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2012 FAI Annual Seminar

The Safety and Integrity of

Ammonia Storage Tanks

Venkat Pattabathula

Global Ammonia Technology Manager

Incitec Pivot Ltd

Brisbane, Australia

Incitec Pivot

• Largest fertiliser manufacturing and distributing company in Australia

• Has largest explosive grade AN manufacturing base in North America, operates as Dyno Nobel

• One of the key values of the company

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Presentation Outline

1. Introduction

2. Types of ammonia tanks

3. Tank design and safety aspects

4. Tank commissioning & decommissioning

5. Risk Based Inspection

6. Incidents

7. Summary

History of Ammonia

• Ammonia being produced for the last 100 years, first commercial production by BASF in Germany

in 1913.

• Currently about 165 million tonnes of ammonia

produced per annum worldwide.

• Storage of ammonia since industrial production,

initially in high pressure bullets and Horton Spheres.

• Low pressure (atmospheric) ammonia storage at

-33DegC widely accepted, safer and cost effective and storage capacity up to 50,000 tonnes.

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Types of Ammonia Tanks – Single Wall Tank

Insulation

Low Temp.

Carbon Steel

Piles

Double wall tank (double containment)

Insulation

Inner Tank

Piles

Outer Tank

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Double wall double integrity (full containment) with insulation

in annular space

Insulation

Inner Tank

Piles

Outer Tank

Double wall double integrity (full containment) with insulation

on outer tank

Insulation

Inner Tank

Piles

Outer Tank

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Tank Design Features

- Tank shall be

• double wall double integrity (DWDI) with insulation on outer

tank

• designed for internal pressure of 14 kPag.

• designed, fabricated, erected and tested per API-620

Appendix R.

• elevated on piled concrete slab foundation of about 2

meters.

• hydrotested of both inner & outer tanks.

• designed for cyclonic wind and earthquake conditions per

country standards.

• provided with drain lines in both inner & outer tanks.

Tank Materials

• Both inner and outer tanks shall be of welded construction.

• Low temperature certified carbon-manganese

steel, impact tested at or below -40DegC.

• Welding and Charpy V-notch testing per QA

standards.

• Load bearing underneath the tanks with treated wood such as lignostone or equivalent.

• All nozzles/manway welds in the lower strakes

shall be post weld heat treated- stress relieved.

• No hard stamping of materials.

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Tank Relief

• A minimum of two pressure relief valves and two

vacuum breakers.

• Only one relief or vacuum breaker be taken off-line

during operation.

• Relief valves and safety devises per API-2000.

• A permanent N2 connection to maintain tank

pressure as one of the layers of protection in low-

low pressure scenario.

• Emergency shut-off valve in liquid supply line to

activate on high-high pressure.

Safety Aspects

• Remote shut-off valves in liquid ammonia main inlet and

outlet line to/from ammonia storage tank.

• The refrigeration system shall be based on recognized and

proven industrial compressors.

• There must be an auto compressor loading/unloading facility

for tank pressure control.

• Stand-by equipment for critical duties and utilities.

• The design shall take into account a closed vent and drain

system for ammonia.

• Redundancy in critical instrumentation & control

• Thermal relief valves in the ammonia lines where there is a

possibility of blockage or heat ingress.

• Fugitive ammonia emissions shall be minimised.

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Safety Aspects-cont’d

• A flare for controlled venting under extreme emergency

situations

• Any venting of ammonia to the flare shall be avoided or

minimised.

• Ammonia leak detection system

• Lightning protection and earthing protection

• Emergency power to one of tank boil-off refrigeration

compressor

• Wind direction indicator

• Emergency plant lighting

Electrical & Instrumentation

• Fitted with earthing bosses, no copper conductor stripes in direct contact with ammonia.

• Three independent level and pressure indications.

• High level shut-off valve to close the supply to the

tank.

• Adequate lighting in the storage area.

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Piping and Insulation

• All flanges shall be minimum of 150# rating.

• Bottom liquid nozzle connections shall be of 300#

rating.

• No screwed connections

• Insulation to be designed for Max +50C and Min

-40DegC.

• External insulation to be covered with a

continuous flat aluminium vapour barrier.

• No water ingress on the tank shell and base to

prevent ice formation.

• Spiral type stairway to the tank top.

Tank Non-Destructive Testing (NDT)

• Install waveguides to carry out acoustic emission (AE) testing.

• Conduct initial AE tests during hydrotest of the

tank to identify any construction defects.

• A second AE test during first filling of liquid

ammonia after cooling down operation.

• Hydrotest at maximum operating level of tank.

• Inspection Test Plan (ITP) to include witness

points during all stages of construction.

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Tank Commissioning

• Purge with nitrogen until the measured oxygen in

the discharge gas is less than 4%.

• Purge with ammonia vapour until the oxygen in

the tank is <0.5%.

• Cool the tank down to as low as possible with

injection of liquid ammonia at a cooling rate lower

than 2C/hour, preferably using a spray system.

• Measure the temperature in the tank away from the gas inlet.

• Take samples from the ammonia liquid in the tank and analyse them for water and oxygen.

Tank Decommissioning

• Empty the tank to the absolute minimum liquid level.

• Evaporate the remaining ammonia in a way that ensures

uniform and slow heating, not exceeding 2C/hour.

• Purge with warm ammonia or nitrogen until all liquid

ammonia is removed.

