NACE MR0175 (also published as ISO 15156) is the international standard for selecting metals that resist sulphide stress cracking and stress corrosion cracking in sour, H2S-containing oilfield environments. It sets hardness limits and H2S thresholds for parent metal and welds, so a "NACE-compliant" material is one qualified for sour service within defined operational limits.
What does NACE MR0175 cover?
NACE stands for the National Association of Corrosion Engineers, but is commonly used as shorthand for the standard itself. The association began as a small group of corrosion engineers on a regional study and grew into an international body focused on corrosion in industrial processes. Its full title is "Metals for Sulphide Stress Cracking and Stress Corrosion Cracking Resistance in Sour Oilfield Environments", and it specifies the materials that can be used in specific oil and gas environments. A "NACE-compliant" product is one that meets NACE MR0175 and can therefore be considered for sour service within its operational limits.
| Covers | Selecting metals resistant to sulphide stress cracking and stress corrosion cracking in sour, H2S-containing oilfield environments - hardness limits and H2S threshold limits for both parent metal and welds. |
|---|---|
| Applies to | Carbon and low-alloy steels, cast irons, and corrosion resistant alloys specified for oil and gas production. |
Why does it focus on hardness?
Hardness is the only practical material measurement that can be taken in the field to validate a specification, so it is central to the standard. It correlates reasonably with overall mechanical properties and is applied to both the parent metal and any welds. The standard sets H2S threshold limits above which precautions against environmental cracking become necessary.
How is the standard structured?
NACE MR0175 started as a US standard and has since been adopted by ISO, now published and maintained as ISO 15156-3, and in 2003 NACE MR0103 was issued to cover sulphide stress cracking in petroleum refining. MR0175 itself has three parts:
- General principles for selecting cracking-resistant materials.
- Cracking-resistant carbon and low-alloy steels, and the use of cast irons.
- Cracking-resistant corrosion resistant alloys and other alloys.
Because the standard focuses only on sulphide stress corrosion cracking, it does not address general corrosion or pitting. Nor does it stipulate minimum mechanical properties, the manufacturing route or general testing standards, so it is not a complete selection tool on its own.
How are the H2S limits set?
Thresholds are established from a combination of laboratory evaluation and operator experience, and the document continues to evolve as alloys are added and limits refined. Limits vary widely between alloys and alloy families: for some, they account for chlorides, pH, temperature, hardness, yield strength and CO2, while for others they are less strictly defined. Where the H2S thresholds are exceeded, MR0175 allows fit-for-purpose testing to qualify a material for a specific application.
As a default, our stock is produced to meet the NACE standard where applicable.