinstalled to prevent the return of product to the rail cars.

Provisions shall be made so the loading assembly can be swung to one side and held outof the way of moving tank cars when not in use. Where a rack is required it shall be ofsteel frame construction with nonskid metal flooring. Stairs and the main walkway shallhave handrails.

6.2.3 Marine Loading and Discharge

The design of marine loading and discharge facilities is specific to both the individualpier and the marine transportation unit(s) selected to serve it. A number of designissues, both general for marine berths and specific to LPG berths should be considered,such as site selection, berth layout/spacing, and berth pier and pipeline design to reducethe risk of vessel collision with loading platforms, transfer lines and berthing structures.Information on such issues is available in the Marketing Engineering StandardEE.3M.86 “Marine Facilities, Design, Specification and Evaluation” and DP XV-J“Safety in Plant Design Docks, Loading Racks and LPG Storage Facilities.” It isrecommended that the designer seek assistance from ExxonMobil Research andEngineering (EMRE) for guidance in LPG marine facilities matters.

An existing jetty shall be inspected and approved by EMRE for operation prior to anyjoint venture commitment. For a new jetty, the following surveys shall be carried out toestablish the design basis:

1. Bathymetry – to determine water depth for navigation, channels, anchorageand maneuvering areas.

2. Tidal Range – to determine tide conditions.

3. Current – to determine current velocities and directions for surface, mid-depthand bottom current.

4. Wind – to determine wind velocities and direction for wind loadingconsideration.

5. Wave/Swell – for terminals at exposed locations to determine wave height,direction and period.

6. Geotechnical – to determine soil conditions, extent, thickness, strength anddeformation of soil layers.

7. Earthquake – to determine seismic conditions.

8. Environmental – to establish baseline data and provide environmental impactassessment.

9. Fleet Data – to establish vessel physical dimension, mooring plans andmanifold details. Data can be obtained from ExxonMobil Supply.

6.2.4 Marine Pier Installations

The jetty shall be constructed of non-combustible materials. A floating pontoon jetty isnot acceptable for LPG operations. The jetty design shall be certified by EMREEngineering or approved designated consultant. The jetty design shall include but notlimited to:


1. the ability to absorb lateral load that is expected when berthing tankersmooring.

2. corrosion protection.

3. spill containment (if jetty is used for loading/unloading multiple products).

4. vehicle access to facilitate maintenance.

The jetty may be used for loading/unloading multiple products other than LPG providedit is designed and constructed for LPG operations in addition to meeting relevantExxonMobil’s standards and specifications for loading/unloading other products.

Breasting facilities are required to absorb the energy of the berthing vessel, to protectother facilities and to provide points of contact for the moored vessel. Commonarrangement for tanker pier is shown in Fig 6.2.4-a which shows two free standingbreasting dolphins. Number of breasting dolphins may be increased to accommodatevessels of larger sizes. Breasting dolphins should be place symmetrically about thecenter of the loading platform piping manifold. All berths shall be deep enough andlong enough so that the tanker operated at the deepest draft shall have adequate UKC(underkeel clearance) during any stage of tide. Berthing dolphins should be well lit andmarked with reflective material to provide clear target for the pilot for night berthing.

The berthing operations should be reviewed to establish the number of tugs and otherberthing aids (bow thrusters, berthing monitoring systems). Issues related to rapid andfail safe communications, including providing the ship with a control box to shut downshore pumps and close EBVs in the event of an emergency, should be considered.Quick release mooring hooks should be considered, so that the vessel can be removedfrom the berth area quickly in the event of an emergency.

Mooring facilities should be arranged as symmetrically as possible about the centerlineof the piping manifold. Breast line mooring points shall be located so as to:

1. Provide mooring line leads as near as possible to 90 degrees to thelongitudinal centerline of the vessel.

2. As far aft and as far forward as possible.

Spring line mooring points should be located to provide mooring line leads as nearlyparallel as possible to the vessel’s longitudinal axis. Mooring points should be locatedto keep all lines at vertical angle less than 25 degrees and not more than 50 m from thevessel. Mooring structure should be arranged so that all lines in the same service areapproximately the same lengths.

An anemometer shall be provided to monitor wind conditions, so that cargo transfercan be shut down at pre-determined wind limits. Flammable gas detectors should beinstalled in the berth loading/discharge manifold area to detect product leaks and soundthe alarm in the berth area as well as the control center.

Corrosion protection of steel structures above elevation of at least 3 m below riverbedor seabed shall be provided. Protection may be provided by coatings, increasedthickness of steel member (corrosion allowance) and cathodic protection.

Dock Operations Building

The structure for operator on duty, if provided, shall be located such that the operatorcan observe the product transfer system clearly. However, the structure shall be 15 mfrom the most hazardous area where ignition is mostly likely to occur. It shall also belocated near a safe emergency evacuation route.

Layout shall provide for structural support, operating area for transfer of product,gangway access to tanker, spring mooring lines and fire protection. Lighting in all work


areas shall have an average illumination of 100 lux and shall be suitable for both dayand night operations.

Pumps are generally used for loading and unloading vessels. Loading pumps are onshore and unloading pumps are normally on the ship. Piping shall not be routed belowthe jetty.

Loading, discharge and vapor return lines from the Marine Pier to the shore shall havetwo emergency block valves (EBV), one at the pier manifold and one at the shore side.These valves shall be remotely operated. The valves shall either be operable for 15minutes in the event of a fire by fireproofing power supplies or incorporate fusibleelements, which will allow closure when melted. Valves, which close automatically onloss of power (fusible elements), shall be designed to limit their closure rate as a resultof power failure in order to prevent hydraulic surge. Emergency shutdown buttons shallbe positioned at the manifold and at the exits to the pier. Consideration shall be given toEmergency Shutdown Buttons at the Emergency Egress locations as well. Riskassessment may be used to determine whether the pier shutdown buttons should activatethe pier EBVs only or activate the entire plant emergency shutdown system.

Fig 6.2.4-a: Common arrangement for tanker pier Loading Platform

Electrically insulating flanges are required for stray current protection on marineloading and unloading lines for both vapor and liquid. Without insulating flanges,currents could be developed by ship or dock cathodic protection systems or by galvanicpotential differences between ship and shore. Installation shall be such that the pierpiping is insulated from both the on-board piping and the shore piping (the latter tomaintain the separation of the pier cathodic protection system). All plant flow lines(except for the dock lines as mentioned above), shall be electrically continuous.

Dock lines shall have the insulating flanges as close to the presentation as possible (i.e.for loading arms the insulation flange shall be installed at the outboard arm, behind thetriple swivel and any support which comes in contact with the ship; for hose strings, onehose shall be electrically discontinuous). This will ensure electrical isolation betweenthe vessel and the pier.

An insulating flange, when new, shall have very high electrical resistance, typically over10 million Ohms. Insulating flanges in service shall have at least 1000 Ohms resistance;a lower value means that deterioration has occurred and maintenance is needed.

Electrical bonding connections (bonding wire) shall not be used between the vesseland the pier piping. Because of cathodic protection systems for the dock or ship orgalvanic potential differences between ship and shore, a current may exist through the


bonding wire, which can spark on connecting or disconnecting. In circumstances wherethe government authority requires bonding wires, every effort shall be made to educatethe authorities about the dangers of such practice. If a bonding wire is used, the wireshall include an explosion-proof switch. Before the wire is attached to the vessel, theswitch shall be in the open position. After the wire is attached to the vessel, the bondingcircuit can be closed using the explosion proof switch. The procedure shall be reversedto disconnect the bonding wire.

All electrical equipment shall be suitable for the electrical area hazard classificationwhere it is installed.

Normally, LPG Cargo Transfer Equipment is empty when not in use. Appropriatepiping for depressurizing and venting shall be included at the pier manifold. Also,depending on the operations and vessels involved, vapor return lines may be required.

Critical dock services which shall be protected against fire exposure include thefollowing: fire mains, dry pipe foam headers, systems associated with the control andactuation of emergency block valves, quick-release hooks or other emergency facilities,and any other instrumentation or communications systems which are essential during anemergency.

LOCALEMERGENCY PUSH BUTTON

Insulating Flanges if Pier in Salty orBrackish Water

LIQUID

VAPORTERMINAL ESS

EBV

EBV

EMERGENCY PUSH BUTTONON SHORE

EBV

EBV

Emergency ReleaseSystem

Figure 6.2.4 b. : Emergency block valves in marine loading and unloading

As far as possible, the layout of the above systems shall provide at least 7.5 m spacingfrom the berth manifolds to avoid fire exposure from three dimensional fires at theselocations. Sections unavoidably extending within the 7.5 m distance shall befireproofed. The critical systems shall also be protected against spill fires burning on thewater surface below the dock structure, by locating these systems above the deck or byfireproofing. An alternative method for the fire main is to install a remote operateddump valve at each extremity to establish flow in the event of fire (see GP 3-2-3).

6.2.4.1 Marine Cargo Dock Hose

Marine Cargo Dock Hose shall not be used for refrigerated or partially refrigerated LPGCargo Transfer. For pressurized LPG, the use of all steel Marine Loading Arms isrecommended, however, under certain circumstances, (i.e. when the throughput rate andthe volumes are small and cargo transfer is infrequent) use of Marine Cargo Dock Hosemay be acceptable for existing facilities. A formal LPG Cargo Transfer RiskAssessment can be of help in determining whether use of Marine Cargo Transfer DockHose may be used. EMRE's memorandum on “LHG Marine Cargo TransferFire/Explosion Risk Assessment Procedure” (93 CMS2 010) can serve as a startingpoint for such an assessment. Marine Loading/Unloading Hoses shall be designed asfollows: Working pressure of 2,415 kPa and a Bursting pressure of 12,075 kPa

GP 3-11-1 shall be used for the purchase specification of Marine Cargo Dock Hose.The ERE report EE.76E.92 provides details on the purchase specification, inspectionand retirement criteria. The report EE.40E.94 “Marine Dock Hose Technology andPractice Training Video with its companion Application Guide” is also a source ofuseful information regarding hose purchase specification, inspection and testing, hosehandling and retirement criteria.


Marine loading (barges) arms/hoses shall be capable of accommodating the combinedeffects of change in draft and tidal changes. Marine barges loading arms/hoses shall bedesigned and tested periodically in accordance with OCIMF, Design and ConstructionSpecification for Marine Loading Arms and United States Coast Guard (USCG)requirements (33 CFR 156) or equivalent. Test pressure shall be 125 percent ofmaximum operating system pressure. Hydrostatic test shall be carried out at least once ayear.

Figure 6.2.3.2: Emergency release coupling in marine loading and unloading

6.2.4.2 Marine Loading Arms

New or renovated facilities shall conduct cargo transfer with all steel Marine LoadingArms. Hard arm material shall be Schedule 80 Seamless Steel - ASTM Specification A-106, Grade B. Terminals in pressurized LPG service which use Marine Cargo DockHoses shall consider upgrading to Marine Loading Arms. A formal LPG CargoTransfer Risk Assessment can be of help in determining the need for the upgrade.EMRE's memorandum on “LHG Marine Cargo Transfer Fire/Explosion RiskAssessment Procedure” (93 CMS2 010) can serve as a starting point for such anassessment. GP 3-11-2 covers the requirements for the design of Marine Loading Armsand associated equipment (such as Quick Connect/Disconnect couplers, Accessories,Range Monitor Systems and Emergency Release Systems (ERS)). Regarding ERS,reference shall be made to EEEL ERS Guidance Note for GP 3-11-2.

Emergency Release Systems (ERS) are recommended for new and existing LPG arms.An ERS consists of dual isolation valves at the ship/loading arm connection. The ERS

allows for rapid, automated disconnect in the event of an emergency with little loss ofproduct. As general guidance, circumstances where LPG transfer without an ERS maybe used are as follows:

1. Facility is a loading terminal, and


2. Arm is equipped with a range monitoring system which shuts down loadingpumps and closes remote operated block valve at base of loading arm in eventvessel begins to approach limits of loading arm operating envelope, and

3. Total arm contents that might be spilled in the event the arm is damaged byship motion is less than 500 liters of LPG, and

4. Surge analysis has been conducted to ensure there is minimal risk of piperupture in event of emergency shutdown described in item 2 above, and

5. Probability of excessive ship motions is minimal based on historical recordsand average wind and current conditions at the site.

6. Relatively infrequent marine transfers.

The decision whether to equip LPG Loading Arms with ERS can be made after an LPGCargo Transfer Risk Assessment. The considerations described above are assessed indetail in EMRE's memorandum on “LHG Marine Cargo Transfer Fire/Explosion RiskAssessment Procedure” (93 CMS2 010).

NOTE: Vapor cannot be evacuated from the last tank to be discharged because there isno vapor line to shore.

Figure 6.2.4.3: LPG ship unloading with compressor without vapor return line to shore

6.2.4.3 Discharging System without Vapor Return

If a ship is equipped with two or more tanks and compressors, it can discharge through asingle line without a vapor return system. This is accomplished by selectively drawingvapor from one tank in the ship and forcing it into another, causing the discharge. Asliquid is exhausted from the tank, the empty tank may then be used as a vapor source


while a loaded tank is being discharged. The piping arrangement and successive steps inthe operation are shown in the schematic flow diagram in Figure 6.2.4.3. Since there isno vapor line to the shore tanks in this system, the vapor cannot be evacuated from thelast tank to be discharged.

Loading Arm shall conform to OCIMF publication “Design and ConstructionSpecification for Marine Loading Arm”. Pipelines on pier shall be adequately bondedand grounded. If excessive stray currents are encountered, insulating flanges or jointsshall be used.

6.2.5 Pipeline Dispatch and Receipt

The designer should consult with the pipeline company and the delivery company(refinery) to establish detailed mutual agreement on design specifications, ownership,metering and operating responsibility for the pressure reducing station located in theplant. Pressure rating of receipt manifolds, type of pressure reducing valve,overpressure protection and emergency shut-down procedures shall be established.Point of transfer of product and maintenance/inspection responsibility shall beclarified.

A remote operated, fail safe emergency block valve (EBV) shall be provided at thereceiving/dispatching station on incoming and outgoing pipelines. This valve shall beincorporated into the plant emergency shutdown system (ESS). In addition, it may beequipped with automatic shutdown features (fusible element). Quarter turn ball valveswith hydraulic or pneumatic actuators are the preferred choice. There shall be aninsulating flange to separate the plant piping from the pipeline cathodic protectionsystem.

Safety in LPG Design LPG CYLINDERS 7-1

7 LPG CYLINDERS

7.1 Cylinder Purchasing SpecificationsThis section describes the Purchasing Specifications of portable LPG (small) containersusually referred to as “Cylinders” or “Bottles.”

Cylinders are Loan Delivery Equipment (LDE). This means that they are purchased andowned by the LPG facility, but stay mostly with the customer for LPG consumption.They are designed to be refilled at a filling plant. Safety of LPG cylinders is important,the general public as customers is in direct contact with the cylinders. It is thereforeimportant that LPG cylinders, together with all associated fittings and controls, e.g.;valves, gas flow pressure regulators and hoses, be manufactured to the latestinternationally recognized and approved design standards and correctly specified fortheir intended duty.

This Purchasing Specification has been produced to assist in determining that the LPGequipment purchased for market place use, meets acceptable standards of safety,integrity and reliability. Primarily, this requires special attention to internal cleanlinessof cylinders and quality of elastomers/rubbers, used in valves/regulators andassociated hoses, for safeguarding against LPG leaks and hazardous pressure/flowconditions.

7.1.1.1 Quality Control Systems

Whatever the type of equipment, all manufacturers should be formally accreditedwithin an internationally recognized standard for product quality control. As aminimum, this would mean EN/ISO 9001/2 or BS 5750. If candidate manufacturers arenot currently accredited with these standards they should show evidence of progressingtowards these standards.

Manufacturers should agree to Quality Assurance Auditing of their manufacturingunit(s) and Quality Control (QC) systems, to be carried out at the discretion of thepurchaser by their designated employee or agent.

Whenever possible, equipment should be certified for LPG service as described in“Quality Assurance” in Chapter 1.

7.1.1.2 Manufacturing Records

To ensure reliable and efficient quality control, monitoring of equipment integrity andfault tracing after delivery, manufacturers shall be required to maintain full records ofraw material quality laboratory analyses, or official certification of fit for purpose, foreach batch of material or component used in their cylinders.

7-2 LPG CYLINDERS Safety in LPG Design

Manufacturers shall also operate a recognized quality control (QC) system, when one isnot specifically required within a design or manufacturing standard. QC records shall bemaintained for each batch purchase.

7.1.1.3 Post Sales Equipment Batch Rejection

A significant change in purchasing policy is the introduction of a means of improvingmarket place safety by introducing Post Sales Equipment Batch Rejection Criteria.This requires all equipment found to be faulty either before or after placing into themarket place, to be immediately withdrawn and examined for cause of the fault. Themain concerns being LPG leaks, hazardous gas supply pressures and or any othermalfunction. As part of a purchasing agreement, manufacturers shall agree tocooperating fully with the investigation and if found to be replicated or unresolved,consideration being given to replacing the whole batch.

Simply replacing faulty equipment within, or reasonably beyond, a Guarantee period isinappropriate without investigating and resolving the cause of the fault. This policyapplies to valves, regulators, and hoses as well.

Figure 7.1.2: Typical domestic LPG cylinder

7.1.2 Cylinder Specifications

As a minimum, all cylinders in use or being processed and handled shall comply withinternationally recognized design standards. Where national standards are in force,these may be used, providing they are at least equivalent to, or derived from, thosestandards referred to in sub-section “Manufacturing Standards and Design.” A mostimportant requirement contained within these guidelines, which is not dealt with by anyof the listed standards, is that of internal cleanliness of the cylinders, not only byremoval of pressure test water, but the prevention of iron oxide and mill scale and/or itsremoval. See sub-section “Cylinder Heat Treatment” later in this chapter.


7.1.2.1 Manufacturing Standards and Design

Cylinders shall be designed, fabricated, tested and marked (or stamped) in accordancewith Department of Transportation (US DOT 4B 4BW-240), equivalent industrystandards or local regulations. Although some of the standards listed below permit theuse of aluminum as a cylinder construction material and brazing for fabrication, neitherof these materials or joining processes are recommended nor should they be used forrefillable LPG cylinders. Only steel and electric arc welding specified within thesestandards are recommended.

Examples of appropriate standards are:

1. US Standards DOT 4B/4BW - 240.

2. International Standard ISO 4706.

3. European Standard EN 84/527.

4. British Standard BS 5045 Part 2 1989.

5. French Standard NF M88-703.

6. Malaysian Standard MS 641/642.

7. Australian Standard SAA AS B239.

8. Japanese Standard JIS B 8233.

Figure 7.1.2.1: Two piece and three piece cylinders

For reference, the following material specification is quoted, which is used forDOT 4BA cylinders.

Carbon 0.22% maximumSilicon 0.45% maximumManganese 1.60% maximumPhosphorus 0.04% maximumSulfur 0.04% maximumPhosphorus and sulfur 0.07% maximum

The material shall be proven to be able to withstand less than 10% of permanent stretchwhen undergoing hydrostatic stretch test. All parts of welded cylinder bodies and allparts welded to the body shall be made of compatible materials. The cylinder can befabricated in 2 piece or 3 piece welded design. Figure 7.1.2.1 shows the typical drawingof a two and three pieces welded cylinder. Opening on the cylinder may be providedwith a boss welded onto the cylinder. Tapered internal threads of ¾” NGT shall beprovided on the boss for attachment of the cylinder accessories. In case DIN 477


thread is used there shall be clear marking on the cylinder (preferably on the bung)to distinguish from NGT threaded cylinders. If delivered without valve a lug or capshall be provided for each cylinder to cover the opening to prevent foreign material fromentering the cylinder.

7.1.2.2 Manufacturing Measurement Tolerances

The size of portable cylinders shall be up to a maximum of 50 kg. The service pressureof the cylinder shall be at least 1,660 kPa based on 100% commercial Propane attemperature of 54 °C. Maximum filling limits for cylinders shall be based on localstandards. In the absence of local standards, or when local standards allow a higherlimit, the maximum safe quantity that can be filled into the cylinder shall be such thatthe cylinder will not be more than 95% liquid full at a temperature of 54 °C.

All cylinder dimension tolerances shall be compatible with those of cylinder valves,filling plant equipment and handling devices. This information shall be obtained fromequipment suppliers and inserted into the purchasing specifications, to suit theirindividual circumstances. Otherwise, serious damage and possible hazardoussituations may develop within the plant.

The following sub-section highlights critical dimensions, which shall be established,prior to placing orders for cylinders.

Following superficial dimensions shall be fixed:

1. Overall diameter.

2. Overall height.

3. Valve bung thread.

4. Height of valve filling orifice above cylinder base.

5. Maximum angle of valve from perpendicular (0.5 degrees from top of valvebung is recommended maximum).

For most refillable cylinders it is not cost effective to specify both the tare weight andthe internal volume, due to slight variations in diameter, height and metal thickness.Internal volume shall be specified as it is key to preventing overfilling. The internalvolume specification shall have a tolerance of +1% or less of the rated nominal cylinderwater capacity.

7.1.2.3 Cylinder Attachments

The design of the footring shall be stable and allow the cylinder to stand firmly on asubstantially level surface without any support. The bottom of the cylinder shall have aminimum clearance of 20 mm from the ground. Design of foot-rings shall comply withthe following:

1. Foot rings shall be rolled from steel having equivalent strength as the maincylinder body and be designed to protect the cylinder against impact damageif it is dropped. The top of the foot-ring shall be of castellated design topermit at least six welding lugs and to provide unrestricted air circulation forthe cylinder base, through rectangular apertures for a nominal 60% of the ofits overall rolled length.

2. The base of the foot ring shall be rolled to at least an internal “J” or “d”section to provide additional reinforcement and a rounded surface tominimize damage to cylinder handling and standing surfaces. A flat, sharpedged finish shall not be accepted. Six equally spaced 5 mm diameter waterdrain holes, shall be drilled through the bottom of the “J” section. Theseholes shall be angled to allow trapped water to drain away from the foot-ringand not become self-blocked when the cylinder is standing on a firm flatsurface.


Neck ring valve protection and lifting handles shall be designed as follows:

1. Preferred valve protection is by a neck-ring welded to the cylinder body,which shall be manufactured from forged or rolled steel, having equivalentstrength as the cylinder body. A steel cap screwed to the bung is allowable.The disadvantage of the steel cap is that the customer or retailer needs to havethe discipline to always screw it back before returning the cylinder. Valveprotection caps from plastic shall not be permitted.

2. The neck-ring shall be of sufficient height to allow another cylinder to bestacked on top without contacting the valve of the cylinder underneath. Itshall also have an external diameter which permits secure, tilt free stackingbut with sufficient clearance for easy manual separation of the stackedcylinders.

3. The neck ring shall be open at one side to provide full access to the valve forfixing top or side connecting LPG gas flow regulators, which ever isspecified. It shall allow for valve apertures, such as gas outlet connection andpressure relief valve to be positioned to an unrestricted opening in the neckring without over stressing the valve tightening torque during its insertion.

4. For nominal 6 kg to 15 kg capacity cylinders, which may be manually lifted,the neck ring shall be designed with two handles to permit lifting with twohands for safe stacking or transporting without strain.

7.1.2.4 Cylinder Markings

Cylinder shall be marked in accordance with local regulations. Where any of the abovedesign standards do not specify, the following shall be clearly stamped on the side of theneck ring, or on the cylinder body top, providing the cylinder body thickness is noless than 3.48 mm thick.

Pro

pert

y of

: E

sso

Tar

e w

eigh

t: 1

2.5

kg L

PG

wei

ght:

12

kg

Wat

er c

apac

ity: 2

6.2

l.

Des

ign

Spe

cific

atio

n:D

OT

-4B

-240

Man

ufac

ture

r: K

eloi

lD

esig

n P

ress

ure:

1.6

6 M

Pa

Yea

r m

anuf

.5-1

999

Ret

st 5

-200

8S

eria

l No.

E34

5236

Figure 7.1.1.4: Cylinder makings

1. Flammable.

2. LP-Gas, LP-GAS, Propane, or Butane.

3. Design Specification number.

4. Name or identification logo of manufacturer.

5. A serial number of the cylinder.

6. Design pressure (If not included within the design specification).

7. Date of manufacture (MM/YY).

8. Tare Weight in kg to nearest 100 g including valve.


9. Weight capacity of Propane and Butane.

10. Water capacity in liters.

11. Owner’s logo.

12. Re-test date (for future use).

7.1.2.5 Cylinder Heat Treatment

All of the above manufacturing standards require cylinders to be heat treated afterwelding. This may be by be stress relieving (annealing) between 625 oC to 650 oC, orby normalization at about 900 oC. The former is preferred, to reduce the tendency forinternal oxidation of the cylinder surface by heat blistering of mill scale. However, ifnational standards require the latter, some means of preventing this phenomenon shall beemployed during heat treatment. For instance, inerting with Nitrogen or providing anOxygen reducing atmosphere within the cylinder and/or the heat treatment furnace areconsidered appropriate methods.

Heat treatment shall be homogeneous, on either a continuous or batch basis, within aclosely controlled furnace, preferably with Oxygen level control, to minimize external aswell as internal oxidation. Additional safeguard against direct flame impingement onthe cylinders shall also be provided to prevent over heating “hot spots,” on any part ofthe cylinder body.

7.1.2.6 Cylinder Finishing

Following the hydraulic testing, all cylinders shall undergo several important finishingprocesses before they are ready for receipt for filling processes.

Next , the cylinders shall be shot blasted. Shot blasting standards shall comply with USStandards SSPC SP6-63; NACE 3, or their equivalents within ISO 8501/1 depending onthe type of paint finish required. It may be carried out in an air blast machine or wheelpropelled using steel or iron grit only as prescribed by ISO 8503/1.

Immediately after shot blasting, the paint finish for the cylinders shall be carried out.All paint regimes shall include a stove baking process. In addition the following shallbe considered:

1. When local environmental conditions are highly corrosive, pre-treatment ofcylinders by zinc spraying or zinc phosphating is recommended. The formeris generally regarded the more durable and resistant to impact scratching etc.,although it may be more expensive to apply.

2. For environmental reasons water based epoxy paints are preferred. If this isnot feasible, normal epoxy paint finish in accordance with local requirementsand experience.

Internal cleanliness is a highly important quality control requirement for safety ofcylinder LPG in the market place. LPG may suffer odor depletion, “odor fade”, in newcylinders due to reaction of certain stenching agents with cylinder contaminants.Therefore, manufacturers shall ensure and guarantee internal cleanliness of cylinders,especially with regard to free water and particulate matter such as mill scale, “weldsplash” and any other form of iron oxide. Air-blowing and then vacuum cleaning shallcarry out the cleaning process.

Next the tare weight of the cylinders shall be determined:

1. Tare weighting of the cylinders, shall be undertaken with a full electronicload base scale, capable of an accuracy of 0.05% of its full weighing capacity.

2. All cylinders with an LPG capacity of between 6 and 50 kg, may be tareweighted to the nearest 100 g.


3. Tare weights shall be permanently punched onto the cylinder neck-ring orbody.

Valve fitting is the next step in the cylinder manufacturing process:

1. All valves shall comply with and be approved for their market userequirements.

2. An approved, non-hardening valve thread sealant paste or tape shall beapplied. For hygiene reasons, PTFE based sealant pastes are preferred tolead base. PTFE tape may be used providing it is manufactured to arecognized national standard, e.g.: BS 4375.

3. The valves shall be tightened in accordance with the valve manufacturersspecification, or to that value stipulated within an approved valve designspecification referred to in Section "Cylinder Valve PurchasingSpecifications." These torque maximum values shall not be exceeded even toalign the valve outlet and/or pressure relief valve (PRV) to requiredorientation.

Leak testing of all cylinders is important step in preventing leaks.

1. Following fitting of valves, all cylinders shall be leak tested by filling with airto 7 bar (0.7 MPa) gauge pressure and completely the immersing cylinder in awater bath and looking for leaks by bubble observation. Any bubbles,however small, shall result in rejection of the cylinder.

2. If the leaks are from a valve thread, the valve may be re-tightened to no morethan the torque specification limit. If the leak persists, its cause shall betraced and remedied. Faulty valve bung threads may be re-tapped or requirethe cylinder to be scrapped. No attempt shall be made to re-tap the valvethread. Faulty valves shall be reported to the cylinder purchaser and/or valvesupplier.

3. If bubbles are observed coming from the weld of a cylinder, that cylindershall be rejected. If two or more weld leaks are observed per batch, the entirebatch shall be rejected unless the source of the leaks is identified andrectified.

4. If a leak is observed coming from a cylinder body material itself, allproduction with the batch of steel being used, shall be stopped and the matterreported to the cylinder purchaser for deciding further action.

Prior to delivery, all cylinders, shall be evacuated down to a vacuum (absolute) pressureof a nominal 10 kPa (75 torr). To prevent damage to paint work, during transport,cylinders shall be protectively wrapped, as circumstances and experience demand.Cylinders shall be labeled or otherwise signed in accordance with purchaser instructionsand or local national safety requirements, but as a minimum, this shall include a durablehazard warning label.

7.1.2.7 Record Retention.

To assist with any incident investigation and or cylinder re-qualification or scrapping,records shall be kept of all of the following against cylinder serial number:

1. Cylinder batch number and order details.

2. Manufacturing steel batch analysis.

3. Tare weight.

4. Water volume capacity.

5. Test or Working Pressure.

6. In addition, full records shall be kept of all tests as required by DOT4B/4BW240 Standard.


7.2 Cylinder Valve Purchasing SpecificationsAs with cylinders, a wide range of valve designs, types and sizes are in use worldwide.LPG valves in vapor service may be (a) manually operated, side entry valves and themost widely used one is called POL (Port-O-Lite) valves with the female (CGA510) ormale outlet connection or (b) automatic, self closing, top entry valves and the popularsystems in the market are Compact, Jumbo and Snap-Tight. LPG valves in liquidservice are always manually operated valves with a dip tube and the most widely usedone is the CGA555 with male connection. Except where it is explicitly forbidden bynational authorities, all cylinders irrespective of valve type shall be fitted with a pressurerelief valve.

