ISO 15156 / NACE MR0175

Covers — selection and qualification of metallic materials resistant to sulfide stress cracking (SSC), stress-corrosion cracking, and related cracking in H2S-containing (sour) upstream oil and gas production. Part 1 gives general principles; Part 2 covers carbon and low-alloy steels; Part 3 covers corrosion-resistant alloys, all keyed to environmental severity (H2S partial pressure, in-situ pH, chloride).

Does NOT cover (exclusions) — the following are governed elsewhere:

• Sour refining/downstream service → ISO 17945 / NACE MR0103.
• The line-pipe/product material spec itself → API 5L and the ASTM/API material standards.
• The pipeline/piping design code → ASME B31.8 / B31.4.

MR0175/ISO 15156 governs material/hardness limits for sour upstream service; MR0103 covers the refinery side.

MR0175/ISO 15156 sets material qualification requirements for sour service:

• Environmental Classification — H2S partial pressure, in-situ pH, and chloride define the SSC severity region.
• Carbon/Low-Alloy Steels — hardness limits (base metal, weld, HAZ) and processing to resist SSC.
• Corrosion-Resistant Alloys — qualified alloys with environmental limits (temperature, H2S, chloride).
• Qualification — laboratory testing and documented compliance for the intended environment.

ISO 15156 / NACE MR0175 is the governing material standard for sour (H2S-containing) upstream oil and gas production. It classifies the environment by H2S partial pressure, in-situ pH, and chloride, then defines which metals — and at what hardness and processing — resist sulfide stress cracking and related environmental cracking. Carbon/low-alloy steels get hardness limits; corrosion-resistant alloys get qualified environmental envelopes.

It is a materials-qualification standard, not a design code: the pipeline is designed to B31.8/B31.4 and made from API 5L pipe, but the material selection and hardness control must comply with MR0175 for sour service. The refinery counterpart is MR0103.

Engineering Note: Sour-service compliance hinges on weld and HAZ hardness, not just base metal — a compliant base steel welded without hardness control can still fail by SSC at the weld, so qualify and control the whole welded assembly.