In NACE MR0175, is 0.3kPa ppH₂S the lower limit for sour service compliance? What happens at lower partial pressures of H₂S?
What Is Sour/Non-Sour Service in NACE MR0175/ISO 15156?
This webpage provides an answer to a common question regarding the definition of sour/non-sour service in NACE MR0175/ISO 15156. The response clarifies that there is no defined “”non-sour”” limit, as steels can still be susceptible to cracking even below the limit of 0.05 psi (0.3 kPa). The implication of this is reinforced by Annex C, which identifies the demarcation between “”sour”” and “”non-sour”” environments.
CRAs and Environmental Cracking Resistance
Regarding CRAs, the degree of environmental cracking resistance can vary widely, and there is no defined “”non-sour”” limit in ISO 15156-3.
How OGC Energy Can Help
At OGC Energy, our team can help define sour service requirements, including CRA selection and HIC resistance at low ppH₂S. We can also evaluate materials selection at ppH₂S below 0.3kPa, and help clients with the interpretation and implementation of NACE MR0175.
This question pertains to NACE MR0175/ISO 15156-2 Clause 7.2.1.3.
Reference: ISO 15156 Maintenance Panel Inquiry #2009-11, Part 1 and Part 2.