NACE MR0175 / ISO 15156 Applicability for Metallic Materials

NACE refers to NACE International, the corrosion-control organization whose standards and technical activities became part of AMPP (Association for Materials Protection and Performance) after NACE International and SSPC combined in 2021. The legacy name NACE MR0175 remains widely used in oil and gas specifications.

NACE MR0175 / ISO 15156 is a materials-selection standard for metallic materials exposed to defined H₂S-containing environments in oil and gas production and natural-gas treatment. Its purpose is to reduce the risk of H₂S-related cracking by defining requirements and qualification routes for materials used in those environments.

The standard does not identify a single “NACE grade.” Applicability depends on the material family, metallurgical condition and the actual sour-service environment.

How the ISO 15156 series is divided

For stainless steels, duplex grades and nickel alloys, the relevant acceptance route moves principally into Part 3. Carbon and low-alloy steels are addressed principally in Part 2.

What problem is the standard addressing?

The standard is concerned with cracking mechanisms associated with H₂S-containing production environments. For carbon/low-alloy steels, the scope includes resistance to mechanisms such as sulfide stress cracking and related hydrogen-assisted cracking phenomena. Part 3 addresses cracking-resistant CRAs and other alloy families.

It is important not to stretch the scope into a universal corrosion standard. ISO 15156 is focused on materials selection/qualification against specified H₂S-related cracking risks within its stated oil-and-gas-production scope. It does not replace all design-code, corrosion allowance or general/localized corrosion requirements.

“NACE compliant” is not a complete material designation

A grade name by itself does not establish compliance.

For sour service, acceptability can depend on factors such as:

• material family and exact grade;
• chemical composition;
• heat-treatment condition;
• hardness;
• cold work;
• weld metal and HAZ condition;
• H₂S partial pressure;
• pH;
• chloride concentration for relevant alloys;
• temperature;
• elemental sulfur or other environmental factors where applicable;
• qualification by listed material route or testing.

The applicable parameters differ by material family. That is why it is risky to use a generic table saying “Grade X is NACE compliant” without stating the environment and metallurgical condition.

Carbon and low-alloy steels: Part 2

ISO 15156-2 provides requirements and recommendations for selecting/qualifying carbon and low-alloy steels in H₂S-containing oil and gas production environments.

Hardness control is a major feature because hard microstructures can increase susceptibility to sulfide stress cracking. Fabrication and welding therefore matter as much as the base grade name.

A mill certificate showing the right base chemistry does not automatically prove that a welded component will meet the complete sour-service requirement after fabrication.

Stainless, duplex and nickel alloys: Part 3

ISO 15156-3 covers corrosion-resistant alloys and other alloys. This includes material families commonly encountered in oil and gas projects such as:

• austenitic stainless steels;
• ferritic/austenitic (duplex) stainless steels;
• nickel-based alloys;
• other CRA families within the standard's scope.

Acceptance can be conditional on environmental limits and material condition. For duplex stainless, for example, the practical review must consider more than a PREN number; heat treatment, hardness, microstructure/phase balance, welding and the actual sour environment can all be relevant.

Do not copy generic HRC or temperature limits from a secondary table into a PO without checking the exact grade entry and environmental limits in the governing edition.

What information should the purchaser provide?

A sour-service RFQ should do more than write “NACE MR0175.” Depending on the project, the materials engineer may need to define relevant service information such as:

• H₂S content / partial pressure;
• operating and design temperature;
• pressure;
• pH / aqueous phase conditions;
• chloride level for CRA selection;
• material/product form;
• welding condition;
• required qualification route;
• hardness/testing requirements;
• governing edition and any project supplements.

Without the service environment, a supplier may be unable to determine whether a particular CRA is acceptable within the standard's environmental limits.

2026 edition status

As of 19 September 2026:

• ISO 15156 Parts 1, 2 and 3:2020 remain the published fourth edition.
• AMPP lists ANSI/NACE MR0175-2021 / ISO 15156-2020 as the active/revised adoption.
• ISO is developing a fifth edition; draft documents are progressing through the standardization process.

A draft is not automatically the contract requirement. For procurement, use the edition explicitly invoked by the client/PO and monitor the new edition when it is formally published.

Common mistakes

“NACE applies only to carbon steel”

False. Part 3 covers CRAs and other alloys.

“316L is NACE, so it is acceptable everywhere”

Incomplete. Acceptance depends on the applicable environmental limits and material condition.

“The MTC says NACE, therefore the fabricated item is compliant”

Not necessarily. Welding, hardness, cold work, heat treatment and component-level requirements can matter.

“MR0175 is the standard for any equipment containing H₂S”

Too broad. Its stated scope is oil and gas production and natural-gas treatment/sweetening environments. Other industries/services can invoke different NACE/AMPP or design standards.

MetalMate takeaway

NACE MR0175 / ISO 15156 covers both carbon steels and corrosion-resistant alloys. Part 2 addresses carbon/low-alloy steels; Part 3 addresses stainless, duplex, nickel and other CRAs. Compliance is an environment-and-condition question — not a sticker attached to a grade name.

References

• ISO, ISO 15156-1:2020 — General principles: https://www.iso.org/standard/79658.html
• ISO, ISO 15156-2:2020 — Carbon and low-alloy steels: https://www.iso.org/standard/79659.html
• ISO, ISO 15156-3:2020 — Corrosion-resistant alloys and other alloys: https://www.iso.org/standard/79660.html
• AMPP, ANSI/NACE MR0175-2021 / ISO 15156-2020: https://content.ampp.org/standards/book/1139/ANSI-NACE-MR0175-Petroleum-and-Natural-Gas
• ISO, ISO/DIS 15156-1, fifth edition under development: https://www.iso.org/standard/88380.html