7.2.1 Manufacturing Design Standards

All valves and their components, irrespective of design, shall be manufactured inaccordance to a recognized international or equivalent national standard. Examples ofsuch standards bodies and applicable manufacturing standards are as follows:

1. International Standards Organization (ISO).

2. Committee of European Normalization. (CEN/EN) TC 286 WG 2(Draft).

3. UK LPGA Code of Practice 15 1994.

4. Japanese Institute of Standards (JIS) B8245.

5. Malaysian & Singapore Standards.

At the time of writing, an important new European Design Standard designation numberCEN TC 286 WG 2 N67, is in late draft stage, but the forecast date of final versionspreclude its inclusion within these guidelines. In the interim, it is recommended thatexisting standards already in use shall be retained, but shall now include the followingadditional requirements:

Figure 7.21: Compact, POL, and liquid take-off cylinder valves

7.2.1.1 Dimensions and Materials

No changes to existing valve dimensions shall be made without consulting withappropriate owner’s personnel, as changes may impact on cylinder filling operations,market place acceptance and safety.


All materials shall be compatible with all commercial grades of LPG and chemicallyand physically resistant to possible trace contaminants such as re-active volatile sulfidesand water vapor.

7.2.1.2 Valve Body

A Copper/Zinc/Lead (forging brass) alloy designated Cu.Zn40.Pb2 shall be used andshall provide a tensile strength of 360 - 400 N/mm2 and a Brinell Hardness HB of 80-85.Suitable standards for the composition and properties of this brass are:

1. DIN 17 660 -Alloy 2.0402.

2. BS 2782/2784 Alloys CZ 122 or 128.

3. JIS H3250, C3771 BE.

The finished valve shall not exhibit internal or external deformation following fitting toa cylinder after applying tightening torque to the maximum value stipulated within thevalve manufacturing standard, or as advised by the valve manufacture. Cylinder valvesshall have a minimum rated working pressure of at least 1,725 kPa. One-piece valvebody design is preferred to two-piece since there is chance of failure at the threadedconnection causing leakage after prolonged use.

7.2.1.3 Seals and Internal Fittings Materials

All elastomer/rubbers and plastics used for internal valve seals, operation and externalregulator connection seals shall be suitable for LPG at operating temperatures rangingfrom –20 oC to 60 oC. They shall also be manufactured in accordance with arecognized international standard, which pays particular attention to:

1. Chemical resistance(Swelling/solvency) to lubricants and other normaloccurring LPG components.

2. Aging.

3. Low /High Operating Temperatures.

4. Ozone Attack (Cracking) etc.

Suitable standards, which include the above requirements, are:

1. European Standard EN 549.

2. BS 6505.

7.2.1.4 Pressure Relief Valves and Other Internal Fittings

Except where it is expressly forbidden by national authorities, cylinder valves shallincorporate a pressure relief valve in its body. Pressure relief valves shall be designed toensure a minimum LPG release rate and conditions in accordance with NFPA 58 1992,Appendix E. The pressure relief valve shall relief only vapor pressure. The set pressureof the relief valve shall be not less than 2,415 kPa.

Although allowed by NFPA 58, fusible plugs are not recommended for LPGcylinders.

All springs and other internal fittings used in valve designs shall be corrosion proof,and resistant to chemical attack, sufficient to guarantee protection for at least ten yearsirrespective of location.

7.2.1.5 Valve Markings

Valves shall be permanently stamped and or embossed with the following information:

1. Manufacturer's name/logo.


2. Date of Manufacture (Month & year).

3. Pressure Relief Valve Setting.

4. Marking of valve thread (NGT, DIN).

7.2.1.6 Liquid and Dual Off-take Valves

Manufacturers of liquid off-take valves, shall ensure that they are specifically designedfor this duty and are manual closing type. They shall be protected against physicaldamage. Materials shall be metal and suitable for LPG service. Cylinder valves shallhave a minimum rated working pressure of at least 1,725 kPa. Cylinder valve shallcome complete with a pressure relief valve. The pressure relief valve shall relief onlyvapor pressure. The set pressure of the relief valve shall be not less than 2,415 kPa.Pressure relief valve shall be designed to minimize the possibility of tampering. Thevalves shall incorporate an excess flow check device and have outlet connecting threadswhich prevent them being connected to a vapor LPG system. Shutoff valve shall not belocated between the excess flow valve and the cylinder. This also applies to dualpurpose (Liquid or Vapor) off-take valves. In addition, such valves shall alsoincorporate a self closing device, which prevents liquid LPG release to the atmosphere,if the valve is accidentally opened before connecting to a sealed system. Valves usedfor liquid or dual off-take shall be clearly and permanently marked to indicate liquidhandling. Color coding may be considered.

Where pressure relief valves are fitted, they shall at all times be exposed only to thecylinder vapor space.

7.2.1.7 Records and Shipping

The valve manufacturer shall keep and maintain records of valve details for eachbatch supplied, which include specifications and laboratory analyses of all materialsused for valve manufacture. This shall be sufficient to trace any faults subsequentlyfound, back to the specific raw material batch supplied by original equipmentmanufacturers (OEM).

Pre-Delivery Packing - All valves shall be securely wrapped and packed to preventdamage and contamination during delivery.

7.3 Regulator Purchasing SpecificationsThere is a very wide range of regulator designs associated with cylinder LPG. Theseguidelines are mainly for non-adjustable regulators, which are directly fitted tocylinders. Their general principles may be applied to those, which are remotelymounted, but otherwise directly connected to no more than one or two cylinders. Singleor two stage regulators are acceptable. Cylinder regulators shall be constructed ofmaterials suitable for LPG service. The connection of the cylinder regulator to thecylinder valve shall be compatible with the cylinder valve.

Regulators, connected to multi-cylinder manifold installations are not considered withinthis chapter. For multi-cylinder installations, a two-stage regulator system, as discussedin “Container Regulators” in Chapter 10, is typically installed.

Regulator performance characteristics shall be clearly and unambiguously stated andagreed upon with manufacturer in writing. Once fixed, such performance criteria shallonly be changed by joint agreement and again in writing.

Unless otherwise requested, all regulators shall be guaranteed to be interchangeablewith those in existing use and in so being, provide a safe and otherwise trouble freefitting to the cylinder valves.


Regulators may incorporate an excess flow check device, which is designed to cut offgas flow in event that the gas supply hose to an appliance becomes unattached or issevered. Such devices shall specifically meet the following acceptance criteria:

1. Gas flow shut-off is not activated within normal regulator LPG throughputrating.

2. Gas “leak-by rate”, following activation, shall not exceed that required bylocal/national safety authorities, or a maximum of 60 grams/h which ever islower.

3. It will re-open automatically when the hose is re-connected, but only with gasappliance valve in the off position.

7.3.1 Manufacturing Design Standards

All regulators, shall be manufactured to an internationally approved current designstandards. Examples of such standards are:

1. BS 3016.

2. UL 144.

3. JIS B8238.

4. prEN 12864 (Standard in final draft stage since 1997).

SpringMembrane

Pressure Control Valve

Figure 7.3.1 a: Cylinder regulator principle

7.3.1.1 Materials, Regulator Body, and Internal Fittings

All materials shall be compatible with all commercial grades of LPG and chemicallyand physically resistant to possible trace contaminants such as reactive volatile sulfidesand water vapor and salt spray environment attack.

Regulator bodies shall be manufactured from a generally non-corrosive metal only. Ifzinc alloy is used, it shall conform to ISO 301:1981.

All springs and other internal fittings used in regulator designs shall be corrosionproof, and resistant to chemical attack, sufficient to guarantee protection for at least tenyears irrespective of location.

7.3.1.2 Non-metallic Components

All elastomer/rubbers and plastics used for internal and external components shall besuitable for LPG at operating temperatures ranging from –20 °C to +60 °C. They shallalso be manufactured in accordance with a recognized international standard, whichpays particular attention to:


1. Chemical resistance (Swelling/solvency) to lubricants and other normaloccurring LPG components.

2. Aging.

3. Low/High Operating Temperatures.

4. Ozone and Salt Attack (Cracking) etc.

Use of adhesives for fixing regulator components shall not be permitted.

Suitable manufacturing material standards for seals and diaphragms, which include theabove protection requirements are:

1. European Standard designate pr (preliminary) EN 549.

2. BS 6505.

In addition to requirements within non-metallic components, materials used for themanufacture of laminated reinforced diaphragms shall be specifically required to betested for resistance to de-lamination in accordance with Standard Pr EN 549. However,resistance to de-lamination shall also be tested for by immersion in Propylene for 72 hat 20 (+/-5) oC.

Figure 7.3.1-b: "Snap-On" two stage cylinder regulator (SRG)

7.3.1.3 Regulator Markings

The minimum permanently stamped or embossed markings for regulators shall be:

1. Name of manufacturer.

2. Production date(MM/YY).

3. Designed outlet pressure.


4. Grade of LPG.

5. Maximum rated gas flow.

6. Direction of gas flow.

Pre-Delivery Packing. All regulators shall be securely wrapped and packed to preventdamage and contamination during delivery. Regulator packing shall include customerfitting and operating instructions.

Figure 7.3.1-c: Compact Cylinder Regulator (Kosan)

Figure 7.3.1-d: "Quick-on" cylinder regulator, child proof, single button, excess flow valve (Cavagna)

7.4 Hose Purchasing SpecificationsThis section of minimum standards covers cylinder hoses used for domestic appliances,maximum working pressure of 35 kPa and industrial application, maximum workingpressure of 2,415 kPa. Cylinder hoses shall be manufactured to BS, JIS, UL or


equivalent standard or meets local requirements. The date of manufacture (MM/YY)shall be permanently marked on each hose. Cylinder hoses shall be fabricated ofmaterials resistant to the action of LPG both as liquid and vapor. Hoses for industrialapplication shall be designed for working pressure of 2,415 kPa with a minimum of 5:1safety factor. For industrial application, hose shall come with assembly consisting of aflexible hose, a tee-check valve and a ball valve shall be used. The hose assembly shallhave a design capability of withstanding a pressure not less than 4,830 kPa.

Purchased LPG hoses for customer appliances, shall meet internationally recognizedapproved manufacturing standards. Plastic hose shall not be used in LPG service.Manufacturers shall clearly and durably mark hoses as below and no hoses shall bepurchased unless so marked:

1. Manufacturers name/logo.

2. Manufacturing standard number.

3. Current year of manufacture.

4. The words "LPG" or equivalent.

Typical cylinder hose manufacturing standards are listed below.

For high pressure hoses, which are pre-fitted with screw connections by themanufacturer and which are normally used for connecting cylinders to manifolds, highpressure, or wall mounted regulators.

1. BS 3121 (Hose Type 2) 1991.

2. DIN 4815 Part 2.

3. JIS K6347.

4. NF Gaz M 88-768.

For low pressure hoses that are normally used to connect regulators to LPG appliancesoperating up to 200 mbar gas pressure.

1. BS 3212 (Hose Type 1) 1991.

2. DIN 4815 Part 2.

3. JIS K6347.

4. NF Gaz D36-161.

The length of the hose shall not exceed 2 m if installed indoors and can be greater than 2m if installed outside building. However, the length shall be as short as possible. Hosesshall not be installed with sharp bends or twists and shall be protected against physicaldamage. Hoses shall not be concealed from view or used in concealed locations. Hosesshall not extend from one room to another nor pass through any partitions, walls,ceilings, or floors.

7.4.1 Hose clips

All hoses must be securely fixed to the connectors. For low pressure connections,tension clips or screw type clips are sufficient. For high pressure hoses the connectionmust be screw type with a compressed clamp which is prefabricated the hosemanufacturer. High pressure hose connections must not be repaired locally butexchanged against new hose connections. The use of rubber slip ends shall not bepermitted except for domestic appliances where the working pressure is less than 35kPa.


7.5 Cylinder Filling PlantThis section of minimum standards covers the LPG cylinder filling plant withinExxonMobil’s fence.

The cylinder filling plant shall have manual or automatic cylinder filling capabilities,leak check equipment, weight check equipment, cylinder evacuation units, conveyorsand associated motors. The LPG cylinder filling shed shall be of open shed design. Thefloor level shall be 1.1 meter above the road level for easy unloading/loading ofcylinders from/to trucks. The area shall be well ventilated to minimize the accumulationof LPG vapors.

The LPG supply from the storage to the filling plant shall be by pump. An emergencyshutdown valve shall be provided on the piping system supplying LPG to the fillingfacility. Emergency shutdown pushbuttons shall be provided at strategic location/s toensure that the filling plant shuts down safely during emergency. Location of theemergency shutdown pushbuttons shall be located such that they are still operableduring fire situation. The electrical area classification of the filling plant shall be inaccordance with Chapter 2. The LPG filling equipment shall be designed for 1,725 kPato accommodate LPG filling with anticipated higher Propane composition.

Public access to areas where LPG is stored and transferred shall be prohibited. Toprevent trespassing or tampering, the LPG filling plant shall be enclosed by an industrialfence not less than 2 m high unless it is otherwise adequately protected (e.g. within agreater fenced area). Sufficient clearance shall be provided to allow maintenance to beperformed. Warning signs “NO SMOKING” and “NO OPEN FLAME” shall be postedin the filling plant. Fire protection and gas detectors shall be provided in accordancewith Chapter 8.

7.6 Cylinder FillingCylinder filling may be manual, automated or fully integrated automated. Fullyintegrated/automated cylinder filling lines are complex, custom designed equipment andLPG supply volume and pressure requirements are likely to be specific to eachindividual line.

The facilities provided in a plant for handling cylinder maintenance, testing, and fillingwill depend on the volume of product to be filled into cylinders, the type and variety ofcylinder to be processed (ranging from 3.9 to 48 kg), and project economics.

Total cylinder filling and storage capacity requirements shall be determined byestablishing the maximum number and size distribution of the cylinders to be filled tomeet average daily/seasonal demand. Then, peak daily demand shall be established inthe same manner. Finally, provision for future business growth shall be added to theprevious two values, since incremental equipment capacity and operating space(particularly) can be incorporated in a new plant design at a small fraction of the costsincurred in expansion of the same plant after it is constructed. All of the aboveinformation will be needed to define the number, type and layout of scales.

Average and peak capacity requirement determinations shall include allowances forinterruptions of normal operation by such contingencies as power failures, mechanicalbreakdowns, and product supply shortages.

The designer shall next determine the optimum strategy for meeting peak demand, bybalancing capital cost of providing additional instantaneous filling capacity against thedisadvantages of filling and storing cylinders during off-peak periods. Evaluation of thelatter alternative shall include:


1. A risk analysis of warehousing a larger inventory of pressurized cylinders.This risk potential may be partially mitigated by providing remote/satellitestorage depots for filled cylinders. Many national safety authorities regard apreviously used depressurized cylinder awaiting refilling to be as hazardousas a full one. Local limits on permissible cylinder quantity transported in onevehicle load may also affect storage arrangement.

2. A financial analysis of the costs of increased filled cylinder inventory.Cylinders are usually the largest single asset item in LPG plants that have asignificant filling operation.

Figure 7.5.2: Cylinder filling adapter (SRG)

7.6.1 Cylinder Processing and Filling

The pump supplying the product to the filling shed shall not be oversized since thiswould keep the automatic pressure control valve to the supply tank always wide open,which would impair control. Investment in the “carrousel” system may justify provisionof an installed spare supply pump.

The line feeding the cylinder filling shed shall be provided with a remote operatedemergency block valve (EBV) and several local actuation push-buttons distributed atstrategic locations in the shed to activate the plant Emergency Shutdown System(ESS). A fail safe, quarter turn ball valve with hydraulic or pneumatic actuators is the


preferred choice. The valve shall meet API-607 fire-resistance tests. The valve shall belocated outside the filling shed.

The Emergency Shutdown System shall also activate a valve that closes the air supply tothe filling machine. Should there be a fire, this may prevent escalation by eliminatingthe air, which would normally, blow through melted plastic/copper air lines.

7.6.2 Manual Filling System

A Manual filling connection and a beam type scale (preferably double beam) may beadequate if small quantities of various sized cylinders are to be handled. The scaleweighing range shall be such that the maximum is equivalent to approximately twice theload, which will be applied by the largest filled cylinder. The scale shall be located in aplatform or within a room specifically designed for cylinder filling. The base andplatform of the scale shall be set flush with the surrounding floor level. Appropriatemeans for transporting the cylinders are required. The scale shall be capable ofproviding accuracy within the limits prescribed by the local authority.

A well supported manifold shall be provided, at a convenient height, to receive productfrom the marketing plant pumping station. The manifold shall include a lateral fittedwith positive shutoff valves. The shutoff valves are fitted with hoses of convenientlengths to reach the cylinder valve without in any way applying a strain upon thecylinder. The end of the charging hose is fitted with a quick-acting, positive shutoffvalve and a filling adapter or coupling suitable for attachment to the cylinder valvebeing utilized. A steel I-beam provides rigid support to keep all parts in correctalignment. The manifold piping is 32 mm pipe size for strength and rigidity.Restrictions are held to a minimum to allow for fast filling.

The fitting at the end of the charging hose may be manually secured to the cylindervalve and in most instances can be of a type which will permit hand tightening of theconnection. Devices are available where a resilient seating means is used to form a gas-tight seal without the use of a wrench. The quick-acting shutoff device and the adapteror coupling may be supported from above by a counter balance so the unit remains in aconvenient location when disengaged and, at the same time, supports the hose end whenattached to a cylinder valve. This minimizes the weight applied to the cylinder and, inturn, the scales. Units of this type may be installed singularly or with manifoldsaccommodating any number of scales required for a particular operation.

As an alternate to the manually secured coupling or adapter at the end of the charginghose, certain valves are adaptable to the use of a device which may be secured byhooking, snapping or otherwise engaging the valve with the application of downwardpressure. In other cases a connector may be utilized which engages the valve body,forcing and sealing the end of the adapter or coupling within the inlet of the valve.

7.6.3 Automated Filling System

An automated filling system may be justified if larger quantities of one cylinder sizehave to be filled, possibly including electronic weigh scales to assure greater productcontrol precision. Simple automatic systems may be justified for modest throughputlevels and are found in many small plants worldwide. Fully-integrated, automatedprocessing systems are justified where very large quantities of one cylinder size must befilled. These systems utilize a rotary filling head, or carrousel, similar in principle to amotor oil filling head. However, special vapor retaining connect/disconnect systems areincorporated due to high product vapor pressure. Fill weight may be checkedcontinuously by a load cell-actuated electronic weighing system.

Simple automation can be achieved by using the scales, manifold and charging hose ofthe manual system, but installing an automatic valve in the lateral from the manifold. A


sensing device is attached to the scales and is responsive to the upward movement of thebeam. A pneumatic system, using compressed air, permits the control valve at themanifold to remain in an open position until the movement of the scale beam, whichcloses the control valve, actuates the relay. With the poise set at the appropriate pointon the beam (allowance being made for any weight, which may be exerted by the hose)the flow of incoming liquid shall be shut off when the desired weight is reached.

As a modification of this system, a solenoid valve may be substituted for the controlvalve at the manifold with an explosion-proof mercury switch activated by themovement of the scale causing flow of incoming liquid to cease when the proper weighthas been reached.

7.6.3.1 Unitized Automatic Scales

Scales shall be accurate to within 1/10 of 1 percent throughout their entire range. Scalesshall be of the double-beam type or constructed so that individual adjustment can bemade for tare and net weights. It is recommended that scales be designed for thefollowing adjustments:

Recommended Range Tare and Net Contents Fine Adjustments

0.5 – 5.5 Kg 14 g

5 – 60 Kg 113 g

NOTE: A set of check weights shall be available within each filling plant to calibrateall scales daily.

Figure 7.5.3.1-a: Filling with conveyor

Automated systems are also available which are "unitized" in that the scales andautomatic control device are fabricated as a single unit. These units are constructedwith the control mechanism completely encased within cabinetry. The accuracy of thescales is reported to be plus or minus 50 grams. In operation, larger tolerances may benecessary depending upon the fluctuation in the product pressure, speed of filling, theamount of product to be filled, and friction in hoses, pipes and fittings. The scales areprovided with two roller weights representing the weight of the product to be chargedand the tare weight. Further, a sliding weight for the fine adjustment of the tare isincluded. Higher precision is obtainable with “load cell-actuated” electronic equipment.


A four scale filling plant is illustrated in Figure “Filling with conveyor” above, usingautomatic filling scales with a “keyboard” type of weight adjustment. The fillinghead attached to the individual filling hose provides an automatic means of attachmentto cylinder valves with threaded outlets. A conveyor system brings the cylinders to thefour stations and, likewise, removes them. A pneumatic lifting device is located undereach charging position so the scale platform may be elevated through the conveyor,lifting the cylinder to a position where its weight may be determined.

From Pump

Manifold

Scale Frame

Trip Valve

TripValve

Beam in Raised position

Beam Horizontal

Beam when Cylinderis not Filled

Filling HoseScale Beam

Alternate Trip Valve Installation

Pilot Vapor Pressurefrom Air Compressor

Filler Valve

Pivot Point

Approx 20%of Scale Beam Length

Figure 7.5.3.1-b: Typical automatic filling for cylinders

This type of system may be utilized with two or more stationary scales erected after eachother on the chain conveyor. The system includes pneumatic indicators, a countingdevice, and stops for fully automated operation of the inlet and outlet of the cylinders.The capacities are limited by the following operator actions:

1. Fetching of cylinder from conveyor, and placing on scale.

2. Connecting of cylinder valve to filling head, adjusting scale, and starting thefilling.

3. Disconnecting of filling head, removing cylinder from scale, and placing it ona transport conveyor.

The figure above illustrates an automatic cylinder filling valve attached to a chargingmanifold, which may service any number of additional units. The automatic valve canbe isolated from the manifold by a positive shutoff valve. It is necessary to connect asuitable supply of compressed air to the unit in order to operate the relay pilot and mainshutoff device. The lifting of the scale beam when the desired filling amount has beenreached actuates a trip or “bleed” valve installed on the scales.

The manufacturer indicates that the device is designed with a positive feather-touchcontrol, which prevents vibration or sudden jars from causing improper cutoff.Operation of the unit requires no electrical or mechanical power. The automaticcylinder filling valve is designed specifically for use with a beam scale and is notadaptable directly for use with a dial scale. When the desired amount of fuel has beenput into the cylinder, the rising scale beam contacts the trip valve and shuts off the fillervalve. A red button indicator appearing on top of the filler valve visually indicates thiscondition.

7.6.3.2 Cylinder Handling

Chain conveyor systems may be utilized to eliminate manual transport of cylinders.With one system the cylinders are loaded directly on to the chain conveyor from ahighway transport or from the empty cylinder storage area and conveyed directly to the


filling scales. The cylinders are taken from the conveyor, placed on the scales for fillingand then returned to a second conveyor, which moves the units either to the highwaytransport or to the filled cylinder storage area. Cylinders shall still be inspected fordamage and re-inspection date prior to loading onto the conveyor or at some point in thesystem before filling.

A second system employs a continuous conveyor configuration and is particularlyadapted to the charging of 33 kg or 45 kg cylinders. The system can, however, beadapted for filling smaller cylinders. In this system the empty cylinders are carried tothe filling scales on the chain conveyor and accumulate before the scales. The operatorreleases a group of empty cylinders, which pass on to the scales and are stopped bypneumatic equipment so that they are arranged with each cylinder in the correct positionat each scale.

Cylinder receipt

Visual external control

for damage, valveintegrity, corrosion

Accept orReject

Attach filling adaptor

Read Tareweightinput tareweight into scale

Control of refurbishment

datePass or

Refurbish

Fill cylinder

Stop fillingmove cylinder from scale

Control correct filling weightby reconciling tare-weight and actual

weight on indepen-dent scale

Control leak from valve and

bung

Wash cylinder

Load cylinder on truckor store in plant

Cylinder delivery

Fix cylinder capor seal

Figure 7.6.4-a: Cylinder filling process


A pneumatic lifting device consists of a bottom frame with bearing brackets into whichthe lifting table is placed. The lifting table is raised and lowered by means of apneumatic cylinder operated by automatic controls. The charging hose is connected andthe lifting table of the scale is activated in order to lift the cylinder free of the chainconveyor. After filling is completed and the charging hose is disconnected, the cylinderis lowered to the chain by releasing the control. As soon as all the filled cylinders arelowered on to the chain conveyor the “stops” are opened and a new operating cyclebegins. The filled cylinders are then carried to a check scale, which is also built into thechain conveyor system. This system is ideal for heavy cylinders as it eliminates manuallifting.

Figure 7.6.4-b: Automated filling plant with carrousel


7.6.4 Integrated Automated Filling Plant

Integrated, automated filling plants are laid out for high capacity and utilizespecialized equipment. They require extensive preliminary study, and large investment.The best practice for an integrated cylinder filling process is shown in Figure 7.6.4-a“Cylinder filling process.” The designer shall rely on packaging experts, both fromwithin the company and from equipment fabricators and vendors, to design theequipment and determine the level of automation justifiable. The designer's primaryresponsibility will be to provide the packaging specialists with a preciseduty/performance specification for the proposed filling system. This manual confinesdiscussion of integrated, automated filling systems to a review of the capabilities ofvarious system components, and a summary of information needed to solicit proposalsfor automated systems.

The schematic plant layout (Figure 7.6.4-b: “Automated filling plant with carrousel”)combines all equipment components discussed above to create an automated plantcapable of continuously filling 1000 to 1200 cylinders (11-13 kg) per hour. Onelocation operates an 800 cylinder/hour plant with one operator, one forklift driver andone supervisor.

7.6.4.1 Degree of Automation

Once the filling plant throughput requirements are established, comparative investmentsand operating costs for various degrees of automation can be determined. These valueswill permit the designer to conclude whether the plant shall have:

1. Individual weigh scale filling machines.

2. Chain conveyor systems.

3. Depalletizers/palletizers.

4. Fully automated operation incorporating a filling carrousel.

Key factors to be considered in justification of automation are:

1. Estimated capital cost of equipment components and installation.

2. Present and projected cost of labor at various skill levels for the life of theproject.

3. Estimated equipment maintenance costs, preferably supported by actualexperience with identical equipment elsewhere, and applicable localregulations at the site.

Most recent designs of filling machines allow the processing of cylinders of differentsize. Cylinders have to be filled in batches. After one batch is finished the carrousel isstopped to adjust to the next cylinder height.

7.6.4.2 Carrousel System

For higher processing capacities, the use of a carrousel filler such as shown in Figure7.6.4.2-a “Typical Cylinder Filling Carrousel” is justified by its efficiency. A carouselis a rotating table upon which a number of automatic filling scales are equally spacedaround the outer edge. The carrousel becomes an integral part of the chain conveyorsystem. Depending on conveyor system complexity, empty cylinders may be routedfrom a number of sources to the carrousel. Cylinders accumulate on the carrousel inletsection of the conveyor, and then are transferred, one at a time, to one of the multiplecarrousel scales by an automatic intake device. As the carousel slowly turns, anoperator places a cylinder on the platform of a scale, attaches the filling head, sets thenet charge weight and tare weight on the scale and opens a valve to start filling. Whenthe cylinder is filled, the automatic filling valve is tripped to the closed position. Thecylinder may then pass over check scales. The number of scales placed on a carouselwill depend upon the cylinder filling rate required within the plant. Carousels are


available with 4 – 36 scales per unit. The size of the carousel shall be selected on thebasis of the expected future filling rate.

Figure 7.6.4.2-a: Typical cylinder filling carrousel (Siraga)

Figure 7.6.4.2-b: Large cylinder filling carrousel (Crisplant)

The following operating sequence is then performed by the carrousel:

1. The filling head at the end of a charging hose is either manually orautomatically connected to the cylinder valve. Manual connection may be


necessary with screw type fittings, while automatic connection is feasiblewith click-on/clamp-on type fittings.

2. The scale is adjusted (a) manually for cylinder tare weight, using a single-dialor digital keyboard weight adjustment, or (b) automatically using self-adjusting scales programmed from a digital keyboard-programmedcomputer. Fill weight is predetermined when the size of cylinder to beprocessed is selected.

3. The cylinders are filled in less than one revolution of the carrousel. LPGsupply to each cylinder is shut off automatically when the correct fill weightis reached.

4. The filling head is either manually or automatically disconnected as thecarrousel revolution is completed.

5. The filled cylinders are automatically transferred to a check scale with dial ordigital readout.

6. After weighing, the cylinders are automatically transferred to the outletsection of the chain conveyor.

Figure 7.5.4.3-a: Unloading pallets to destacker

Figure 7.5.4.3-b: Pallet feeding into the conveyor system

Carrousels are produced with varying numbers of scales, or filling stations, up to amaximum of 48. Maximum carrousel filling capacity is approximately 1200 cylindersper hour. Carrousel design is adaptable to filling all sizes of cylinders.

Where adequate volume demand exits, the filling carrousel permits achieving acontinuous maximum production rate with minimum operating work force. In order to


realize the full potential of this equipment, it shall be installed as a part of an integratedfilling plant that incorporates all support facilities needed to operate the carrouselcontinuously at capacity.

The filling method briefly described in the prior discussion is predicated upon theprocessing of a group or batch of cylinders of a uniform size or capacity, observing thetare weight of each cylinder, and in turn adjusting the tare weight component of thescales. Operating in this manner it, is not necessary to adjust the fuel weight componentsince uniform cylinders are being processed. It should be noted that by using thismethod, a correct filled weight may be obtained regardless of the contents of thecylinder when presented to the carrousel. In other words, this system ensures thatcylinders will not be overfilled since the scales will trip when the combination of thefuel weight and tare weight is reached.

Figure 7.5.4.3-c: Check weight scale

A filling procedure using a predetermined quantity is not recommended since itinvolves time consuming procedures like cylinder emptying. Utilization of constanttare weight is also not recommended since different suppliers may manufacturecylinders over a long period.

7.6.4.3 Cylinder Filling Support Functions

The support equipment items required to create a fully integrated, automated cylinderfilling plant based on the carrousel are as follows:

Equipment to unload cylinders to be filled from the incoming transport and place themon the conveyor system. Palletization of cylinders is desirable for high volume filling,distribution, and sales operations.


Equipment to feed a conveyor system shall consist of a fork lift truck, a destacker, anda depalletizer with a ram to eject the unloaded cylinders onto the conveyor. Readyaccess to a second lift truck and driver is desirable in event of destacker, depalletizer, orpalletizer breakdowns. Figure 7.5.4.3-a “Unloading pallets to destacker” shows aforklift unloading pallets to the destacker.

Cylinder counting equipment: An automatic cumulative counter should be providedto count all cylinders remaining on the line, which will now be filled, as part of controlprocedures. The cylinders next enter the carrousel filling process.

Carrousel Cylinder Filling: Tare weights, connection, filling and disconnection weredescribed in section 7.5.4.2 “Carrousel System.”

