ISO 15156-3:2020 addresses the selection and qualification of corrosion-resistant alloys (CRAs) and other alloys against cracking in H2S-containing oil and gas production environments. It covers sulfide stress cracking (SSC), stress corrosion cracking (SCC) and galvanically induced hydrogen stress cracking (GHSC). This guide covers the fourth edition, published in November 2020, with particular attention to duplex stainless steel, super duplex stainless steel and nickel alloys. It is an original technical overview of the supplied standard. Use the complete document and assessed service conditions for material acceptance and project decisions.
ISO 15156-3:2020 PDF — Download Standard
What Is ISO 15156-3:2020?
Part 3 provides material requirements for CRA and other alloy equipment used in sour oil and natural gas production and natural-gas treatment plants. It supplements the relevant design codes, regulations and product specifications. The ISO 15156 series is associated with NACE MR0175/ISO 15156. Suitability depends on the actual alloy, product condition, manufacturing route and environmental exposure. A grade name or a general claim of “NACE compliance” does not establish acceptance for every sour-service application.
The document addresses cracking resistance; it does not establish resistance to general metal loss or localized corrosion. Its scope includes equipment such as wells, wellheads, flowlines, field facilities and natural-gas treatment equipment, with exclusions in Table 1. Refining and downstream equipment require separate assessment of the governing requirements.
Standard at a Glance
| Item | ISO 15156-3:2020 |
|---|---|
| Edition | Fourth edition, November 2020 |
| Materials | Stainless steels, nickel-based alloys and other alloy groups listed in Annex A |
| Cracking mechanisms | SSC, SCC and GHSC |
| Normative annexes | Annex A: material and environmental provisions; Annex B: laboratory qualification |
| Informative annexes | Annex C: purchasing information; Annex D: nominated test conditions |
| Related framework | ISO 15156-1 general selection and qualification principles |
ISO 15156 Part 1 vs Part 2 vs Part 3
| Part | Main role | Purchasing implication |
|---|---|---|
| ISO 15156-1 | General principles for material selection and qualification | Define service conditions and the qualification basis |
| ISO 15156-2 | Carbon and low-alloy steels; provisions for cast irons | Check the relevant steel, hardness, welding and cracking requirements |
| ISO 15156-3 | Cracking-resistant CRAs and other alloys | Check alloy-specific environmental and metallurgical limits |
Part 2’s general carbon-steel hardness provisions cannot be transferred automatically to duplex stainless steel or nickel alloys. Apply the relevant Part 3 material group and Part 1 framework.
Service Environment and Qualification Routes
Clause 5 identifies interacting factors including chemical composition, strength, heat treatment, microstructure, manufacturing method, finished condition, H2S exposure, in situ pH, chlorides and other halides, oxygen or elemental sulfur, temperature, galvanic effects, tensile stress and exposure time. Assess applied and residual stress together.
Clause 6.1 permits selection using Annex A, successful laboratory qualification under Annex B, or satisfactory documented field experience consistent with Part 1. Annex A environmental limits apply together, including all table remarks and metallurgical requirements. Limits for named equipment must not be generalized to other applications.
Include shutdown and upset conditions, such as low-pH condensed water. Annex A production-environment limits do not cover injection or flowback of chemicals that lower in situ pH. Materials used beyond the listed environmental limits, or in alternative metallurgical conditions, need an appropriate qualification basis. The equipment user must verify qualifications and retain the supporting documentation.
Duplex and Super Duplex Stainless Steel
Annex A.7 addresses duplex stainless steels. Table A.24 covers use for any equipment or component; Table A.25 addresses downhole tubular components, packers and other subsurface equipment. Select the applicable table before checking composition, heat treatment, ferrite and environment.
| Provision | Requirement or interpretation |
|---|---|
| Table A.24 material groups | 30 ≤ FPREN ≤ 40.0 with Mo ≥ 1.5%, and 40.0 < FPREN ≤ 45; check the applicable row and remarks |
| Table A.24 delivery condition | Wrought, cast and HIP duplex: solution annealed and liquid quenched or otherwise rapidly cooled; ferrite 35%–65% by volume; no ageing heat treatments |
| Table A.25 special applications | Solution annealed, liquid quenched and cold worked; ferrite 35%–65%; maximum hardness 36 HRC, together with the relevant environmental limits |
| Elemental sulfur | NDS means no data submitted to establish acceptability in an environment containing elemental sulfur |
For example, the Table A.24 rows with a chloride ceiling of 180,000 mg/l list a maximum temperature of 232°C and H2S partial-pressure ceilings of 10 kPa for the lower PREN group and 20 kPa for the higher PREN group. These are conditional combinations, not universal operating ratings for 2205 or 2507. Apply the entire selected row, its remarks and the required material condition. A statement that an individual parameter has no set limit does not imply that every combination of parameters is acceptable.
