NACE MR0175 / ISO 15156: Materials for Sour-Service (H2S) Equipment

Key points at a glance

Compliance here is about selection and qualification, not a material grade. A specific grade meets the standard only when its heat treatment, hardness, and environmental limits are all accounted for, there's no such thing as a blanket "NACE-proof" label.

ANSI/NACE MR0175 and ISO 15156 are the same document. AMPP (once known as NACE International) and ISO publish it jointly under two different names.

The standard deals with cracking caused by H2S: sulfide stress cracking (SSC), hydrogen-induced cracking (HIC), stepwise cracking (SWC), SOHIC, and chloride stress-corrosion cracking (SCC) as well.

It comes in three parts. Part 1 lays out general principles. Part 2 covers carbon and low-alloy steel. Part 3 addresses corrosion-resistant alloys, or CRAs.

Hardness, grade, and the environmental envelope together determine compliance, H2S partial pressure, in-situ pH, chloride content, temperature. Outside those qualified limits, a grade simply isn't compliant anymore.

Scope: what NACE MR0175 / ISO 15156 covers

NACE MR0175 / ISO 15156 governs metallic materials in oil-and-gas production equipment where hydrogen sulfide (H2S) can cause cracking. The standard covers material selection, qualification, hardness control, fabrication, and the test envelope a grade must pass. Think of it as the specification layer that sour-service grade choices have to conform to. Why H2S cracks steel in the first place is a separate question, addressed under sour service and H2S cracking.

What is sour service: and when does the standard apply

A fluid counts as "sour" once it carries enough H2S to risk cracking. The standard sets the entry threshold for a gas environment at an H2S partial pressure of ≥ 0.05 psia (0.3 kPa abs) in the gas phase. Above that line, a material has to be selected and qualified to NACE MR0175 / ISO 15156. Risk tracks partial pressure, not concentration alone, so the same mol-% H2S turns more aggressive as total system pressure climbs.

The three parts of the standard

MR0175 vs ISO 15156: same document, two names

ANSI/NACE MR0175 and ISO 15156 are the same joint publication, not competing standards. Historically, NACE MR0175 was the North American document and ISO 15156 the international one. They got harmonized into a single three-part standard that's maintained jointly now. A requirement citing either name resolves to the identical technical content. Sometimes you'll see it written as "ANSI/NACE MR0175/ISO 15156:2015."

MR0175 (production) vs MR0103 / ISO 17945 (refinery)

Scope matters when you're specifying the right standard. MR0175 / ISO 15156 covers upstream oil-and-gas production: wells, wellheads, flowlines, separators. ANSI/NACE MR0103 / ISO 17945, by contrast, applies to downstream refinery wet-H2S service. Citing the wrong document is a common spec error. The two standards share some ground but rest on distinct qualification bases, and they aren't interchangeable.

The cracking mechanisms it guards against

The standard exists to stop failures driven by H2S. Each mechanism behind that failure has its own predicate.

• Sulfide stress cracking (SSC), hardened steel and other high-strength materials crack under tensile stress when exposed to H2S. Hardness limits are the main control.
• Hydrogen-induced cracking (HIC) / stepwise cracking (SWC), atomic hydrogen builds up at inclusions in carbon steel. It blisters, then links up into stepwise cracks. No external stress is needed for this one.
• SOHIC (stress-oriented HIC), HIC damage aligns under stress near welds, bridging into a through-wall path.

Chloride stress-corrosion cracking (SCC) is another limit on austenitic CRAs. They're susceptible to it, and the interaction with H2S narrows their operating window further.

The failure physics show up in detail in two places: sour service and H2S cracking and stress-corrosion cracking. The compliance route follows below.

Key requirements

Hardness limits (the 22 HRC rule)

For carbon and low-alloy steels under Part 2, the standard caps hardness at 22 HRC (≈250 HV) to resist SSC. That applies to base metal, weld, and, critically, the heat-affected zone (HAZ). CRAs under Part 3 carry their own material-specific hardness caps. One of the most common sour-service spec errors is forgetting the HAZ hardness check after welding. The limit has to be met as fabricated, not just on the mill plate.

Environmental limits: the SSC region concept

No grade stands compliant on its own. It's compliant within a defined envelope of H2S partial pressure, in-situ pH, chloride content, temperature, and elemental sulfur presence. Part 3 sorts these into SSC regions (0–3), each one rougher than the last. An alloy can pass with flying colors in a mild region and get flatly ruled out in a severe one. That's the reason service conditions need to be nailed down before anyone picks a grade.

Heat-treatment & fabrication controls

Compliance comes down to delivered condition. Plate and forgings arrive in the qualifying heat-treated condition, solution-annealed CRAs, normalized and HIC-tested carbon steel, and welding procedures have to keep weld and HAZ hardness within limits. Cold-work limits apply too. The MTC has to document heat-treat condition and hardness, so conformance can actually be proven.

Grades & product forms covered: and which Nandini supplies

This is a bridge from the specification to buyable material. Nandini Steel stocks and exports sour-service grades, with the NACE-relevant tests documented right on the certificate. Compliance is always stated within the standard's envelope, never as a blanket claim.

Corrosion-resistant alloys (Part 3)

Incoloy 825 (UNS N08825) is the sour-service CRA workhorse. A Ni-Fe-Cr alloy (Ni 38–46%, Mo 2.5–3.5%, Cu 1.5–3%, Ti-stabilized), it resists sour service and conformsTo NACE MR0175 / ISO 15156 Part 3 within defined limits, and its combined resistance to reducing and oxidizing acids is why it is chosen over 316L/904L in mixed-acid and sour-gas duty. It conforms to ASTM B424 / SB-424 and is available as sheet and plate (Incoloy 825 coil is limited). Buyers routinely call it "Inconel 825", the correct designation is Incoloy / Alloy 825 (N08825), and getting it right on the PO and MTC avoids receiving-inspection disputes. See what is Incoloy 825 and welding Incoloy 825.

