Materials and Corrosion for Sour Service

MP 55-P-19Materials and Corrosion for Sour ServiceJuly 1998

Materials and Corrosion for Sour Service

MP 55-P-19

July 1998

Scope

This Mobil Engineering Practice (MEP) shall be used for the design of sour service materials for onshore and offshore production and processing facilities.

This MEP covers general requirements for sour service materials used in upstream surface facilities, from the wellhead wing valve to sales. These include onshore and offshore facilities as follows:

Wellsites

Production separation systems

Pipelines

Compressor stations

Gas processing plants

Oil batteries

Injection systems

RATIONALE: Materials in accordance with NACE MR0175 are acceptable, with modifications as noted herein. This Practice does not cover downhole material selection.

Table of Contents

1. References

The following publications form a part of this Practice. Unless otherwise specified herein, use the latest edition.

1.1. MEPSMobil Engineering Practices

MP 03-P-02Pressure Casting Inspection

MP 11-P-01Fired Heaters - Design and Fabrication

MP 12-P-01Pressure Vessels-Design & Fabrication

MP 13-P-10Shell & Tube Heat Exchangers-Design & Construction

MP 13-P-15Air-Cooled Heat Exchangers-Design & Construction

MP 16-P-01Piping-General Design

MP 16-P-30APiping - Materials and Service Classifications (M&R)

MP 16-P-40Piping-Fabrication, Erection, Inspection, & Testing

MP 20-P-01Offshore Pipeline Design

MP 20-P-02Line Pipe and Bend Material

MP 32-P-01General Requirements for Instrumentation

MP 35-P-01Painting - General Requirements

MP 35-P-81Painting - Internal Coatings - Tanks, Vessels, Piping and Tubulars

MP 57-P-02Pressure Containing Equipment - Welding & Inspection

1.2. Mobil Tutorials

EPT 03-T-09Acid Gas Removal (E&P)

EPT 08-T-03Materials for Sour Service

1.3. APIAmerican Petroleum Institute

API STD 661Air-Cooled Heat Exchangers for General Refinery Service Third Edition

API STD 1104Welding of Pipelines and Related Facilities Eighteenth Edition

1.4. ASMEAmerican Society of Mechanical Engineers

ASME B31.3Process Piping

ASME B31.4Liquid Transportation Systems for Hydrocarbons, Liquid Petroleum Gas, Anhydrous Ammonia, and Alcohols

ASME B31.8Gas Transmission and Distribution Piping Systems

ASME SEC IIAASME Boiler and Pressure Vessel Code, Section II: MaterialsPart A: Ferrous Material Specifications

ASME SEC VIII1995 Boiler & Pressure Vessel Code 1996 Addenda: Pressure Vessels

1.5. ASTMAmerican Society for Testing and Materials

ASTM A105/A105MStandard Specification for Carbon Steel Forgings for Piping Applications

ASTM A106Standard Specification for Seamless Carbon Steel Pipe for High-Temperature Service

ASTM A216/A216MStandard Specification for Steel Castings, Carbon, Suitable for Fusion Welding, for High-Temperature Service

ASTM A234/A234M REV AStandard Specification for Piping Fittings of Wrought Carbon Steel and Alloy Steel for Moderate and High Temperature Service

ASTM A352/A352MStandard Specification for Steel Castings, Ferritic and Martensitic, for Pressure-Containing Parts, Suitable for Low-Temperature Service

ASTM A370 REV AStandard Test Methods and Definitions for Mechanical Testing of Steel Products

ASTM A420/A420MStandard Specification for Piping Fittings of Wrought Carbon Steel and Alloy Steel for Low-Temperature Service

ASTM A516/A516MStandard Specification for Pressure Vessel Plates, Carbon Steel, for Moderate - and Lower-Temperature Service R(1996)

ASTM A578/A578MStandard Specification for Straight-Beam Ultrasonic Examination of Plain and Clad Steel Plates for Special Applications

ASTM A703/A703M REV AStandard Specification for Steel Castings, General Requirements, for Pressure-Containing Parts

ASTM A788Standard Specification for Steel Forgings, General Requirements

ASTM E44Standard Definitions of Terms Relating to Heat Treatments of Metal

ASTM E140Standard Hardness Conversion Tables for Metals, (Relationship Among Brinell Hardness, Vickers Hardness, Rockwell Hardness, Rockwell Superficial Hardness, Knoop Hardness, and Sclerscope Hardness)

1.6. NACENational Association of Corrosion Engineers

NACE MR0175Sulfide Stress Cracking Resistant Metallic Materials for Oilfield Equipment

NACE TM0177Laboratory Testing of Metals for Resistance to Specific Forms of Environmental Cracking in H2S Environments Errata Sheet

NACE TM0284Evaluation of Pipeline and Pressure Vessel Steels for Resistance to Hydrogen-Induced Cracking

2. General

The design of sour service materials for onshore and offshore production and processing facilities shall be in accordance with requirements of this MEP, unless superceded by more stringent local regulations.

The Practice defines sour service for gas and multiphase systems. Guidance is also presented here on material aspects that help minimize the risk of failures due to various forms of hydrogen damage, such as:

Sulfide stress cracking (SSC)

Hydrogen induced cracking (HIC)

Stress-oriented, hydrogen induced cracking (SOHIC)

This Practice also provides design, fabrication and inspection guidance, to ensure that the materials supplied are in a condition that minimizes the risk of damage from hydrogen.

RATIONALE: The following Mobil Tutorials are available for reference: EPT 03-T-09, Acid Gas Removal and EPT 08-T-03, Materials for Sour Service.

2.1. Criticality of Service

This Practice provides guidance on the criticality of the service for which a particular facility is being designed. The criticality of the service depends not only on the severity of the production fluids, but also on the consequences of failure.

2.2. Selection of Materials

The selection of materials for use in sour service depends on many factors in addition to the level of H2S.

