NACE MR0175 / ISO 15156 Safety & Relief Valves
What NACE MR0175 / ISO 15156 requires for safety & relief valves — applicability, key and testing requirements, the alternative standards, and compliant supply with full certification.
What does NACE MR0175 / ISO 15156 require for safety & relief valves?
NACE MR0175 / ISO 15156 (Petroleum and Natural Gas Industries - Materials for Use in H₂S-Containing Environments (Sour Service), NACE International (now AMPP) / ISO) sets the design, material and testing requirements for safety & relief valves in its scope. NACE MR0175 (now jointly published as ISO 15156) is the governing standard for material selection in equipment exposed to wet hydrogen sulphide (H₂S) - commonly called 'sour service'. It defines hardness limits, heat treatment requirements, and acceptable material grades for valve bodies, trim, and fasteners in H₂S-containing oil, gas, and water service. Non-compliance can cause sulphide stress cracking (SSC), hydrogen-induced cracking (HIC), or stress-oriented HIC, leading to catastrophic brittle fracture.
Applicable Pressure Classes
Key Requirements
- Carbon steel (A216 WCB, A105): maximum hardness 22 HRC (PWHT required for cast bodies)
- Low-alloy steels: individual hardness limits per NACE Table B.1
- Martensitic stainless (13Cr trim, stems): maximum 22 HRC for NACE service
- Austenitic SS (316L, CF3M): acceptable without restriction in most zones
- Nickel alloys (Alloy 625, C276): acceptable for most sour service without restriction
- Cold-worked SS is restricted - solution annealed condition required
- Welding and hard-facing procedures must produce surface hardness ≤22 HRC in HAZ
- Weld consumables and procedure qualification per NACE MR0175 Annex B
Testing Requirements
- Hardness testing: all valve bodies, bonnets, stems - per NACE MR0175 limits
- Charpy impact testing (where required by NACE MR0175)
- Weld hardness survey for hard-faced seats
- PWHT verification (where required)
Alternative Standards for Safety & Relief Valves
Other standards that also govern safety & relief valves — useful for spec cross-acceptance.
Related Standards
Connected Engineering
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