Alloys for Sour Service: NACE MR0175 and NACE MR0103
Every grade below is one a mill has certified to a sour service standard – not one that is merely reputed to suit H2S. Where the acceptance carries a condition, the condition is stated with it.
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Hydrogen sulphide cracks susceptible metals under stress, and it does so without warning and without general corrosion to give notice. The two standards that govern material selection against it are widely quoted and frequently confused, and a great deal of published material names alloys as “NACE grades” without saying which standard, which condition or which environment. This page states what we can actually certify and what each acceptance rests on.
The Two Standards Are Not Interchangeable
NACE MR0175 / ISO 15156 is the upstream standard. It covers materials for use in oil and gas production where H2S is present – wells, wellheads, downhole tools, valves and production flowlines. Part 3 is the one that matters for corrosion-resistant alloys: it lists them by material type and sets limits on hardness, heat-treatment condition and the environment itself.
NACE MR0103 / ISO 17945 is the downstream standard. It covers materials for refinery and petrochemical equipment in wet H2S service. It is a different scope with different acceptance rules, written for process plant rather than for wells.
Material accepted under one is not automatically accepted under the other, and a specification that names only “NACE” has not said which. Several of the grades below are certified to both, which is worth confirming on the certificate rather than assuming.
Grades We Stock and What Certifies Them
| Grade | UNS | MR0175 / ISO 15156 upstream |
MR0103 / ISO 17945 downstream |
|---|---|---|---|
| Alloy 600 | N06600 | Yes | Yes |
| MONEL® 400 | N04400 | Yes | Yes |
| MONEL® K-500 | N05500 | Yes – age hardened, hardness controlled | Yes |
| INCONEL® 625 | N06625 | Yes | Yes |
| INCONEL® 718 | N07718 | Only to API 6A CRA – see below | Only to API 6A CRA – see below |
| INCOLOY® 825 | N08825 | Yes | Yes |
| HASTELLOY® C-22® | N06022 | Yes | Yes |
| HASTELLOY® C-276 | N10276 | Yes | Not sourced |
| 904L | N08904 (1.4539) | Yes | Yes |
| 254 SMO® | S31254 | Yes | Yes |
| Alloy 926 | N08926 (1.4529) | Yes | Not sourced |
| Duplex 2205 | S32205 / S31803 | Yes | Yes |
| Super duplex 2507 | S32750 | Yes | Yes |
| Sanicro® 35 | N08935 | Yes – type 4a and 4c materials | Yes |
| ELGILOY® | R30003 | Yes | Yes |
| MP35N® | R30035 | Yes – to 35 HRC, or 51 HRC cold reduced plus aged | Not sourced |
| HAYNES® 25 (L-605) | R30605 | Yes | Not sourced |
“Not sourced” is not the same as “not acceptable.” It means no document we hold names that grade against that standard. Ask and we will obtain a certificate against the standard you need before you commit to the material.
Acceptance Is Conditional, Not a Property of the Alloy
ISO 15156-3 does not approve alloys in the abstract. It lists them by material type and attaches limits – on hardness, on heat-treatment condition, and on the service environment itself: H2S partial pressure, temperature, chloride content and in-situ pH. The same UNS number can be acceptable in one condition and outside the standard in another, which is why the certificate has to state the condition and the hardness result rather than just the grade.
Two grades on this page make the point plainly:
- INCONEL® 718 is a precipitation-hardened alloy, and the ageing practice decides the answer. Ordered to API 6A CRA – solution annealed, age hardened, hardness controlled – it is certified to both MR0175 / ISO 15156-3 and MR0103 / ISO 17945. Ordered to AMS 5663 it is aged to a higher hardness and is not covered. Both are alloy 718 and both are UNS N07718, so the grade designation alone will not tell a buyer which one arrived. Name the route on the purchase order.
- MP35N® is included to a maximum of 35 HRC, and 51 HRC only in specific cold reduced plus aged conditions. Material harder than the applicable cap falls outside the listing however good the alloy is.
The same logic applies to MONEL® K-500, which is also age hardened, and it is why the certificates we hold for it record a surface hardness result rather than only a composition.
What to Send Us When You Enquire
Sour service enquiries answered from a grade name alone tend to need a second round. Send these and we can confirm the grade, the condition and the certification in one:
- Which standard the project calls for – MR0175 / ISO 15156, MR0103 / ISO 17945, or both.
- The service environment: H2S partial pressure, temperature, chloride content and pH.
- The product form, size and quantity, and any client or end-user specification that governs (an API 6A CRA or oil-company specification changes the answer).
- The certification level you need – EN 10204 3.1 as standard, 3.2 and third-party inspection on request.
Material ships from our Mumbai stockyard with the manufacturer's certificate. See our export markets and supply locations, or send us the enquiry.
Frequently Asked Questions
What is the difference between NACE MR0175 and NACE MR0103?
The short answer is that MR0175 is upstream and MR0103 is downstream. MR0175, published jointly as ISO 15156, governs materials for oil and gas production equipment exposed to H2S – wells, wellheads, downhole tooling and production flowlines. MR0103, published jointly as ISO 17945, governs materials for refinery and petrochemical equipment in wet H2S service. They are different scopes with different acceptance rules, so material accepted under one is not automatically accepted under the other. Several of the grades we stock are certified to both.
Does an alloy comply with NACE MR0175 on its own?
No. ISO 15156-3 lists corrosion-resistant alloys by material type and sets limits on hardness, heat-treatment condition and the service environment – H2S partial pressure, temperature, chloride content and pH. An alloy is acceptable within those limits and not outside them, which is why the certificate has to state the condition the material was supplied in.
Is INCONEL® 718 acceptable for sour service?
It depends entirely on the specification it is ordered to. Alloy 718 supplied to API 6A CRA in the solution annealed and age hardened condition, with hardness controlled, is certified to NACE MR0175 / ISO 15156-3 and MR0103 / ISO 17945. The same alloy supplied to AMS 5663 is aged to a higher hardness and is not covered. Order the sour service route explicitly – the UNS number alone does not distinguish them.
What documentation comes with sour service material?
An EN 10204 3.1 mill test certificate naming the sour service standard, the heat treatment condition and the hardness result, issued by the manufacturer rather than by us. Where a project requires it we can arrange 3.2 certification and third-party inspection. Tell us the H2S partial pressure, temperature, chloride level and pH and we will confirm which grade and condition suits before quoting.