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NACE MR0175

Overview

NACE MR0175 / ISO 15156 defines material requirements for equipment operating in sour environments containing hydrogen sulfide (H₂S). It prevents failures such as sulfide stress cracking (SSC), hydrogen-induced cracking (HIC), and stress-oriented HIC (SOHIC).

Standard Body: NACE / ISO

Equivalent: ISO 15156 Parts 1, 2, 3

H₂S Threshold: > 0.05 psia

Material Types: Carbon Steel, CRA

Failure Mechanisms

  • SSC: Sulfide Stress Cracking
  • HIC: Hydrogen-Induced Cracking
  • SOHIC: Stress-Oriented HIC
  • Galvanic corrosion

Material Requirements

  • Maximum hardness: 22 HRC (250 HV)
  • Applies to base metal and heat-affected zone (HAZ)
  • Strict heat treatment requirements for stainless steel
  • CRA qualification per ISO 15156-3
  • Full material traceability with test certificates

Material Hardness Limits

Material Condition Max HRC Max HV Notes
Base Metal 22 250 Includes HAZ
Weld Metal 22 250 PWHT required
Hard Facing As approved As approved Special qualification
Bolting Per Table A.2 Per Table A.2 B7M / L7M typical

Documentation & Compliance

All materials must be supported by certified material test reports (MTRs) confirming compliance with NACE MR0175 / ISO 15156. Traceability must be maintained throughout fabrication.

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