Figure 7.5.4.3-d: Leak detection unit

Check weighing/Overfill detection equipment: The system shall next provide a devicethat is capable of accurately weighing moving cylinders and detecting over/underfillsituations. The device shall also eject those over/underfill cylinders from the line onto abranch “decant/refill” conveyor. The Figure 7.5.4.3-c “Check weight scale” shows anoverfill check weight scale to control whether filling matches correct figures for eachfilled cylinder as it moves along the conveyor system, automatically rejecting overfills.Weight readings are manually checked periodically on a statistical basis to guard againstcontinuous filling error. Statistical data shall be kept for each carrousel scale as well asfor the overfill check weight scale.

Leak detection equipment: A leak detection device capable of detecting leaks of 0.5grams/hour, and shunting the leaking cylinders to a reject conveyor is next required.The automatic leak detection is likely to require review and endorsement by localregulators. Figure 7.5.4.3-d “Leak detection unit.” shows such a unit, which mayfunction on the basis of either (a) cylinder pressure drop in 3 seconds, a time interval


consistent with 1200 cylinder/h. filling rate, or (b) hydrocarbon vapor detection in thesame time interval. In some countries the law requires that dipping the cylinderscompletely under water perform leak detection. This is an effective test provided thewater surface is allowed to become calm and is not disturbed by the submersion process.Figure 7.5.4.3-e “Seal leak detection unit” shows a machine that is capable of detectingseal leaks.

Figure 7.5.4.3-e: Seal leak detection unit

Cylinder capping equipment: Next, a machine shall be provided to apply either plasticor metal sealing caps to the cylinder valve outlet connection. Figure 7.5.4.3-f “Typicalvalve cap” shows such a sealing cap. If acceptable to local regulators, plastic seals shallbe used because they are probably more effective than metal seals.

Figure 7.5.4.3-f: Typical valve cap

Cylinder washing and drying equipment: The Figure 7.5.4.3-g “Inside of a water jetwashing machine” shows a high pressure jet water washing cabinet without brushes thatcleans the cylinders while they continue to move along the conveyor. Wash water is


freed of sediment and recycled. High pressure air jets then dry the valve area of thecylinders. After washing, the cylinders must be manually subjected to a visualinspection and transferred to a branch “reject” conveyor if they are deficient, for repairor scrapping.

Figure 7.5.4.3-g: Inside of a water jet washing machine

Figure 7.5.4.3-h: Cylinder stacker

Re-palletizing and shipping equipment: The filled cylinders are now ready formovement into a palletizer-stacker, and then for removal by lift truck to outbound


transport or a filled cylinder storage area. The integrated filling plant's conveyor systemis ideally configured in a loop, so that the filled cylinder outlet is as close as possible tothe empty cylinder inlet, thereby permitting a single lift truck and operator to serve bothends of the conveyor line.

Figure 7.5.4.3-i: Cylinder painting cabinet

7.6.4.4 Cylinder Maintenance Facilities

Generally it is preferred that cylinder maintenance and re-testing is performed byspecialized third party companies outside the filling plants. Cylinder manufacturers arebest equipped to perform this task. However, if this is not viable, cylinder maintenancemay be performed inside the filling plant. This section of minimum standards covers thebuildings, structures and equipment used for maintaining LPG cylinders. The LPGcylinder maintenance shed shall be of open shed design. The area shall be wellventilated to minimize the accumulation of vapor cloud. The shed shall be constructedof noncombustible materials. The maintenance shop typically includes a shot blastingunit, spray painting or dip painting equipment, a dry oven, conveyors and associatedelectric motors. Utility station such as plant air and plant water shall be provided tomaintenance shop. Plant air and plant water piping shall be clearly identified either bylabeling or color coding. The electrical area classification of the filling plant shall be inaccordance with Chapter 2.


Cylinder painting equipment: Some plants may include cylinder painting. Thisequipment includes a water curtain using recycled water to dispose of over spray mist.An overhead jack that rotates the cylinder while it is coated by an automatic spray gunengages cylinders on the conveyor. A protective shroud shall be incorporated into therotating jack to protect top cylinder valves normally used in operations. If desired, asecond paint station using a spray gun equipped with a stencil mask can apply atrademark or text to the cylinder after the base painting coat is applied. Typically, paintwould be applied to a statistical fraction of all cylinders, say one in five. Thisintermittent operation would be controlled automatically.

At offsite locations, subcontractors may advantageously perform several of theoperations discussed above. They may include cylinder painting, cylinderdepressurization, air purging, and subsequent repair and re-qualification of rejectedcylinders and/or their valve assemblies.

Concurrent use of the offsite subcontractor facilities to augment storage space for emptyand/or full cylinders may achieve additional economic benefits. It is recommended thatany design study for a new plant, or for major modification of existing facilities, includea thorough exploration of incentive for subcontracting support operations of the typediscussed above at locations away from the main plant.

Figure 7.5.4.3-j: Cylinder pallet storage

7.6.5 Purchasing Guidelines for Filling Plants

There are three reliable filling plant manufacturers who are well established in themarket and have produced a large number of safe filling plants. All vendors are deeplyinvolved in fully automated filling plants, which rely heavily on electronics forfilling/check weigh scales, leak detection and bar code or data matrix control of cylinderprocessing and stock control. However, the designers are primarily fabrication andconveyor systems engineers with relatively limited knowledge of LPG properties andoperations. They are dependent almost entirely on third party filling plant operators forfield experience for developing the practical aspects of their designs. The adverse effectof intense competitiveness between the manufacturers on quality, performance claimsand guarantees needs to be very carefully safeguarded against. Consequently, it isimportant to specify and obtain agreement and or clarification on safety andperformance guarantees etc., in writing, prior to placing orders, on items discussedin the next paragraphs.


7.6.5.1 Safety and Integrity of Equipment Design

Vendors should submit designs with due consideration given to the owner’s LPGSpecifications. Consideration should be given to auto- refrigeration, especially ofPropane at –42 °C, irrespective of climatic conditions. The design should also maintainequipment safety and performance under all anticipated environmental conditions of theplant location.

The vendor shall provide formal recognized “certification” of all materials ofconstruction and assembly. This shall include all materials and equipment, “bought in”by the vendors, with specific attention to elastomer seals, pipe thread and flangejointing, LPG transfer hoses and electrical parts, including prevention of staticelectricity.

All major equipment shall be designed and manufactured to approved standardsacceptable to the appropriate national regulations or LPG Design Guidelines in thisbook, which ever are the more stringent. This applies in particular to LPG piping,flanges and fittings, pumps and compressors and the classification of electricalequipment.

All main steel work, e.g.; palletizers, carrousel and conveyor chain frames, shall befabricated from hot rolled or forged sections. Pressed and folded steel shall notgenerally be accepted for major frame members. Possible exceptions may bepermissible for small modular constructions, which can be readily removed or replaced,if damaged.

Care shall be taken to electrically ground electrically isolated metal parts around themachinery to prevent accumulation of static charge. In particular, this pertains to metalparts suspended by rubber for flexibility or metal connections attached to plastic/rubbertubing.

All machines shall reset automatically. In the case of shutdown or emergencyshutdown, moving parts shall automatically reset back to their starting positions. It isnot recommended to install protective caging between filling machinery. Cylindersshall be accessible at all times.

All services required of the vendor’s equipment should be thoroughly considered andagreed upon before signing of contracts, in particular; instrument air supply (airpressure, volume and quality), electric power (including voltage fluctuation range), andwater (pressure, volume, quality). Detergents for cylinder washing (compatibility withplant water treatment system) shall be compatible with environmental requirements.

Emergency shutdown system (ESS) considerations shall be included. Vendorequipment shall be specified as compatible with the existing system and fail safe, i.e.;sealed against release of LPG during emergency shut down and or failure of operatingmedia.

7.6.5.2 Performance Criteria and Guarantees.

All vendors should provide overall and specific guarantees of equipment safety as wellas performance. The owner should specify and agree with the vendor’s pre- and postcommissioning “acceptance” criteria, as appropriate, in writing. This is of particularimportance to retrofitting equipment to an existing plant. Previous discussions with allvendors, revealed serious gaps and shortfalls in their guarantee cover.

Vendors tend to be overly optimistic when making claims about their newdevelopments. The owner should be careful to request proof of performance andreliability from case histories, i.e. proven track record. It is obviously important that theowner does not unknowingly become a proving ground for any relatively newequipment developments.


Indemnity clauses differ quite markedly between vendors. The owner should clarify andagree to the details with the vendor. Such clauses range from possible incidents arisingfrom, pre- and post-commissioning by vendor personnel, through to market place safety,unreliability of check scales and/or of leak detection equipment.

Key criteria to be covered include: cylinder filling rates, and tolerances for fill weight,check weight and leak rates at the required cylinder filling and chain conveyor speeds,under normal local operating conditions. These criteria would usually require a vendor'sengineer to visit the plant, to be “fully” acquainted with local operating conditions.

Filling scale fill tolerances shall be geared to appropriate National weights andmeasurement. It is important to note that the “overall filling accuracy” mentioned in theExxonMobil Product Control Manual should not be quoted to the vendor. The ownershall request “guaranteed” filling accuracy from the vendor, per cylinder size and fillingrate. With the exception of 45 − 50 kg cylinders, most vendors can usually meetrequirements of the Product Control Manual.

7.6.5.3 Pre-Delivery Testing of Equipment.

All equipment shall be pre-tested by the vendor, especially pressure testing of LPG pipework and hoses. See also “Performance Criteria and Guarantees” above in relation torequired cylinder filling rates and conveyor speeds. Certification of the safety of allelectric items and circuitry, especially electronic scales and computerized systems shallbe checked. Many of these are now designed to be intrinsically safe, but this shouldspecifically checked.

7.6.5.4 Installation and Commissioning

The owner should be satisfied that sufficient details are agreed to with the vendor onhow installation and commissioning are undertaken, without prejudicing guaranteesof equipment reliability and performance. This may include direct involvement bythe vendor in both installation and commissioning as well as training of ownerpersonnel.

7.6.5.5 After Sales Service

All vendors claim to provide a reliable after sales service. Vendor staffing is largely bypersonnel involved in equipment manufacture. However, some vendors have or areestablishing local offices, so details of what services are available on a 24 hour notice, asa minimum, should be obtained.

To augment their normal services, all vendors provide contract Periodic PreventiveMaintenance Services. Details on these services may be obtained and compared withavailability/capability of local skills.

7.6.5.6 Records, Drawings, Maintenance, Spare Parts

The vendor shall provide all records of approval certification and manufacturingstandards for all materials, equipment and tests as appropriate.

Accurate plant drawings and operational service diagrams, especially wiring diagrams,shall also be supplied, together with maintenance and inspection schedules, with specificreference to “bought in” items. Note that all vendors are highly dependent upon bought-in materials and equipment which require instructions and recommended maintenanceand inspection schedules from the original manufacturers. Spare parts shall be itemizedwith recommended frequency of fitting. This is particularly important for elastomerseals in liquid phase LPG use.


7.6.6 Third Party Cylinder Filling Plant

This section of minimum standards covers a third party cylinder filling plant whereExxonMobil LPG cylinders are filled. Local standards shall be followed. In theabsence of a local standard or if the local standard is less stringent, the followingminimum standard shall apply.

The structure of the LPG cylinder filling shall be of open shed design. The area shallbe well ventilated to minimize the accumulation of vapor accumulation. Pumps shall beused to transfer the LPG from the storage to the filling plant. At least one emergencyshutdown valve shall be provided on the piping system supplying LPG to the facility.Emergency shutdown device/s shall be provided at strategic location/s to ensure thatthe filling plant shuts down safely during emergency. Location of the shutdowndevice/s shall be such that they are still operable during fire situation. The electricalarea classification of the filling plant shall be in accordance with Chapter 2.

Working pressure of LPG to the filling station unit shall be a maximum of 1,725 kPa.A separate weight check scale shall be provided to check the weight of the filledcylinders before dispatching them out of the filling facility.

Public access to areas where LPG is stored and transferred shall be prohibited. Toprevent trespassing or tampering, the LPG filling plant shall be enclosed by an industrialfence not less than 2 m high unless it is otherwise adequately protected (e.g. within agreater fenced area). At least 2 means of emergency access from the fenced or otherenclosure shall be provided. Sufficient clearance shall be provided to allowmaintenance to be performed. Clearance of at least 1 m shall be provided to allowemergency access to the required means of egress. The outside storage area for filledcylinders shall be a minimum distance of 7.5 m from cylinder filling facilities. Relevantsigns such as “NO SMOKING” and “NO OPEN FLAME” shall be posted around theperimeter and in the filling plant.

7.7 Cylinder Distribution

7.7.1 Distribution Center

Cylinder distribution strategy may, in some cases, require the installation of distributioncenters. This is typically the case where one large filling plant serves several demandcenters. Large trucks transport the cylinders back and forth between the filling plant andthe Distribution Center. From there, small trucks, principally pickup trucks owned bythe resellers or dealers, are used for delivery to end-users.

Regulatory compliance (land status, classification and zoning laws) is a basicrequirement. Sites in industrial zones are preferred, housing and public areas shall beavoided. The area shall be freely ventilated (not located in a terrain depression). Sizeand shape of land shall be large enough to satisfy spacing requirements based on storecapacity stipulated in Table 7.7.1. Safe truck access has to be included in theseconsiderations. The area shall be preferably fenced with a 3 m high chain linked fence.

LPG cylinders shall be stored upright and well ventilated, preferably in an open-airloading platform. Where inclement weather can frequently preclude work, or requiredby local regulations, the Distribution Center may be provided with a roof, constructed ofnoncombustible, lightweight, friable material that would break up quickly in a fire.Sufficient space shall be maintained between the underside of the canopy and thehighest stacked cylinders to facilitate application of cooling water in the event of a fireemergency.


Drains shall be avoided in the floor of the storage place. The platform floor shall belevel and provided with suitable hard standing for LPG cylinder handling. Normally,the platform would be elevated, such that it is at the same level as the back of the truck.However, if the platform is at ground level, particular precautions have to be taken that,when unloading, cylinders are not damaged. Appropriate warning signs are to beprominently displayed i.e. “No Smoking or naked Flames” “Highly Flammable LPG.”Electrical fittings used on the platform and under the roof of the storage area shall besuitable for Zone 2 area classification. Other areas such as yard lighting or officelighting shall be suitable for normal service.

Table 7.7.1 shows the spacing requirements for Distribution Centers:

Quantity* of LPGStored

Kg

Size of LargestStack

kg

Distance toProperty Line

m

< 30000 < 7000 8

< 50000 < 9000 9

< 60000 < 10000 10

< 100000 < 10000 11

< 150000 < 20000 12

< 250000 < 30000 15

> 250000 < 30000 20

Table 7.7.1: Spacing to property line in Distribution Centers

*Nominally “empty” cylinders have to be considered as “full” for above calculationsunless the cylinders are stored under the following conditions:

1. The “full” and nominally “empty” cylinder storage area is clearly marked.

2. Full cylinders are always stored in the “full” area, nominally “empty”cylinders are always stored in the “empty” area.

3. A gangway with a separation distance of at least 3 m is maintained betweenthe nominally “empty” and “full” cylinders.

4. Individual unpalletized stacks (either full or empty) shall be separated by 1.5m distance for accessibility. For palletized stacks the gangway distance shallbe a minimum distance of 2.5 m.

Domestic cylinders shall be stacked in the following manner:

1. Manual stack: Maximum 3-cylinder high for cylinders up to 15 kg contentand maximum 2-cylinder high for cylinders above 15 kg up to 26 kg.

2. Wooden Pallets: Maximum 2-pallet high and each pallet at 2-cylinder-high.

3. Caged Steel Pallets: Filled cylinders - up to 4-pallet high and each pallet atone-cylinder high. Empty cylinders - up to 6-pallet high).

Cylinders above 20 kg shall be stored upright without stacking.

Fire protection facilities for the Distribution Center are designed for first aid use only.Following firewater capacities are recommended:

1. For LPG storage up to 25 tons 800 l/min at 7 bar for at least 1 hour.


2. For LPG storage exceeding 25 tons 2300 l/min at 9 bar for 1 hour and at least2 firewater monitors.

It is expected that public fire brigades would provide backup during LPG fires. Specificrequirements by individual Fire Department Offices may differ and the Project Engineerwill have to present his case to the fire authority for a system, which will suit thelocation in terms of associated fire risks.

7.7.2 Dealer and Reseller Cylinder Storage

In some cases dealers or resellers may store considerable numbers of cylinders on theirown premises. The preferred location for cylinders stored for resale is outside buildings.Fence and door are adequate means of control to the storage premises. Firefightingcapability is normally limited to a 9 kg dry powder extinguishers but depending onconditions, the local firefighting authorities may require more protection (firewalls etc.).Storage outside of buildings shall be located in accordance with Table 7.7.2 and at least1.5 m from any doorway in a building frequented by the public. The table reflectsrequirements in NFPA 58, 5.4.1.

Following are the explanations for the column headings in the spacing table below:

1. Nearest important building or group of buildings.

2. Line of adjoining property that may be built upon.

3. Busy thoroughfares or sidewalks.

4. Line of adjoining property occupied by schools, churches, hospitals, athleticfields, or other points of public gathering.

5. Dispensing station.

Quantity of Horizontal Distance to:

LPG Stored,

Kg

1. and 2.

m

3. and 4.

m

5.

m

< 227 0 0 1.5

227+ to 1134 0 3 3

1134+ to 2721 3 3 3

2721+ to 4540 6 6 6

> 4540 7.5 7.5 7.5

Table 7.7.2: Spacing in reseller cylinder storage (from NFPA 58)

If cylinders are stored inside buildings or structures the buildings and structures shall beone story in height and shall have walls, floors, ceilings, and roofs constructed ofnoncombustible materials. Exterior walls, ceilings, and roofs shall be constructed asfollows:

1. Of lightweight material designed for explosion venting, or

2. If of heavy construction, such as solid brick masonry, concrete block, orreinforced concrete construction, explosion venting windows or panels inwalls or roofs shall be provided having an explosion venting area of at least0.1 m2 for each 1.4 m3 of the enclosed volume.


The floor of such structures shall not be below ground level. Any space beneath thefloor shall be of solid fill or the perimeter of the space shall be left entirely unenclosed.The floor level is preferably 1.1 m above the road level for easy unloading/unloading ofcylinders.

The structure shall be ventilated using air inlets and outlets, the bottom of which shallbe not more than 150 mm above the floor, and shall be arranged to provide airmovement across the floor as uniformly as practical and in accordance with thefollowing:

Where mechanical ventilation is used, air circulation shall be at least 0.3 m3/min×m2 offloor area. Outlets shall discharge at least 1.5 m from any opening into the structure orany other structure.

Where natural ventilation is used, each exterior wall [up to 6.1 m in length] shall beprovided with at least one opening, with an additional opening for each 6.1 m of lengthor fraction thereof. Each opening shall have a minimum size of 32,250 mm2, and thetotal of all openings shall be at least 720 mm2/m2 of floor area.

Heating shall be by steam or hot water radiation or other heating transfer medium withthe heat source located outside of the building or structure or by electrical applianceslisted for Class I, Group D, Division 2 locations, in accordance with NFPA 70, NationalElectrical Code.

Walls of attached structures shall have a fire resistance rating of at least 1 hour. Thereshall be no openings. Common walls for attached structures used only for storage ofLP-Gas shall be permitted to have doorways that shall be equipped with 1 1/2-hour (B)fire doors. Common walls at points at which structures are to be attached be designed towithstand a static pressure of at least 0.7 MPa per 0.1m shall have the following :

Rooms within structures shall be located in the first story and shall have at least oneexterior wall with unobstructed free vents for freely relieving explosion pressures.

Fire detection and firefighting requirements shall be as per local fire authorityrequirements.

Safety in LPG Design FIRE PROTECTION 8-1

8 FIRE PROTECTION

8.1 Passive and Active Fire ProtectionIn developing safety and fire protection guidelines for LPG facilities, the greatestconcern is failure of tanks containing LPG whether large tanks or domestic cylinders.The probability of this type of failure can be made virtually negligible by properlyengineering and operating facilities, in accordance with the guidelines in this manual.Although avoidance of such risks is of prime importance, it is necessary to protectagainst emergency situations that can still occur.

Safety in LPG plant design is incorporated in two ways, by passive protection and byactive means of mitigation. Passive protection is achieved by adequate spacing, bymounding or fireproofing, and by providing equipment with the appropriate electricalarea classification. Active means of mitigation are achieved by providing emergencyshutdowns, emergency block valves and an adequate firefighting system. Fireproofingand firefighting equipment is discussed in this chapter. Electrical classification isdiscussed in “Electrical Area Classification” in Chapter 2. Also an example of an“Emergency Shutdown System” is shown in Chapter 2. Emergency block valves ontanks and loading facilities are discussed in “Emergency Block Valves on Bulk LPGTanks” in Chapter 3 and “Emergency Block Valves for Piping” in Chapter 5. Thephysical properties of LPG, which are important for understanding the safety and firehazard implications, are discussed in Chapter 12 “LPG PROPERTIES.”

Bulk LPG tanks at Refinery, Upstream, and Marketing plants shall be protected with theapplication of firewater and/or fireproof insulation. A deluge or fixed spray system shallprotect aboveground spheres, which are discussed in this chapter. Aboveground bulletsshall be protected by a fixed spray system or fixed fire monitors which are capable ofreaching the whole bullet surface area. Insulation may be substituted for deluge or spraysystems, provided fire water is still available by at least a hydrant system. Generallyboth fireproofing and a deluge/spray system are not used unless risk analysis shows aneed to further mitigate the effects of fire.

8.1.1 Fireproofing, a Passive Fire Protection

Fireproofing of structural supports, tanks, instrumentation and control tubing, andvalve actuators shall be considered when evaluating the fire protection systems forLPG storage. The function of fireproofing is to reduce the rate of temperatureincrease during fire exposure. The mechanism for reducing the rate of temperatureincrease can be absorption of heat through chemical breakdown of the protective coatingor resistance to heating using thermal insulation, depending on the nature of thefireproofing.

8-2 FIRE PROTECTION Safety in LPG Design

As a passive fire protection system, fireproofing provides protection without dependingon detection systems or alarms. Mechanical or electrical failures have no effect on itsperformance. Fireproofing also provides time to evacuate neighboring areas.

On the other hand, in a fire, fireproofing provides only a finite period of protection.Without the addition of water, failure of fireproofed equipment will occur if the fireburns long enough. Further, the type of fireproofing shall be selected carefully to ensurecompatibility with the storage area environment both from the standpoint of fireproofingapplication or installation and long-term durability of the fireproofing.

Fireproofing can be used in combination with active water fire protection systems as ameans of protection until the water system is activated, as a back-up in the event thesupply of water is interrupted, or if the water application rate available is less than whatis desirable.

The fireproofing material shall provide equivalent to a fire endurance of 1.5 hours perUL 1709. The fireproofing system shall be designed to withstand exposure of directflame impingement (as per GP-14-3-1) . It shall also be non-corrosive, inert under fire,resistant to weather and hose streams.

8.1.1.1 Fireproofing Applications

Fireproofing practices for Refineries and Upstream facilities are described GP 14-3-1.In Marketing LPG storage facilities, fireproofing shall be considered for use in thefollowing areas:

1. Structural Supports: Fireproofing used on steel supports for LPG tanks canprevent collapse in the event of fire. On spherical tanks and verticalcylindrical tanks, structural supports shall be fireproofed from ground level tothe intersection of the support with the tank shell.

2. With horizontal cylindrical tanks (bullets), steel saddles and verticalsupport steel shall be fireproofed to the intersection of the saddle with thetank if the saddle is greater than 300 mm height at its lowest point.Exceptions for horizontal tanks below 7.6 m3 and vertical tanks below 0.5 m3

are discussed in NFPA 58. Thickness of the fireproofing material shall beprovided per “Fire Resistant Coatings” in this Chapter.

3. Pipe Supports: Fireproofing shall be provided on all pipe supports within 15m of a tank and on all pipe supports within the spill containment area.

4. Tank Shell: If, based on substandard spacing in existing installations, a riskassessment determines a higher risk, fireproofing of the tank shell may be theonly viable solution to alleviate the risk. For new plants it is required toprovide adequate spacing as per Chapter 2 “PLANT SITE.” and fireproofingshall not be applied considered a solution take credit for substandard spacing.

5. Emergency Block Valves: Actuators and cabling of Non-fail-safe valvesshall be fireproofed in order to function during the first 15 minutes of anemergency. The valve body does not need fireproofing since it is fire safe bydesign. Fail-safe installations do not need fireproofing since by definition thefire is supposed to destroy the cabling or ducts and thereby cause short circuitor pressure loss which in turn closes the valve.

8.1.2 Fire Resistant Coatings

There is a number of fire protective or insulating coatings available that could beconsidered for use on an LPG tank. The factors involved in selecting such a coatinginclude:

1. Intended application (i.e., stationary tank, tank truck or railway car).

2. Amount of fire protection time required.


3. Use of water sprays and type of water.

4. Required maintenance.

5. Material's physical properties.

6. Material's application properties.

7. Atmospheric corrosivity.

8. Weight limitations.

9. Cost of economics.

With these factors in mind, short descriptions of various fire protective coatings andthermal insulating systems follow.

8.1.2.1 Dense Concrete

Dense concrete or gunite have been used successfully for many years and are thematerials of choice in refineries, chemical plants and terminals. Concretes made withPortland cement have a density of 2220 - 2380 kg/m3. Such concrete can be formed inplace or pneumatically sprayed to the required thickness using steel reinforcement suchas galvanized 14 US gauge steel mesh with openings of 50 mm by 50 mm. The meshshall be spaced the required distance from the substrate, usually half the thickness of theconcrete or gunite. See ExxonMobil Engineering Report EE.50E.88 for a recommendedformulation and mixture.

Concrete and gunite are durable and can be satisfactorily applied by most contractors.The disadvantages of these concretes include relatively high weight, high thermalconductivity, need for steel reinforcement and the installation cost and time involved informing them in place. The underlying steel shall be coated prior to applying theconcrete or gunite, and, also, in corrosive atmospheres, it shall be top-coated.

8.1.2.2 Lightweight Concretes

Non-proprietary lightweight concretes are made of lightweight aggregates such asvermiculite and perlite and cements that are resistant to high temperatures.Additionally, a number of lightweight cementitious concretes (such as Carboline'sPyrocrete 241, et. al.) are available and have been used. Chloride-containinglightweight concrete shall not be used because of their innate corrosion potential. Drydensities range from 400 to 1270 kg/m3. Pneumatically applied material is about 20percent heavier than lightweight concrete poured in place.

Lightweights are often sprayed, troweled or formed in place using reinforcing mesh.The substrate shall be coated and reinforcement shall be required. A top coat for thelightweight concretes is recommended to prevent moisture from penetrating; otherwise,corrosion may occur, along with cracking and spalling in freezing climates.

Lightweight concrete materials are fairly durable and have limited maintenancerequirements. They are capable of withstanding direct flame impingement up to1090 °C; they can withstand thermal shock and high-pressure hose steams; and they canbe satisfactorily applied by most contractors.

The disadvantages of lightweight concrete materials include the need to maintain a goodsurface coating so that moisture cannot penetrate. Additionally, lightweight concretesare also more susceptible to mechanical damage than are dense concrete materials.

8.1.2.3 Pre-formed Inorganic Panels

Pre-formed inorganic panels are pre-cast or compressed fire-resistant panels made of alightweight aggregate and a cement binder or a compressed inorganic insulating materialsuch as calcium silicate and perlite. The panels are attached to the substrate bymechanical fasteners that are designed to withstand exposure to fire without appreciable


loss of strength. An example of this type of material is COROC II and Hubiliteinsulating panel boards.

When panels are used outdoors, an external weatherproofing system is usually requiredto prevent moisture from penetrating. All joints shall be caulked or sealed with mastic.

Pre-formed materials have several advantages including: they can be applied cleanly;there is no curing time; and they have low conductivity. One disadvantage of pre-formed materials is the necessity for labor-intensive application when these panels mustbe fitted to tanks because of their diameter; therefore, they may not be practical.

8.1.2.4 Masonry Blocks and Bricks

Masonry blocks of lightweight blast-furnace slag (used as coarse aggregate) aresometimes used. These units are laid up with staggered joints not more than 6 mmthick. The joints shall be made using fire-resistant mortar, such as a mixture of 1 partlime, 4 parts Portland cement, and 12 parts perlite.

Brick and block are no longer commonly used because of their high installation cost andfairly extensive maintenance requirements. Brick-and-block assemblies tend to crackand admit moisture, which can lead to serious corrosion and spalling. They shouldprovide adequate protection where currently installed, but should not be used in newinstallations.

8.1.2.5 Subliming, Intumescent, Ablative Organic Coatings

Organic coatings (such as “Chartek” or “Pittchar”) can provide fire resistance throughone or more of the following mechanisms:

1. Intumescent epoxies expand to several times their volume when exposed toheat and form a protective insulating ash or char at the barrier that faces thefire.

2. Subliming mastics absorb large amounts of heat as they change directly froma solid to a gaseous state.

3. Ablative mastics absorb heat as they lose mass.

Organic coatings are sprayed on the substrate in one, two or more coats, depending onthe required thickness. Reinforcing fabric or wire is needed for application to LPGtanks, tank trucks and railroad cars.

The main advantage of organic fire resistant coatings is that they are lightweight. Theyare suitable for use on existing equipment supports that may not be able to handleadditional weight or are located in less accessible areas.

Because of complex application characteristics, the need for adequate film thickness andproper bonding to the substrate, only vendor-approved, experienced applicators shouldbe employed. A disadvantage is that they may tend to shrink while curing;specifications should therefore indicate the wet thickness that will yield the required drythickness. To ensure proper application and thickness, a qualified inspector shouldfrequently check the applicator's work. A manufacturer's representative is frequentlyused to supervise the application and to serve as the inspector.

Substrate preparation and priming of the steel is important to adequate bonding.Intumescent coatings require a top coat to prevent moisture from penetrating andcausing failure. The surface coating should be inspected and renewed according to thevendor's recommendations.

The use of fire hoses on an intumescent coating during a fire may be detrimental; part ofthe protective char may wash away. Also, coatings may be less durable than more


traditional concrete materials when subjected to mechanical impact and abrasion.Several coatings should not be used where equipment or piping must be steam cleaned.See also GP 19-1-1 “Paints & Protective Coatings.”

