Question:I was wondering if you could assist me in interpreting the partial pressure limitation for Carbon Steels referenced in part 2 section 7.1.2 and A.2. Is there a partial pressure max limit for carbon steels? If so, where is the reference in NACE MR0175/ISO 15156?
The partial pressure mentioned in Section 7.1.2 is the partial pressure of H2S in the gas phase in equilibrium with the water in the production fluid. Annex C gives information on how to calculate H2S partial pressure.
Regions 1, 2, and 3, Figure 1, cover usual conditions above 0.3 kPa. Note 1 mentions the unknown performance of steels above 1 MPa. The maximum partial pressure limit for carbon steels depends on many variables as noted in 15156-2 Clause 6. Currently a NACE TM0177 test with 100 kPa H2S, ~2.7 pH, room temperature, 50 g/L NaCl is considered to cover all normal production conditions for carbon steels.
This question is in relation to NACE MR0175/ISO 15156-2 Clause 7.1.2
Reference: ISO 15156 Maintenance Panel Inquiry #2010-09