Valve Standard Reference
NACE MR0175 / ISO 15156
NACEPetroleum and Natural Gas Industries — Materials for Use in H₂S-Containing Environments (Sour Service)
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'.
Overview — NACE MR0175 / ISO 15156
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.
Scope
Applicable to all pressure-containing metallic components exposed to wet H₂S service in oil and gas production and processing. Covers valve bodies, bonnets, stems, closures, fasteners, and weld overlay materials. Defines sour service threshold: H₂S partial pressure ≥0.0003 MPa (0.05 psia).
Applicable Valve Types
All valve types used in sour gas/oil service
Particularly critical: gate valves, ball valves, check valves, globe valves
Safety relief valves on sour service vessels
Applicable Pressure Classes
Key Requirements — NACE MR0175 / ISO 15156
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 — NACE MR0175 / ISO 15156
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)
Documentation Required for NACE MR0175 / ISO 15156 Compliance
NACE MR0175 compliance certificate on valve data sheet
Hardness test records (Brinell or Rockwell) for all CRAs and CS components
PWHT records (time-temperature charts)
Welding procedure qualification records (WPQRs) with NACE hardness compliance
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