Other failure modes may be important, depending on the specific production condition. This Practice, however, does not specifically address other failure modes that may be experienced in facilities as a result of other aggressive species. When appropriate, cautionary comments are provided with respect to other failure modes. Nevertheless, materials shall be selected in consultation with a material specialist and shall take account of the effects of possible failure modes, in addition to those resulting from H2S.

RATIONALE: Production environments and upstream processing units may contain constituents that cause damage to materials, as a result of failure modes other than those specifically related to H2S. Some examples of these are:

Chlorides: Failure of stainless steels and nickel alloys from stress corrosion cracking (SCC) at elevated temperatures in aqueous systems; pitting and crevice corrosion of some lower grades of stainless steels in stagnant aqueous systems

CO2: Corrosion of low alloy steels in CO2-containing environments

Amines: Corrosion of carbon and low alloy steels in amine treatment units, including SCC; corrosion in amine treatment units from degradation products

Elemental sulfur: Corrosion where elemental sulfur is deposited

High Temperature: Exposure to high temperature, 260(C (500(F), hydrogen sulfide can cause sulfidation of carbon and low alloy steels

RATIONALE: Consult a specialist for advice on the suitability of materials to use where other corrosive constituents may be present.

RATIONALE: Sections 2 through 6 provide guidance on material requirements. Section 7 provides guidance on fabrication and inspection. These are followed by a number of appendices, which give guidance on how the requirements relate to design and procurement of specific equipment.

RATIONALE: Sections 1 through 7, in conjunction with the relevant appendices, provide the necessary information to complete the Mobil Data Sheets for this MEP, covering the equipment being purchased, some of which are included in other relevant MEPS.

3. Sour Environments

RATIONALE: Sour environments are defined as fluids containing water as a liquid and with hydrogen sulfide exceeding the limits defined in Paragraphs 3.1 and 3.2. These environments may cause SSC of susceptible materials.

Caution: It bears noting that highly susceptible materials may fail in less severe environments.

Pipelines and other equipment handling dehydrated sour gas shall be designed, in accordance with this Practice, to handle the process upsets. Hydrogen-assisted cracking is affected by complex interactions of various parameters, including the following:

1. Chemical composition, strength, heat treatment and microstructure of the material 2. Hydrogen ion concentration (pH) of the environment3. Hydrogen sulfide concentration and total pressure 4. Total tensile stress (applied plus residual) 5. Temperature 6. Time

3.1. Sour Gas Service

Materials shall be selected in accordance with this Practice if the gas being handled is at a total pressure of 448 kPaa (65 psia) or greater and if the partial pressure of H2S in the gas is greater than 345 kPaa (0.05 psia). Figure 1 (or 2) provides a convenient method for determining whether the partial pressure of H2S in a sour environment exceeds 345 kPaa (0.05 psia).

Figure 1: Sour Gas Systems (Customary Units)

Figure 2: Sour Gas Systems (Metric Units)

RATIONALE: A few examples are provided:

1. Partial pressure of H2S (100 ppm or 6.7 grains per 100 standard cubic feet (SCF) at a total pressure of 1,000 psia exceeds 0.05 psia (Point A on Figure 1).2. Partial pressure of H2S in a system containing 0.005 mol percent H2S (50 ppm or 3.3 grains per 100 SCF) at a total pressure of 200 psia does not exceed 0.05 psia (Point B on Figure 1).

3.2. Sour Multiphase Service

Sour multiphase fluids are fluids containing oil, gas and water in any combination when any one of the following criteria are met (Figures 3 and 4):

0.0005 percent0.02 mol percent H2S in the gas and the partial pressure of H2S >345 kPaa (0.05 psia)

20.02 percent5 mol percent H2S in the gas and a total pressure >1827 kPaa (265 psia)

515 mol percent H2S in the gas and the partial pressure of H2S >69 kPaa (10 psia)

>15 mol percent H2S in the gas phase

Figure 3: Sour Multiphase Systems (Customary Units)

Figure 4: Sour Multiphase Systems (Metric Units)

Sour multiphase service applies only to production equipment containing commingled or emulsified oil, gas and water. In production equipment where phase separation occurs (e.g., separator, treater, FWKO, etc.), the environment is defined as sour service, in accordance with Section 3.1.

RATIONALE: Users are cautioned that regulatory authorities may define sour service differently than this Practice, for any of a number of reasons. If in doubt about local definition of sour service, consult with the appropriate regulatory authorities.

For pressure equipment, when process conditions are such that a wet sour gas environment exists in one area but a "non-sour" multiphase system exists in another area, the equipment shall be suitable for the more severe condition.

3.3. Sour Aqueous Phase

Sometimes the dissolved H2S, expressed as ppm by weight, in an aqueous phase, becomes the criterion for sour service. For example, where the partial pressures of H2S are not readily available, Mobil uses 50 ppm by weight H2S in aqueous phase, as a minimum, for defining sour service.

3.4. Criticality of Sour Service

Two categories of service are specified where the severity of service is used to define the selection of materials, design, fabrication and inspection requirements.

The classification of severity depends on the various factors associated with the probability and consequences of failure, plus local considerations and economic impact.

3.4.1. Risk Assignment Factors

Loss Prevention specialists provide guidance on the consequences of a failure, while material specialists give guidance on the likelihood of a failure. Risk assessments shall be made in consultation with these specialists to ensure optimum performance.

Factors associated with the assignment of risk are as follows.

3.4.1.1. Critical Sour Service

High pressure (> 448 kPaa (65 psia) for gas systems and >1827 kPaa (265 psia) for sour oil and multiphase systems)

High H2S partial pressure or high ppm in liquid

High environmental sensitivity

Threat to people

High impact on production losses

Long field life

3.4.1.2. Non-Critical Sour Service

Low pressure (< 448 kPaa (65 psia) for gas systems and < 1827 kPaa (265 psia) for sour oil and multiphase systems)

Low H2S partial pressure or low ppm in liquid

Low environmental sensitivity

Remote from personnel

Low impact on production losses

Short field life

3.4.2. Examples of Sour Service Conditions

Following are examples of conditions that are typical of critical and non-critical sour service. The two examples presented are at the extremes of service risk. Individual cases shall be reviewed to establish their criticality and how the material requirements shall be specified.

