NACE MR0175 / ISO 15156

NACE

Goals:

• Discuss new standard & changes

• Describe failure mechanisms

• Discuss Kimray offering & changes

NACE

National Association of Cowboy Entertainers

NACE

National Association of Corrosion Engineers

History• Interest begin in the 1950s after WWII. Natural

gas was beginning to be used by industry. Sour gas was encountered in wells being drilled.

• Standard is based on 50 yrs of experience.• Main goal is to prevent failures that would allow

exposures to people and the environment.• Standard applies to down hole, Xmas Tree, &

surface facilities. NOT process plants, refineries, etc.

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History• Fatalities from an accident in West Texas

prompted the Texas Railroad Commission to ask the industry to write a document to help prevent such incidents in the future.

• Failure mode identified as SSC & SCC.• Materials failing were identified as

materials with HIGH HARDNESS & HIGH TENSIL STRENGTHS

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BACKGROUND• The new standard addresses issues which were not

considered in the previous version of NACE MR0175-2002.

• The new standard acknowledges, in addition to SSC, other potentially catastrophic failure mechanisms resulting from sour environments.

• Mechanisms specified in MR0175/ISO 15156 include – as chloride stress corrosion cracking, – hydrogen-induced cracking and stepwise cracking, – stress oriented hydrogen-induced cracking, – soft zone cracking – galvanically-induced hydrogen stress cracking;

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The new standard:– addresses the synergistic effects of H2S with

other environmental factors (chloride content, temperature, pH, etc.) on the cracking resistance of many listed materials;

– limits the use of many of the listed metals through additional environmental restrictions which were not taken into account by the previous NACE MR0175 versions.

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Structure of New Document• The new NACE MR0175/ISO 15156 consists of 3 parts:

• Part 1- General Principles for Selection of Cracking-Resistant Materials

• Part 2- Cracking-Resistant Carbon and Low Alloy Steels, and the use of Cast Irons

• Part 3- Cracking-Resistant CRAs (Corrosion-Resistant Alloys) and Other Alloys

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CHANGES - Responsibilities• “It is the responsibility of the user to determine the

operating conditions and to specify when this standard applies. The manufacturer is responsible for meeting metallurgical requirements. It is the user’s responsibility to ensure that a material will be satisfactory in the intended environment.”

• The owner company is a user.• These are NOT users.

– An equipment manufacturer is NOT a user.– An mill is NOT a user.– A distributor is NOT a user.– A consultant or contractor are NOT users.

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It’s the User's Responsibility to:• select the carbon and low alloy steels, cast irons, CRAs

(corrosion-resistant alloys) and other alloys suitable for the intended service. (Part 1: Section 5 & Section 6)

• document the selection and qualification of materials used in the H2S environment. (Part 1: Section 5 & Section 9)

• assume the ultimate responsibility for the in-service performance of all materials selected by the end user or delegates.– For example, the end users is still responsible for materials

selected by delegated Engineering Consultants/ Engineering and Procurement Companies (EPC).

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The Supplier/Manufacturer is responsible to:

• Although there is no direct reference to supplier/fabricator responsibility in MR0175/ISO15156 the following sections imply responsibility. – cooperate and communicate in an exchange of information

between the equipment users and materials suppliers/manufacturers concerning required or suitable service conditions. (Part 1: Section 5)

– ensure the material purchased meets the equipment users requirements and the requirements of the standard. (Part 3: Section 7)

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• The manufacturer is responsible for meeting metallurgical requirements. It is the user’s responsibility to ensure that a material will be satisfactory in the intended environment.

• Paragraph 1.6.2 is a disclaimer-type of statement: “Materials included in this standard are resistant to, but not necessarily immune to, SSC and/or SCC in stated conditions. Improper design, manufacturing, installation, selection, or handling can cause resistant materials to become susceptible to SSC and/or SCC.”

• This is telling the user: You are responsible for materials selection. We cannot guarantee successful use or no failures or cracking, etc.

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The new edition spells out more clearly that materials selection is up to the user—NACE cannot give advice and will not get involved in negotiations or a dispute between users and manufacturers.

CAUTION: THERE MAY BE REGULATORY REQUIREMENTS THAT SPECIFY REQUIREMENTS IN MR0175 IN SOME LOCATIONS.

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Materials Included In MR0175 (with conditions):

Ductile IronCarbon Steel304 Stainless Steel316 Stainless Steel17-4 PH Stainless Steel

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Materials Excluded In MR0175:

Cast IronFree Machining SteelBrassCopper303 Stainless Steel

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Changes: Affecting only the Carbon Steel Alloys

• Regions of environmental or SSC severity. (Figure 1 of Part 2: Clause 7.2.1.2)– Four severity regions are defined based on the effect of the in situ pH and H2S partial

pressure on the carbon and low alloy steels. This differs from previous editions where only the partial pressure of the H2S was considered.

• Hardness requirements for welds (Part 2: Clause 7.3.3.2)– Three different hardness test methods are acceptable for weld procedure

qualification: Vickers (HV10 or HV5), Rockwell 15N, and HRC (with specified restrictions). This differs from previous editions where HRC was the primary basis of acceptance.

• Consideration of HIC/SOHIC/SZC/SWC (Part 2: Section 8) – These additional cracking mechanisms, which result from the synergy of H2S

exposure and various material factors (steel chemistry, hardness and manufacturing methods) should also be considered.