8.1.2.6 Thermal Insulating Systems

Two thermal insulating materials are recommended not only as insulating materials butalso as fire resistant coatings. Suitable materials are listed in GP 14-3-1. A material likefoamed glass block is applied in two layers, each 50 mm thick, with staggered joints. Asteel jacket is also required. This steel jacket serves two purposes:

1. In the event of a fire it holds the insulation in place and prevents it fromshattering and failing structurally.

2. It provides protection from fire hose impingement during fire fightingfunctions.

These systems are frequently used where thermal energy conservation is required; foamglass can be designed and used for both cold and hot service. Poor fitting of thecladding over any porous insulation or gaps in insulation blocks can lead to corrosionunder insulation discussed below.

Watertight coverto protect columninsulation

Sphere

Figure 8.1.2.7: Corrosion protection of sphere columns

8.1.2.7 Corrosion Prevention behind Coatings

Experience has shown that improper protection of the steel under fireproofing orimproper application of the fire proofing can lead to corrosion behind fire protectivecoatings. Concrete has been used extensively, and corrosion has been found frequentlybehind concrete and gunite coatings. The causes for such corrosion have beendetermined in several applications and include:


1. Improper surface preparation and application.

2. Protective steel coating not applied when required.

3. Inadequate concrete mixes (compressive strength as low as 103 - 138 bar).

4. Inadequate rain shedding designs employed.

5. Little or no maintenance after application.

6. No external protective coating applied to fire resistant coatings.

Each of these factors in its own way can be applied to each of the insulating or fireprotective coating discussed above. It is important that each fire protective system beproperly applied and maintained. Special care shall be taken when designingfireproofing for sphere columns. The upper end of the sphere column shall have aninclined watertight steel girder which positively prevents the ingress of water betweenconcrete and column.

8.1.2.8 Selection of a Fire Resistant or Insulating Coating

For stationary LPG bullets or spheres the system of choice as noted previously is denseconcrete or gunite. Others have been used but, if an insulating system is required, then itis recommended that foam glass block be applied. To protect foam glass from flameand fire hose impingement, it shall be jacketed with a steel jacket.

Alternatives to concrete are lightweight cementitious coatings or proprietary lightweightconcretes such as Pyrocrete 241, which has been used successfully within the companyfor a number of years. These require no protective jacket.

Coatings on tank trucks or rail cars are normally provided only when required by localregulations. Intumescent epoxy coatings have been applied successfully on over-the-road tank trucks in some Far East locations for several years. When required for tanktrucks or railway cars, an intumescent epoxy “Chartek III” or PPG's “Pittchar” shall beused, mainly because of their ability to absorb road shock damage.

8.1.2.9 What Thickness Is Required?

There is no easy answer to this question and it pertains to each of the fire protectivecoatings discussed previously. There are several guidelines including the following:

1. The most conservative guideline is API 2510 which states that the fireresistant coating must give 1-1/2 hours protection in a UL 1709 fire whenexposed on a 10W49 steel beam. There is no indication if it is to be exposedin a contour or box design, but for organic coatings and lightweights thecontour design is recommended.

2. Global Practice 14-3-1 recommends that for a critical application to a 19 m3

capacity or greater tank, fireproofing with 38 mm of high density concrete orgunite shall be used.

3. Independent testing facilities, such as Germany's BAM F90 where testrequirements are less demanding than API 2510, require 90 minutesprotection for an LPG tank using venting LPG as coolant in a non-controlledfire.

4. Other National laws (in US and overseas) regarding both rail and trucktransportation require various criteria affecting thickness.

It is recommended that for LPG tanks or other stationery storage API 2510 be followed.

For truck tanks, there are no clearly defined procedures; therefore, it is recommendedthat national rules be followed. Do not follow the advice of proprietary coatingmanufacturers unless there is documented laboratory testing that such coating thicknessmeets local or national law. Additionally, consider long term durability (10-20 years) in


the atmosphere, resistance to mechanical damage, need for thermal insulation, corrosionof the underlying steel, ease of repair, and others.

8.2 Fire Protection System Design PhilosophyMost LPG fires originate as smaller fires that have the potential to become larger andmore hazardous. Such fires may not occur as a result of tank failure, but because ofpump or piping leaks, or tank overfills. Human failure, such as overfill or improperwater draining, can also lead to an LPG release. Unless controlled, the leak can igniteand the fire can escalate rapidly. A primary objective of the features described in thissection is to break that chain of events and control incidents at an early stage. See alsoAPI Standard 2510A “Fire-Protection Considerations for LPG Facilities.”

Design for optimum safety of LPG facilities varies with differences in the size and typeof operations and in plant operating environments. The greatest concern is fire, and thefundamental philosophy is as follows:

1. Prevent releases and fires by proper design, sound operating practices, andregular training of personnel.

2. Provide a system of valves (Emergency Block Valve) that can be operatedlocally or remotely, to isolate storage tanks and transfer equipment in case ofa leak, fire or other emergency.

3. Provide a means of protecting LPG tanks and tanks from overheating in caseof fire.

The properties of LPG are such that a small release, if not controlled, can escalate veryquickly into a major event. Therefore, fire protection equipment shall be designed forrapid actuation and for the largest credible scenario.

The first step in determining fire protection requirements is to divide the plant into riskareas. DP XV-G, “Equipment Spacing” defines areas separated by 15 m of relativelyopen space as separate risk zones. Fire can normally be contained to one risk area.Spacing, firewalls, drainage, and emergency block valves are design elements that willlimit the spread of a fire and allow firefighting access.

For example, in a large plant the marine piers, truck loading, and cylinder filling areasmay be separated by spacing and segregated drainage. The figures for spacing givenin Chapter 2 “PLANT SITE” are considered adequate for this separation. A smallredistribution center would be considered one risk area.

Cooling by firewater is the basic fire protection for LPG distribution facilities. Theextent and capacity of the firewater system is based on the assumption that only onemajor fire will occur at one time. Thus, the sizing and layout (Design Practices XV-J)of major components of the system is based on the fire contingency at the risk areahaving the largest requirements. The system shall be sized to provide firewater for thefire area and for cooling all equipment in the vicinity of the fire area. Sizing guidelinesfor Refining and Upstream facilities are discussed in Design Practices XV-I and GP 3-2-3. For Marketing terminals and bulk plants, the system configuration and spacing isoutlined in Chapter 2 “PLANT SITE” and sizing of the firefighting facilities is discussedbelow.

While the main purpose of the firewater system is to provide cooling in case of fire itshall be mentioned that monitor and hose streams, and water spray systems, can also beused to disperse vapor releases.

The maximum firewater flow requirement is generally for the LPG tank area. Requiredwater rates for these and other risk areas are in “Firewater Pumps in Plant.”


Fire protection for redistribution centers, for bulk customer and dealer installations,shall be designed as required by local law. However, a risk assessment may requirehigher than normal protection. This has to be decided case by case. Guidelines foremergency planning can be found in the ExxonMobil Marketing Operations Guide(Grey Book) “PLANT EMERGENCY PLANNING.”

Requirements in this chapter cover the basic needs of most facilities, but modificationsmay be necessary for specific situations. Local regulations shall always be followed.Equally important, fire protection equipment shall be suitable for the response capabilityof the plant itself and of public emergency agencies and mutual aid partners.Emergency planning shall reflect all of these factors. Development of those plans andtesting them with practice drills will often show where improvements can be beneficial.

8.2.1 Firewater System, an Active Fire Protection

Reliability is a primary consideration in the design and layout of the firewater system.The system shall be designed for easy testing to assure dependability, adequate flowrate, and adequate coverage of the protected equipment.

In a plant handling other products in addition to LPG, an integrated system is normallyprovided. Firefighting foam may be available for gasoline or other fuels, but it shall notbe used on an LPG spill or fire. Application of foam will not control vapors orextinguish an LPG fire; in fact, by adding heat, it is likely to increase the vaporizationrate with unpredictable and undesirable consequences.

Provisions for fire protection shall comply with the requirements of API STD 2510 andAPI Publication 2510 A.

8.2.1.1 Firewater Source

A large body of unlimited water such as the sea, a lake, or a river is the preferredfirewater source. The suction pipe shall designed such that it is always fully submergedirrespective of tidal conditions. Where this is not available, wells or a municipalsupply can be used if sufficient capacity and reliability are available. Municipal sourcesused for drinking water shall be protected against contamination by positive means, suchas a break tank with the water inlet at the top above the maximum level. The fire watersystem shall be suitably protected from freezing where necessary.

Where the source is limited, water storage shall be provided, sufficient to provide fulldesign flow for a minimum of 4 hours for Marketing Terminals and 6 hours forRefining and Upstream Facilities without interrupting other essential users at theplant. The difference between both is based on experience and the complexity of units.Also, the water source must be capable of supplying one half the maximum firewaterdemand on a continuous basis after the storage capacity has been used. Storage can bein tanks, ponds, or reservoirs. Refining or Upstream facilities shall have a connectionbetween the cooling water system and the firewater system as an emergency back-up.

8.2.1.2 Firewater Pumps in Plant

The main firewater pumps shall have a total capacity no less than the demand of thelargest risk area. At least two pumps shall be provided, with independent powersources for drivers. This may consist of one diesel plus one electric or, two dieselpowered pumps. Alternatively, the drivers of all firewater pumps may be electricmotors provided a backup diesel generator system capable of supporting all firewaterpumps’ drivers is available. The decision should be based on reliability of electricalsupply.


Rated capacity of any single pump normally does not need to exceed 50% of the totalrequirement. For small terminals where the pump size is the same or smaller than localfire trucks, consider providing connections so the fire truck can operate in parallel in theevent of failure of one of the pumps.

RAILWAY

GATE

OFFICEBUILDING

FIREPUMPS

FIRE

WATERTANK

Propane Loading

RAIL CARS

Butane Loading

EMPTYCYLINDERS

FILLEDCYLINDERS

CYLINDERFILLING

MOUNDEDTANK

Earth Mound

MOUNDEDTANK

RemoteImpoundment

Pumps

Sphere

Bullets

Spray Wa te r

Hose Ree l

Sp ray Wa te rSp ray Wa te r Sp ray Wa te r

F i rewate r Ma in Gr id

Hydrant

Hydrant

Hydrant

Mon i to r

Mon i to r

DelugeSys tem

Spray Wa te r

Sp ray Wa te rSp ray Wa te rSp ray Wa te r

Hydrant

Figure 8.2.1: Typical Firewater system in a Marketing Terminal

Where support by local fire brigade is weak or questionable, three pumps, eachproviding 50 percent firewater design capacity, would normally be considered toprovide sufficient reliability. The third pump would be available when one of the firsttwo is down for maintenance or fails in service. Likewise, two 100 percent pumps maybe specified. One would be "primary" while the other would serve as a spare. Pumpsare normally sized no larger than 568 m3/h but can be larger if a single firewater demandexceeds this. When two 50% pumps are provided, the site shall have a plan for backupprotection during maintenance downtime of one pump. Upstream, due to the remotenature of many facilities, requires 100% coverage at all times, i.e. two 100% pumps orthree 50% pumps. Diesel drivers shall match the power requirements of the pump.Engines shall be equipped with a closed-circuit cooling system employing a water-


cooled heat exchanger or a radiator with fan. It shall be noted that the horsepowerrequirement is greater for a radiator with fan cooling system than for a water-cooled heatexchanger system. This shall be carefully considered when determining the size ofengine needed. Water quality (hardness, corrosivity, sludge content) shall be evaluatedwhen determining the type of cooling system provided. Heat exchangers are prone toplugging and failure under conditions of poor water quality and may prove to beunreliable under such conditions. Enough fuel shall be on hand at the Diesel pumps tooperate at maximum fuel use capacity for four hours in Marketing and six hours inRefining and Upstream Facilities.

The pumps shall have remote and local start capability. Primary fire pumps shall besequentially and automatically started by a drop in fire main pressure. Further pressuredrop shall automatically start the secondary fire pumps. Manual starting of the primaryand secondary fire pumps is acceptable provided that the facility is manned 24 hours andproper procedure for fire water startup has been established. The staged pre-set timersare typically set at 5 – 10 second delays.

Care shall be taken to ensure that the chosen system allows pumps to be tested withminimal impairment of the total fire protection system. Additionally, the flow-measuring device shall be located for accurate testing throughout the pump capacitycurve.

Figure 8.2.1.2-a: Firewater Diesel

System design depends on the combination of pumps and pipe sizing to deliver properpressure to spray systems, hydrants, and other users. At least 5.5 bar gauge pressureshall be available at design rate at the farthest point in the mains from the pumps. Hand-held hoses are difficult to control above 8 bar gauge. To stay within this operatingrange, pump discharge pressure shall not be less than 8.6 bar gauge at ratedcapacity; 10 bar gauge is a reasonable maximum.

A flat pump curve is necessary because a wide range of flow rates will be needed fordifferent contingencies. The pressure rise at shutoff shall not exceed 20%, and at 150%of rated capacity the head shall not be less than 65% of design. The firewater rate willdepend on the exposure. Following rates from NFPA 2510A are used to calculate thefirewater requirements:


Tank Cooling (radiation): 4.2 liters per minute per m2;

Tank Fire Engulfment: 10.5 liters per minute per m2;

Jet Fire Impingement: 1000 - 2000 liters per minute; at point of contact

For a three sphere (20 m diameter) installation, the basis for the firewater rate would beas follows: assume the central tank on fire. The two adjacent tanks would need cooling.The calculation would be:

Tank area: π x 202 = 1256 m2

Tank on fire would need: 1256 x 10.5 = 13188 liters per minuteAdjacent tanks would need: 2 x 1256 x 4.2 = 10550 liters per minuteFor potential jet fires add: 2000 liters per minuteTotal firewater demand: 25783 liters per minuteFor larger tanks credit may be taken for tank areas not under directflame radiation.

System pressure shall be controlled at the pump discharge by a pressure controller,bypassing excess flow back to the water source. Higher pressures, and additionalcontrols, may be needed if the plant is very large or there are significant differences inelevation.

Figure 8.2.1.2-b: Firewater pump

Continuous positive pump suction shall be provided. Priming devices are notrecommended because of concerns about reliability. This means that submerged verticalcentrifugal pumps are needed to lift suction from the sea or other waterway. Horizontalcentrifugal pumps are suitable only if the source is above the pump; for example, from atank. Suction screens or strainers shall be provided if foreign material is present whichcould plug the suction lines or pumps. Either traveling or double removable screens,cleanable with the pump in service, shall be used.

A flow meter is recommended, such as an averaging type pitot tube, to permit testing theperformance of each pump. The instrument can be located in the main firewater gridpiping, where it can also be used to measure flow to deluge and spray systems. It canalso be located in the bypass line back to the source.

A jockey pump shall be provided on a pressurized wet pipe firewater system tomaintain water pressure. The jockey pump shall be sized such that it will pressurize the


firewater system to 690 kPa gauge in 2 minutes. Firewater main pressure shall bemonitored at a continuously manned location and alarm upon low pressure in thesystem. The jockey pump is not considered as part of the overall plant firewatercapacity, although it may be used for other utility purposes. Shutoff valves shall beprovided on each pump discharge to permit maintenance work without disrupting thefirewater system. Shutoff valves shall be positive shut-off valves.

8.2.1.3 Firewater Distribution Piping in Plant

A grid or looped pressurized firewater system shall be provided, capable of supplyingwater at the required rate to any part of the plant. The fire mains enclose each risk areain a loop, and the loops are interconnected to form a grid. Isolation valves shall beprovided so that in the event of any single piping failure:

1. No more than 300 m of pipe containing users (hydrants, hose reels, sprays,monitors, etc.) can be lost; and

2. The piping to only two adjacent sides of any risk area can be lost.

Piping within a risk area supplying more than two users shall be connected to twoseparate sections of the fire main separated by a valve in the main. Lines to two or moreusers shall also be valved at each end where they connect to the main.

Fire mains shall be sized by hydraulic calculations to supply required rates. Aminimum 150 mm nominal pipe size is recommended. Pipe flow velocities shall notexceed 6 m/s in any area of the distribution system piping. In freezing climates, allsections of the piping system that are normally filled with water shall be buried 300 mmbelow the frost line. Firewater connections to monitors, hose reels, sprays etc. infreezing climates shall be winterized. Above-grade sections shall normally be dry perGP 3-2-3 para. 3.17. Piping material shall preferably be welded steel; flanged cast ironmay also be used, except in Upstream applications. Buried steel pipe shall be suitablycoated and wrapped for corrosion protection. Cement lined pipe shall be required forsalt water service, and is recommended for fresh water, to minimize corrosion. Theresidual pressure at the hydrant outlet shall be the basis for determining the hydraulicsfor the firewater piping system. The minimum residual pressure shall not be less than690 kPa gauge.

Pipe which is one size larger than calculated required pipe NPS shall be used indesigning firewater piping system to deliver the specific flow rates since internalcorrosion and scale formation in unlined steel pipe may reduce the flow capacity overtime.

8.2.1.4 Firewater Deluge for Tanks

A water deluge is a system where water is applied at the top of a tank and allowed to rundown. Lines shall be at least 75 mm in size. In addition, a fixed spray system shall beused to wet the lower hemisphere of the sphere. Where monitors are available whichcan fully wet the lower hemisphere, they may be substituted for the lower spray system.This type of system is most effective for spheres because the tank geometry assists inevenly distributing the water. It can be built from large diameter piping that is not proneto plugging and is more likely to survive an explosion. A disadvantage is that soot andcarbon from a fire may inhibit wetting the surface, particularly the underside of thesphere. The lower spray systems, or monitors, are used to protect the underside. Arecent change in the GP-3-2-3 requires now firewater coverage of the lower hemisphere

If necessary, weirs shall be used to improve water distribution and prevent “dry spots.”Especially the area behind columns needs careful ducting of deluge water. Theadequacy of the water coverage shall be determined by means of performance tests. Ifwater could accumulate behind weirs they shall be provided with drain holes to preventcorrosion.


Water is usually applied over the tank by a single large nozzle at least 38 mm diameter,with inverted bowl deflectors to direct the flow downward. Manholes, pipingconnections, and ladders often interfere with uniform coverage, so weirs and baffles canbe used to improve distribution.

The system shall be manually operated from a safe location outside the spill containmentarea and at least 15 m from the tank being protected. The location of the actuating valveshall be prominently marked. In locations with limited manpower, the system shall beremotely operable from a manned location. Deluge valves shall be designed to be easilyreset without removal of faceplate or other disassembly of the valve. Deluge valvesshall be designed to fail in the open position on loss of control power.

8.2.1.5 Firewater Sprays

Water spray systems consist of a network of small spray nozzles, arranged in rows orgrids over the tank or equipment being protected. This type of system is moresusceptible to plugging, which results in reduced and unequal water application. Waterspray systems are also more susceptible to damage from an explosion than delugesystems or monitors.

Figure 8.2.1.5-a: Large bore firewater vortex spray nozzle

A spray system is normally dry, with open nozzles, and is operated by a single valve.The system shall be manually operated from a safe location outside the spill containmentarea and at least 15 m from the equipment being protected. The location of the actuatingvalve shall be prominently marked. In locations with limited manpower, the systemshall be remotely operable from a manned location or may be activated automatically.

A skilled and experienced specialist, using hydraulic calculations should design systems;otherwise it is likely that flows will not be uniformly distributed. Several features areneeded to minimize plugging. A strainer with a valved 50 mm blow-off connectionshall be installed in the main feeder pipe to the sprays. Mesh size shall be 50% or thespray nozzle diameter. Nozzles shall have a minimum orifice diameter of 13 mm;diffusers or deflectors to form the spray pattern shall be external. The maximumopenings of the strainer shall be 6 mm and the ratio of free screen area to pipe cross-sectional area shall be no less than 3:1. Water distribution within the nozzle discharge


pattern shall be uniform; hollow-cone patterns shall not be used. The pattern shall bereasonably unaffected by changes in water flowing pressure within the anticipatedpressure range. Nozzles shall spray well-dispersed droplets throughout the dischargepattern, with approximately 85 percent of the droplets ranging from 200 – 400 micronsin diameter. A waterspray nozzle pressure of not less than 414 kPa is acceptable.Carbon steel piping downstream of the strainer shall be internally galvanized, and flush-out connections shall be provided. Corrosion-resistant stainless steel and copper-nickelalloy is preferred to galvanized pipe, although they are more expensive.

Spray systems shall be designed as shown in Figure 8.2.1.5-b. If at all possible flushvalves should be installed at the end of the header which can be opened before each test.In cold climates the system must be self draining.

Spraywater

Settling rust and debris

Figure 8.2.1.5-b: Spray nozzle design minimizing plugging

Spraywater Settling rust and debris

Figure 8.2.1.5-c: Unfavorable spraywater design leading to plugging.

8.2.1.6 Hydrants in Plant

A sufficient number of hydrants shall be installed to supply the required water rate toeach risk area. They provide backup protection in case a primary system such as adeluge or water spray is disabled. Hydrants can provide water to pumper trucks, mobilemonitors or hand-held hoses, directly from the plant firewater system. Depending on thenumber and size of hoses, a hydrant can supply 130 to 170 m3/h of water. When apumper truck is used, it can boost the pressure, increasing flow to 250 m3/h.

Hydrants shall be located within 50 m of any point where water will be required.However, they shall be accessible in emergencies, and shall be along roadways and not


within risk areas. Maximum spacing between hydrants is 90 m, measured along roadsor accesses ways. Hydrants shall be located on at least two sides of each LPG tank sothe tank can be reached by at least 3 streams of water from hose lines not longer than90 m.

Hydrants shall be 102 mm diameter with two 65 mm hose connections. Each hydrantshall have two valved and capped hose connections, and a larger valved and cappedconnection to supply a pumper truck. The length of suction hose required shall notexceed 7.5 m. Connections shall be compatible with municipal and mutual aidfirefighting equipment. Hydrants shall be self-draining in freezing climates. The steelhydrant barrels shall be hot-dip galvanized after welding. Unless a local fire departmenthose connection is specified male hose thread, 65 mm to NST (refer to NFPA 194) maybe used.

8.2.1.7 Firewater Monitors may be Fixed or Mobile

Fixed monitors provide practical and flexible firewater coverage, and shall beconsidered if emergency response forces are limited. A monitor can be quickly aimed,activated and locked in position by a single person, who is then free for other tasks. Amonitor has an effective range of about 30 m, and if strategically placed can protect twoor more risk areas. Monitors can be bolted directly to hydrants with no additionalpiping. They shall be accessible in an emergency, between 15 and 30 m from theequipment protected. Depending on ship size, monitors on piers may have to beremotely operated.

Monitors shall be of brass or bronze construction, with double ball bearing swivels and alocking device. Nozzles shall be about 110 m3/h capacity, adjustable for fog or straightstream type.

In terminals, tank truck and tank car loading and unloading positions shall be protectedby fixed water monitors with adjustable fog-to-straight-stream nozzles located on eachside of the loading and unloading installations. Installation of fixed water monitors shallbe considered at large or high-risk consumer installations.

Mobile monitors shall have the same capabilities as described above but are moreflexible because they can be moved around to cover larger areas. However, they requiremore time and manpower to deploy. The monitor shall be furnished with two hoseconnections, and two 15 m lengths of hose, which can be stored on the trailer. Eachconnection requires a check valve to protect against a burst hose. For rapid deployment,hoses shall remain connected to a hydrant or valved outlets from a firewater main.

8.2.1.8 Internal Firewater Flooding of Tanks

Pressurized LPG storage at refineries and upstream gas plants shall be provided withwater flooding facilities to inject water and displace LPG in the lower portion of LPGtanks, in the event of a tank leak, per GP 3-2-3 para 9.4. Marketing facilities mayprovide connections if required by risk considerations. The key to such an installation isto have water pressure available to overcome the sphere pressure. In the case ofPropane or Propane rich storage, or sometimes Butane storage, higher pressure water isprovided via a pumper truck.

8.2.1.9 Hoses and Hose Reels

Fire hoses are for use by plant or municipal brigades, usually as backup for deluge andspray systems and monitors. Two to four men may be needed to handle a typical 65 mmsize hose. The time needed for deployment can be reduced if hoses and nozzles areavailable at the plant. Hoses shall be stored in cabinets because they can be deterioratedby solar radiation. Nozzles shall be constant-volume, adjustable combination straight


stream/fog types, made of brass. Live hose reels shall be permanently connected to thefire main system.

One person can put hose reels into action more quickly than the larger hoses where ateam is required. Fixed hose reels typically hold 30 m of 32 to 38 mm hose of the firmtype that can be stored on the reel without collapsing.

8.2.1.10 Drainage Against Area Flooding During Firefighting

Spills of LPG liquid (and heavier-than-air vapor releases) shall drain away from productstorage, transfer areas, and buildings. It is also important to avoid accumulation ofwater where it could interfere with emergency actions. The drainage system for eachindividual risk area shall be sized for the maximum rate of rainfall, or design firewaterrate, whichever is greater. Plant-wide drainage capacity is usually set by the maximumrainfall rate, assuming this exceeds the firewater requirement for the largest risk area.

8.2.1.11 Dry Powder Fire Extinguishers

The preferred strategy for fighting an LPG fire is to isolate the fuel at its source and tocool exposed equipment. LPG fires shall not be extinguished unless the fuel supply canbe isolated; otherwise a vapor cloud may form and create a greater hazard.

However, portable fire extinguishers shall still be provided in LPG plants, primarily toprotect against fires involving other materials. In plant areas outdoors, type BC or ABCdry chemical extinguishers are most suitable. Portable extinguishers with about 9 kg ofagent can readily be carried and used by one person. Typically two extinguishers shallbe provided at strategic locations throughout plants. Examples for such locations are:marine piers, truck and rail racks, cylinder filling sheds, pumps, compressors; andredistribution centers.

Larger wheeled units with about 70 kg of agent are more powerful, but normally twopeople are needed for handling and maneuvering. They shall be placed near truckloading racks, and can be considered on piers unless congestion would limit theirmobility.

Dry chemical extinguishers are also effective indoors, but the agent is messy and candamage electrical and electronic equipment. Carbon dioxide extinguishers arerecommended for substations, computer rooms, and similar locations with sensitiveinstruments and switch gear. Halon extinguishers (type BC) are no longerrecommended because of environmental concerns. Pressurized water extinguishers canbe considered for offices where combustible materials such as wood, paper, and plasticare the main sources of fuel. Extinguishers for use indoors shall be mounted near exit,and shall be of a size that can readily be carried around in the building.

8.2.2 Protection Requirements

8.2.2.1 Aboveground Tanks – Bullets and Spheres

Spheres shall be protected with either a water deluge system, per GP 9-2-1 (preferred),or a fixed spray system discussed later in this chapter. Water deluge systems are notrecommended for horizontal bullets, or for protection of transfer operations which shalluse firewater sprays. Although fireproof insulation may be substituted for deluge orsprays provided fire water is also available, generally deluge and sprays are preferred.

Spray systems shall be used on horizontal LPG bullets, cylinder filling and storageareas, and truck and rail loading/unloading areas. For horizontal bullets, a fire watermonitor system capable of wetting the whole bullet surface may be substituted forsprays. If three or more tanks are closely spaced, less than 15 m shell-to-shell, they shall


be fireproofed if a fire water monitor system is used, per GP 14-3-1. This is because theclose spacing will make fire water coverage more difficult.

At least two portable fire extinguishers each having a minimum capacity of 9 kg of drychemical with a B: C rating shall be provided. Emergency controls, if provided, shall beconspicuously marked, and the controls shall be located so as to be readily accessible inemergencies.

8.2.2.2 Buried/Mounded Drums

Mounding or burial of storage drums shall be considered as adequate protection withoutfurther need of firewater for these tanks. For mounded drums, the sand shall bestabilized with a layer of grout or other material to prevent erosion from rain orfirewater hose streams. At least two portable fire extinguishers each having aminimum capacity of 9 kg of dry chemical with a B: C rating shall be provided.Emergency controls, if provided, shall be conspicuously marked, and the controls shallbe located so as to be readily accessible in emergencies.

8.2.2.3 Pump and Compressor Stations

A live hose reel shall be provided covering the entire area of the pump and compressorarea with 30 m long hose. Live hose reel shall be permanently connected to the firemain system and the nozzles shall be complete with shutoff ball valves. Adjustable fog-to-straight- stream nozzles shall be provided on live hose reels equipped with 30 m of 32or 38 mm fire hoses. At least one portable fire extinguishers having a minimumcapacity of 9 kg of dry chemical with a B: C rating shall be provided. Emergencycontrols, if provided, shall be conspicuously marked, and the controls shall be located soas to be readily accessible in emergencies.

8.2.2.4 Truck Loading and Unloading Facilities

Tank truck and tank car loading and unloading positions shall be equipped with drychemical fire extinguishers as follows: one 15 kg dry chemical extinguisher for eachfour positions. Since the only safe way to extinguish an LPG fire is to shut off theproduct supply, dry chemical fire extinguishers are required for other purposes, such assmall spills or burning materials after the product has been shut off. At consumerlocations, tank truck unloading positions shall be equipped with dry chemical fireextinguishers.

Either a water spray system or fixed water monitors shall be designed for truckloading and unloading area. Sufficient number of 30 m long live hose reel shall beprovided to cover the entire area of the truck loading/unloading area. Live hose reelshall be permanently connected to the fire main system and the nozzles shall becomplete with shutoff ball valves. Adjustable fog-to-straight-stream nozzles shall beprovided on live hose reels equipped with 30 m of 38 mm fire hoses.

At least two portable fire extinguishers each having a minimum capacity of 9 kg of drychemical with a B: C rating shall be provided for the truck loading/unloading area.Emergency controls, if provided, shall be conspicuously marked, and the controls shallbe located so as to be readily accessible in emergencies.

8.2.2.5 Vaporizer

At least one portable fire extinguisher having a minimum capacity of 9 kg of drychemical with a B:C rating shall be provided. This requirement is optional if thevaporizer is installed near LPG tanks where fire extinguishers are already provided.


8.2.2.6 Cylinder Filling Plant

Water spray system shall be designed for filled cylinder storage area. Sufficientnumber of 30 m long live hose reels shall be provided to cover the entire area of thecylinder filling plant. The hose reels shall be permanently connected to the fire mainsystem and the nozzles shall be complete with shutoff ball valves. Adjustable fog-to-straight- stream nozzles shall be provided on live hose reels equipped with 30 m of 32 to38 mm fire hoses.

At least two portable fire extinguishers each having a minimum capacity of 9 kg of drychemical with a B: C rating shall be provided for the LPG filling plant. Emergencycontrols, if provided, shall be conspicuously marked, and the controls shall be located soas to be readily accessible in emergencies.