3.4.2.1. Critical Service Conditions

Under critical service conditions, every precaution is taken to avoid a failure.

Production fluids are very corrosive, are at high pressure and have high H2S content.

The facility is close to habitation in an environmentally sensitive area and a production shutdown would be environmentally detrimental.

3.4.2.2. Non-critical Service Conditions

Under non-critical service conditions, less stringent requirements are in effect for the materials of construction without compromising safety.

Production fluids are only mildly corrosive; the H2S content and pressure are low.

The facility is far from habitation and a production shutdown would not be detrimental.

3.5. Acronyms

The following abbreviations and acronyms are used in this MEP and also supplement those contained in NACE MR0175. Additional definitions related to heat treatment may be found in ASTM E44.

BWButt Welding

CECarbon Equivalent

CMLCement Mortar Lined (Pipe and Piping Components)

CRACorrosion Resistant Alloy

CRA-SCRA-Solid

CRA-CCRA-Clad, where CRA cladding is metallurgically bonded to a steel substrate

CRA-HCRA-HIP, where CRA powder is applied by Hot Isostatic Pressing (HIP)

CRA-LCRA-Lined, where CRA liner is fitted to a steel substrate. It is not metallurgically bonded to steel but may be a very tight shrink fit, depending on the process of installation.

CRA-OCRA-Overlayed, where CRA is applied by fusion welding and is metallurgically bonded to the substrate

CRA-TCRA-Thermally Sprayed, where a thin layer of CRA is applied by thermal spraying; it may or may not be metallurgically bonded

CSCarbon Steel

ERWElectric Resistance Welded

FBEFusion Bond Epoxy (coating)

FRPFiber Reinforced Plastic (typically fiberglass)

HAZHeat Affected Zone of Weldment

HFHard Faced (e.g., Satellite)

HICHydrogen Induced Cracking

IIWInternational Institute of Welding

IPCInternally Plastic Coated (Pipe & Fittings)

LASLow Alloy Steel

MTMagnetic Particle Testing (also known by MPI)

PcmParameter of Crack Measurement

PELPolyethylene Lined

PQRProcedure Qualification Report for Weldment

PTLiquid Penetrant Testing (also known by LPI)

PWHTPostweld Heat Treatment

RTRadiographic Testing

SCCStress Corrosion Cracking

SMYSSpecified Minimum Yield Strength

SOHICStress-Oriented Hydrogen-Induced Cracking

SOLSockolet

SSCSulfide Stress Cracking

SWSocket Welding

TOLThreadolet

UTUltrasonic Testing

WCTungsten Carbide

WFMTWet Fluorescent Magnetic Particle Testing

WOLWeldolet

4. Ferrous Metals

4.1. Carbon and Low Alloy Steels

4.1.1. Carbon Steels

Carbon steels shall be in accordance with the attached appendices.

When required by equipment tables later in this Practice, carbon steel plate shall meet the requirements of Appendix A, B or C, as applicable.

4.1.2. Carbon Equivalent (CE)

Carbon equivalent is a measure of the hardenability of carbon and low alloy steels as a result of welding. The CE is based on the content of specific elements in the parent metal. The IIW formula for CE is:

CE = + +

Where the elements are in weight percents

RATIONALE: CE in excess of 0.43 usually requires preheat in welding and/or PWHT to satisfy hardness requirements.

4.1.3. Cracking Parameter (Pcm)

Very low carbon steels (< 0.10 weight percent carbon) are usually micro-alloyed in order to achieve desired strength. In those cases, CE is not a good measure of hardenability and the use of a cracking parameter (Pcm) is recommended instead.

Pcm = C + + + + + 5B

Where the elements are in weight percents

RATIONALE: Pcm in excess of 0.24 usually requires preheat in welding and may cause HAZ cracking. A lower Pcm may be required for thicker materials (38 mm ((1.5 in), to avoid cracking.

4.1.4. Cold Formed Bends

All cold formed bends in carbon steel, including U-tubes for heat exchangers and fired heaters, shall be stress-relieved at a minimum temperature of 610C (1130F) or fully normalized, if the as-bent hardness exceeds 225 HB or if the plastic strain used during bending exceeds 5 percent.

RATIONALE: Cold formed bends in low alloy and micro-alloyed steel also require stress relief, but selection of time/temperature parameters shall be made in consultation with a Mobil material specialist.

RATIONALE: For wall thickness greater than 13 mm (0.5 in) and for grades of steel with SMYS above 360,000 kPa (52,000 psi), consult with a Mobil material specialist to assess the allowable plastic strain. The cold forming degrades the toughness of the steel.

4.2. Micro-Alloyed Steels

RATIONALE: When micro-alloyed steels are specified, some special considerations regarding welding and heat treatment apply. A Mobil material specialist shall be consulted.

4.2.1. Vanadium, Niobium and Titanium Alloyed Ferritic Steels

For vanadium, niobium and titanium alloyed ferritic steels, the vanadium content shall not exceed 0.05 percent, the niobium 0.05 percent, the titanium 0.02 percent and their combined content shall not exceed 0.10 percent. When these elements are used for alloying, the soluble aluminum to nitrogen ratio shall not be less than 2:1, with the nitrogen less than 0.015 percent.

RATIONALE: These elements, when combined with nitrogen, degrade the toughness of the HAZ of the field weld.

4.2.2. Pipeline Steels

Micro-alloyed steels used in the manufacture of line pipe shall meet the requirements of the appropriate sections of MP 20-P-02.4.3. Free Machining Steels

Free machining steels, including all free machining grades of stainless steels, shall not be used.

RATIONALE: Free machining steels are steels to which elements such as sulfur, selenium or lead have been added intentionally to improve machinability. These steels are extremely susceptible to SSC, HIC and hydrogen assisted cracking.

4.4. Cast Iron

Non-ductile forms of cast iron shall not be used for pressure containing parts in sour service.