The 36 HRC provision belongs to the specific Table A.25 applications and material condition. It is not a universal acceptance limit for all duplex pipe. Product specifications, customer requirements and applicable qualification evidence must also be checked.
PREN and Actual Chemical Composition
Clause 6.3 uses the calculation FPREN = Cr + 3.3(Mo + 0.5W) + 16N, with element contents expressed as mass percentages. Use actual chemical composition from the material analysis, rather than nominal grade composition. Compare calculated values directly with the specified absolute limits without rounding a failing result into acceptance.
PREN supports classification and comparison of pitting resistance. It does not independently demonstrate cracking resistance or corrosion suitability in an H2S-containing oilfield environment. A higher PREN also requires attention to manufacturing control and potentially harmful phase formation.
Welding and Fabrication Requirements
Clause 6.2.2 requires welding procedures and qualification records to be available for inspection. Evidence of adequate cracking resistance must cover conditions at least as severe as the proposed application, using the relevant Annex A provisions, Annex B testing or documented field experience. Where Annex A requires weld hardness qualification, the normal methods are HV10, HV5 or Rockwell 15N unless the equipment user approves otherwise.
For duplex weld qualification, A.7.2 requires examination of weld metal, heat-affected zone and parent material at 400× magnification. Grain boundaries must have no continuous precipitates; the combined intermetallic, nitride and carbide content must not exceed 1.0%, with sigma phase no more than 0.5%. Ferrite in the weld root and unreheated cap must be 30%–70% by volume, determined in accordance with ASTM E562.
HAZ hardness must satisfy the applicable parent-metal maximum, and weld-metal hardness must satisfy the limit for the alloy used as the welding consumable. Do not substitute the parent-material ferrite range for the weld range. Fabrication, cold work and thermal processes can change material properties; assess the final delivered condition under Clause 6.2.3 and the relevant alloy provisions.
Purchasing and Documentation Checklist
Clause 7 and Annex C support a purchasing specification agreed between the equipment user, supplier and manufacturer. Include:
- Alloy designation, product form, equipment application and applicable manufacturing specification.
- ISO 15156-1 and ISO 15156-3, with the required editions.
- Temperature, H2S exposure, minimum in situ pH, water-phase chlorides, elemental sulfur and other relevant exposure conditions.
- The selected Annex A material group, table and row, or the application-specific qualification route.
- Actual chemical composition, heat treatment, final strength, hardness and microstructure evidence as applicable.
- WPS/PQR records, weld hardness and duplex phase-balance examination where required.
- Additional SSC, SCC or GHSC testing and agreed acceptance criteria where applicable.
- Traceability connecting the supplied material to its test records and qualified environmental limits.
Materials selected for a special application under Annex B must be traceable to the environmental conditions of that application. Retain the records so later operating changes can be assessed against the original selection basis.
Frequently Asked Questions
Does ISO 15156-3 cover duplex and super duplex stainless steel?
Yes. Annex A.7 addresses duplex stainless steels by material type, composition and applicable equipment use. Check the actual material condition and full environmental limits.
Is PREN above 40 enough to establish sour-service suitability?
No. PREN alone does not establish acceptance. The relevant composition range, manufacturing condition, microstructure, environmental limits and qualification basis must also be satisfied.
Is 36 HRC the maximum hardness for every duplex pipe?
No. The 36 HRC provision in Table A.25 applies to specified downhole and subsurface applications in the stated condition. Do not apply it universally.
Does compliance guarantee immunity to cracking?
No. The standard establishes cracking resistance within defined conditions. Selection remains dependent on the intended service and supporting evidence.
Does Part 3 replace ASTM A790 or ASTM A789?
No. Product specifications address manufacture and product requirements; ISO 15156-3 adds sour-service material selection and qualification requirements.
Can a material be used beyond Annex A limits?
An appropriate qualification through Annex B laboratory testing or documented field experience under Part 1 may support defined conditions. Keep those limits and records explicit.