8.2.2.7 Cylinder Storage

All storage areas shall clearly display a warning notice with the words “LPG STORE.”

Warning signs “STOP MOTOR”, “NO SMOKING”, “FLAMMABLE GAS” shall beposted at all LPG cylinder storage area. The locations of the signs shall be determinedby local conditions, but the lettering shall be large enough to be visible and legible.

Sufficient number of 30 m long live hose reel shall be provided to cover the entire areaof the cylinder storage area if the water capacity of the total LPG cylinders storedexceeds 15 m3. Live hose reel shall be permanently connected to the fire main systemand the nozzles shall be complete with shutoff ball valves.

Adjustable fog-to-straight-stream nozzles shall be provided on live hose reels equippedwith 30 m of 38 mm fire hoses.

Fire-fighting foam shall not be used for LPG fire.

At least two portable fire extinguishers each having a minimum capacity of 9 kg of drychemical with a B: C rating shall be provided for the cylinder warehouse.

8.2.2.8 Cylinder Maintenance Shed

Sufficient number of 30 m long live hose reels shall be provided to cover the entire areaof the cylinder maintenance.

At least two portable fire extinguishers each having a minimum capacity of 9 kg of drychemical with a B: C rating shall be provided for the cylinder maintenance shed.

8.2.2.9 Firewater at Marine Piers

Firefighting monitors shall be installed at the berth, primarily to providecoverage/cooling for the berth manifold area and the cargo transfer equipment. Theymay also provide a method for dispersing LPG vapors in the event of an accidentalrelease. Berth monitors shall provide assistance to the vessel's firefighting system andshall be able to cover the vessel's manifold area.

In addition, berths receiving vessels in the international trade shall have ISGOTT firewater connections installed at the berth to provide the vessel with fire water in the eventof an emergency. Fire water connections for a fire boat to connect and increase theberth's firewater capacity shall be considered. If firewater connections are installed,they shall be located at least 60 m away from high risk areas. Detailed description of thefirewater requirements and firefighting equipment requirements for marine terminals areprovided in EMRE's report EE.5TT.81 “Fire Protection and Safety Guidelines forMarine Terminals.”


The following fire protection shall be provided:

Installation Requirements (Minimum)

Barge pier or wharf fortransfer of Class I products,or any product heated aboveits flash point, and Class Iproducts in drums

Fire main and hydrants with firewater supplyof at least 340 m3/h

Portable fire protection including monitorsand portable fire extinguishers

8.2.3 Flammable Gas Detectors

Flammable gas detectors may be provided as early warning. Installations shall be basedon risk considerations. Plants close to housing that may be unmanned during the nightwould need higher protection than plants in uninhabited areas.

A minimum level of leak detection is already called for on all new pump seals. Theintegrity of the pump seal can be further upgraded to one of the higher sealing categoriesdescribed in Chapter 4, “Shaft Sealing,” to both reduce the chances of pump seal failureand provide better containment should the pump seal fail. In addition to pump seals,new compressor seals, depending on risk considerations may also be provided with aleak detection device.

Leak detection may also be provided around loading/unloading locations, which do nothave continuous surveillance, and around LPG tanks, through the use of flammable gasdetectors. Decisions to provide this additional monitoring would typically be made as aresult of a risk analysis. The analysis would typically consider local conditions, theproximity of the storage to the fence line and populated areas or to process equipmentand ignition sources, and the volume of storage or frequency of loading/unloadingoperations. When flammable gas detectors are applied to loading/unloading points, thedesign shall be tolerant of hydrocarbon that will be present around the transport vesseldue to breaking connections. If not, false alarms will render the system ineffective byfrequent nuisance alarms. Additional detail on flammable gas detectors is provided inDesign Practices Section XV-K, “Flammable Gas, Toxic Gas, and Fire DetectionSystems.”

LPG detection system shall be designed as “PRE-FIRE” early warning system. As such,automatic water application system (i.e. deluge, water spray) shall not be activated byLPG detection system alone.

Open path detectors are now reliable and a few instruments can cover large areas. Todetect leaks from groups of equipment or facilities within the same line of sight, open-path gas detects shall be installed. For example, open path gas detectors can be used todetect release of LPG from a row of pumps or compressors. Their signal may be used toactivate the Emergency Shutdown System. An audible alarm is needed at the controlroom and, if the control room is not permanently manned, also a local audible alarm.Some local regulations always require local alarm. During times when the plant is notmanned, the alarm may be transmitted to a security company.

Also point detectors are acceptable. They may be installed to detect leaks fromindividual release sources. Individual release sources includes pump seals, compressorseals, flanges, safety relief valves venting to atmosphere, sewer vents and smallpipes/connections which are prone to failure due to vibration or corrosion. One pointdetector may be used to detect gas leaks from several individual release sources whichare located nearby. However, the coverage or sensing area of the point detector mustnot exceed those specified by the manufacturer. If coverage area is too large for onedetector, additional point detectors shall be installed.


Detectors shall initiate an alarm at the following:

1. A measurement of 20 –2 5 percent LEL - at least 100 decibels audible andvisual alarms. The alarm condition shall not be considered cleared until thespecific detector reading has dropped below 20–25 percent LEL. Operatorresponse shall be required to clear the audible and visual alarms.

2. A measurement of 50 – 60 percent LEL – activate an emergency ALARMand at least 100 decibels audible / visual alarms. The alarm condition shall notbe considered cleared until the specific detector reading has dropped below20 – 25 percent LEL. Operator response shall be required to investigate causeof emergency, take corrective action before clearing the audible, visual alarmsand resetting the emergency ALARM system.

These detector shall sound alarm at the site and at a constantly attended location if thesite is not continuously manned.

The detectors shall be installed not more than 100 mm above grade level. At least onegas detector shall be installed at each of the following locations:

1. LPG tanks.

2. Truck loading/unloading rack.

3. Cylinder filling shed.

4. Jetty - near manifold flanges.

Gas detectors shall be positioned based on site conditions and requirement taking intoaccount of manufacturer’s recommendation.

8.2.4 Fire Detectors

Minimum requirements can be supplemented with additional fire protection, dependingon each plant's situation. Factors which may make this desirable include limitedemergency response capability; proximity to populated areas or public roads; risk fromadjacent facilities; future development of the area; availability of utilities; andtopography of the site. Fire detectors are an appropriate design feature to provide earlywarning thus reducing risks. Additional fire detector details are provided in DesignPractices Section XV-K “Flammable Gas, Toxic Gas, and Fire Detection Systems.”

Numerous mechanical and electronic devices are available to detect the environmentalchanges created by a fire. The most sophisticated type is the optical flame detector,which “sees” a fire directly, without depending on air currents to transport smoke or hotgases to a sensor. This is a significant advantage outdoors. Flame detectors can beuseful in emergency response by reducing the time interval between the outbreak of afire and its control, which is important in an LPG installation.

When an optical device is desired, the infrared (IR) detector designed specifically forhydrocarbon fires is recommended. IR detectors are more reliable and less vulnerable tofalse alarms than ultraviolet (UV) detectors. The ability to discriminate between firesand false alarms can be improved by adding a second sensor, either IR or UV.

Considerable care and expense are needed in design, installation, and maintenance ifflame detectors are to be beneficial. A detector can only save time in identifying anemergency, and there may be better ways to do it. Flame detectors shall be considered ifall the following conditions exist:

1. Continuous surveillance not feasible with available personnel.

2. Early warning by other means not feasible: gas and seal leak detectors.

3. Capability exists for prompt response: fire suppression, shutdown, andisolation, whether automatic or manual.


4. Available technical expertise for equipment selection, design, installation.

5. Ongoing maintenance support available.

All flame detectors have a wide field of view, typically around a 90° angle. Thissuggests a small number of detectors could cover a large area, but there are other factorsto consider. Response is not instantaneous, because the detector to satisfy its designcriteria for a fire must accumulate enough information. The sensitivity and responsetime of a detector depend on fire size, distance, and the position of the fire in its field ofview. And as distance increases, obstructions become more of a problem, and falsealarms become more likely. Requirements for audible alarms are as discussed under“Flammable Gas Detectors.”

Heat sensing detectors, also discussed in DP XV-K, are an alternative to optical flamedetectors. Response from heat sensing detectors is slower, but false alarms are reducedcompared with optical detectors. Two types of point heat sensing devices, pilot headswith fusible plugs and nylon tubing, have been used with success to automaticallyactuate deluge or spray systems. When fire detectors are deployed at locations withspray or deluge systems, the site shall evaluate automating the deluge/spray system withthe fire detection. In the case of LPG tanks, prompt actuation of deluge/spray systemswill reduce any BLEVE potential.

Safety in LPG Design TRANSPORTATION 9-1

9 TRANSPORTATION

9.1 Means of Product MovementThis chapter discusses the various types of equipment used to convey product betweenrefineries and marketing terminals, from terminals to distributors, or from terminals toend users. Ship or rail car normally transports large quantities while road transportationdominates transportation in smaller parcels. The LPG is transported in pressure tanks,which are mounted to ship, rail car or truck. Ships are also often equipped withrefrigerated tanks.

The discussion in this section cites basic, generally accepted standards for equipmentdesign that will provide satisfactory LPG transportation if more specific nationalstandards do not exist. Need for “custom design” can be avoided since vendors havestandardized equipment designs for tank trucks, portable containers and rail tank cars.General guidelines are defined to assist in selecting the most efficient truck power trainsand suspensions for various types of service.

9.2 Road Bulk Transportation EquipmentTwo classifications of road transport are considered:

1. Large capacity transports for point-to-point product delivery from a supplysource to a single destination.

2. Smaller route delivery trucks (Mini-bulk) designed to load at a terminaland deliver product to a number of end users efficiently grouped on aperiodically served loop route.

9.2.1 Truck Design and Procurement

As a guide for the design, fabrication, testing, and inspection of a road transport unit,reference DOT (ICC) Specification MC331, “Cargo Tanks Constructed of SteelPrimarily For Transportation of Compressed Gases” and NFPA 58, Section 6 “VehicularTransportation of LP-Gas” shall be referenced. All welded piping on truck transportsshall be fabricated and tested in accordance with ASME Code for pressure piping,Section 3, Petroleum Refinery Piping B31.3.

LPG road transport units may be in the form of a single tank mounted on a semi-trailerwith the motive power and a portion of the load being carried by a tractor. In certainareas, motor vehicle restrictions and/or road conditions may necessitate the use of a unitconsisting of a tank mounted directly on to a truck frame. The primary design goal istransportation of the maximum legal payload safely and efficiently by minimizing theweight of the vehicle and tank. Local regulations will determine the configuration that

9-2 TRANSPORTATION Safety in LPG Design

best achieves this objective. To select the most efficient and safest vehicle for a givenlocation, procurement has to consider terrain, weight regulations, road characteristics,frequency of stops, round trip mileage and local tax structures, and speed limits asfollows:

1. Hilly terrain and steep grades will require comparing the advantages oflarger engines versus transmissions with more forward speeds, consideringtotal drive train cost and vehicle weight effects. Engine weight will affectpayload. Two-speed rear axles are another (somewhat costly) possible designsolution. More braking capability will also be required.

2. Stringent weight limits may justify high cost light weight components suchas fiberglass cabs and aluminum wheels; however, rough road surfaces maymake affect light weight components such that they fail prematurely.

3. Rough road surfaces may warrant investing in more sophisticated tractorsuspensions, and shock absorber-mounted orthopedic seats for drivers, toreduce driver fatigue and maximize driver safety and efficiency.

4. In congested traffic conditions with a high percentage of stop and go driving,engine speed versus torque characteristics will affect the amount of gearshifting required, and correspondingly, driver efficiency. This may warranttruck automatic transmissions, but their advantages should be weighed againstincreased unit cost, lower fuel efficiency, and loss of some payload capacity.

5. Cost and spare parts availability, and the ability to provide adequatemaintenance should also be considered.

6. In several countries Diesel engine powered trucks are mandatory. However,with all the electronics now built-in modern Diesel trucks they may serve asignition sources as do gasoline driven vehicles.

The vendor should offer at least two power train options for each truck proposal, andthese should be supported by geared speed versus engine speed charts.

9.2.2 Basic Design Considerations

Before selecting a specification for an LPG road transport unit, local regulations shall beexplored thoroughly since regulations from the following authorities may have to betaken into account:

1. Authority concerned primarily with pressure tanks.

2. Motor vehicle authority.

3. Weights and measures authority.

4. Agency primarily concerned with the transportation of a hazardouscommodity.

5. Authorities responsible for the operation of bridges and tunnels.

It is recommended that Specification MC 331 and Division III of NFPA 58 be utilized asa guide for the design, construction, inspection, and testing of road transports in theevent that a mandatory specification does not exist. Specification MC 331 embodies atank designed and constructed fulfilling the requirements of the ASME Boiler andPressure Vessel Code, Section VIII for unfired pressure vessels. Tanks intended forstatic storage must not be used for deliveries.

Tanks shall have metal tank data plates welded to the tank in a conspicuous andaccessible place with vessel code and class to which it is made, manufacturer name andtank serial no, water capacity, minimum and maximum working and design pressures,date of original and subsequent tests, operating temperature ranges.


9.2.2.1 Working Pressure on Truck Tanks

According to Specification MC 33,1 the design pressure shall not be less than 6.9 bargauge nor more than 34.5 bar gauge. NFPA 58 limits are more restrictive. It isrecommended that a working pressure of 17.25 bar gauge be adopted for all LPG roadtransport units. This working pressure would allow use of the vehicle for Propane,Butane and their mixtures. If there is a long range use for a transport vehicle exclusivelyfor Butane it may be designed for 10.75 bar gauge. In addition, the design is to take intoaccount the allowance for vehicle acceleration and deceleration both horizontally andvertically. Acceleration and deceleration shall be assumed as 1 g (9.81 m/sec2)indirection of travel, and 2 g in the transverse horizontal direction, vertical accelerationboth upwards and downwards at 5 g.

9.2.2.2 Tank Openings and Valves

Tank nozzles and valves are fitted internally, recessed into the tank shell or positionedso to minimize the risk of impact damage and to prevent unauthorized access. NFPA 58requires that tank fittings and appurtenances be protected against damage by either: theirlocation, e.g. behind the vehicle frame or bumper, a protective housing or recessing.The following indicates the opportunities available.

Pressure relief valves may be of a recessed type in which working parts of the valve donot extend beyond the shell of the tank. As an alternate, an internal spring-type safetyrelief valve may be installed within a well or recess lowering all working parts below thesurface of the shell. PRVs on transportation tanks shall be tested or replaced every 5years. Where local codes explicitly permit longer testing times, they may be followed,up to 10 years. In some countries (Central Europe) the installation of PRVs on trucks isprohibited and the tanks are designed for the maximum pressure specified by localcodes.

Gauging devices, such as visible float gauges, rotary gauges, fixed liquid level gauges,and pressure indicators, may be installed within recesses. The pressure gauge must beconnected to the vapor phase.

Liquid or vapor connections necessitate the use of pipe, valves, etc. to extend beyondthe primary valve installed within the tank flange or coupling. Internal Excess FlowValves on all liquid outlet lines and vapor return lines The accidental removal of theexterior portion of the valve will, in most cases, permit the valve element within the tankto remain closed, or if open at the time of an accident, will effect automatic closure. Theliquid inlet line shall be protected by a backflow check valve. All filling and dischargeconnections to tank to be provided with quick closing internal valves, and a manual orautomatic shut-off valve. All inlets and outlets must be labeled to designate function.

All liquid and vapor lines shall be capable to be closed by a Truck Emergency ShutdownSystem. Shutoff shall be manual at two points at the front and rear end of the truck tankand by a remote handheld device carried by the driver. Activation maybe electrical orby radio.

NFPA 58 also requires certain valve arrangements on vapor and liquid openings toprevent excessive discharge of gas in the event a connection is accidentally broken. Forvapor and liquid withdrawal openings either a shutoff valve located as close as possibleto the tank in combination with an excess flow valve in the tank, or an internal valvewith excess flow protection shall be required. For vapor and liquid inlet openings eithera shutoff valve located as close as possible to the tank in combination with a back-flowcheck valve or an excess flow valve in the tank, or an internal valve with excess flowprotection shall be required. From all the NFPA options, liquid inlets are recommendedto have only back-flow check valves and not excess flow valves. Vapor inlets arerecommended to have excess flow valves, as check valves would not allow for liquidwithdrawal in the event of an overturn.


The control mechanism for self-closing internal valves shall be arranged with aninterlock so the forward motion of the vehicle will release the valve holding mechanismand cause the valve to close shall the valves be accidentally left in the open position.This may be accomplished through an interlock with the brake system or the ignitionsystem. An interlock with the brake system is recommended. There are a number ofpackaged control devices available for this application.

9.2.2.3 Piping, Tubing, and Fittings on Truck Tanks

It is recommended that only Schedule 80 pipe be utilized if the joints are welded orwelded and flanged. This shall conform to ASTM Specification A-106, Grade B, orequal. This is more stringent than section 3.3 of NPFA 58, which permits Schedule 40piping.

All valves, fittings, pumps, pipework and accessories to be located behind under-runprotection bars or be located as such, that they are protected to minimize risk of damage,or leakage in a vehicle accident or roll-over. Installations where the pump is notmounted directly on the liquid discharge connection shall be arranged with a minimumlength of suction pipe sloping downward from the outlet to the pump suction withoutirregularities or pockets.

Figure 9.2.2.3: Lifting lugs on tank trucks will help should recovery be needed

Threaded joints shall be minimized. On any vehicle the use of threaded joints shall bereduced to an absolute minimum. The maximum size thread tolerated on a truckinstallation is 32 mm. All welding fittings (welded fittings to be socket weld) shall becompatible with Schedule 80 pipe. All threaded fittings shall be extra heavy forgedsteel (3000#). All threaded connections shall be secured with pipe joint compoundspecifically approved for liquid LPG. The use of Teflon tape is discouraged sinceduring a fire it will melt and create additional leakage and add fuel to the fire. Note thatthis recommendation is different from that given for cylinder valves since those are oflow melting material anyway.

All welded piping shall be fabricated and tested in accordance with ANSI Code forpressure piping, Section 3, Petroleum Refinery Piping B31.3.


Ideal designs minimize the need for flexible connections by attaching as muchpiping/equipment to the tank as possible. If piping or equipment is attached to the truckchassis provisions shall be made to compensate for stresses and vibrations in thepiping system. The piping system configuration and its restraints shall provideflexibility.

The filling connection shall lead directly into the vapor space of the tank. Spray fillingwill lower the pressure in the tank and does not have the adverse effects associated withfuels spray loading. If two filling connections are utilized, at least one connection shallbe fitted with a tube to the top of the tank in order to facilitate the final filling of thetank.

The manhole in the tank shall have least 610 mm in diameter. Tank must have thelowest possible center of gravity which when fully loaded, does not exceed 1.75 meters.Overall stability is important and a static tilt angle of 25 degrees must be possible whenfully loaded.

9.2.2.4 Anti-Surge Baffles in Truck Tanks

An LPG tank, when in transit, is only partially filled with liquid; therefore, relativelysevere “loading” may develop as a result of the movement of the cargo. The possibilityof including anti-surge baffles within the tank shall be reviewed with the transportsupplier, considering local operating conditions before a specific design is finalized.

9.2.2.5 Safety Controls on Trucks

Interlocks: In the operation of a tank truck delivery unit, there are a number ofprocedures which are repeated several times in the course of a working day; therefore,the possibility of an error and in turn a potential hazard is always present. These can beeliminated as there are safety controls available, which either program the operator'sactivities or act as an override to correct any inappropriate action on the part of theoperator. The following is an indication of the operations which may be monitored orwhich may be automatically performed:

1. An interlock may be applied to the truck braking system to preventmovement while product is being transferred.

2. A lock may be placed on the vehicle so it is incapable of being moved untilthe dispensing hose has been returned to the vehicle and attached in anappropriate location.

3. A lock may be placed on the vehicle until the filling hose has beendisconnected from the liquid filling connection.

4. A lock may be placed on the vehicle until the liquid discharge valve or anyother quick closing internal valve has been released and closed.

5. A lock may be placed on the movement of the vehicle until the power takeoff has been disengaged and the pump has ceased to function.

6. A safety control is available which can be programmed for a tank truckdelivery unit depending upon the type of equipment used. As an example, thedevice can be programmed so it is necessary to set the brakes first, open themain liquid discharge valve, engage the pump, then, complete the dischargeoperation. The hose shall be returned and secured, the pump disengaged andthe main liquid discharge valve closed before the vehicle can be moved.

The tank, when on truck, shall not exceed maximum allowed overall height (in thecountry) and not to be closer than 150 mm to prime mover/tractor cab. Chassis andrunning gear to have local statutory approval and meet local axle load limits. Turntablecoupling (where fitted) in good condition, meeting manufacturers specification anddesign.


Suspension to be appropriate for local terrain, bushings in good order, and fullycompliant with relevant statutory regulations and meeting manufacturers design.Braking system to be fully compliant with relevant statutory regulations and in fullworking order. All tires (including spare) to have minimum of 3 mm tread, no mixingof sizes and type on same axle.

Landing legs are optional (i.e., weight consideration) but if not fitted, trailer to havepads on underside of trailer for portable landing legs, designed and capable ofsupporting a fully loaded trailer.

Drive shaft Protection: Consideration shall be given to protecting the tank from beingstruck by the vehicle drive shaft in event of a universal joint failure. Housings or bafflescan be used.

Figure 9.2.3.3-a: Typical single tank semi-trailer instrumentation

Truck lights: Trucks, trailers, and semi-trailers transporting LPG shall not be equippedwith any artificial light other than electrical. Lighting circuits shall have suitable over-current protection (fuses or automatic circuit breakers). All wiring shall have sufficientcurrent carrying capacity and mechanical strength, and shall be secured, insulated andprotected against physical damage. Tank/Trailer side clearance lights and rear trafficindicator, brake lights to be fitted and in working order, and comply with local statutoryregulations. Electrical wiring to be installed and protected (i.e., in conduit) to avoid fireor short circuit in normal conditions of use. Semi trailer to be in electrical continuitywith prime mover/tractor. Connectors for air and electrics to be in good condition andmounted on the trailer such that the cables will not be fouled by prime mover mountedequipment.

Under-run bar shall be fitted to rear of rigid or trailer, across width of the tanker. Thebar to be secured to the subframe. Near and off side under-run protection shall be fittedand secured to the subframe. All wheels shall be fitted with mudguards.

Minimum of 4 brass earthing pins to be fitted (2 each side), connections the body to befree of paint, dirt and grease. An earthing cable (15 m) to be fitted adjacent to pumpoutlet.

Delivery hoses to be fitted with “pull away couplings”(either on truck or at all plantside) and to be in good condition and fit for purpose, and securely stored on trailer/tankduring driving.

Trailers to have 2 x 9 kg dry chemical fire extinguishers (one on each side), in additionto prime mover 2 x 9 kg dry chemical fire extinguishers.

Capacity of tank/trailer to be clearly labeled (50 mm letters) near fill point of trailer.

All wheel hubs to be equipped with full complement of bolts, correctly tightened.


Toolbox (lockable) to be fitted to appropriately store tools/adapters/fittings.

9.2.3 LPG Truck Discharge System

9.2.3.1 Pumps on Trucks

While LPG pumps at the refinery or terminal fill the tank trucks relatively quickly thedischarge of product from the truck will take longer since it has to be done via the pumpinstalled on the truck. A truck tank may be fitted with a pump flanged directly to theliquid outlet. At the completion of the operation, the vapor contents will remain withinthe tank as the pump is incapable of transferring vapor.

Truck pumps are operated through a power take-off by the truck engine. Mostlypositive displacement sliding vane pumps are used on trucks and therefore shall beequipped with a suitable pressure actuated bypass valve permitting flow from thedischarge to the suction or to the tank. Centrifugal pumps are not suitable for outboard,power take-off, transport unloading. After selecting a pump, the manufacturer'srecommendation shall be observed in selecting a strainer. A pump shall be specificallydesigned for liquid LPG and preferably be flanged. It shall also be designed andrecommended for use on a delivery truck.

Figure 9.2.3.2-a: Bypass valve

The capacity of the pump should be selected considering the average volume of eachindividual delivery or discharge and the rate at which the product can be received. Thefollowing is offered as examples for selecting pumps on trucks typically used forcustomer delivery.

Pumps for tank truck delivery service are available with a discharge capacity of 380liters per minute. This type of pump is suited to filling relatively large fixed storagetanks with high capacity filler valves.

When the average tank being filled is approximately 760 liters capacity and the fillervalve has a relatively low capacity, a pump capable of 110 to 190 liters per minute maybe adequate.

A pump should also be analyzed from the standpoint of maintenance as it is importantthat the wearing parts can be replaced with minimum effort. A pump, which requiresremoval from the installation in order to be repaired, is not desirable.


The unit shall also be capable of evacuating the same tanks, which it normally would becharging. In normal operation, it may be necessary to evacuate the contents of a fixedfield LPG tank because of a defect in the unit or because of the necessity of moving theunit. With the inclusion of the evacuation feature in the tank truck delivery system, theliquid can be withdrawn from a supply tank and discharged into the delivery tank;therefore, the unit has the capability of charging or fueling without depending upon apump or compressor at the plant.

Selection of a pump establishes the maximum discharge rate and an appropriate metercan be selected. The meter shall have a sufficiently high range so it can accuratelymeasure the maximum anticipated discharge rate through the system. Variousaccessories may be added to the meter depending upon the type of dispensing proceduredesired.

9.2.3.2 Bypass Valve for Truck Pumps

The selection of a bypass valve is dependent upon the capacity of the pump and shall besufficient to prevent the overpressuring of the system and, in turn, excessive wear on thepump. A bypass valve, which is capable of sensing complete closure of the dischargeline and opening for full pump capacity, is desirable. The Figure “Installation of bypassvalve in truck piping system” below illustrates where to install it in the system. Atypical bypass valve is designed to bypass full pump capacity when the valve at the hoseend is closed.

Figure 9.2.3.2-b: Installation of bypass valve in truck piping system

9.2.3.3 Hoses and Hose Reels on Trucks

LPG tank trucks may be able to utilize plant hoses when discharging at the plant. Withthis arrangement the plant hose can be equipped with a positive shutoff valve at itsouter end, thereby eliminating the necessity of bleeding or venting the hose uponcompletion of the operation.

If the discharge operation is performed using a hose or hoses provided with the roadtransport, a suitable venting arrangement shall be included in the transport piping systemso the hose can be safely vented after the unloading has been completed (see sections6.1.5 and 6.1.6). A tubing vent may be run from a point just downstream of theoutboard transport shutoff valve to the top of the tank. The hose, complete with plugs orcaps, shall be suitable for liquid LPG and shall be rated for a minimum working pressureof 17.25 bar gauge or, preferably, 24.2 bar gauge. When carried on a transport, hosesshall be contained within a tube designed for the purpose and attached to the vehicle ortank with closures at both ends.


The marketing plant loading facility provides hoses or conduits for the tank truckdelivery loading. Swivel hard arms are recommended for this purpose.

An evacuation hose approximately 10 to 20 meters in length shall be provided toconnect the suction connection on the tank truck delivery unit with a fixed storage tankfrom which the liquid contents are to be withdrawn. The hose shall be approximately 25mm nominal size and be rated for a working pressure of 17.25 bar gauge.

A dispensing hose, 19 mm or 25 mm nominal size shall be employed. The length of thehose shall be determined considering the maximum distance from a safe convenientdischarge location for the tank truck delivery unit to the most remote fixed storage tanks.The hose, as in all cases, shall be specifically designed for LPG service and be rated for17.25 bar gauge working pressure.

Figure 9.2.3.3: Typical single tank semi-trailers

Where necessary, a vapor return hose shall also be provided with the length beingequal to that of the dispensing hose; the size shall be 13 mm or 19 mm nominal. A hosereel is recommended as an accessory on a tank truck delivery unit since it reduces wearand tear on the hose, ensures that the hose is properly stored when the vehicle is inmotion and can aid in developing a more efficient delivery operation.

9.2.3.4 Shutoff Valves on Truck Tanks and Hoses

A shutoff valve utilized as the primary valve in any mobile tank connection shall be of aquick closing internal type with a means of remote control whenever possible.Limitations regarding the use of these valves are usually dependent upon size. Somerelatively small connections cannot be fitted with this type valve as they are notcommercially available. The mini bulk distribution system requires the driver operatorto watch the tank while being filled but also requires him to be able to shut down theLPG flow on short notice. This is generally done by a handheld remote wirelessconnection to the truck valves. In case the button on the instrument is released, thevalve on the truck closes and the pump stops.


Figure 9.2.3.4: Typical retail cargo vehicle LPG transfer system

9.2.3.5 Liquid Meters

When liquid meters are used, they shall be selected to operate within the manufacturer'srecommended minimum/maximum rated capacity.

Materials used in the construction of meters shall be suitable for use with LPG andmaintain suitable performance over the range of operating conditions the meter will besubjected to. Cast iron shall not be used unless the material is of an approved gradehaving adequate ductility and impact resistance over the full pressure and temperaturerange of the system.

Liquid meters shall have the following accessories installed, either as part of the meterassembly or externally, to enable accurate meter readings.

A fine mesh strainer at the meter inlet. The typical coarse mesh strainer used in thepump suction is not adequate for the meter.

A differential valve to provide a back pressure against the meter and the pump and tomaintain the system pressure above the product vapor. This prevents vaporization of theliquid as it passes through the meter.


A vapor eliminator to remove vapor from the liquid before it passes into the meter. Theeliminator consists of a small tank with either a float-operated mechanism or a constantbleed orifice to circulate LPG vapors back to the LPG tank.

Consideration shall be given to the requirements for a temperature compensator. Atemperature compensator converts the measured meter volume reading at thetemperature of the product as it passes through the meter so the meter will register theequivalent volume at a standard temperature of 15.6 °C.

When liquid meters are used to measure the volume of LPG being transferred from onetank to another or from a pipeline, meters and accessory equipment shall be installed inaccordance with the procedures stipulated in the API MPMS 5.1. Meters shall beprotected from accidental damage either by their location or by other structural means.Meters shall be accessible to personnel for operational purposes and taking meterreadings. Inlet and outlet piping shall be arranged and supported so an excessive load isnot imposed on the meter.