RATIONALE: Some ductile forms of cast iron may be suitable; consult a Mobil material specialist.

4.5. Austenitic Stainless Steels

In addition to the limitations outlined in NACE MR0175, the 300 series stainless steels, including their low carbon grades, shall not be used in services where the temperature and chloride concentration fall within the stress-cracking region defined by Figure 5. Gaskets are exempted from this requirement for operating temperatures of 120C (250F) or less. Socket welds or threaded connections that present a crevice on the process side shall be avoided.

RATIONALE: When conditions of chloride concentration and temperature do not permit the use of austenitic stainless steel, a Mobil material specialist shall be consulted. An alloy with increased nickel content, possibly combined with a molybdenum addition, shall typically be selected, depending on the severity of the process conditions (e.g., 20-CB-3, Incoloy 800, Incoloy 825, Inconel 625, Hastelloy C-276, Titanium).

Figure 5: Chloride Stress Cracking Region for Austenitic TP 304 & TP 316 Stainless Steel

4.6. Ferritic Stainless Steels

Ferritic stainless steels that meet the requirements of NACE MR0175 are acceptable. However, special considerations apply to their selection, manufacture and use. Prior to purchase or use of these materials, a Mobil material specialist shall be consulted.

RATIONALE: Ferritic stainless steels are easily welded without preheat and/or PWHT to meet HRC 22 hardness. However, grain growth in the HAZ drastically reduces the toughness of the weldment; therefore, caution is recommended when selecting these alloys for welded construction for service at temperatures below approximately 21C (70F). In addition, most design codes limit the use of ferritic stainless steels for pressure containing service to a maximum temperature of 343C (650F) because of embrittlement at elevated temperatures.

4.7. Martensitic Stainless Steels

Martensitic stainless steels that meet the requirements of NACE MR0175 are usually acceptable. However, special consideration applies to the selection, manufacture, heat treatment and use of these alloys. Consequently, a Mobil material specialist shall be consulted prior to their use.

RATIONALE: Laboratory tests have shown some of the 400 series materials to be acceptable in service temperatures up to 150C (300F). Above this temperature, these types of steels corrode at a faster rate than carbon and low alloy steels. In addition, the exact maximum level of H2S that the 400 series stainless steels can tolerate, before they suffer sulfide stress cracking, is not known.

4.8. Precipitation Hardening Stainless Steels

Precipitation hardening stainless steels that meet the requirements of NACE MR0175 are generally acceptable. However, special consideration applies to the selection, manufacture, heat treatment and use of these alloys. Consequently, a Mobil material specialist shall likewise be consulted prior to their use.

RATIONALE: NACE MR0175 contains very specific requirements concerning heat treatment of precipitation hardening stainless steels. It is necessary to adhere to these requirements for optimal resistance to hydrogen assisted cracking mechanisms. Failures have occurred in service with improperly heat treated materials.

RATIONALE: Failures have occurred with 17-4 pH that was in compliance with the requirements of NACE MR0175. The behavior of these materials in a sour environment depends on a number of aspects, including temperature, chloride content, H2S content and material condition.

4.9. Duplex Stainless Steel

Duplex stainless steels that meet the requirements of NACE MR0175 are generally acceptable. However, duplex stainless steels are fairly new and knowledge about their use changes rapidly. A Mobil material specialist shall be consulted before selection and establishment of fabrication techniques regarding these materials.

RATIONALE: The H2S partial pressure limitations for UNS 31803 specified in NACE MR0175 shall be acceptable for most applications. However, the limitations can be altered based on chlorides in the environment, strength level of the alloy and stress level. Alloys other than UNS 31803 may have other limitations.

RATIONALE: Welding filler metals and procedures are critical and shall be optimized to provide proper austenite to ferrite ratios in the weld metal and HAZ.

5. Non-Ferrous Metals

The non-ferrous metals shown in NACE MR0175 are acceptable. Any applicable Mobil modification for these materials is listed below.

5.1. Nickel-Copper Alloys

Nickel-copper alloys shown in NACE MR0175 are acceptable.

Nickel-copper alloys such as UNS N04400 (Monel 400) and N04405 (Monel R405) in sour service shall be limited to temperatures less than 150C (300F).

RATIONALE: Nickel-copper alloys are known to suffer sulfidation attack at temperatures of 176C (350F) or higher. This direct reaction with the environment results in metal loss through formation of nickel and copper sulfides. As with several non-ferrous alloys, NACE MR0175 contains very specific requirements concerning hardness and heat treatment condition of UNS N05500 (Monel K-500). It is necessary to adhere to these requirements for optimal SSC resistance. It also bears mention that some failures have occurred in material with hardness exceeding the NACE MR0175 limit.

5.2. Other Nickel-Base Alloys

Many nickel-chromium, nickel-iron-chromium and nickel-iron-chromium-molybdenum alloys are acceptable for sour service according to NACE MR0175. Selection of these alloys is suggested when chlorides are present and SCC of the 300 series stainless steels is likely to occur. Heat treatment and hardness requirements of NACE MR0175 shall be strictly adhered to in order to prevent cracking in sour service, due to hydrogen absorption by galvanic coupling and/or corrosion.

5.3. Copper Alloys

Copper-nickel alloys, such as UNS C70600 (90/10 Cu/Ni) and UNS C71500 (70/30 Cu/Ni) alloys, are acceptable under NACE MR0175; however, they have high corrosion rates in sour service.

RATIONALE: In selecting copper-nickel alloys, it bears noting that they generally have corrosion rates in excess of 0.25 mm/year (10 mil/year) in sour service at temperatures between 95120(C (200250(F).

Copper alloys such as brass and bronze shall not be used in process streams containing amines, ammonia or H2S, nor in applications where atmospheric exposure to H2S occurs.

RATIONALE: When exposed to ammonia/amine environments, the brasses may suffer dezincification, a process whereby zinc is selectively removed from the brass. In some of these environments, the copper alloys may experience stress corrosion cracking.

