ISO 17945 / NACE MR0103

Covers — metallic material and fabrication requirements (hardness limits, welding controls, heat treatment) to resist sulfide stress cracking in the wet-H2S environments of petroleum refining and downstream processing.

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

• Upstream sour production materials → ISO 15156 / NACE MR0175.
• The piping/vessel design code → ASME B31.3 / BPVC Section VIII.
• Damage-mechanism background and inspection → API RP 571 / API 570.

MR0103/ISO 17945 governs sour-service material/hardness in refining; MR0175 governs the upstream side.

MR0103/ISO 17945 sets material requirements for sour refining service:

• Hardness Limits — base metal, weld, and HAZ hardness caps to resist SSC.
• Welding & Heat Treatment — controls (including PWHT where required) to meet the hardness limits.
• Material Selection — carbon/low-alloy steels and other materials qualified for the defined sour environment.
• Documentation — evidence of compliance for the intended refinery sour service.

ISO 17945 / NACE MR0103 is the refining and downstream counterpart of MR0175, setting the material and hardness requirements needed to resist sulfide stress cracking in wet-H2S refinery process environments. Where the upstream MR0175 maps severity by H2S partial pressure, MR0103 applies its requirements to the sour refinery environments it defines.

It is a materials/fabrication standard invoked on refinery equipment and piping datasheets for sour service, working alongside the piping design code (B31.3) and the damage-mechanism and inspection references (RP 571, API 570). Hardness control of welds and HAZ is central.

Engineering Note: Do not interchange MR0103 and MR0175 — refinery (downstream) sour service uses MR0103, upstream production uses MR0175; specifying the wrong one can leave equipment either under- or over-qualified for its actual sour environment.