Figure 9.2.3.5: Liquid meter installation at rear side of mini-bulk truck (Sasso)

9.3 Road Cylinder TransportationSimilar requirements discussed above under “Truck Design and Procurement” alsoapply for cylinder transportation trucks. The road conditions, grades, etc., which thevehicle must traverse shall be determined first, then the loading which will be applied tothe vehicle shall be analyzed. The vehicle shall possess adequate capacity for the “payload” and be sufficiently powered to negotiate the roads over which it must travel, at areasonable speed. To properly handle industrial cylinders during unloading, trucksshould be equipped with mechanical or hydraulic tail-gates.

Dual axle trucks and tractor-trailers (articulated trucks), purchased for the transport ofcylinders, shall be carefully analyzed to determine that they are capable of handlingcurrent or future pallet designs. The bed, together with sideboards or stakes, shall be ofsufficient strength to support and retain the maximum number of filled cylindersexpected. The height of the bed shall be considered in relation to the loading or


unloading dock. A tractor-trailer shall be equipped with a “landing gear”, ofsufficient strength to support a full load, so that the tractor may be utilized for purposesother than supporting the tractor-trailer during loading or unloading operations.Following are international codes, which may be referenced for information on roadcylinder transport:

1. The Australian Standard 1678 “Emergency Procedure Guide - Transport ofCompressed and Liquefied Gases.”

2. The Australian Code for “Transport of Dangerous Goods by Road and Rail.”

Figure 9.4: Typical rail LPG unloading site

9.4 Rail Tank CarsThere is limited value in a detailed discussion of LPG rail tank car design in a manualintended for international use. Pressure tank cars have long been used extensively forLPG transport. However, their capacity and external dimensions, as well as externalfittings and running gear, are determined by the widely varying characteristics of thevarious national railways (e.g. rail gauge, quality of roadbed, minimum allowed radiusof main line rail curvature, banking of curves, and maximum design train speed).Therefore the designer of rail receiving or loading facilities or the purchaser of rail tankcars is best advised to seek the guidance of rail transport regulatory authorities andequipment suppliers in the jurisdiction where the facility is to be constructed ormodified.


LPG rail car appurtenances are arranged such that they are protected in case ofaccident or derailment. One way of doing this is to concentrate all tank penetrations ina vertical cylindrical protective dome, with a hinged top cover, located at the top centerof the horizontal tank. Another way is to provide a recess on the side of the tank andlocate appurtenances therein. In countries (Central Europe) where risk from derailmentsis considered low, the appurtenances have been installed below the tank.

1. Pressure Relief Valves are installed in the vapor space and are of the internalspring type. The fabricators will determine the start-to-discharge pressuresetting and flow capacity of the devices. Certain countries do not permit theinstallation of pressure relief (Central Europe). Tanks on such rail cars aredesigned to contain the maximum pressure.

2. Liquid Outlet: Usually there will be two liquid outlets provided within therecess/dome. Each shall be fitted with a manually controlled positive shutoffvalve under which is fitted an excess flow check valve. The intake of theliquid draw-off is located at the bottom of the tank.

3. Vapor Connection: A single vapor connection is provided, fitted in a similarmanner to the liquid outlet except that the excess flow check valve terminatesin the vapor space.

4. Gauging Device: A gauging device in the form of a slip tube gauge is utilizedto determine the liquid level within the rail car.

5. Sampling System: Some rail cars have a tube extending to the bottom of thetank and fitted with an excess flow check valve connecting to a positiveshutoff valve within the dome. This installation may be used to take a sampleof the cargo to verify the contents or to confirm that the tank has beencompletely unloaded.

9.5 MarineBarge or ship either as a containerized shipment or as bulk cargo may transport LPG.As a containerized shipment, cylinders or portable containers may be utilized providedthe cylinders or containers meet basic requirements. Care should be exercised inpreparing the shipment so it will meet the regulatory and safety requirements, whichmay be applicable to the vessel, the waterways traveled and the ports at which the cargois loaded and unloaded.

As bulk cargo, non-refrigerated LPG may be transported by barge or by tank ship.Barges may be constructed with containers mounted directly to the deck or may beintegrated within the structure. The decision should be dependent upon the anticipatedcondition of the waterways traveled.

As a tank ship cargo, the product may be refrigerated in order to use low pressuretanks, which reduce containment weight and increase cargo weight. The design of atank ship should be developed considering the condition of the product at the loadingpoint, the facilities available at the delivery point, the volume of product available whenloading and the storage or receiving capacity at the delivery point. In particular, if arefrigerated LPG cargo ship is designed to supply pressurized storage terminals the shipshall have sufficient heat exchange equipment to increase the temperature of theproduct downstream of the unloading pump to ambient levels. While heating could beaccomplished on shore or the receiving tank may be designed to accept low temperatureLPG, designing the ship without heat exchange equipment would limit its deliverycapabilities.

When selecting marine transportation for LPG, ships with vertical multistage onboardpumps units should be preferred. The ships pumps will have to provide sufficient headto overcome the pressure in the ambient temperature LPG tanks.


Design of marine LPG transportation equipment is a specialized endeavor, whichbenefits from technical experts in the field. ExxonMobil Research and EngineeringCompany and ExxonMobil marine transportation specialists should be consulted whenin selecting designers and constructors. In addition EMRE has published extensivedesign guides, and can offer assistance in the design and construction of marine pierfacilities for LPG.

The basic design code for the cargo containment and transfer systems on bulk LPG shipsis the International Code for the Construction and Equipment of Ships CarryingLiquefied Gases in Bulk (referred to as the “IGC Code”) published by theInternational Maritime Organization (IMO). This code conforms to the requirements ofmost countries of registry, exporting countries and importing countries. A notableexception is the United States, which has regulations for both U. S. flag ships, andforeign flag ships that call at U. S. Ports. These regulations, administered by the U. S.Coast Guard, are defined in the Code of Federal Regulations, Title 46, Chapter I, Part38, Liquefied Flammable Gasses, Part 153, Ships Carrying Bulk Liquid, Liquefied Gas,or Compressed Hazardous Materials and Part 154, Safety Standards for Self-PropelledVessels Carrying Bulk Liquefied Gases.

In addition to requirements for the liquefied gas containment and transfer systems, shipsshould meet numerous other national and international standards specified by the ship'scountry of registry, classification society, and intended port states. These standards willusually be established at the outset of a project to suit the ship's intended service.

Safety in LPG Design CUSTOMER INSTALLATIONS 10-1

10 CUSTOMER INSTALLATIONS

10.1 Cylinder Bank InstallationsThis section of minimum standards covers the cylinder bank installation requirementsfor industrial and commercial areas where ExxonMobil LPG is supplied.

Public access to areas where LPG is stored and transferred shall be prohibited. Toprevent trespassing or tampering, every LPG storage place shall be enclosed by a fenceor cage or ventilated cabinet. Sufficient clearances shall be provided to allowmaintenance and safe exchange of cylinders.

Figure 10.1.1: Multiple cylinder installation

10.1.1 Design of Cylinder Banks

LPG cylinders are preferably located outside of buildings and in well ventilatedsurrounding. The cylinders shall be installed under shade whenever possible. Theyshall not be installed directly under windows or adjacent to doors. They may bepositioned against walls and secured by chains against tumbling. Where unavoidable,cylinders may be located inside buildings. Locations shall be carefully chosen such that

10-2 CUSTOMER INSTALLATIONS Safety in LPG Design

leaking LPG could not accumulate in basements and that the location would not impacton escape routes. If necessary, PRV outlets must be piped to a safe location outside thebuilding. At a safe location the gas will be allowed to dissipate to a concentration belowlower flammable limits. Mechanical ventilation, air-conditioning intakes, openings ofbuildings or sewer system openings shall not be close (less than 1.5 m) to such locations.

Local regulations may govern cylinder group installations. In the absence of localregulations, typically, 20 industrial 50 kg LPG cylinders may be installed in one group.Depending on customer needs it could be less but the total number must not be morethan 30 industrial cylinders. If more LPG is used (requiring more than 30 cylinders tobe installed) a container may be a better (safer and more economic) solution. If this isnot feasible a second group of cylinders may be installed but a minimum distance of7.5 m from the first group must be kept. The cylinders are all connected to a manifoldwhich is divided at the center by an automatic switchover regulator. 50% of thecylinders are in use while the other 50% are in reserve.

10.1.2 Installation of Cylinder Banks

LPG cylinders shall be installed at location least frequented by personnel and necessaryprecautions shall be taken to prevent tampering. Cylinders shall be installedaboveground and set upon a firm foundation which shall be substantially level.Flexibility shall be provided in the connecting piping. Cylinders shall be positioned sothat the pressure relief valve is in direct communication with the vapor space of thecylinder. Cylinders shall not be stacked one above another when in use. Loose or piledcombustible material and weeds and long grass shall not be permitted within 3 m of anycylinder.

Fire protection shall be provided in accordance with local regulations and localauthority shall be consulted for final approval. As a minimum, there shall be one 9 kgdry powder fire extinguisher located at a safe distance from the cylinder bank.

10.1.3 Vaporization Rate in Cylinders

In order to maintain a sufficient flow of vapor to a user, it is important to properlyestimate or calculate the vaporization rate. Depending on local code requirements forcustomer controlled piping; insufficient vapor rates could result in either a trip of thevapor supply or a loss of flame and continued feeding of vapor. In the latter case,continued flow of LPG may result in gas accumulation and a potential for explosion.

The vaporization rate of an LPG container or cylinder is influenced by many factors.Precisely calculating the vaporization rate of a given cylinder is difficult. In themajority of cases when 11 kg or 12 kg domestic cylinders are used, the requiredvaporization rate is sufficiently low so that problems do not arise. Typically, regulatorsfor domestic cylinders allow a take-off rate of 1 to 1.5 kg/h. In the event that largercylinders are utilized, the vaporization rate from a single cylinder may not be sufficientto meet customer demand. In this case, multiple cylinder installation can be used.

If there is any doubt regarding the vaporization capacity within a cylinder or a bank ofcylinders, the pressure within the cylinder(s) may be monitored and, in this way, asubstantial decrease in cylinder pressure may be interpreted as an indication thatadditional vaporization capacity is required. By so doing, the lack of available vapor ora shutoff of the vapor supply may be prevented. For customer comfort two cylinderbanks may be installed. Such installations may permit automatic switch-over from onebank to the other if the first bank is empty. However, in that case the customer shouldget an alarm so that a new set of filled cylinders can be ordered.

If a mixture of Propane and Butane is used, the former will vaporize preferentially. Atthe end of the vaporization process the liquid heel in the cylinder will consist only of


Butane. As a result the vapor pressure in the cylinder will keep dropping throughout thevaporization.

The Figure 10.1.3-a: shows how approximately a 70% Butane, 30% Propane mixtureevaporates. At the end of the evaporation process all Propane is vaporized. In thecalculation it was assumed that the temperature in the cylinder was constant at 25 °C.Of course, this assumption is for very little consumption and may therefore not berealistic, but it serves to demonstrate the effect.

0

0,2

0,4

0,6

0,8

1

11 10 9 8 7 6 5 3 2 1 0

Mass Remaining in Cylinder, kg

Wei

gh

t F

ract

ion

Bu

tan

e

Composition of Vapor

Composition of Liquid

Figure 10.1.3-a: LPG composition as cylinder is emptied

0

0.5

11.5

2

2.5

3

3.54

10 9 8 7 6 5 4 3 2 1 0

Mass Remaining in Cylinder, kg

Pre

ssu

re in

Cyl

ind

er, b

ar g

Figure 10.1.3-b: LPG pressure change as 10 kg cylinder is emptied

The Figure 10.1.3-b: shows the pressure drop during the above vaporization process. Ifthe temperature would be allowed to drop, the pressure may drop even lower.


10.1.4 Icing or Sweating on Cylinders.

Any indication of “icing” or “sweating” on the cylinder is an indication that thevaporization capacity is being exceeded and additional cylinders should be installed. Asthe vaporization capacity is exceeded, ice will form on the exterior of a cylinder inrelationship to the humidity within the surrounding atmosphere. During periods inwhich the air is relatively dry, icing or sweating may not occur; however, the surface ofthe cylinder will be noticeably chilled and, with an increase in humidity, ice or waterdew accumulation may be anticipated. As ice forms on the exterior of a cylinder itprovides an additional barrier to the transfer of heat; therefore, the overall efficiency ofthe cylinder as a vaporizing unit is diminished. Dew on the exterior of the cylinder hasthe same effect. It will tend to vaporize and take heat of vaporization from the cylindercooling it further down. As noted above, insufficient vaporization rates may lead incertain situations to a loss of flame with subsequent accumulation of LPG vapor.

10.2 Containers at Customer SitesThis chapter covers the spacing and site requirements and the design of abovegroundand underground or mounded LPG containers for domestic and commercial storagewhich are refilled on site. It does not cover cylinders connected in use in banks, orcylinders in storage awaiting use or distribution. Typically these containers are between1 and 300 m3 in size.

Containers for domestic storage and commercial storage containers should be fabricatedto conform to ASME codes, or an equivalent standard when recognized by localregulations. The code followed shall be acceptable to the regulatory authority where thecontainer is to be used. Procedures to establish Design Pressure, Design Temperature,and Critical Exposure (Minimum Design) Temperature are the same as explained in thesection “Bulk Storage” in Chapter 3.

When the LPG supplier (ExxonMobil) owns containers, the responsibility for thecontainers remains with the supplier. Therefore, the use of an inspection service isrecommended to assure continuing quality assurance oversight throughout the contractwith a container manufacturer.

Each container shall be completely identified by the nameplate, which is permanentlyattached to the container. Nameplate requirements may vary based on local codes.Typical commercial or domestic containers with fittings are shown in Figure: 10.2.7.They are designed for horizontal installation, with dual lifting lugs for deployment.Four steel feet permit setting the container on a pre-poured concrete foundation slab.Where there is potential for flooding, the container shall be fixed to the foundation slab.The foundation must be heavier than the total buoyancy of an empty tank.

10.2.1 Spacing and Location of Containers

Spacing of containers to the nearest important building, property line, or othercontainers at customer sites shall be in accordance with requirements in the country. Inabsence of any local requirements spacing as per Table 10.2.1 is suggested.

The number of containers in a group is limited to 6 containers. If more than one suchinstallation (group of 6 containers) is made, each installation shall be separated from anyother installation by at least 7.5 m. Do not apply the minimum distances betweencontainers to such installations. The designer shall not install multiple containerssimply for the purpose of reducing spacing to the property line. The need for multiplecontainers shall be justified based on operating requirements.


Maximum watercapacity (m3 ) Minimum separation distances (m)

Abovegroundcontainer

Underground or moundedcontainers

From buildings, propertyline, etc. to

Of anysinglecontai-ner in agroup

Of allcontai-ners in agroup

Frombuildings,prop. lineor fixed

source ofignition

Betweencontainers

Valveassembly Container

shell

Betweencontainers

Lessthan 0.5 1.5 2.5 1 2.5 0.3 0.3

0.5 to2.5 7.5 3 1 3 1 1.5

2.5 to9.0 27 7.5 1 7.5 3 1.5

9.0 to135 450 15 1.5 7.5 3 1.5

135 to337.5 1,015 22.5 11 3 3

Above337.5 2,250 30

¼ of sumof

diametersof adjacentcontainers 15 3 3

Table 10.2.1: Spacing of containers at customer sites

The following shall apply to above ground containers installed along side of buildings:

1. ASME containers shall be located and installed so that the discharge from thecontainer pressure relief device is at least 1 m horizontally away from anybuilding opening that is below the level of such discharge. And not less than1.5 m in any direction away from any exterior source of ignition, openingsinto direct-vent (sealed combustion system) appliances, or mechanicalventilation air intakes.

2. The filling connection and the vent from liquid level gauges on ASMEcontainers filled at the point of installation shall be not less than 3 m in anydirection away from any exterior source of ignition, openings into direct-vent(sealed combustion system) appliances, or mechanical ventilation air intakes.

LPG containers, whether aboveground or underground or mounded, shall be installed inthe open air outside buildings. Containers to be located downgrade and downwind frompossible ignition sources. LPG containers shall not be stacked one above the other. Thearea including LPG containers and related equipment shall be enclosed by an industrialtype fence at least 2 m high unless it is otherwise protected, e.g. being within a largerfenced area or otherwise isolated from public access. Unless the area is smaller than50 m2, there shall be at least two means of exit at adjacent sides of the fence. The gateshall open outwards, shall not be self-locking and shall open into an unobstructed openspace. An exception to the above is when the container is provided with a positivemeans of denying access to valves and fittings other than pressure relief valves, e.g. by aventilated hinged cover that can be locked, or by a blank flange or plug on drainconnections. Where damage from vehicular traffic is a possibility, means of protectionshall be provided, e.g. by the use of crash barriers, bollards or non-continuous toewalls.


No permanent source of heat shall be located within 1.5 m of an LPG container. LPGcontainers shall not be located directly beneath electrical power cables. For cablescarrying less than 1.0 kV, the LPG container shall be sited at least 1.5 m from a linedrawn vertically downwards from the power cables. For cables carrying 1.0 kV orgreater voltage, the distance shall be increased to 7.5 m.

No horizontal separation shall be required between an aboveground LPG container andunderground containers containing flammable or combustible liquids installed inaccordance with NFPA 30.

Fire protection of LPG containers at customer sites shall follow requirements of thelocal fire services.

10.2.2 Designing Customer Storage Systems

10.2.2.1 Piping Arrangement for Customer Installation

Storage containers at consumer locations shall be designed for 100 percent Propane toprovide for future flexibility of product mix.

Figure 10.2.2: Consumer LPG Facility

Figure 10.2.2 illustrates a consumer LPG facility. This figure shows containerconnections and service line for a permanently mounted container at a consumerlocation. If transport hoses can reach the storage container, piping from connections (1)and (2) can be eliminated. Valve outlets shall be fitted with hose adapters. The liquidvolume between the block valve at the unloading vehicle and the block valve of the plantmust be minimized.

Vent line valves at unloading connections shall be equipped with spring-loadedactuators that must be manually held open. Thermal relief valves shall be locatedbetween all shutoff valves. LPG vapor piping systems downstream of the first-stagepressure regulator shall be sized so that all appliances operate within theirmanufacturer’s specification.

The container valving may be different in case a vaporizer is required. In such cases, aliquid off take to a vaporizer may be installed, with a pressure regulator on the


container vapor outlet itself. This pressure regulator system would serve as a back-upduring vaporizer shut-down.

10.2.3 Sizing Of Containers and Vaporization Rates

Sizing of containers involves two aspects. One is the maximum consumption per hourrequired by the customer. The other is the supply and shipping logistics. Maximumconsumption can be satisfied by natural or enforced vaporization. Containers for theformer need to be larger than for the latter. According to supply logistics containersshall be sized to receive incoming shipments while maintaining a minimum reserve ofthe number of days demand equal to one-half of the shipping time from the supplysource. LPG is commonly shipped to consumer locations in bulk in trucks or rail tankcars

10.2.3.1 Natural Vaporization

An important characteristic of LPG is that, when in a storage container, it can use theheat from the surrounding air to change from a liquid to a vapor. When withdrawalstarts, heat is taken initially from the liquid itself, resulting in a drop of liquidtemperature. Because the product is at a lower temperature, heat starts to flow from thesurrounding air through the container wall into the product. The rate at which this heatflows depends primarily on the temperature difference between the air and the product.The greater this difference, the larger the rate of heat transfer. Normal Butane willremain a liquid at atmospheric pressure when ambient temperatures are below its boilingpoint of 0 °C. Propane will remain a liquid at atmospheric pressure when ambienttemperatures are below its boiling point of – 42 °C. At temperatures above these boilingpoints, rapid vaporization will take place as long as the pressure is at or slightly aboveatmospheric.

Figure 10.2.3.1: Vapor pressures of Butane and Propane mixtures


LPG is typically stored as a liquid under pressure. Under inactive conditions, eachproduct in a closed container has a defined pressure versus temperature relationship i.e.the vapor pressure (see Figure 10.2.3.1). Regardless of the amount of liquid in acontainer and provided some vapor space exists, the internal pressure will correspond tothe vapor pressure of the product at the temperature of the liquid.

When the liquid stored is 100 percent Butane or 100 percent Propane, the vaporconditions will be uniform. However, when the product is a mixture of Butane andPropane, the vapor above the liquid mixture will always have a higher percentagevolume of the lighter product (Propane), regardless of the proportion in the liquid state.Since Propane will vaporize at a faster rate than Butane, the first quantity of vapor takenfrom such a container will have a higher content of Propane than the succeeding vapor.As vapors are withdrawn, both the vapor and the liquid will have increasingly higherButane content.

When vapor is being withdrawn from a container, the internal pressure is lowered untilthe rate of conversion from liquid to vapor is equal to the rate of vapor withdrawal. Iftoo much vapor is withdrawn the pressure drops to dangerously low levels which maylead to flame-out or other undesirable situations. For such installations a vaporizer maybe needed, which is described later in this chapter. The size and the shape of a containerare important when vaporization must take place within the container. Given the samevolume a long container brings more vaporization as compared to a short one.

The container surface area that is in direct contact with the liquid is an important factorknown as the wetted surface area. The liquid surface area in contact with the vaporhas very little effect on vaporization. More heat will be transferred for vaporizationwhen a container is full than when it is nearly empty. In addition, the following factorswill have an influence on the container vaporization rate:

1. Ambient temperature of the atmosphere.

2. Size and color of the container.

3. Exposure to solar radiation.

4. Amount of frost, ice or insulation on the container wall.

5. Circulation of air around the unit and wind conditions.

Precise calculations can be developed in order to determine vaporization rates, however,due to the variation in various factors mentioned in the above list, reliance upon theestimated formula will usually suffice in the selection of a container for Propane only.

10.2.4 Sizing Containers for Vaporizing Liquid

Certain factors must be known in order to determine the proper size for a container whenit is to be used to vaporize the liquid stored in it to replace vapor being withdrawn fromthe space above the liquid. These include:

1. Maximum quantity of LPG to be vaporized per hour.

2. Number of hours per day that vapor is required.

3. Minimum allowable container pressure or minimum allowable inlet pressureto first-stage regulator.

4. Type of product or percentage of mixture.

5. Minimum anticipated ambient temperature during period of maximumvaporization.

6. Relative humidity of atmosphere at time of minimum ambient temperatureand maximum vaporization.

7. Minimum liquid level in container at time of maximum vaporization.


There is quite some experience with company engineers to calculate or estimatecontainer sizes. The following is not meant to replace those methods or experiences.The methods described below shall help the inexperienced engineer to understandcontainer sizing. These methods in this guideline are conservative in sizing LPGcontainers for natural vaporization, i.e. they will be rather on the large side than toosmall.

10.2.4.1 Sizing Small Containers for Natural Vaporization.

Calculation Example 1: The customer needs 9 kg/h at a pressure of 1 bar. The coldestoutside temperature is 20 °C. The LPG mixture is 30% Propane and 70% Butane.

First determine the maximum possible temperature differential. According to Figure10.2.3.1 at 5 °C the pressure of a 30/70 mixture would be just above 100 kPa (1 bar).With a minimum outside temperature of 20 °C the usable temperature differential wouldbe 20 – 5 = 15 °C. Entering the x-axis of Figure 10.2.4.1 at 15 °C temperaturedifferential and going to the next container size above 9 kg/h it turns out that a 1.75 toncontainer would be sufficient for the purpose.

Calculation Example 2: The customer has a 5 ton container and needs LPG at apressure of 0.5 bar. Can he run on 100% Butane if the coldest outside temperature is 19°C? How much LPG can be taken off?

According to Figure 10.2.3.1 the pressure of 100% Butane at 19 °C is about 90 kPa (0.9bar). The temperature at 50 kPa (0.5 bar) is 10 °C. So, the usable temperaturedifferential would be 9 °C. Entering the x-axis of Figure 10.2.4.1 at 9 °C shows thatButane in a 5 ton container could still vaporize Butane at a rate of about 12 kg/h.

0

5

10

15

20

25

0 5 10 15

Usable Temperature Differential, C

Vap

ori

zati

on

, kg

/hr

5 ton

3,5 ton

1,75 ton

1 ton

0,5 ton

Figure 10.2.4.1: Vaporization of LPG in 0.5 to 5 ton container (remaining container volume 25%)


10.2.4.2 Sizing Larger Containers to Satisfy Natural Vaporization Requirements

Often, containers larger than 25 tons are equipped with vaporizers. However, in tropicalclimates with almost constant temperatures customers may prefer to save the operationalcost of the vaporizer. When using LPG mixtures the designer must anticipate that thepressure in the container decreases as the liquid level drops. This is due to the fact thatPropane boils off first (see Figure 10.1.3-b). In Figure 10.2.4.2 the vaporizing capacityat a container level of 25% volume is shown for a 10 ton, a 25 ton and a 50 toncontainer, containing 100% Propane. The minimum pressure anticipated is 0.5 bar. Ifthe container contains more volume obviously the vaporization will be higher but this isnot taken into account since only the lower vaporization is of interest. Depending onvaporization requirements, such containers may need a refill once they reach 25%. Ifonly LPG at certain mixtures is available (and not pure Propane) the customer must beaware that the pressure in the containers drops as the container level decreases (seeFigure 10.1.3-b) since first the Propane components vaporize.

0

50

100

150

200

250

-20 0 20 40

Ambient Temperature, C

Vap

ori

zati

on

, kg

/hr

50 ton

25 ton

10 ton

Figure 10.2.4.2: Vaporization of Propane in 10 to 50 ton containers (at a container volume of 25%fill and a delivery pressure of 0.5 bar)

10.2.4.3 Sweating, Ice or Frost Formation

The formation of ice or frost will reduce the flow of heat into the liquid. Water presentin the air will condense onto the container’s outer surface when the surface temperatureis below the dew point of the air. The dew point temperature of the air varies with thedegree of humidity and the dry bulb temperature of the air.

When the surface temperature of the container is at or below 0 °C, any water on thesurface will freeze to frost or ice. Frost or ice on the container surface will act asinsulation and reduce the rate of heat transfer from the air to the liquid. Therefore, thewithdrawal of vapors from a container shall be limited to that volume which canvaporize without reducing the product and container shell temperatures to below thedew point whenever that temperature is below 0 °C.


Typically, in tropical climates ice or frost formation is not a problem. However,sweating can often be seen on containers. This is a sign of too high vapor load for thiscontainer. Often there are multiple container installations which were designed properlybut not operated properly. The users or fillers often leave only one container on line(which is then sweating). All containers must be opened such that the pressure in thesystem is as high as intended by the designer. Continuously withdrawing LPG vaporfrom an underground or mounded container is not recommended since the gas supplywould not last long and serious sweating on the container surface would acceleratecorrosion. Such container installations typically have vaporizers.

10.2.5 Enforced Vaporization by Means of Vaporizers

The alternative method to obtain vaporization of the LPG liquid uses separatevaporizers. The LPG liquid is piped directly from the bottom of the storage container tothe vaporizer. Heat required for vaporization is provided by electricity, steam, hot wateror water-glycol solution. Direct-fired vaporizers need to comply with all design andinstallation requirements in NFPA 58.

Vaporizers offer advantages even when the expense of providing the heat for thevaporization is considered. If the size of the container required for natural vaporizationis larger than the volume required for receipt and reserve volumes, it may be possible toinstall smaller storage capacity and save in total investment by using a vaporizer. Also,the gas from a vaporizer will match the characteristics of the entering liquid and will benearly uniform throughout the withdrawal of liquid from the storage container. Whilethe pressure during natural vaporization drops as the liquid level is lowered duringconsumption it will remain constant when using a vaporizer installation. One drawbackof the vaporizer installation is the fact that all components, also the Oily Residue willpass the vaporizer. Therefore provisions must be made (KO drum) to collect oilycondensate after the vaporizer.

Vaporizers shall be designed, constructed, installed and tested in accordance with arecognized and appropriate pressure container code, NFPA 58, 59 and manufacturerrecommendations. LPG vaporizers supplied shall be from reputable manufacturersapproved by ExxonMobil.

Pump

Vaporizer

Supply

Pump

Vaporizer

Supply

Direct Feed-out SystemSemi Feedback System

Vaporizer

Supply

Feedback SystemCommercial/Domestic Supply where Vaporizer is not Required

Supply

High Pressure Regulator

Low Pressure Regulator

Figure 10.2.5: Typical container and vaporizer installations


The Figure 10.2.5 “Typical container and vaporizer installation” illustrates containersupply installations schematically. The installation on the upper left side of the figureshows a typical Propane container. Because of its high vapor pressure, a vaporizer isnormally not required. A first stage high pressure regulator is usually installed in thecontainer dome. A second stage regulator is installed in the supply line immediatelybefore distribution to the consuming appliances. Two stage regulators are recommendedfor maximum operating reliability by virtue of more uniform gas pressure, and enhancedsafety in the event of a regulator failure.

The remaining three installations on Figure 10.1.3 show frequently used configurationsfor vaporizers and containers. These are typical of commercial and domestic Butanesupply systems. The liquid supply line shall preferably originate in a supply valve withdip tube located in the dome, rather than as shown (for simplicity). If there is a remotepossibility that the stored liquid temperature could fall as low as the –7 °C, the boilingpoint of liquid Butane, the arrangement shall be a “feedback” or “semi-feedback”system. Then, the container would not be subjected to a vacuum, which mightcompromise it structurally or affect gas supply pressure at appliances. The “direct feed-out” system would be suitable for Propane in situations where a vaporizer is needed toprovide comparatively large instantaneous gas capacity from limited storage. Need forthe indicated optional pump will depend on the relative elevations of the container andthe vaporizer, line pressure drop, and the operating pressure range in the container.When designing the system the minimum possible ambient temperatures have to betaken into account so that vapors are not subjected to dew point conditions (see Table10.2.5).