RATIONALE: UNS C61300 (Aluminum Bronze) and UNS C44300 (Arsenical Admiralty Brass) have been successfully used in sour service when amines or ammonia are not present.

5.4. Lead and Lead Alloys

Lead, lead alloys and lead-bearing (free machining) alloys shall not be used in sour service.

5.5. Dissimilar Metals and Galvanic Coupling

Coupling of dissimilar metals in a corrosive environment might lead to problems of crevice corrosion, hydrogen charging or pitting attack. With dissimilar metals coupled, the more anodic metal may suffer crevice corrosion and/or pitting. In some cases, the more anodic metal might corrode and cause hydrogen charging of the more cathodic (corrosion resistant) metal. This charging may lead to cracking of the more resistant metal. Coupling of dissimilar metals is only a problem when the more anodic metal, by itself, will corrode in a specific environment.

RATIONALE: When dissimilar metals must be connected, the cathode-to-anode area ratio shall be minimized. For example, tubing in a heat exchanger shall never be anodic to tubesheets or shells, in order to prevent an unfavorably large cathode-to-small-anode area ratio.

6. Non-Metallic Materials

6.1. Elastomers

The equipment supplier shall be consulted with respect to elastomer recommendations (and supporting test data and service experience) for the project service conditions. These service conditions need to be clearly identified for this selection process.

Table 1 lists service and temperature ranges for several elastomers commonly used as O-rings and other components.

Table 1: Service and Temperature Ranges for Common Elastomers

(Note 1)Nitrile (Buna-N) (Note 6)Viton (FMK) (Note 5)Teflon (PTFE) (Note 4)Ethylene Propylene (EPDM)AflasKalrez

H2S C-20 to 120 (Note 2)-20 to 150N.R.N.R.-20 to 200-20 to 260

F0 to 250 (Note 2)0 to 300N.R.N.R.0 to 4000 to 500

CO2CN.R.-20 to 150-20 to 150N.R.-20 to 200-20 to 260

FN.R.0 to 3000 to 300N.R.0 to 4000 to 500

Amines & InhibitorsC-20 to 95-20 to 95N.R.-20 to 150-20 to 200-20 to 260

F0 to 2000 to 200N.R.0 to 300 (Note 3)0 to 4000 to 500

NOTES:

1. Temperature conversions used above are approximate.

2. Acceptable when partial pressure of H2S < 6.9 kPaa (1 psia).

3. MEA/DEA only.

4. Plastic flow under shearing stress shall be considered.

5. Viton may show embrittlement due to H2S induced vulcanization effects.

6. Other synthetic rubbers like Neoprene may be acceptable, subject to agreement with the Mobil material specialist.

RATIONALE: During selection of elastomers, other process and design conditions shall be considered. These include life at high temperatures, resistance to other species such as inhibitors, the quantity of filler, filler types for various elastomers, the type of cure and different grades of elastomers within the broad classifications (e.g., Viton) given in Table 1.

RATIONALE: Viton, Teflon, Aflas and Kalrez are proprietary formulas that may vary according to the vendor. Caution shall be exercised in application.

6.2. Fiber Reinforced Plastic

Fiber reinforced plastic (FRP) may be used for some sour water service. However, the variety of FRPs and their various conditions warrant careful consideration prior to their use. Their low fire resistance may preclude use in some locations.

6.3. Gaskets

Gasket materials shall be selected in accordance with MP 16-P-30A.

6.4. Packing

Packing materials shall be selected in accordance with piping, valve and equipment guides.

7. Bolting

7.1. Exposed Bolting

"Exposed bolting" under NACE MR0175 is "Bolting that is exposed to the sour environment or that is buried, insulated, equipped with flange protectors or otherwise denied direct atmospheric exposure "

Where a facility has both sour and non-sour production equipment, all process bolts and nuts are considered "Exposed Bolting" under NACE MR0175.

RATIONALE: Identification and control of the various types of nuts and bolts at a given facility are impractical. Standardization of a worst case sour or low temperature service is typical for each facility.

Where a facility requires low temperature bolts and nuts, all process bolts and nuts are considered low temperature service.

Table 2 outlines the appropriate material specification.

RATIONALE: Note that bolts specified in Table 2 are slightly lower in tensile and yield strengths than those normally used. (Refer to Note 2 in the table.)

Table 2: Material Specifications for Selection of Exposed Bolting

Material and ServiceBolting SpecificationNut Specification

Carbon Steel

Standard temperature, critical or non-critical sour service (Notes 1 and 2)A193/A193M Gr.B7MA194/A194M Gr.2HM

Low temperature, critical or non-critical sour service (Notes 1 and 2)A320/A320M Gr.L7MA194/A194M Gr.7M

NOTES:

7. Standard temperature service refers to operation at temperatures from 120C (250F) to 29C (-20F). Low temperature service refers to operation at temperatures in the range of 45C (-50F) to 29C (-20F). When selecting the operating temperature, consideration shall be given to code requirements, local climatic conditions and process conditions, including the effects of upset, startup and shutdown.

8. When pressure/temperature ratings cannot be achieved using B7M or L7M bolting, high alloy, precipitation hardenable, high strength bolting shall be used. Special ordering instructions may be necessary to satisfy the strength requirements of the equipment standard and the heat treatment and hardness requirements of NACE MR0175. Consult your materials specialist.

8. Platings and Coatings

8.1. Metallic Coatings

Metallic coatings (electroplated, electrolyses and thermal spray) shall not be allowed as a stress corrosion cracking control method. Where plating is used for corrosion or wear resistance, the material upon which the plating is deposited (substrate) shall conform to this Practice. Cadmium and galvanized zinc plating is unsuitable for hydrogen sulfide service, due to rapid corrosion.

8.2. Non-Metallic Coatings

In non-critical sour service applications at lower operating temperatures, under 93C (200F), the use of non-metallic coatings, such as epoxies or phenolics, may be considered. The coating specified shall be compatible with the process conditions. The installation and QA/QC requirements shall be individually specified for the application and be in accordance with MP 35-P-81.

