What is the minimum partial pressure of H₂S that requires compliance with NACE MR0175?
Minimum Partial Pressure of H₂S for NACE MR0175 Compliance
NACE MR0175 is an international standard that specifies requirements for metallic materials in oil and gas production environments exposed to H₂S. Compliance with NACE MR0175 is based on the partial pressure of H₂S (ppH₂S) present in the environment.
Compliance with NACE MR0175
According to ANSI/NACE MR0175/ISO 15156, production conditions with ppH₂S below 0.3 kPa (0.05 psi) do not require special precautions for carbon and low-alloy steels.
Highly Susceptible Carbon and Low Alloy Steels
However, highly susceptible carbon and low alloy steels (e.g., high strength, heavily cold-worked) can still be prone to H₂S-related damage mechanisms, even below these limits. Additionally, the risk of Hydrogen Induced Cracking is present for partial pressure of H₂S below 0.3 kPa (0.05 psi).
Maximum ppm of H₂S Allowed without NACE MR0175
For corrosion-resistant alloys (CRAs), there is no ppH₂S lower limit, meaning precautions need to be taken whenever the possibility of H₂S is present. It’s important to note that CRAs are not immune to H₂S damage mechanisms, but their resistance to corrosion can help prevent damage.