Press Propane Mix Mix Mix Mix Mix Mix Mix Mix Mix Butane

100 90/10 80/20 70/30 60/40 50/50 40/60 30/70 20/80 10/90 100

Bar (g) Dew Point in ºC

1.0 -43.0 -36.0 -30.0 -25.0 -20.0 -15.5 -12.0 -9.0 -6.0 -3.0 0.0

1.5 -33.5 -26.0 -18.5 -14.0 -9.5 -5.0 -1.5 2.0 5.0 8.0 11.0

2.0 -26.5 -19.0 -11.0 -6.0 -1.5 3.0 6.0 10.0 13.0 16.0 19.0

2.5 -20.0 -13.5 -5.0 0.0 4.5 9.0 12.0 16.0 19.0 22.6 25.5

3.0 -14.0 -6.0 0.0 5.5 10.0 14.0 17.5 21.5 24.5 28.0 31.0

3.5 -9.0 -2.0 4.6 9.5 14.0 19.0 22.0 26.0 29.5 33.0 36.0

4.0 -5.5 2.0 8.5 13.5 18.0 23.0 26.5 31.0 34.0 37.5 40.5

4.5 -2.0 5.5 12.0 17.5 22.0 27.0 30.0 34.5 38.0 41.5 45.0

5.0 1.0 9.0 15.5 21.0 25.5 30.0 34.0 38.0 42.0 45.5 49.0

6.0 7.0 16.10 21.5 27.0 32.0 36.5 40.5 45.0 49.0 52.5 56.5

7.0 12.0 20.0 27.0 32.5 37.5 42.0 46.5 51.0 55.0 59.0 62.5

8.0 17.0 25.0 31.5 37.0 42.5 47.0 52.0 56.0 61.0 65.0 68.0

9.0 22.0 29.5 36.0 42.0 47.0 52.0 57.0 61.0 65.0 69.5 73.0

10.0 26.0 33.5 40.0 46.0 51.5 56.0 61.5 65.5 69.0 73.5 78.0

Table 10.2.5: Dew points in different LPG mixtures in relation to pressure

Sizing of a vaporizer is not complicated. The basis figure to be known is the peakconsumption. For a single appliance this is the hourly consumption (kg/h). If the unit isstarted up daily add 50% for accommodating the additional consumption during start-up.If there are multiple consumers (multiple restaurant kitchens) consumption for allappliances shall be added up since the may all consume at the same time (lunch andevening peak hours). Choice of the vaporizer is optimum if two or three units wouldcover multiple consumers. Depending on required reliability one single consumer maybe adequately served by one single vaporizer. It shall be borne in mind that vaporizerinstallations typically have an emergency back-up with an natural vaporization line


directly from the container. The use of a vaporizer is indispensable forunderground/mounded container installations

It is important that there be a clear understanding as to where the designer'sresponsibilities end in the system leading to the point of end use. Generally, thepoint of demarcation is at the outlet of the high pressure regulator for non-vaporizersystems, or at the container's liquid and vapor connections in the case of vaporizersystems; however, this demarcation shall be confirmed formally in a written documentexecuted by supplier and customer.

10.2.5.1 Installations of Vaporizers

This section of minimum standards covers indirect fired LPG vaporizers to be installedin end user facilities using ExxonMobil supplied LPG. Local standards shall befollowed. In the absence of a local standard or if the local standard is less stringent, thefollowing minimum standard shall apply.

Vaporizer houses shall not have drains to sewers or sump pits. A strainer shall beinstalled in the liquid inlet to the vaporizer. A knockout pot shall be installed at theoutlet of the vaporizer to remove heavy hydrocarbons. Vaporizers shall be located inaccordance with the minimum distances from other equipment in accordance with Table10.2.5.1.

ExposureMinimum Distance

Required (m)

Aboveground LPG Container 3

Relief Valve of Underground LPG Container 3

Point of Transfer (Truck) 3

Nearest Important Buildings or Adj. Property Line 1.5

Table 10.2.5.1: Minimum Distance Required for LPG Vaporizers

10.2.6 Installation of Containers

10.2.6.1 Aboveground Installation

Aboveground containers shall be placed on concrete foundations. If the location couldbe flooded the container shall be fixed and the foundation shall provide adequateanchors or weighting such that the container would not float, even if empty. Productidentification and safety signs shall be installed at the container. The “NO SMOKING”sign shall be clearly legible at the safety distance applicable and from points of access tothe storage site. Grounding requirements are defined in “Grounding Connections forTanks” in Chapter 3. Large customer tanks (>10 tons) need two grounding connections,smaller tanks may have only one. A conductive lug, free of rust or color will serve as anattachment point for the truck bonding cable.

10.2.6.2 Underground Installation

Underground containers shall be protected from superimposed loads, e.g. vehiculartraffic loads, either by fencing or protecting them with a reinforced concrete slab orother load-bearing means. If the area for the container is not fenced off, the containermanhole cover and container fittings shall be protected against damage and tampering.Mounded containers shall be protected either by fencing off the area around the moundor by other adequate means.


Underground containers shall be surrounded by sand that is not aggressive in terms ofcorrosion. Minimum coverage on top is 0.3 m of sand. A concrete slab may be added.If traffic moves over the slab, no load shall be conveyed to the tank. Mounded tanksshall be covered similar to the requirements (0.9 m) mentioned in Chapter 3. Forsmaller tanks the cover may be less provided the cover cannot be eroded by rain orfirewater.

Underground installation greatly reduces fire risk and security problems. Where spacingis tight or not available, underground installation may be chosen.

Figure 10.2.6.1: Typical container

Underground containers and their fittings, valves, pressure relief valves, gauging devicesand regulators shall be adequately protected against corrosion. Proper drainage shall beprovided for the housing dome to eliminate accumulation of water. The followingguidelines shall be observed when installing underground containers:

1. Only ASME containers constructed for underground service and markedaccordingly shall be installed underground.

2. All fittings, including any plugged openings, are plugged tight and free fromleaks. Containers may be pressurized with air or LP-gas vapor to makecertain there are no leaks.

3. The container is purged in accordance with generally accepted industrypractices. (See NPGA Safety Bulletin 133 and the LPG Safe OperationsGuide).

4. Rust, dirt and other foreign matter have been cleaned from the surface of thecontainer, and the container has been visually inspected for gouges, dents, pitsor other defects.

5. The external surface of underground tanks shall be Grit blasted to SA 2½standard or chemically treated and coated with an adequate paint system withspecialist advice. Shop applied coatings are preferred, but field applicationsare also acceptable. Irrespective of type and application method of coatings, aholiday test on the coating shall be carried out immediately prior toinstallation on site.

6. All points of contact shall be protected while the container is being loadedand transported. Damage to the protective coating shall be prevented.

7. All underground containers and piping shall be cathodically protected unlesswritten tests of soil samples indicate that it is not required. Failure to providecathodic protection can cause hidden corrosion and leaks as well asweakening of the tank wall over time.


8. The bottom of the hole shall be level and free of rock. If rocks are present, a150 mm bed of sand shall be used. For completely buried tanks, the holeshall be dug to a proper depth to provide for the housing dome to extend farenough above ground level to prevent entrance of water (50 to 150 mm iscommon practice), allowing for grading away from the dome.

Figure 10.2.6.2: Underground installation

9. The top of the container shall be at least 150 mm below grade, unless thecontainer might be subject to abrasive action of physical damage fromvehicular traffic or from other causes such as in LP-gas service stations. Inthis case, it shall be placed not less than 600 mm below grade or equivalentprotection shall be otherwise provided (such as by the use of a concrete slab)to prevent imposing the weight of a loaded vehicle directly on the containershell (NFPA 58- Par.3.2.4.8 a).

10. For mounded systems, the same general procedure shall be followed, exceptthat the housing dome would be above ground, and the above ground surfacearea of the tank shall be covered with at least 300 mm of earth or sand.

11. In the flood plain and high water level areas, provisions shall be made toadequately secure the container to the ground, or to a concrete slab, to preventflotation. Local soil conditions may require other provisions to allow properdrainage from within the housing dome.

12. Precautions shall be taken to prevent damage to the tank coating whilelowering the tank into the hole and while back filling. Any damage to thecoating shall be carefully repaired. Any small unprotected areas of a coated,wrapped and cathodically protected tank and piping system will be subject toconcentrated corrosive action resulting in the possibility of severe metal lossand ultimately a leak. A conductive lug, free of rust or color will serve as anattachment point for the truck bonding cable.

13. Back fill shall be free from rocks or similar abrasives. Clean, dry sand ispreferred. See Figure 10.2.6.2.

14. Because the installed container should be adequately anchored if flotation is apossibility and shall be leak tight with a slight positive nitrogen pressure, itcould be maintained empty. However, it is preferred that the container befilled immediately after installation is complete.

15. Where underground containers are installed in locations subject to infrequentvehicular movement, sufficient provision shall be made to prevent the weightof such vehicular traffic from damaging the container or appurtenances. Thetop of the tank shall be at least 600 mm below grade or be protected by aconcrete slab or equivalent.


16. Barriers shall be provided to protect the housing dome, relief valve dischargestacks, filling risers and any appurtenances that extend above grade level.

17. Product identification and safety signs shall be installed adjacent to thehousing dome and filling risers. The “NO SMOKING” sign shall be clearlylegible at the safety distance applicable and from points of access to thestorage site.

18. For underground tanks that are embedded in watertight concrete casings andsand-bed, observation wells with PVC casing of at least diameter 50 mm with0.5 mm slots shall be installed. Observation wells shall be installed at twodiagonal corners of the underground tank(s) and shall extend to a depth of600 mm below the bottom of the tank(s).

10.2.7 Container Fittings and Piping

Figure10.2.7: Typical fittings needed on containers

Containers, regardless of size, shall be equipped with the following:

1. pressure relief valve (PRV).

2. fixed level dip tube.

3. filling connection.

4. level indicator.

5. pressure gauge.

6. drain valve.

7. inspection nozzle.

8. multivalve.

9. bottom liquid off take (optional).

10. vapor offtake connection.

11. Regulator.

All directly connected appurtenances shall be closely grouped on the top center of thehorizontal container shell, and protected against mechanical damage by a steel domewith a hinged cover. On larger containers all the nozzle connections may be installed onthe manhole cover if possible. The pressure relief valve shall not be installed under thedome, as this would interfere with discharge.


Piping requirements for customer installations vary widely from country to country.Therefore, it is recommended that local codes and requirements be followed. If thereare no local codes, NFPA 58 Section 3.2 shall be followed.

10.2.8 Container Valves and Accessories

10.2.8.1 Filler Valve

For new fill line installations, an isolation valve (preferably a ball valve) shall be locatedat the tank with a single back check filler valve adjacent to it. When it is necessary tolocate the filling connection at a point remote from the filler valve, the fillingconnection shall be fitted with a single back check filler valve. A positive shutoff valvecan be installed immediately behind the single back check filler valve in order toprovide maximum safety. Double back check filler valves shall not be used in place ofan isolation valve and single check valve in new installations.

Figure 10.2.8.1: Double back check filler valve

10.2.8.2 Vapor Service Valve

A vapor service valve may be provided as a separate unit or may be incorporated aspart of the combination valve. The valve shall preferably incorporate a back seatingfeature. An excess flow check valve shall not be incorporated with the inlet of thedevice, unless local regulations ask for it. With an excess flow check valve installedthere is a possibility of an interruption in service to gas-consuming devices due to highdemand. This could cause a flameout followed by resumption of flow when local codesdo not require safety shutdowns on loss of gas supply.

10.2.8.3 Liquid Service Valve

An internal positive shutoff valve shall be installed for liquid off take service from thebottom of the container. For liquid off take service from the top of the container, anexcess flow check valve shall be installed within the container, and a positive shutoffvalve installed immediately adjacent.

All containers 475 liters or more in capacity shall be fitted with a connection for thepurpose of emptying the container of liquid. This requirement may be satisfied by theuse of a bottom mounted lock type excess flow check valve installed within thecontainer, which shall normally be plugged. Removal of the plug and the installation ofa nipple or adapter to which a positive shutoff device is attached can activate theconnection for the withdrawal of liquid. In order to ensure the proper procedure in


activating the valve, an instruction tag shall be attached to the plugged excess flowcheck valve.

10.2.8.4 Excess Flow Check Valve

In domestic storage containers, excess flow check valves shall be included as integralparts of vapor return valves. They shall also be installed either as an integral part of theliquid service shutoff valve or within the liquid outlet of the container with a separateshutoff valve installed immediately adjacent. Excess flow valves permit the flow ofliquid or vapor in either direction. Excess flow is controlled in only one direction (thedirection of the arrow stamped in the valve). If flow in that direction exceeds apredetermined rate the valve automatically closes.

Figure 10.2.8.4: Excess flow check valve

10.2.8.5 Liquid Level Measurement

Visible Float Gauge: A visible float gauge is the first choice for level measurement incustomer containers. It shall be installed under the valve guard or hood for protection.The liquid level can be observed without discharging LPG vapor or liquid, however,accuracy may not be always adequate.

Rotary Gauge: A rotary gauge may be used in customer containers if there is no hazardin connection with the LPG discharge necessary for the measurement.

Fixed Level Gauge: Each container shall be fitted with a fixed liquid level gauge. Thegauge shall be fixed to indicate an 85% filling level.

Slip Tube Gauge: A slip tube gauge is not recommended on containers of 10,000 litersor lower capacity. A slip tube gauge shall only be installed when there is a strong needfor greater measurement accuracy than float gauge or rotary gauge can provide, andwhen electric power is unavailable to operate a servo-gauge or radar gauge which wasdiscussed in Chapter 3.

10.2.8.6 Pressure Indicator

Each container in excess of 10,000 liters capacity shall be fitted with a pressure indicator(PI), which may be part of a combination valve. In containers 10,000 or less in capacity,a pressure indicator is an optional feature; if used, there shall be a shutoff valve betweenthe container and the PI.


10.2.8.7 Regulators

All regulators shall be designed and installed in accordance with NFPA 58 orequivalent. Regulators for outdoor installations shall be designed, installed, or protectedso their operation will not be affected by freezing, sleet, snow, ice, mud, or debris. Thisprotection is permitted to be integral part of the regulator. All materials used toconstruct the regulators shall be resistant to the action of LPG under service condition.

Regulator shall be designed for outdoor installation. Regulators shall be incorporatedwith an integral relief valve. or shall have a separate relief valve to limit the regulatoroutlet pressure. An integral or separate overpressure shutoff device shall be provided toshutoff the flow of LPG vapor when the outlet pressure of the regulator reaches theoverpressure limits. Regulators with an overpressure protection device and a ratedcapacity of more than 147 kW (10.6 kg Propane per hour) shall be permitted to be usedin two-stage systems where the second-stage regulator incorporates an integral orseparate overpressure protection device.

Figure 10.2.8.5: Visible float gauge

Integral two-stage regulators shall be provided with a means to determine the outletpressure of the high pressure regulator portion of the integral two-stage regulator.Exception: Automatic changeover regulators shall be exempt from this requirement.Integral two-stage regulators shall not incorporate an integral pressure relief valve in thehigh pressure regulator portion of the unit. Regulators shall be designed so as to drainall condensate from the regulator spring case when the vent is directed down vertically.

At low flow rates, a single stage system may be suitable. Check with manufacturers. Athigher flow rates it is typical to use two stage pressure regulation. The first regulatorreduces the pressure to about 1.5 bar gauge (150 kPa) and the second regulation steplowers it to about 30 millibar gauge (3 kPa). For multiple tank installations only one set


of regulators shall be installed as opposed to individual sets on each tank. This is toprevent “pressure cycling” of the system, which would be caused by slight differences inregulator adjustment or different heat input or vaporization.

Aluminum or zinc is permitted for approved regulators. Zinc used for regulators shallcomply with ASTM B86, specification for zinc-alloy die casting, or equivalentstandards. Nonmetallic materials shall not be used for upper or lower casings ofregulators. Regulators shall have the manufacture date (MM/YY) permanently markedon the body.

First-stage and second stage regulators shall be installed outside of buildings. The firststage regulator shall be as close to the storage as practical. First-stage or high-pressureregulators shall be directly attached or attached by flexible connectors to the vaporservice valve of a container or to a vaporizer outlet. The regulators is permitted to beinstalled with flexibility in the interconnecting piping of manifolded containers orvaporizers.

Figure 10.2.8.7: Container regulator

The point of discharge from the required pressure relief device on regulating equipmentinstalled outside of buildings in fixed piping systems shall be located as follows:

1. More than 1 meter horizontally away from any building opening below thelevel of discharge.

2. More than 1.5 meter in all directions from any source of ignition, openinginto direct-vent appliances or mechanical ventilation air intakes.

3. Not beneath any building unless the space is well ventilated.

Installation of the regulator shall minimize accumulation of LPG condensate. Regulatorinlet piping shall be cleaned at the time when the regulator is installed as foreignparticles that entered the regulator may cause it to malfunction. The pressure regulatorsshall be installed in location where tampering of the regulator by unauthorized personnelis prevented.

10.2.8.8 Multivalve

The multivalve combines the double back check filler valve, vapor equalizing valve withexcess flow, pressure relief valve with protective cap and chain, service line shutoff


valve, fixed liquid level gauge, float gauge opening and plugged pressure gauge openingin one unit. Using various available combination valves that combine all of the fittingsrequired can reduce the number of shell penetrations. This Single Outlet System createsa higher and more congested equipment profile within the dome, and is likely to increasemaintenance time. The disadvantages should be weighed against the reduction in shellpenetration achieved.

10.2.8.9 Pressure Relief Valves

All LPG tanks, vaporizers, positive displacement pumps’ discharge shall be providedwith one or more spring loaded or pilot operated pressure relief valves. Sizing of thevalves will depend on the container surface and is described under: “Pressure Relief inMarketing Terminals” in Chapter 3.

Suitable thermal relief valves shall be provided on liquid lines that can be blockedbetween two shutoff valves. Other equipment that can be blocked between shutoffvalves shall be provided with protection from overpressure due to thermal expansion ofthe liquid.

Figure 10.2.8.8: Multivalve for vapor and liquid withdrawal

The pressure relief system shall be protected from the closure of any block valvesinstalled between the tank and the pressure relief valve or between the pressure reliefvalve and its discharge vent outlet. This protection may be achieved by one of thefollowing procedures:

1. Installing the pressure relief valve without block valves.

2. Providing excess pressure relief valve capacity with multiway valves,interlocked valves, or sealed block valves arranged so that isolating onepressure relief valve will not reduce the capacity of the system to below therequired relieving capacity.

3. Locking or sealing the block valves open with a lock. The key must be inpossession of an authorized person.

Multiple pressure relief valves can cover total required relief valve capacity. These shallbe installed with a manifold that includes provision for selectively closing off anyparticular relief valve to permit removal for inspection while the remaining valves


provide for the discharge capacity required for the container. Alternatively, Multiportrelief valve may be used.

Weep holes on the bottom of pressure relief valve stacks shall be equipped with a 90degree elbow to deflect a discharging vapor stream away from any container shell orpiping.

Discharge vents shall lead to the open air or to a flare system. Positive design andoperational steps shall be taken to prevent the discharge of liquid LPG from atmosphericvents. Such steps include automatic shutdown of filling operations prior to overfilling.Discharge vents shall be protected against mechanical damage. If discharge ventsrelieve to the atmosphere, they shall be designed to prevent entry of moisture andcondensate. This design may be accomplished by the use of loose-fitting rain caps anddrains. Drains shall be installed so that the discharge will not impinge on the tank oradjoining tanks, piping, equipment, and other structures. Discharge vents shallterminate a minimum of 3.0 m above grade with a final discharge vertically upward.Discharge shall be to an area that has the following characteristics:

1. The area prevents flame impingement on tanks, piping, equipment, and otherstructures.

2. The area prevents vapor entry into enclosed spaces.

3. The area is above the heads of any personnel on the tank, adjacent tanks,stairs, platforms, or the ground.

Pressure relief valves on equipment within buildings shall be piped to a point outside thebuildings and shall discharge vertically upwards.

Pilot operated pressure relief valves shall be designed so that the main valve will openautomatically and protect the equipment if the pilot valve fails. Pilot operated valvesshall be provided with a backflow preventer.

10.2.8.10 PRV Testing Requirements

Pressure relief valves in LPG service normally operate in a clean, non-corrosiveenvironment. Furthermore, PRVs are constructed of corrosion resistant materials, andare installed so as to be protected against the weather. Because of added odorization, aleak around a PRV is likely to be discovered during inspection. Pressure relief valves inLPG service have shown a good reliability over the years. However, since nomechanical device can be expected to remain in operative condition indefinitely, it isrecommended that the PRV be replaced when the container is tested/reconditioned, ormore frequently if required by local regulations.

Safety in LPG Design AUTOMOTIVE LPG 11-1

11 AUTOMOTIVE LPG

11.1 Automotive LPG Stations

11.1.1 Design of Automotive LPG Equipment

This section sets out the minimum design standards for the LPG facilities in a servicestation for the refueling of motor vehicles running on LPG. The general minimumstandards for bulk installations and for different components as laid down in the othersections shall apply except where specifically modified by this section. Local standardsshall be followed. In the absence of a local standard or if the local standard is lessstringent, the following minimum standard shall apply.

LPG tanks at Retail Outlet Stations may be mounded or buried to eliminate the risk of aBLEVE. Furthermore, there are limited requirements with regard to minimum distancesto buildings in the neighborhood. A mounded or buried system will require an internal,submerged pump. External inspection for corrosion damage is not easy, cathodicprotection is recommended.

Since there is no formal formula to calculate the LPG tank capacity the following shouldbe considered. The frequency of unloading operations shall be minimized since eachadditional unloading operation constitutes an increased risk. The tank shall be sized toallow for a weekly supply pattern, e.g. 2% of annual sales volume.

Aboveground tanks shall be installed with sufficient liquid head as required by thedesign of the pump. Underground tanks situated below driveway shall be adequatelyprotected by reinforced concrete slabs or chamber designed by a qualified structuralengineer. The manhole cover and the tank fittings open to access from the top shall beprotected against damage and tampering.

For underground tanks, submersible pumps of a reputable make specifically approvedby ExxonMobil shall be installed. Installation shall be in strict accordance with themanufacturer’s instructions. Submersible pumps must be installed in barrels such thatthe pump unit can be taken out for servicing without having to gas free the whole tank.

Following are international Codes on Automotive LPG:

1. Autogas, CPR 8-1, CPR 8-1s, Netherlands (in Dutch).

2. The Australian Standard 3509 “LP Gas Fuel Vessels for Automotive Use.”

11.1.1.1 Remote Operated Emergency Block Valves

The Emergency Shutdown System (ESS) shall be designed and executed as a fail safesystem. All valves with a diameter larger than 1.6 mm shall be part of the Emergency

11-2 AUTOMOTIVE LPG Safety in LPG Design

Shutdown System. There are 3 types of motive energy to operate the Emergency BlockValves: Hydraulic, Air and LPG vapor. The valve shall be a fail safe, spring loaded,quarter turn valve meeting API 607 fire-resistant testing.

1. Systems driven by LPG vapor: This type of motive energy isrecommended. It has the advantages of sufficient vapor always beingavailable and a relatively simple system layout.

2. Air driven system: This type of motive energy is recommended if reliable airsupply is readily available. Air supply should be separate from air used forpressuring tires since the latter may be emptied by users. Also air forEmergency Block Valves may need drying since condensed water can causeinternal corrosion in the valve actuators.

Hydraulic system: This type of motive energy is not recommended since even smallleaks influence its reliability.

Emergency shutoff valves shall be installed as close as practicable to the liquid andvapor inlet/outlet connections on the tank, except where a back flow check valve isinstalled and except on the drain connection. A master emergency switch shall beprovided to shut off the power to the pumps and dispensers and to close off all theemergency shutoff valves installed on the tank connections and at the dispensers. Thisemergency switch shall be so positioned as to be readily visible to the public and withineasy reach for quick operation in cases of emergency. It shall be clearly identified bysignage.

11.1.1.2 Layout

LPG tanks shall be located such that the minimum separation distances shown in Table11.1.1.2-a are not exceeded.

Storage Minimum Separation Distance (meters)

From Site Boundary, Buildings,Fixed Sources of Ignition, etc. Between Tanks

Underground

WaterCapacity ofTank ( m3 )

AboveGround

BuriedPortion

Valve Assembly,Filling Point, etc.Aboveground

AboveGround

UnderGround

0.5 to 2.5 3 3 3 1 1.5

2.5 to 10 7.5 3 7.5 1 1.5

10 to 150 7.5 3 7.5 1.5 1.5

Table 11.1.1.2-a: Minimum separation distances for LPG tanks

Separation distances of LPG facilities from each other and from other features of theservice station shall not be less than that given in Table 11.1.1.2-b. LPG dispensers maybe installed adjacent to other LPG, petrol or Diesel fuel dispensers as long as they are offlameproof construction.

Pumps other than submersible pumps shall be installed as close to the tank liquid outletvalve as possible, but not underneath an aboveground LPG tank.


Safety relief valves shall be fitted with vents with outlets at least 1.8 m above the top ofthe tank and not less than 3m above ground level. The vent outlets shall be at least 4.5m away from the property line or any fixed source of ignition.

LPG dispensing facilities shall not be permitted in service stations built underneathbuildings.

LPG TankLPG

Tank FillConn.

LPGPump

LPGDispen

ser

M Vehi.LPG FillConn.

LPG Tank 1diameter

Nil Not belowTK

3 m 3 m

LPG Tank FillConnection

Nil - Nil 3 m 3 m

LPG Pump Not belowTK

Nil - Nil Nil

LPG Dispenser 3 m 3 m Nil - Nil

Motor Vehicle LPGFill Connection

3 m 3 m Nil Nil -

Undergr. petrol TK,manhl. or fill conn.

1.5 m 3 m 3 m 3 m 3 m

Aboveground petroltank

6 m 6 m 6 m 6 m 6 m

Petrol tank vent 3 m 3 m 3 m 3 m 3 m

Flameproof fuelpump / dispenser

3 m 3 m Nil Nil Nil

Non-flameproof fuelpump / dispenser

As Table 11.1.1.2-afor fix. source of ign.

4.5 m 4.5 m 4.5 m

Parked cars 1.5 m 3 m 1.5 m 1.5 m 1.5 m

Site bound. buildgs,fix. sources of ign.

As Table 11.1.1.2-a 4.5 m 4.5 m 4.5 m

Table 11.1.1.2-b: Separation distances of LPG facilities from each other and from other features ofthe service station

11.1.1.3 Overfill Protection

All tanks shall be equipped with an overfill protection device. A variety of overfillprotection devices are available. The available systems range from high-tech electroniccapillary measuring systems to simple mechanical systems with a floater or amechanical meter.

When the maximum filling level is reached, the system shall transmit a signal to thefilling valve and then close the valve within a predetermined time lapse (approx. 15seconds).

11.1.1.4 Piping System

To avoid excessive pressure in the liquid lines, a thermal relieve valve shall be installedbetween two block valves.


Excess flow valves or non-return valves shall be installed in all LPG lines from/to thetank. The type of valve to be used depends on the flow direction of the LPG. Installexcess flow valves in both underground liquid and vapor lines at the dispenser.

A vapor release valve shall be installed at the filling point to enable the tank truck driverto release the vapor in the filling hose before and after the filling operation. Themaximum quantity to be released is 1 kg. The quantity sets limits for the size/length ofthe filling hose. The liquid capacity of the filling line shall not exceed a volume of 200liters.

Underground pipes conveying liquid LPG shall be either:

1. Installed in a concrete lined duct which is subsequently filled with clean sand,or

2. Buried at a depth below ground of at least 1 m. The route shall be indicatedby markers on the ground surface.

Underground LPG vapor or liquid pipes shall not be embedded in concrete.

Figure 11.1.1: Piping and instrument diagram of automotive LPG installation

11.1.1.5 Dispensing Equipment

The dispensing system shall consist of the following essential components:

1. A vapor separator to separate vapor from the liquid before metering.

2. A meter to measure the volume of liquid delivered.


3. A differential valve to prevent the formation of vapor beyond the vaporseparator and in the meter.

4. A flexible hose and filling nozzle. An excess flow valve as near as practicablebefore the inlet of the flexible hose.

5. Hydrostatic relief valves.

6. A pump switch to control any remotely located electric pump. Securityfeatures to prevent unauthorized use or tampering.

7. A driveaway protection coupling on the hose.

8. An emergency shutoff valve at the base of the dispenser that will close off theliquid supply upon being hit, in addition to the normal means of closure as anemergency shutoff valve.

The driveaway protection “beak-away” coupling shall be shall be able to disconnect inthe event of a force of no greater than 600 N. It shall be capable of being re-assembledwithout the need for draining the hose, the use of special tools, or the replacement ofparts.

The filling nozzle shall be of the low emission transfer type. It shall mate with thefilling connection on the receiving container on the vehicle such that, when they aredisconnected after refilling, no more than 4 milliliters (cm3) of liquid shall be released tothe atmosphere. It shall not be possible to discharge LPG unless connected to a fillconnection on the vehicle. It shall not have any latching device.

11.1.1.6 Hose Requirements

All hoses for tank filling shall be approved for LPG services. The responsibility for thefilling hose stays with the transportation company.

The flexible delivery hose (dispenser) shall be manufactured to a recognized standardsuch as BS 4089, AS 1869, UL 21 or equivalent. It shall be of stainless steel wire braidor nylon reinforced synthetic rubber and shall have a design working pressure of not lessthan 25 bar and a burst pressure of not less than 100 bar.

The length of a delivery hose may vary from 3 to 5 meters. In the delivery hose a“break away” coupling shall be installed. It is important to follow manufacturers’installation requirements for the break away installation. It is recommended to performan initial test to ensure that the break away connection works as installed. The deliveryhose shall be so secured on the dispenser that it cannot lie on the ground with potentialsof being run over by vehicles. Damaged hoses shall be replaced. Authorized contractorfirm may only carry out replacement.

11.1.1.7 Bulk Filling System

Prior to starting any discharge operation, an earth connection shall be made between thetank truck and the LPG installation at the Service Station. The earth connection shall beindependent of the hose connection. A 24 volt signal from the tank truck will open thefilling valve. When the maximum filling level is reached this 24 Volt signal will beinterrupted by the overfill protection system and will close the filling valve. This meansthat the filling valve is always in a closed position during idle times. The EmergencyShutdown System (ESS) on the tank truck is part of this 24 volt signal system.Activating the push button of the truck ESS will also close the filling valve. In caseswhere the bulk truck cannot come close to the LPG tank, a remote unloading point maybe installed.

11.1.1.8 Fire Protection

Fire protection shall be designed in accordance local authority which has to be consultedfor final approval.


Warning signs with the words such as “STOP MOTOR”, “NO SMOKING”,“FLAMMABLE GAS” shall be posted at all LPG handling areas. The locations of thesigns shall be determined by local conditions, but the lettering shall be large enough tobe visible and legible from each point of transfer.

Emergency controls, if provided, shall be conspicuously marked, and the controls shallbe located so as to be readily accessible in emergencies.

At least one 20 mm hose reel shall be provided. Water supply shall be at least fromhydrants not more than 100 m away. Firewater piping system shall be constructed ofmetallic material. Plastic material is not allowed. Fire-fighting foam shall not be usedfor LPG fire.