RATIONALE: Properly applied and maintained coatings can provide a barrier layer to separate the process environment from the steel surface. However, the quality of the coating shall be sufficient to maintain that barrier.

RATIONALE: The use of coatings can be beneficial in extending the life of equipment already suffering from damage in service.

RATIONALE: Because of the temperature limits of these coatings, their use shall be limited to the lower temperature ranges.

RATIONALE: For equipment operating above the immersion service temperature limits for non-metallic coatings, corrosion resistant alloy claddings may be considered.

9. Fabrication

9.1. Welding

9.1.1. General

These guidelines supplement MP 57-P-02 for sour service.

9.1.2. Set-on Nozzles

Set-on nozzles with inside diameters equal to the diameter in a vessel or pipe wall are limited to a maximum diameter of 100 mm (4 in). The weld attaching the nozzle to the vessel shall penetrate completely through the nozzle neck and may be either single or double welded.

RATIONALE: Welding to the outside of pipe or vessel walls (e.g., when nozzles or sleeves are attached), creates through-thickness stresses. These stresses increase the steel's susceptibility to HIC, which shall be taken into account when ordering material and qualifying welding procedures.

9.1.3. Backwelding

Backwelding to correct root bead welding defects or misalignment on the inside (process side) of pipe is not permitted.

RATIONALE: In unusual situations, backwelding may be permitted under one of the following conditions:

1. With proper PWHT at a sufficiently high temperature and adequate holding time to reduce residual stresses and lower hardnesses to less than 248 HV10. The adequacy of the PWHT procedure shall be demonstrated during welding procedure qualification testing.

2. By performing the backweld repair before the second pass is applied.

9.1.4. Weld Repair of Carbon and Low Alloy Steel Castings

Weld repair of carbon and low alloy steel castings shall be minimized. If weld repairs are necessary, irrespective of size, all carbon and low alloy steel castings shall be PWHT to reduce residual stress and to reduce the hardness of the casting below 22 HRC.

RATIONALE: Welding procedures shall demonstrate hardness control by providing hardness data taken from the cross-section of a representative weld test coupon. The weld test coupon shall be similar to the casting in terms of geometry, mass and material specification. The user is cautioned that casting segregation may create hard spots that would be undetected by hardness testing.

9.2. Postweld Heat Treatment (PWHT)

9.2.1. Materials Requiring PWHT

PWHT is required for some carbon steels, low alloy steels, martensitic steels and other transformation hardenable metallic materials exposed to higher temperatures, such as experienced in welding or air-arc gouging.

9.2.2. Materials Not Requiring PWHT

1. Materials not requiring PWHT are low carbon seamless pipes with the following conditions:

a) Maximum carbon content of 0.20 percent.

b) CE 0.43.

c) SMYS 50 mm (2 in) (Note 14)

WFMT (Note 15) welds exposed to process

Nozzle WeldsWFMT (Note 15) welds exposed to processNDE per MP 12-P-01

Full UT if > NPS 4 (Note 14)

NOTES:

22. Refer to the tutorial EPT 08-T-03, Materials for Sour Service, for a discussion of factors influencing service category and typical classification of equipment.

23. Economic decisions with respect to use of CRA or carbon steel shall consider life cycle costs, including extended periods between shutdowns and elimination of WFMT during shutdowns and possible elimination of PWHT.

24. UT performed to ASTM A578/A578M S1.1 and S2.2. Any area with one or more discontinuities, which produce a continuous total loss of back reflection and cannot be encompassed within a 25 mm (1 in) diameter circle, is unacceptable.

25. The quality of the coating job shall be closely monitored.

26. Sacrificial anodes shall also be considered for use with coatings, in order to supplement corrosion protection.

27. Refer to Section 9 of this Practice for design and fabrication details.

28. Applies to all longitudinal seams, circumferential seams and nozzle connections (ASME Category D connections).

29. For critical service, internal attachment welds connecting pressure containing parts shall be full penetration to avoid interface for H2 collection (refer to MP 12-P-01).

30. For moderate and mild service, as a minimum, welds connecting non-pressure to pressure parts shall be continuous to seal the perimeter of the part and prevent corrosion behind the attachment (Refer to MP 12-P-01).

31. Vickers indentor load shall be (10 kg.

32. Hardness survey may be by any indentation method for which there is an ASTM standard, except Brinell. Refer to Section 9.3.

33. Applies to non-clad CS. For clad CS, PWHT per ASME SEC VIII, Division 1.34. RT to ASME SEC VIII, Division 1, Paragraph UW51 or equivalent.

35. UT to ASME SEC VIII, Division 1, Appendix 12 or equivalent.

36. Where accessible, after hydrotest WFMT welds are exposed to the process according to ASME SEC VIII, Division 1, Appendix 6 or equivalent. This is in addition to the requirements of MP 12-P-01.

Appendix C: Shell and Tube Heat Exchangers (Refer to MP 13-P-10)

16. Shell and Tube Heat Exchanger Material

Table C1: Shell and Tube Heat Exchanger Material, Design, Welding, Fabrication and Non-Destructive Examination Options for Various Sour Service Categories (TEMA and ASME SEC VIII, Division 1)

(Note 1)Critical ServiceNon-Critical Service

Material Selection Options

Shell, Head and ChannelHIC tested plate to Appendices K and L Killed carbon steel with grid UT of plate to ASTM A578/A578M Level 2; (Note 3)

CRA Clad Plate (Note 2)Restricted chemistry material

Pipe, Fittings and ForgingsKilled carbon steelKilled carbon steel

CRA or CRA clad or overlayed CS to match

TubesRefer to Section 4Refer to Section 4

Design & Fabrication (Note 4)

WeldsFull penetration welds (Notes 5 and 6)Full penetration welds (Notes 5 and 7)

NozzlesRadiographable vessolets/sweepolets designs preferredSet-in or set-through designs preferred

Set-in or set-through designs acceptableSet-on designs allowed for openings (NPS 4