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Changes: Affecting only the CRAs• Consideration of environmental limits for SCC and GHSC (Part 3:

Section 6)• The new standard provides principles for selecting cracking

resistant materials for use in the presence of H2S in combination with other environmental factors, such as chlorides. The cracking mechanisms addressed include:– SCC caused by the presence of chlorides in the H2S containing

environment. – GHSC caused by the presence of dissimilar alloys, including

weldments in contact with an H2S environment

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New Environmental Restrictions for Alloys (Part 3: Clause A.1.3)

• Depending on the alloy, environmental restrictions may include: – maximum chloride content, – maximum H2S partial pressure, – maximum temperature, – minimum pH– application limits depending on the presence of free sulfur in the

system. • In previous editions of MR0175, several legacy materials had no

environmental restrictions, implying they were suitable for any sour service environment.

• For example, wrought precipitation hardening nickel alloy 718 (UNS N07718) had no environmental restrictions in previous editions of MR0175; in the current standard this alloy has H2S partial pressure limitations based on the maximum operating temperature.

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Changes: New Environmental Restrictions for Alloys (Part 3: Clause A.1.3)

• Some alloys may have a range of acceptable environmental parameters depending on the severity of the in-service conditions.

• The environmental limits listed in Tables A.2-A.42 give the allowable parameters for the H2S partial pressure, temperature, chloride content, presence of sulfur and pH.

• As cracking behavior can be affected by the complex interactions of these parameters, there is some discretionary latitude for interpolation depending on the material’s intended application or service conditions;

• For example, austenitic steels such as AISI 316SS will have different service limitations based environmental parameters such as partial pressure of H2S, temperature, chloride concentration and in situ pH in the production fluid. AISI 316SS and AISI 304SS have a new temperature limit of 140F and H2S partial pressure limits. NACE is evaluating requests for changes.

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Changes: Deletion of Previously Approved Materials

• The general usage of some previously approved materials has been restricted to specified components only.

• For example, 17-4 martensitic, precipitation hardening stainless steel was deleted from the general usage section, but remains an acceptable material for various components of wellheads and Christmas trees, provided a maximum H2S partial pressure of 0.50 psi and minimum pH of 4.5. 17-4 martensitic is no longer allowed as a pressure containing component.

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Changes: Corrosion Resistant Alloy Categories (Part 3: Clause A.1.1)

• A CRA category is a broad-based group of alloys defined in terms of chemical composition, manufacturing process, and finished condition.

• These categories or materials groups (austenitic stainless steels, martensitic stainless steels, etc.) are further split into material types (similar compositional limits) and individual alloys.• For example, Annex A, Table A.2 outlines the environmental and

materials limits for the general usage of austenitic stainless steels (AISI 304SS, AISI 316SS, etc).

• This table is sectioned into general materials type and individual alloys, e.g. UNS S20910.

• The individual alloys tend to have broader environmental limits than those set for the group.

• The UNS S20910 can be used at a slightly higher temperature than AISI 316 at similar partial pressures of H2S.

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Equipment User’s Application Guideline for MR0175/ISO 15156

• This section is to provide the equipment user with a guideline on how to approach a material selection project using the NACE MR0175/ISO 15156 Standard. • 6.1 Select Qualification Method • 6.2  Qualification By Field Experience • 6.3 Qualification by Laboratory Testing

• Equipment user decision flow charts are included in Appendix C and need to be used in conjunction with this section.

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Other Considerations• When using this document there are other considerations

that need to be taken into account. For example: • Using previous versions of MR0175 will require

consideration of:• changes in environmental conditions,• regulatory requirements,• the ability of the supplier and equipment user to

address conflicts between the previous and current versions

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CRACKING MECHANISMS

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What chemical causes corrosion of steel by H2S?

• Hydrogen• Fe + H2S > FeS + 2H0 (in aqueous solutions)

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Hydrogen ions in aqueous solution from acid waters and the H2S form on the surface of the base metal. They migrate into the crystalline structure and combine with other Hydrogen ions to form H2 gas. 100s to 1000s psi pressure can occur.

H0 + H0 > H2 gas

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Forms of Hydrogen Damage

• Hydrogen Blistering (HB)

• Hydrogen-Induced Cracking (HIC)

• Stress-Oriented Hydrogen-Induced Cracking (SOHIC)

• Sulfide Stress Cracking (SSC)

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HYDROGEN INDUCED CRACKING

Concern is that HIC will link up through the wall by stepwise cracking.

Stepwise Cracking (Linked HIC Cracks)

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Sulfide Stress Cracking at Welds

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HYDROGEN BLISTERING

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Hydrogen Damage

• In high purity metal H2 gas does not collect as readily, therefore damage is reduced.

• Kimray ensures the quality of materials used. Other competitors materials have proven to be questionable.

• Damage is dependent on the H2 gas charge rate. How fast the H2 gas is moving thru the metal substrate.

• Sulfide Stress Cracking (SSC)

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Hydrogen Damage

Residual Stresses from Welds can make matters worse.

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Hydrogen Damage

What temperatures are metals more susceptible to Hydrogen Damage? (High, Low or Moderate temps)

At High temps Hydrogen atoms pass right thru the metal. At Low temps Hydrogen charge rates are small. Worse damage occurs at Room Temp. !

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NACE at Kimray

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NACE at Kimray

Kimray can provide most products for NACE service. Certifications and documentation are provided when NACE components and products are ordered.

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NACE at Kimray

There are some limitations:

• Bellows in the 75/150 PG Pilots

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NACE at Kimray

There are some limitations:

• Bellows in the 50 PG Pilot

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NACE at Kimray

There are some limitations:

• Glycol Pumps

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NACE at Kimray

There are some limitations:

• Thermostats

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The standard 112 pilot plug is now produced with NACE compliant material (316 SS).

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NACE at Kimray

Kimray has implemented a new Heat Treating standard that documents the procedures to properly heat treat NACE components.

Kimray also is improving our heat treating process to better ensure NACE compliant products.

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What about elastomers in sour gas?

• NACE does not apply

What is recommended?

• HSN up to 300F

• Aflas up to 500F (Not Recommended below 25F)