• Remove the ammonia gas in the tank by purging with

nitrogen and not with air, to eliminate the formation of an

explosive mixture. To prevent environmental issues, flare all

the ammonia vapour containing streams.

• Remove the nitrogen atmosphere by purging with air until

the oxygen content is >19%. If ammonia is still measured in

the gas phase due to residual oil, breathing equipment must

be used when entering the tank. Residual oil remnants may

require additional clean methods and additional personnel

safety requirements and equipment.

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Risk Based Inspection (RBI)

• Primary inspection method for the tank shall be

the acoustical emission [AE] test method. As a

global inspection technique it is capable of

detecting and locating defects in the area being

monitored.

• AE testing only detects active cracking conditions.

AE signals which indicate the potential for

cracking will require follow up examinations

utilizing UT for confirmation and sizing.

• Additionally inspection must include routine in-

service observation, periodic in-service inspection, and periodic inspection according to API 653.

Risk Based Inspection (RBI)- cont’d

• RBI assessments should be conducted by trained and qualified individuals knowledgeable in RBI

methodology and experienced in tank foundation design, construction, , properties of materials,

corrosion, stress-corrosion cracking, fatigue

cracking, fracture mechanics, and techniques for

storage tank inspection. The RBI assessment is performed following the procedures in API

580/581.

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Stress corrosion cracking (SCC)

• SCC is promoted by the presence of oxygen in combination

with ammonia.

• SCC is minimized when the following actions are taken.

- Special efforts are taken to quickly reduce the oxygen content of the tank when re-commissioning the tank following opening or ventilation.

- Tank commissioning is carried out under controlled conditions

such that the tank cooling rate does not exceed 2 degrees (Celsius) per hour.

- Stress relief or stress reduction techniques are used when making repairs to the tank.

- Use of lower strength weld materials that are compatible with the materials being welded.

- Water [0.2%] is intentionally added to the product in storage.

Inspection Frequency Risk Matrix

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Inspection Criteria

• Routine In-Service Observation

• Periodic In-Service Inspection

• Internal Inspection – Visual

• Internal Inspection – WFMT

• Vacuum Box Inspection

• Pressure- Relieving Devices

• Evaluation per API-579-1/ASME FFS-1

• Repairs to be approved by API-653 certified

inspector.

Ammonia Storage Safety Incidents

“Those who don't know history are destined to

repeat it.” Edmund Burke

• 23 incidents reported in the last 57 years of AIChE Ammonia

Symposium.

• All were given in Table 1 of the paper.

• Many incidents were on stress corrosion cracking (SCC).

• One of the SCC case was at BASF old plant in

Middlesborough, England

• Tank was inspected in 1989, found SCC. Repaired the

defects and tank was recommissioned.

• Tank integrity monitoring system was put in place.

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Rupture of ammonia tank

• In 1990 Symposium, Bengt Orval Andersson reported on Lithuanian fertiliser plant accident happened in March 1989, destroyed a 10,000 tonne-ammonia storage tank.

• Whole ammonia tank slid from its foundation, smashed with great force through a surrounding wall of reinforced concrete, finally landed 40m from the foundation.

• Enormous devastation around the tank, 70cm deep liquid ammonia.

Large quantities of ammonia evaporated, vapour caught fire and whole plant engulfed in flames.

• About 32,000 people evacuated from a nearby town, rescue operation continued for three days. Seven people died, 57 were injured.

• Ammonia tank over-pressured when its contents rolled over.

• Warm ammonia supplied to tank bottom, caused the rollover while tank refrigeration compressors out of service.

Failure of inner shell of a double wall ammonia storage tank

• In 1999, a 5,000 tonne ammonia storage tank

decommissioned at Coromandel Fertilisers Ltd in India.

• Noticed ammonia liquid level in annulus area of the double

wall double integrity tank, ammonia collected from splashing

during ship unloading at high levels.

• Level transmitter indication wrong, inner cup failed when

draining from a hydrostatic head of ammonia in annulus.

• Bottom plates fractured and circumferential welds failed.

Tank repaired, bottom plates renewed.

• Many improvements made on tank instrumentation: new TI

on annulus with a low temp alarm; interlock to trip ammonia

pumps if annulus level reaches 400mm level; separate level

indications for inner tank and annulus and up-to-date

documentation on ammonia tank.

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Ammonia Storage Fatality

• In 2005, NH3 tank emptied out for a repair, at Yara facility in

Rostock, Germany.

• One person killed while recommissioning the tank and

another injured.

• 100 tonnes of ammonia released.

• Tank rupture from high pressure

• Root Cause:

- Thin layer of oil prevented mixing of anhydrous ammonia

with aqueous ammonia which was used to cover tank

bottom. When a valve on tank outlet opened, caused violent

reaction and raised tank pressure causing rupture.

Ammonia Tank Rupture

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Summary

• Different types of ammonia tanks were explained.

• Ammonia storage tank design and safety aspects were

highlighted.

• Guidelines for decommissioning and commissioning

ammonia storage tanks were provided.

• A detailed review of Risk Based Inspection (RBI) was given.

• Twenty three incidents from the last 50+ years of the AIChE

symposium were listed including the root causes and

mitigations put in place (refer Table 1).

Acknowledgement

• Incitec Pivot Management

• My co-authors – Raghu Nayak and Don Timbres.

• Walter Benson, Carl Jaske and Brian Shannon for the review of the paper.

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Thanks

• Fertiliser Association of India (FAI)

• Any Questions Please!!!