Set-on designs allowed for openings (NPS 4, on shells and heads with t(50 mm (2 in)

Construction

WPS/PQR HardnessVickers survey required (Note 8)Survey required (Note 9)

PWHTRequired, 610C (1130F) min (Note 10)Required, 610C (1130F) min (Note 10)

Production Weld Test100 percent required10 percent required

Non-Destructive Examination

Long. and Circ. WeldsFull RT (Note 11)Full RT (Note 11)

Full UT if t>50 mm (2 in) (Note 12)WFMT (Note 13)

WFMT (Note 13)

Nozzle Cat. D WeldsWFMT (Note 13)WFMT (Note 13)

Full UT if > NPS 4 (Note 12)

Tube to Tubeplate WeldsWFMT ferrous metals, PT non-magnetic metalsWFMT ferrous metals, PT non-magnetic metals

NOTES

37. Refer to the tutorial EPT 08-T-03, Materials for Sour Service, for discussion of factors influencing service category and typical classification of equipment.

38. Economic decisions with respect to use of CRA or carbon steel shall consider life cycle costs, including extended periods between shutdowns and elimination of WFMT during shutdowns and possible elimination of PWHT.

39. UT performed to ASTM A578/A578M S1.1 and S2.2. Any area with one or more discontinuities, which produce a continuous total loss of back reflection and cannot be encompassed within a 25 mm (1 in) diameter circle, is unacceptable.

40. Refer to Section 9 of this Practice for design and fabrication details.

41. Applies to all longitudinal seams, circumferential seams and nozzle connections (ASME Category D connections).

42. For critical service, internal attachment welds connecting pressure containing parts shall be full penetration to avoid interface for H2 collection (refer to MP 12-P-01).

43. For moderate and mild service, as a minimum, welds connecting non-pressure to pressure parts shall be continuous to seal the perimeter of the part and prevent corrosion behind the attachment (Refer to MP 12-P-01).

44. Vickers indentor load shall be (10 kg.

45. Hardness survey may be by any indentation method for which there is an ASTM standard, except Brinell. Refer to Section 9.3.

46. Applies to non-clad CS. For clad CS, PWHT per ASME SEC VIII, Division 1.47. RT to ASME SEC VIII, Division 1, Paragraph UW51 or equivalent.

48. UT to ASME SEC VIII, Division 1, Appendix 12 or equivalent.

49. Where accessible, after hydrotest WFMT welds are exposed to the process according to ASME SEC VIII, Division 1, Appendix 6 or equivalent. This is in addition to the requirements of MP 12-P-01.

17. Dissimilar Materials

Tubes shall not be anodic to the tube sheet or shell.

Appendix D: Air-Cooled Heat Exchangers (Refer to MP 13-P-15)

18. Aerial Cooler Material

Table D1: Aerial Cooler Material, Design, Welding, Fabrication and Nondestructive Examination Options For Various Sour Service Categories (API STD 661)

(Note 1)Critical ServiceNon-Critical Service

Material Selection Options

Header Box and Tube PlateHIC resistant plate to Appendix L;Killed carbon steel with grid UT of plate to ASTM A578/A578M Level 2 (Note 3)

CRA Clad Plate (Note 2);

CRA plate

Pipe, Fittings and ForgingsKilled carbon steelKilled carbon steel

CRA or CRA clad

TubesCarbon steel or CRACarbon steel

Design & Fabrication (Note 4)

WeldsFull penetration welds (Notes 5 and 6)Full penetration welds (Notes 5 and 7)

NozzlesRadiographable vessolet/sweepolet designs preferredNozzle design per ASME SEC VIII, Division 1

Set-in designs acceptable

Set-on designs allowed for openings (NPS 4, on header boxes with t(50 mm (2 in)

WPS/PQR HardnessSurvey required (Note 8)Survey required

PWHT, Header BoxRefer to Section 9 (Note 9)Refer to Section 9

Production Weld Tests

Non-Destructive Examination

Header Box WeldsFull RT or UT long seams and end plate welds (Notes 11 and 12)Refer to MP 13-P-15 (Note 10)

Nozzle WeldsFull UT if > NPS 4 (Note 12)Refer to MP 13-P-15 (Note 10)

Full MT all nozzles

NOTES:

50. Refer to Section 3 of this Practice for a discussion of factors influencing service category and typical classification of equipment.

51. Economic decisions with respect to the use of CRA or carbon steel shall consider life cycle costs, including extended periods between shutdowns and elimination of WFMT during shutdowns. Selection of CRA depends on actual service conditions and shall be done in consultation with a materials specialist.

52. UT performed to ASTM A578/A578M S1.1 and S2.2. Any area with one or more discontinuities that produce a continuous total loss of back reflection and cannot be encompassed within a 25 mm (1 in) diameter circle is unacceptable.

53. Refer to Section 9 of this Practice for design and fabrication details.

54. Applies to all longitudinal seams, end plate welds, circumferential seams and nozzle connections (ASME Category D connections.)

55. For critical service, welds connecting attachments shall be full penetration, to avoid interface for H2 collection.

56. For non-critical service, as a minimum, welds connecting attachments shall be continuous to seal the perimeter of the part and prevent corrosion behind the attachment.

57. Hardness survey may be by any indentation method for which there is an ASTM standard, except Brinell. Where Vickers indenter is used, the load shall be (10 kg.

58. Applies to non-clad CS. For clad CS, PWHT in accordance with ASME SEC VIII, Division 1.59. RT to ASME SEC VIII, Division 1, Paragraph UW51 or equivalent.

60. UT to ASME SEC VIII, Division 1, Appendix 12 or equivalent.

61. MT welds to ASME SEC VIII, Division 1, Appendix 6 or equivalent.

18.1. Nozzles and Connections

Equipment shall have flanged nozzles or connections. Slip-on flanges and seal and backwelded threaded connectors shall not be used. Threaded plugs may be used as closures for tube-rolled openings in headers.

18.2. Plug Sheet Plugs

Plug threads shall be coated with a molybdenum disulfide base lubricant.

