Direct answer: NACE MR0175 / ISO 15156 does not approve every nickel alloy for every sour-service condition. Part 3 provides requirements and recommendations for cracking-resistant corrosion-resistant alloys and other alloys in H2S-containing oil and gas production. Compliance depends on alloy category, product condition, hardness or cold work, environmental limits and documented qualification.
What the Standard Covers
ISO 15156 applies to equipment used in oil and natural-gas production and treatment where H2S-related cracking can threaten people or the environment. It addresses mechanisms such as sulfide stress cracking and stress-corrosion cracking. It is not a general corrosion-rate design standard and does not replace a project materials-selection study.
Information Needed Before Selecting a Nickel Alloy
| Input | Why it matters |
|---|---|
| H2S partial pressure | Defines sour severity, not total system pressure alone |
| Temperature | Changes cracking susceptibility and qualification envelope |
| Chloride concentration | Can control localized corrosion and cracking |
| pH and elemental sulfur | Can make the environment more severe |
| Material condition | Cold work, heat treatment, hardness and weld condition affect resistance |
| Applied stress | Residual and operating stresses influence cracking risk |
Alloy 625 and Alloy 718 Are Not Treated the Same
Solid-solution nickel alloys and precipitation-hardened alloys have different restrictions. Alloy 625 is often considered for corrosion resistance, whereas Alloy 718 may be selected for high strength but requires close control of heat treatment, hardness and environmental limits. Verify the exact material table and edition rather than relying on a statement such as “NACE material.”
Procurement and MTC Checklist
- State NACE MR0175 / ISO 15156 edition and applicable part.
- Specify UNS grade, product standard, condition and maximum hardness.
- Require heat-number traceability and EN 10204 3.1 documentation.
- Define welding procedure, filler metal and weld hardness/qualification controls.
- Record the environmental envelope used for acceptance.
- Use additional qualification testing when outside listed limits.
FAQ
Does “NACE compliant” mean suitable for any sour well?
No. Suitability is conditional on the service environment and material condition.
Is an MTC statement enough?
No. The purchaser should verify chemistry, condition, hardness, heat treatment, product form, traceability and the applicable environmental limits.
Does ISO 15156 cover refineries?
Its scope is oil and gas production and natural-gas treatment. Refining service commonly uses other NACE/AMPP documents and project requirements.
Primary References
Engineering note: Values and acceptance criteria must be checked against the edition of the governing standard named in the purchase order. Application-specific design approval remains the responsibility of the purchaser or project engineer.
Post time: Sep-11-2026