904L (N08904) is a super-austenitic stainless (Ni ~25%, Mo ~4.5%, Cu ~1.5%, PREN ~34) that resists chloride pitting and crevice attack, with limited sour applicability under its Part 3 envelope. 316/316L are austenitic stainless steels susceptible to chloride-SCC, so Part 3 restricts their permissible H2S conditions. Duplex 2205 is covered under Part 3 with its own limits.

Carbon & low-alloy steel (Part 2)

A516 Gr 70 NACE-HIC plate is PVQ carbon steel that resists hydrogen-induced cracking when requiresTest HIC per NACE TM0284 is satisfied and hardness is controlled to 22 HRC. It conforms to ASTM A516 / ASME SA-516 plus ASTM A20 and is used in pressure vessels and separators for sour duty. Call out the HIC-tested variant explicitly, plain Gr 70 is not sour-qualified. SA387 Cr-Mo alloy steel is the elevated-temperature Part 2 option.

Equivalents for the compliant CRAs sit in the full cross-reference at UNS / Werkstoff cross-reference.

Testing & qualification to the standard

Qualification comes from standardized laboratory cracking tests, with the results logged on the mill test certificate.

SSC testing: NACE TM0177

NACE TM0177 qualifies resistance to sulfide stress cracking through four distinct methods: Method A (uniaxial tensile), Method B (bent-beam), Method C (C-ring), and Method D (double-cantilever-beam, DCB). Which one you pick depends on the product form and the alloy class involved.

HIC / stepwise-cracking testing: NACE TM0284

NACE TM0284 checks rolled carbon-steel plate for hydrogen-induced cracking. Three ratios, measured on sectioned samples, determine whether a plate passes.

Project specs set a hard ceiling on CLR, CTR and CSR. The heat only passes if every sample comes in under those limits.

Four-point bend: NACE TM0316

NACE TM0316 is a four-point-bend method for evaluating SSC of pipe and plate under a defined applied strain. It's used where a bent-specimen geometry suits the product.

What appears on the MTC

For a sour-service order the EN 10204 3.1 mill test certificate records the heat/cast number, chemical analysis, mechanical properties, heat-treat condition, hardness (to the 22 HRC / material-specific cap), and the HIC results (CLR/CTR/CSR) or SSC test outcome, the documentary proof of NACE conformance tied to the physical heat.

How to order NACE MR0175 / ISO 15156 material from Nandini

1. State the service envelope, H2S partial pressure, in-situ pH, chloride, temperature, and any elemental sulfur. These set which SSC region applies. Use the grade selector to move from envelope to candidate grade.
2. Pick a compliant grade and form, e.g. Incoloy 825 sheet/plate for CRA duty, or A516 Gr 70 NACE-HIC plate for carbon-steel vessels and separators.
3. Specify the NACE basis and tests on the PO, cite "NACE MR0175 / ISO 15156" plus the required tests (HIC per TM0284, SSC per TM0177 where applicable) and the hardness cap, so the heat is supplied in the qualified condition.
4. Receive the 3.1 MTC, an EN 10204 3.1/3.2 mill test certificate is provided with every order, documenting hardness, HIC/SSC results, and heat/cast traceability.
5. Add third-party witness if required, independent inspection (TÜV SÜD, Bureau Veritas, DNV, SGS) can witness testing and release on request.

All sour-service grades come from genuine mill plate: Aperam, Outokumpu, Jindal, POSCO, Nippon Steel, JFE. Products sit ex-stock for immediate dispatch. HIC/SSC testing or a third-party witness will add qualification time to a sour-service order beyond standard dispatch, so flag that requirement at RFQ.

Applications governed by this standard

NACE MR0175 / ISO 15156 sets the pass/fail bar for materials across oil & gas (sour service), sour wells, wellheads, separators, and flowlines, and petrochemical / gas processing wherever H2S shows up. Nandini most often supplies two grades into these sour-service duties: Incoloy 825 and A516 Gr 70 HIC.

Price & lead time for NACE-compliant material

Pricing comes from a live RFQ, not a fixed price table, because sour-service cost swings with grade, thickness, quantity, and the test scope you specify. Standard grades ship ex-stock for immediate dispatch. When HIC per TM0284, SSC per TM0177, or third-party witness inspection is called out, though, build in extra time for that testing and release. Send the service envelope and test requirements along with your RFQ, and you'll get an accurate quote and lead time back.

FAQ

Request a quote for NACE-compliant sour-service material

Nandini Steel has held ISO 9001:2015 certification since 2003, more than 20 years in business now, with over 307 projects completed for 260+ clients across 36+ export countries. The company stocks, supplies and exports NACE MR0175 / ISO 15156 sour-service material, including Incoloy 825 (N08825) sheet and plate as well as A516 Gr 70 NACE-HIC plate. Everything comes from genuine mill sources, and every order ships with an EN 10204 3.1/3.2 mill test certificate. Beyond that, Nandini Steel is a certified specialist in 904L, Alloy 28, Incoloy 800 and Hastelloy.

Send us your service envelope: H2S partial pressure, pH, chloride content, and temperature. Add grade, form, and test requirements, and we'll get you a live quote.

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Review our quality assurance, certifications, and mill test certificate practices, or read about how to specify A516 for a vessel.