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NACE MR0175 / ISO 15156 and Sour-Service Alloys

Standards reference

Quick Answer

NACE MR0175 / ISO 15156 sets the requirements for materials used in oil and gas production where hydrogen sulfide (H₂S) is present. Part 3 covers corrosion-resistant alloys, including nickel alloys such as 625, 718, 825, 925 and C-276, with limits on environment, hardness and heat treatment. Oilfield grades are often also supplied to API 6A718 (alloy 718) or API 6ACRA (age-hardened nickel alloys such as 925).

Updated 7 Oct 2026. Published by Mipra Steel.

What the Standard Does

Hydrogen sulfide can crack susceptible metals under stress. NACE MR0175 / ISO 15156 tells equipment makers and operators which materials can be used in sour service, and under what limits. It has three parts: general principles (Part 1), carbon and low-alloy steels (Part 2), and corrosion-resistant alloys (Part 3). Part 3 lists materials by alloy group and sets environmental limits such as H₂S partial pressure, temperature, chloride content and pH, together with hardness and heat-treatment requirements.

Why This Matters for Scrap

Sour-service rules push operators towards nickel alloys for wellhead equipment, downhole tools, clad flowlines and valve trim. When those assets are replaced or decommissioned, they produce some of the richest nickel alloy scrap on the market:

  • Inconel 625 from clad pipe, weld overlays and valve bodies.
  • Inconel 718 from hangers, valve stems and downhole tools, often to API 6A718.
  • Incoloy 825 from sour-service tubing and clad flowlines.
  • Incoloy 925 from downhole and wellhead components, often to API 6ACRA.
  • Hastelloy C-276 from the most severe service.

Oilfield Specifications on Top of ASTM

API 6A718 covers alloy 718 for oil and gas drilling and production equipment, with tighter controls on microstructure, hardness and testing than general-purpose specifications. API 6ACRA covers age-hardened nickel alloys such as 925. Material certified to these carries very good paperwork, and oilfield offcuts are among the easiest scrap to prove. See oil and gas scrap.

Clad and weld-overlaid pipe needs care: the nickel alloy layer can be a small share of the weight. Declare clad material separately and test both surfaces.

FAQ

What is NACE MR0175?

The standard, also published as ISO 15156, for materials used in H₂S-containing environments in oil and gas production. Part 3 covers corrosion-resistant alloys, including nickel alloys.

Is Inconel 718 NACE compliant?

Alloy 718 is listed in NACE MR0175 / ISO 15156 Part 3 within set environmental and hardness limits. Oilfield 718 is commonly supplied to API 6A718.

What is API 6ACRA?

An API standard for age-hardened nickel-based alloys used in oil and gas drilling and production equipment, including alloy 925.

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