Quick answer
MR0175 is not a steel grade and not a material. It is the standard that states which metallic materials may be used in oil and gas equipment exposed to wet H2S, and under which environmental limits. That is why a “NACE pipe” enquiry that carries only a grade cannot be answered: the material can only be selected against the environment it will see.
What the standard actually covers
NACE MR0175 is published jointly as ISO 15156, and it is organised in three parts:
| Part | Covers | What it decides for a pipe order |
|---|---|---|
| Part 1 | General principles, definitions and the evaluation route | Whether the material falls under the standard at all, and what has to be documented |
| Part 2 | Carbon and low-alloy steels, including those with up to about 13% chromium | The hardness requirement and the environmental limits inside which a carbon steel may be used |
| Part 3 | Corrosion-resistant alloys — stainless, duplex, nickel alloys and others | Whether the alloy can be used in the specific combination of H2S, chloride, temperature and pH, and whether qualification testing is needed |
NACE MR0103 is the refinery equivalent. It addresses a different environment and sets different limits, so a material qualified under one document is not automatically qualified under the other.
The failures the standard exists to prevent
- Sulfide stress cracking (SSC). Crack growth in hard, high-strength steel under tensile stress in the presence of wet H2S. This is the failure that the hardness limits are written for.
- Hydrogen-induced cracking (HIC) and stress-oriented hydrogen-induced cracking (SOHIC). Hydrogen absorbed at the steel surface accumulates at inclusions and laminations, usually in plate and seam-welded products, and cracks develop in the through-thickness direction.
- Stress corrosion cracking (SCC). Cracking in stainless and other corrosion-resistant alloys under specific combinations of chloride, H2S and temperature.
What decides whether a service is sour
The label “sour” is not decided by the fluid name. The inputs that matter are:
- H2S partial pressure in the gas phase, which is the primary screening number.
- In-situ pH of the water phase.
- Chloride content, which is decisive for stainless and duplex grades.
- Operating temperature, including the lowest expected temperature in service.
- Total pressure and the presence of free water, because the H2S has to be in solution to cause cracking.
If those fields are not on the enquiry, the material cannot be selected responsibly. This is why we ask for the partial pressure and the pH rather than the question “is it sour?” — the same fluid can be acceptable for one material and outside the limits for another.
Which grades are not automatically acceptable
| Grade family | Position for sour service |
|---|---|
| A106, A333, API 5L carbon steel | Can be used inside the environmental limits of Part 2; the governing requirement is usually the hardness limit and the documented hardness survey |
| API 5CT N80 and P110 | No hardness ceiling in API 5CT, so they are not automatically qualified for wet H2S service; using them is a qualification question, not a grade choice |
| API 5CT L80 | The grade normally specified for sour-service casing and tubing; it has a hardness ceiling of its own in API 5CT |
| 13Cr, super 13Cr, duplex 2205, super duplex 2507 | Covered by Part 3, where the acceptable envelope depends on H2S, chloride and temperature together; qualification testing is commonly required |
A “NACE compliant” certificate means the material was made and tested to the requirements of the standard. It is not, by itself, a statement that the material is suitable for every possible combination of H2S partial pressure and pH in your well. Suitability is a project-level judgement using the actual environment.
What to write on the order, and which documents to ask for
Put the standard and the environment in the same clause so there is nothing to interpret later:
Material and testing to NACE MR0175 / ISO 15156. Environment: H2S partial pressure [value] kPa, in-situ pH [value], chloride [value], design temperature [value], total pressure [value]. Maximum hardness [value] HRC, verified by hardness survey on [extent]. HIC test to NACE TM0284 [where required]; SSC test to NACE TM0177 method [where required]. Mill test certificate to EN 10204 3.1, plus test reports; 3.2 where a third party countersigns.
Documents to ask for:
- Mill test certificate with the heat number, chemistry and mechanical results.
- Hardness survey results, with the extent and the method stated.
- HIC and SSC test reports where the project requires them, naming the solution, the duration and the acceptance criteria used.
- Heat-treatment records, where the hardness is achieved through heat treatment.
- The third-party inspection certificate, where a witness was required.
What the extra requirements cost in time and money
Sour service changes four things at once: the material route (L80 instead of N80, for example), the heat treatment and the control of hardness across the lot, the test programme, and the documentation. The test programme is the part most often underestimated: HIC and SSC testing runs for days rather than hours, and a failed lot has to be re-made.
Because these items sit on the critical path, the practical advice is to settle the environment and the test requirements at the enquiry stage — before the mill schedules the heat — rather than adding them when the mill test certificate is issued.
Frequently asked questions
Is NACE MR0175 the same as ISO 15156?
Yes. The document is published jointly by NACE and ISO under both numbers. MR0175 is the designation most buyers use; ISO 15156 is the same technical content under the ISO numbering.
What is the difference between MR0175 and MR0103?
MR0175 / ISO 15156 covers oil and gas production environments. MR0103 covers refinery environments. They set different limits, and a material qualified under one is not automatically acceptable under the other.
Does MR0175 cover stainless steel and duplex?
Yes, in Part 3. For those alloys the acceptable envelope depends on the combination of H2S, chloride and temperature, so the environment has to be stated before the grade can be confirmed.
Does a NACE-compliant mill certificate prove the material is suitable for my well?
No. It proves the material met the standard’s requirements for how it was made and tested. Whether it is suitable for your well still depends on your H2S partial pressure, pH, chloride level and temperature — that comparison is what the material selection has to document.
Where to go next
- Sour service — the material selection route for sour wells.
- API 5CT L80 tubing — the grade most often specified for sour service.
- API 5CT 13Cr tubing — the corrosion-resistant option for CO2 service.
- EN 10204 3.1 vs 3.2 — which certificate level to ask for.
Four details and we can quote. The standard or grade, the size and wall thickness, the tonnage, and the destination port. Send them together and we answer with availability and pricing.
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