At least one 9 kg portable dry chemical with a B: C rating fire extinguisher shall beavailable at strategic locations around the station premises. Minimum shall be one ateach LPG dispenser and one in the sales office attendants’ kiosk. These are in additionto whatever is required for the fuel dispensers and fuel storage at the same station.

Figure 11.1.1.7: Remote unloading point

11.1.1.9 Crash Barriers

The filling point shall be protected by means of crash barriers. The crash barriers can bemade of steel pipes filled with concrete. The minimum diameter of the steel pipes is 100mm and the pipes shall extend at least 0.6 m above ground level. The customerdispenser shall also be protected by means of crash barriers. Valves and Instruments onAutomotive LPG Tank

11.1.1.10 Security Around Tank

The LPG storage installation shall be fenced in. The minimum distance from the fenceto the LPG installation is 3 meters. The fence shall be equipped with two exit doors, thedoors shall be placed opposite of each other. The doors shall be kept closed and only beopened by authorized persons. The area inside the fence and at a suitable distance from


LPG tank shall be kept free of vegetation. The following text or pictograms shall beplaced on the fence:

Entry by unauthorizedpersons is prohibited.Smoking & open fire

prohibited

Safety in LPG Design LPG PROPERTIES 12-1

12 LPG PROPERTIES

12.1 Product PropertiesLPG consists of light hydrocarbons, including Propane, Propylene, normal Butane,Isobutane, and Butylenes. The most common LPG components are Propane and normalButane or mixtures of these. At ambient temperature and atmospheric pressure, LPG isa gas. It can be liquefied under moderate pressure or by cooling to temperatures belowits atmospheric boiling point, but will readily vaporize upon release to normalatmospheric conditions. This property permits LPG to be transported as a liquid, andused in the vapor form.

PropertyCommercial

PropaneCommercial

Butane

Molecular Weight 44 58

Liquid Density, (kg/m3), 15 °C @ Vaporpressure

505 580

Vapor Density, (kg/m3), 15 °C @ Vaporpressure

15.3 5.62

Liquid Specific Volume, (m3/ton), 15 °C @Vapor pressure

1.96 1.73

Vapor Specific Volume, (m3/ton), 15 °C @Vapor pressure

65.4 178

Vapor Density, (kg/m3), 15 °C @ Atmosphericpressure

2.0 2.6

Vapor Specific Volume, (m3/ton), 15 °C @Atmospheric press.

500 400

Liquid Specific Gravity 15/15 °C 0.510 0.575

Specific gravity of vapor (air = 1.0) 1.5 2.0

Atmospheric boiling point, (°C ), @ Atmosphericpressure

- 42 - 2

Table 12.1-a: Properties of Commercial Propane and Commercial Butane

12-2 LPG PROPERTIES Safety in LPG Design

PropertyCommercial

PropaneCommercial

Butane

Ignition energy, (mJ) 0.1 0.1

Flash point, (°C ) -104 -60

Auto-ignition temperature range, (°C) 450 - 580 420 - 550

Flame temperature in air, (°C ) 1970 1975

Combustion air, (m3/m3 gas) @ stochiometric 24 30

Lower flammable limit(LFL), % in air 2.0 1.8

Upper flammable limit(UFL), % in air 10 9

Motor Octane Number 100 95

Expansion factor at transition from liquid tovapor at 15 °C

270 240

Cubic Expansion Coefficient of Liquid per °C 0.003 0.002

Table 12.1-b: Properties of Commercial Propane and Commercial Butane

Common properties for Propane, Isobutane and Normal-Butane are shown in Table12.1a and 12.1-b. Selected properties as a function of temperature for Propane,Isobutane and Normal Butane, and commercial mixtures are shown in Figures 12.1-a,-e.

Figure 12.1-a: Vapor Pressures for Butane-Propane Mixtures


400

450

500

550

600

650

-40 -30 -20 -10 0 10 20 30 40 50 60

Temperature, C

Den

sity

, kg

/m3

N - Butane

ISO - Butane

Propane

Figure 12.1-b: Liquid density at vapor pressure as a function of temperature

1.50

1.70

1.90

2.10

2.30

2.50

2.70

2.90

-40 -30 -20 -10 0 10 20 30 40 50 60

Temperature, C

Den

sity

, kg

/m3

Commercial

Comm. Butane

Figure 12.1-c: Vapor density at atmospheric pressure as a function of temperature


0

10

20

30

40

50

60

-40 -30 -20 -10 0 10 20 30 40 50 60

Temperature, C

Den

sity

, kg

/m3

Propane

N - Butane

ISO - Butane

Figure 12.1-d: Vapor density at saturation pressure as a function of temperature

250

270

290

310

330

350

370

390

410

430

450

1 3 5 7 9 11 13 15 17

Vapor Pressure, bar

Lat

ent

Hea

t, k

J/kg

Propane

Butane

Figure 12.1-e: Latent heat of vaporization


12.2 LPG HazardsLPG produces certain hazards unique to this fuel. Concentrated LPG vapor is heavierthan air and tends to stay close to the ground. It drifts downwind and collects in lowspots, and disperses less readily than lighter-than-air gases. Since LPG is mostly storedunder pressure and vaporizes readily, it is difficult to control leaks once they occur.Once LPG is released, it mixes with air to form a flammable mixture. Leakage of asmall amount of liquid produces a much larger volume of vapor, as shown in Table 12.2.This makes it important to prevent leaks, keep ignition sources at a safe distance, anddisperse vapor from leaks before it is ignited.

Property Propane Butane

Liquid Volume 1 1

Resultant VaporVolume 270 230

Volume ofFlammable Mixtureat LFL

12600 12200

Table 12.2: Vapor volumes for Propane and Butane

A leak ignited near its source produces a jet flame, which can endanger nearbyequipment and enlarge the incident. If ignition is delayed and the release is large,enough flammable mixture can accumulate to produce a large Vapor Cloud Explosion(VCE).

The magnitude of a VCE incident depends on the amount of LPG involved. It has beenconservatively estimated that release of as little as 500 kg of LPG may produceconditions under which a VCE might occur. Blast damage from a large VCE can extendbeyond 200 meters and is almost certain to cause secondary effects as tank fragmentsimpact additional piping and equipment.

1

10

100

1000

0,001 0,01 0,1 1 10 100 1000

Mass in Tank, tons

Fir

ebal

l dia

met

er, m

Figure 12.2-a: BLEVE fireball diameter


Potentially more serious is a Boiling Liquid Expanding Vapor Cloud Explosion(BLEVE). Such an event typically starts with a fire near an LPG pressure storage ortransportation tank. The fire heats the tank contents and the internal pressure rises. Ifthere is direct flame impingement on the top (vapor) part of the tank at the initial stageof the fire, BLEVE may happen before the PRV activates. If the tank is still intact, thepressure relief valve may open and continue to discharge.

The lower part of the tank is “wetted” and cooled by boiling product inside, but themetal temperature of the upper “dry” area rises. The “dry” steel may be overheated andweakened until it can no longer withstand the internal pressure, and the tank failscatastrophically. Depending on conditions, failure of a tank may happen from fiveminutes to one hour after the fire begins.

If the tank fails, the boiling LPG in the tank is released resulting in massivevaporization. The vapors will ignite immediately, though there is little or no mixingwith air, and burning occurs at the surface in the form of a large fireball. The size of thefireball can be taken from Figure 12.2-a “BLEVE fireball diameter” above. A 1 kgdisposable LPG container will create a fireball diameter of about 5 m diameter, whereasa 1000 ton sphere BLEVE will result in a fireball of 500 m diameter.

Heat radiation from the fireball will cause serious damage within a sizable radius.Wood and other combustible items will ignite spontaneously at considerable distances.

The damage produced by the blast wave of a BLEVE is less serious because its radius isusually smaller than that for radiant heat from the fireball. Another hazard is fragmentsproduced from the tank failure. This is most serious with horizontal tanks, which tend tobehave as rockets and have traveled over 1000 meters in actual incidents (Mexico City).

A BLEVE is possible for a pressurized container of any size. Failure of a large tank willbe destructive for hundreds of meters. Even a small domestic cylinder can BLEVE;initially, the affected area is limited, but other nearby cylinders and facilities are likelyto become involved. The probability of a BLEVE or VCE is very low, but because ofthe potential severity, it is important to provide sufficient fire protection.

In addition to fire and explosion hazards, LPG also presents personnel hazards includingthe potential for asphyxiation and cold burns. These are described in the LPG SafeOperations Guidelines manual.

0,01

0,1

1

10

100

1 10 100

Pipe Diameter, mm

Rel

ease

Rat

e, k

g/s

Liquid

Vapor

Figure 12.2-b: Propane release rates from guillotine pipe failure


1

10

100

1000

1 10 100

Release Rate, kg/s

Dis

tan

ce, m

Neutral, 5 m/s

Very Stable, 2 m/s

Figure 12.2-c: Propane cloud dispersion to lower flammable limit

0,01

0,1

1

10

100

1 10 100

Pipe Diameter, mm

Rel

ease

Rat

e, k

g/s

Liquid

Vapor

Figure 12.2-d: Butane release rates from guillotine pipe failure

1

10

100

1000

1 10 100

Release, kg/s

Dis

tan

ce, m

Very Stable, 2 m/s

Neutral, 5 m/s

Figure 12.2-e: Butane cloud dispersion to lower flammable limit

Safety in LPG Design Glossary of Terms 13-1

13 Glossary of Terms

ACTIVE FIRE PROTECTION

Active fire protection is provided by firewater, sprays, monitors, dry powder, firebrigade etc. Passive fire protection is provided by spacing, fireproofing etc.

ANSI

American National Standards Institute.

API

American Petroleum Institute.

ASME

American Society of Mechanical Engineers.

ASTM

American Society for Testing and Materials.

AUTO-REFRIGERATION

The chilling effect from vaporization of LPG when it is released or vented to a lowerpressure.

BAR GAUGE

Since bar is always absolute the term bar gauge is used to indicate pressures aboveatmospheric inside systems i.e. the pressure read on the gauge. It is often impractical touse absolute pressures. In this manual some pressures are in bar (absolute), some in bargauge (bar gauge is bar minus one).

BLEVE

Boiling Liquid-Expanding Vapor Explosion. A BLEVE occurs if a tank that is exposedto fire disintegrates suddenly because the tank metal was overheated. This usuallyhappens if cooling by firewater is insufficient.

13-2 Glossary of Terms Safety in LPG Design

BONDING

Bonding means electrically connecting two pieces of equipment that do not have metalto metal contact. Typically this is done during truck loading/unloading. Bonding strapsaround flanges are not needed as the flange studs and nuts provide adequateconductivity.

BULK PLANT

A facility that receives LPG by tank car, tank truck, marine vessel (barge), or piping. Itdistributes this gas to the end user by cylinder (package) delivery, by tank truck, ormarine vessel (barge). Such plants have bulk storage of 7.6 m3 water capacity or moreand usually have either container filling or truck loading facilities or both on thepremises.

BULK STORAGE

Bulk storage includes LPG storage in plants or at large industrial customer sites.

BULLET

A bullet is a large above ground horizontal tank containing LPG. It is typically used forbulk storage at plants and industrial customers. Fireproofing may protect it.

CAR SEALED OPEN

Term used to define a position of a valve during normal operating condition. Car sealwires or other devices should indicate that this position has been maintained at all times.Car sealed valves may be closed for maintenance purposes but then re-opened foroperations.

CATHODIC PROTECTION

Cathodic protection is a technique to reduce corrosion of a metal surface by passingsufficient protective Direct Current to cause the anodic dissolution rate (corrosioncaused by electrolytic properties of the soil) to become negligible.

CAVITATION

If the Net Positive Suction Head at the suction of the pump falls below its (correct)design value the liquid starts boiling and forms bubbles. This occurs in the high velocityzones of the pump, especially at the rotating impeller. The bubbles are unstable andcollapse in zones of higher pressure. The collapsing bubbles impact the metal and erodemetal surfaces, ultimately damaging the pump.

CENTRIFUGAL PUMP

In a centrifugal pump the fluid flows through a rotating impeller where centrifugal forceincreases kinetic energy, which is later converted to a static pressure rise as the fluidvelocity is reduced in a diffuser.

CET

See Critical Exposure Temperature.


CGA

Compressed Gas Association.

CHATTERING

Pressure relief valve chattering is a condition in which the valve opens and closesrapidly. This can lead to leakage or valve destruction. It may be caused by too large aPRV capacity, too high a pressure drop in the connection to the PRV or by a faultysetting of the PRV.

CHECK VALVE

Valve designed to permit flow only into one direction.

COMMERCIAL BUTANE (OR PROPANE)

Have typical specifications that are available from the manufacturing plants.Commercial Butane or Propane contains percentages of other petroleum fractions ofabout the same volatility, such as propylene and Isobutane.

COMMISSIONING, DECOMMISSIONING

Taking a tank, container or cylinder into LPG service or out of service. This happensduring initial filling or before scrapping and before and after any maintenance or testactivity.

COMPRESSED GAS

Any material or mixture having, when in its container, an absolute pressure eitherexceeding 276 kPa (2.76 bar) at 21.1 °C, or exceeding 717 kPa (7.17 bar) at 54.4 °C.

CONTAINER

A container is a small tank containing LPG. Such containers are typically used atcustomer sites for heating, cooking or small industry consumption. They may beinstalled above ground, mounded or below ground.

CONTAINER APPURTENANCES

Items connected to container openings needed to make a container a gas-tight entity.These include, but are not limited to, pressure relief devices; shutoff, back-flow check,excess-flow check, and internal valves; liquid level gauges; pressure gauges; and plugs.

CONTINGENCY

A contingency is a normal or abnormal event during plant operation that could lead tooverpressuring. The magnitude of the contingency will have a direct impact on thesizing of the pressure relief valve.


CRITICAL EXPOSURE TEMPERATURE

The Critical Exposure Temperature (CET) is the minimum steel temperature at which acomponent will be subjected to a pressure greater than 25% of the design pressure. If acomponent is exposed to lower temperatures it may fail through brittle fracture. Thepossibility of auto-refrigeration and the lowest one day mean temperature will be ofinfluence when determining the CET for LPG tanks.

CSO

See Car Sealed Open.

CYLINDER

A cylindercontains LPG for customer consumption. It is normally portable, may bereusable or disposable. Cylinders are also often called “Bottles.”

CYLINDER FILLING

Cylinder filling is a manual, semi-automatic or fully automatic process to fill cylinderswith LPG. Most important in this process are prevention of overfilling and leak control.

CYLINDER FILLING SHED

A well ventilated building in which the filling of cylinders takes place.

CYLINDER VALVE

A valve, used on LPG cylinders, which normally incorporates a shutoff valve and apressure relief valve in one unit. A fusible plug, incorporated in the same valve may berequired while PRV may not be allowed in some countries.

DESIGN PRESSURE

The design pressure is the maximum internal (or external) pressure used to calculate theminimum permissible wall thickness of tanks, drums, containers or cylinders. It isalways higher than the operating pressure. For vacuum conditions the external pressureis the maximum difference in pressure between the atmosphere and the inside of theequipment.

DESIGN TEMPERATURE

The design temperature is the temperature corresponding to the most severe condition ofcoincident pressure and temperature. The design temperature may include both amaximum and a minimum (CET) condition.

DFT

Dry Film Thickness is the thickness of a surface coating once the coating has dried orcured.


DIFFERENTIAL SETTLEMENT

Differential settlement occurs after a structure has been erected. As a result of structuresize and uneven compressibility of the ground, parts of the foundation may sink into theground to different depths and cause stress in the structure.

DIFFERENTIAL VALVE

A special valve actuated by the difference between two pressures. It is usually used tocontrol the higher pressure at a desired amount over the lower pressure.

DIP PIPE, DIP TUBE

A pipe extension from a tank opening or from a valve which extends into either theliquid or vapor space of the tank. It is used to locate the tank liquid level.

DOT

Department of Transportation, US government.

DRY BREAK COUPLING

A dry break couplingworks on the principle that only a negligible amount of product isreleased to atmosphere when the coupling is disconnected. This is achieved bydisplacing the product inside the coupling with two pistons.

ELECTRICAL AREA CLASSIFICATION

The concept of electrical area classification has been introduced to control electricalignition sources around equipment that contains flammable materials. Certain areas in aplant require higher quality electrical equipment to take account of the fact thatflammable mixtures may be present at some time during plant operations.

ELT

See LDE below.

EMERGENCY BLOCK VALVE

An Emergency Block Valve (EBV) is a manual or remote operated valve that is installedupstream of a source of potential leak and can provide tight shutoff. Sources ofpotential leaks are pumps, compressors, loading arms, hoses, cylinder filling, etc.Remote operated valves are activated by the Emergency Shutdown System (ESS).

EMERGENCY RELEASE SYSTEM

An Emergency Release System is provided at certain marine unloading piers. Underemergency conditions it will release the loading arm automatically to prevent damageand product leakage.

EMRE

ExxonMobil Research and Engineering Co., Fairfax, Virginia, USA.


ERE

Former Exxon Research and Engineering Co., Florham Park, New Jersey, USA

EXCESS FLOW VALVE

A device designated to close when the liquid or vapor passing through it exceeds aprescribed flow rate as determined by pressure drop. An excess flow valve allows flowto pass in either direction, but protects against excess flow in only one direction. Thevalve reopens when the design pressure differential is restored.

FAIL SAFE

A device or system “fails safe” if on loss of energy it automatically moves to the safestposition. For valves on LPG tanks this would mean the closed position.

FILLING DENSITY

The percent ratio of the weight of liquefied gas to the weight of water at 15.6 °C, whicha container will safely hold at a specific temperature.

FIRE IMPINGEMENT

Fire impingement occurs if in a fire situation the flames come into direct contact withtanks, containers, cylinders, piping etc. See also jet flames. Flame impingement is oneof the overpressure contingencies since the external heat leads to a temperature andpressure increase inside equipment.

FLEXIBLE CONNECTOR

A short (not exceeding 1 m overall length) component of a piping system fabricated offlexible material (such as hose) and equipped with suitable connections on both ends.

FLOAT (OR MAGNETIC) GAUGE

A gauge constructed with a float inside the container resting on the liquid surface thattransmits its position through suitable leverage to a pointer and dial outside thecontainer, indicating the liquid level. Normally the motion is transmitted magneticallythrough a non-magnetic plate so that LPG cannot be released to the atmosphere by a sealfailure.

FUSIBLE LINK

A link or section in a support, rod, shaft, or cable which will melt at a predeterminedtemperature and cause a valve or fire door to close, or will effect another action for fireprotection purposes.

FUSIBLE PLUG

A low melting temperature metal plug designed to melt and release the pressure in acylinder or piping system at a predetermined temperature. A fusible plug may beincluded in the cylinder valve when specified.


GP / BP

ExxonMobil Global Practices (previously International Practices and before that BasicPractices). Engineering Practices for facility installation.

GROUNDING (EARTHING)

Grounding means electrically connecting major equipment parts (tanks, pumps) to theground. This is to provide quick dissipation of lightning or stray currents.

HARD ARM

A hard piping connection to unload or load LPG on trucks, rail cars or ships. Swiveljoints provide flexibility.

HAZARD

A threat which could cause an accident

HAZOP

Hazard and Operability Analysis is a hazard identification analysis used during thedesign phase of a project. An independent HAZOP team studies all aspects of processrelated hazards to verify that adequate controls are included in the design to control ormitigate those hazards.

HEAT RADIATION

Heat radiation is the transfer of thermal energy from a fire by radiation to equipment. Itis one of the contingencies that create overpressure inside equipment.

HOSE TRACKING PROGRAM

A hose tracking program provides information on the origin of hoses, their age, their testresults, and their anticipated date of retirement.

HYDROCARBON

Organic compounds of hydrogen and carbon whose densities, boiling points, andfreezing points increase as their molecular weights increase.

ICC

US Interstate Commerce Commission.

INERT GAS

A noncombustible, non-reactive gas that renders the combustible material in a systemincapable of supporting combustion by virtue of displacing air.


INSULATING FLANGE

An insulating flange has to be installed to achieve electrical isolation of a piece ofequipment for cathodic protection purposes. Typical application of insulation flangesare around mounded drums, at pipeline terminals and at marine piers. Insulating flangesat piers also prevent any sparking upon disconnecting.

INTERNAL VALVE

A primary shutoff valve for containers that has adequate means of actuation and that isconstructed in such a manner that its seat is inside the container and that damage to partsexterior to the container or mating flange will not prevent effective seating of the valve.

ISGOTT

International Safety Guide for Oil Tankers and Terminals.

JET FLAME

If fluid escapes at a leak under high pressure it usually takes the shape of a long plume.If this plume ignites it forms a jet flame.

KNOCK OUT DRUM

A Knock Out Drum (KO Drum or Liquid Trap) is a container provided at the suctionside of a compressorto prevent intake of liquid, which could damage the compressor.

LEVEL HIGH CUT OFF

A level high cut off is a means to prevent the liquid level from rising too high. This isprovided on tankage or knock out drums on compressors.

LDE

Loan Delivery Equipment. Also called ELT in Mobil heritage, Equipment Loaned toTrade. Tanks or cylinders owned and maintained by the Company but operated by thirdparties (customers).

LOWER FLAMMABILITY LIMIT

Lower Flammability Limit (LFL) is the lowest concentration of flammable vapor in airthat will result in a mixture, which can be ignited. For Propane this is 2.0 volume % andfor n-Butane it is 1.9 volume % in air. If temperature or pressure of the mixture areincreased the LFL will decrease (i.e. will be more dangerous).

LIQUEFIED PETROLEUM GAS (LPG OR LP GAS)

Propane and Butane are called Liquefied Petroleum Gas (LPG) because they will liquefyif subject to higher pressure at atmospheric temperature. They will also liquefy ifrefrigerated at atmospheric pressure. They may be composed predominantly of any ofthe following hydrocarbons or mixtures of them: Propane, Propylene, Butane (n Butaneor Isobutane), and Butylene.


MAGNETIC GAUGE

See Float Gauge.

MAXIMUM ALLOWABLE WORKING PRESSURE

The maximum gauge pressure permissible in a tank or container during normaloperation at design temperature.

MERCAPTANS

A family of chemical compounds similar to alcohol in which sulfur replaces oxygen.Many mercaptans have an offensive odor and are used for odorization of LPG.

MEP

Mobil Engineering Practices.

MINIMUM VAPOR SPACE

The minimum space in a tank, above the liquid level, which is necessary to ensure thatthe tank does not become hydraulically full under normal operating conditions.

MOUNDED TANK

Large horizontal tank containing LPG which is installed above ground level but iscovered by an earth mound which protects it from fire. These tanks need a high qualitycorrosion protection.

NET POSITIVE SUCTION HEAD

Net Positive Suction Head (NPSH) is the pressure at the impeller of a pump. In orderfor the pump to function properly, the NPSH must always be above a certain levelspecified by the pump manufacturer. The pumped product, the product temperature, theproduct vapor pressure, and the suction piping arrangement will influence this.

NFPA

National Fire Protection Association.

NPGA

National Propane Gas Association.

NPSH

See Net Positive Suction Head.


NPQC

Non Process Quality Control is used to ensure that materials of construction andequipment will perform as required per specifications and design. NPQC is often doneat manufacturers sites and may involve tests.

OVERFILLING

LPG expands its volume with a temperature increase. If a tank, container or cylinderisoverfilled an increase in ambient temperature may lead to opening of the pressure reliefvalve and a discharge of LPG. To avoid this, the filling level is limited. Normallytanks, containers or cylinders are filled to 85%, however, this figure may vary dependingon conditions (e.g. if LPG is already at a higher temperature during filling, it cannotexpand much more).

OVERPRESSURE PROTECTION

Equipment containing pressurized fluids by design is limited to a maximum pressure.This maximum pressure is determined by operating conditions and economicalconsiderations. Overpressure protection in form of automatic pressure relief should beprovided to ensure that the pressure inside the equipment remains within safe limits.

PASSIVE FIRE PROTECTION

Passive fire protection mitigates the impact of a fire without relying on rapid detection,alarm, or response. Mechanical or electrical failures have no effect on its performance.Passive protection includes spacing, mounding or burying a tank, or providingfireproofing. These passive measures increase the time available to provide activeresponse, i.e. firefighting response.

POSITIVE DISPLACEMENT PUMP

In a positive displacement pump the fluid is aspirated into a cavity and than expelled bydecreasing the volume of the cavity. The pressure rise is created by displacement force.For LPG, sliding vane, internal gear or crescent pumps are used. In case the dischargeside can be blocked, such pumps should be protected against overpressure by a reliefvalve between the pump discharge and any block valve.

POST-WELD HEAT TREATMENT

Post-Weld Heat Treatment is heating of equipment to a temperature that will reduce thestress that originates from welding on the equipment.

PRESENTATION FLANGE

Dock side flange which makes contact with the ship flange.

PRESSURE RELIEF VALVE

A pressure relief valve (PRV) is a mechanical device that is designed to openautomatically once a certain pressure upstream of the PRV is reached. By this feature itprovides overpressure protection for the equipment.


PUSH-BUTTON

The Emergency Shutdown System may be activated by push-buttons placed in strategiclocations.

PWHT

See Post-Weld Heat Treatment.

REFRIGERATED STORAGE

A tank artificially maintained at a temperature below the nominal ambient temperature.

REGULATOR

Device to reduce and control pressure at a defined level. Usually regulators are installedbetween tankage or cylinders and end users.

RELIEF VALVE MANIFOLD

A piping manifold that may hold two or more relief valves with only one connection tothe tank. Some manifolds, such as the Multi-port manifold manufactured by RegO, aredesigned to permit the removal of one relief valve without disturbing the others orimpairing the relieving capacity required for the tank.

RISK

Probability of an accident occurring within a certain time, together with consequence forpeople, property and environment.

ROLLOVER

The spontaneous and sudden movement of a large mass of liquid from the bottom to thetop surface of a storage reservoir as a result of an instability caused by an adversedensity gradient.

REMOTE IMPOUNDMENT

In the case of LPG leakage under a bullet or sphere a certain amount of LPG mayremain in the liquid phase. By inclining the ground surface and diverting the liquid to ashallow pool, which is located away from the tank, it is possible to divert a part of theliquid to a safer location. Should the vapors ignite the fire exposure to the tank will belower.

SET PRESSURE

The set pressure is the pressure at which a pressure relief valve opens. This is identicalto the design pressure of the equipment.

SELF SEALING COUPLING

A coupling that automatically closes when disconnected and opens when connected. Itis also known as a dry break coupling.


SHUTOFF PRESSURE

Shutoff pressure is the highest pressure that a pump can reach, i.e. the pressure when thedischarge valve is closed.

SLIP TUBE GAUGE

A variable liquid level gauge in which a relatively small positive shutoff valve is locatedat the outside end of a straight tube, normally installed vertically, that communicateswith the container interior. The installation fitting for the tube is designed so that thetube can be slipped in and out of the container so that the liquid level at the inner endcan be determined by observing when the shutoff valve vents a liquid-vapor mixture.

SPACING

The concept of spacing has been adopted to prevent fire from quickly spreading in aplant or at a customer site. By experience the industry has suggested minimumdistances between LPG containing equipment and a variety of other locations. Suchlocations are the fence, the control house, firefighting equipment or other LPGcontaining equipment (loading/unloading etc.). Spacing requirements are incorporatedin most codes.

SPHERE

Large above ground spherical LPG tank. It is typically used for bulk storage at refineriesand large terminals. It may be fireproofed.

TANK

In this Manual the term tank is used for bullets, spheres and mounded drums. The termcontainer is used for smaller customer tanks.

TANK IDENTIFICATION PLATE

Each tank, drum, or container needs to be permanently identified by a name plateindicating all relevant data.

TARE WEIGHT

Weight of cylinder, or any container, before filling. Cylinders are stamped with theirempty tare weight plus weight of valve to be fitted when manufactured.

THERMAL EXPANSION RELIEF VALVE

LPG inside equipment expands under the influence of solar or other external heat. IfLPG is subject to elevated temperatures and it is enclosed inside piping sections that areblocked on both sides, the pressure may rise above design and rupture the piping.Therefore, Thermal Expansion Relief Valves (Hydrostatic Valves) should be provided.

THREAD

National Gas Taper (¾” NGT ) threads are used on cylinderconnections and NationalPipe Taper (NPT) threads are used in other LPG service. Some countries use DIN 477


thread. Both NGT and DIN threads look similar. Therefore, marking of DIN isrecommended on cylinder bungs and valves.

UL

Underwriters Laboratory. US organization for quality controls.

ULLAGE

The space in a tank or container above the liquid level. Ullage is necessary to allow aminimum vapor space above the LPG.

UNDERGROUND TANK

A tank in which all parts are completely buried under the general grade of the facility.

VAPOR CLOUD EXPLOSION

A Vapor Cloud Explosion (VCE) occurs if a large amount of LPG vaporizes (usuallyafter a leak), mixes with air and finds an ignition source. In case all LPG is within theflammable limits the VCE can be severe. The degree of LPG/air mixing is largelygoverned by weather conditions.

VAPOR PRESSURE

The pressure developed over a liquid in a closed container. The vapor pressure of LPGdepends on the temperature of the liquid and the composition of the primaryhydrocarbons present.

VAPORIZER

A heat exchanger designed to supply the heat required to convert LPG from liquid phaseinto vapor.

VESSEL

Ship. In the text of this manual the term vessel is not used for tanks, drums etc. but thetitles of codes use the word vessel for tanks, drums or towers.

VOLATILE LIQUID

A liquid that will readily vaporize at a relatively low temperature, such as normalambient temperature.

WATER CAPACITY

The amount of water, in either weight or volume, at 15.6 °C required to fill a containerfull of liquid water.


ZONE 0

Zone 0 is an electrical area classification. Zone 0 is an area where an explosive gasatmosphere is continuously present, or present for a long period. There is no equivalentUS classification, although Zone 0 would fall under Class 1 Division 1.

ZONE 1

Zone 1 is an electrical area classification. Zone 1 areas are defined as locations wherean ignitable concentration of flammable gases or vapors are likely to occur in normaloperations. It is equivalent to the US Class 1 Division 1.

ZONE 2

Zone 2 is an electrical area classification. Zone 2 areas are defined as locations whereignitable concentrations of flammable gases or vapors are not likely to occur in normaloperation, but may occur under abnormal operation. It is equivalent to the US Class 1Division 2.

safety in lpg design 2000

Documents

lpg design5 piping

piping integrity

tank shutoff valves

bulk lpg tanks

piping location

piping arrangements

emergency block valves

thermal relief valves