Appendix E: Plate Type Heat Exchangers

Plate type heat exchangers shall not be used in critical, sour or toxic service where gasket leaks pose an unacceptable risk.

Experience shows that plate heat exchangers are very reliable and do not have many leakage problems. However, due to the large number of gaskets, there is a potential for leakage and therefore an unacceptable risk in critical service.

RATIONALE: In order to ensure safe, reliable operation in sour service, special attention shall be given to the choice of plate metallurgy, elastomers, bolt up and testing procedures and to hazard mitigation. Mitigation of hazard involves location, gas/H2S detection, alarms, controls, ventilation and operating procedures.

RATIONALE: Maintenance procedures shall prohibit reuse of elastomers, in order to ensure gasket seal reliability.

Appendix F: Fired Heaters

Designs and materials requirements for fired heaters are covered in MP 11-P-01. Heater tube materials for H2S service shall also meet all the requirements of NACE MR0175 and this Practice.

Appendix G: Pipelines (Refer to MP 20-P-01)

19. Gas Pipelines

Table G1: Gas Pipeline Material, Design, Construction and Non-Destructive Examination Options for Various Sour Service Categories

Critical ServiceNon-Critical Service

Material Selection

Pipe and Component Material SystemHIC tested bare steel pipe (Note 1) with HIC resistant steel components (Note 10);Bare steel system (Note 9)

CRA-S system

CRA-C pipe with CRA-S, CRA-C or CRA-O components

Design

BranchesBW tees (Notes 2 and 3)BW tees (Notes 2 and 3)

Construction (Note 4)

WPS/PQR HardnessVickers survey required (Note 5). Refer to Section 9Hardness survey required (Note 6). Refer to Section 9

Repair WeldsPQR requiredPQR required

Backweld not permittedBackweld not permitted

Refer to Section 9Refer to Section 9

PWHTPer CodePer Code

Production HardnessShall be consideredMay be required

Refer to Section 9Refer to Section 9

Non-Destructive Examination

Girth Welds100 percent RT (Note 7)100 percent RT

O-Lets100 percent MT (Note 8)100 percent MT (Note 8)

NOTES:

62. Refer to MP 20-P-02 for procurement of HIC resistant and HIC tested pipe.

63. O-lets shall not be used in sizes greater than NPS 4. When O-lets are permitted in lieu of butt welding (BW) tees for outlet sizes equal to or less than NPS 4, full penetration welds are required for the O-let to run connection.

64. When pigging facilities are included in the design, barred tees shall be used. Welding of bars shall satisfy the requirements of this MEP.

65. Table G1 refers to mainline construction. For above ground piping (e.g., at wellsites, valve stations, pigging facilities, test facilities, compressor stations or pump stations) refer to Section 8 of this Practice.

66. Vickers indentor load shall be (10 kg.

67. Hardness survey may be by any indentation method for which there is an ASTM standard, except Brinell.

68. Interpret using ASME B31.8 and API STD 1104 or equivalent, except incomplete penetration greater than 13 mm (1/2 in), is not permitted. No burnthroughs are permitted.

RATIONALE: Users are cautioned that regulatory agencies may have different restrictions on flaw sizes. Users shall check to ensure compliance with appropriate regulations.

69. Interpret using ASME SEC VIII, Division 1, Appendix 6 or equivalent.

70. Inhibitor system may be required.

71. P < 0.025 percent, S < 0.010 percent; maximum yield strength shall not exceed 550 MPa (80 ksi); macrohardness (22 HRC; microhardness (248 HV (500); ERW pipe ( NPS 2 shall be subjected to the root guided-bend test.

20. Liquid Multiphase Pipelines

RATIONALE: Sour water pipelines would be designed with these same materials. Multiphase pipelines containing appreciable water content and sour water pipelines may also require internal coatings and/or corrosion inhibition for the control of pitting and general corrosion.

Table G2: Liquid Multiphase Pipeline Material, Design, Construction and Non-Destructive Examination Options for Various Sour Service Categories

Critical ServiceNon-Critical Service

Material Selection Options

Pipe And Component Material SystemHIC tested bare steel pipe (Note 1) with HIC resistant steel components (Note 10)Bare standard steel system (Note 9)

CRA-S systemCML steel system

CRA-C pipe and CRA-S, CRA-C or CRA-O componentsIPC steel system

PEL steel system

Design

BranchesBW tees (Notes 2 and 3)Per Code

Construction (4)

WPS/PQR HardnessVickers survey required (Notes 5 and 6)Vickers survey required (Notes 5 and 6)

PWHTPer ASME Piping CodePer ASME Piping Code

Production HardnessOptionalNot required

Non-Destructive Examination

Girth Welds100 percent RT (Note 7)Per ASME Piping Code

O-lets100 percent MT (Note 8)Per ASME Piping Codecomment on min. 10 percent RT good practice

NOTES:

72. Refer to Appendices K and L for guidance with the procurement of HIC resistant and HIC tested pipe.

73. When O-lets are permitted in lieu of butt welding (BW) tees, full penetration welds are required for the O-let to run connection.

74. When pigging facilities are included in the design, barred tees shall be used. Welding of bars shall satisfy the requirements of this MEP.

75. Table G-2 refers to mainline construction. For above ground piping (e.g., at wellsites, valve stations, pigging facilities, test facilities, compressor stations or pump stations). Refer to Appendix A of this Practice.

76. Vickers indentor load shall be 10 kg.

77. Hardness survey may be by any indentation method for which there is an ASTM standard, except Brinell. Refer to Section 9.3 of this Practice.

78. Interpret using ASME B31.8 and API STD 1104 or equivalent, except incomplete penetration greater than 13 mm (1/2 in), is not permitted. No burnthroughs are permitted.

RATIONALE: Users are cautioned that regulatory agencies may have different restrictions on flaw sizes. Users shall check to ensure compliance with appropriate regulations.

79. Interpret using ASME SEC VIII, Division 1 or equivalent.

80. Inhibitor system may be required.

81. P