Non-ideal gas behavoir, HPHT wells and NACE MR0175 – partial pressure of H2S

Question: NACE MR0175/ISO 15156, Part 2, Annex C, Section C.1 states that “The partial pressure of H2S may be calculated by multiplying the system total pressure by the mol fraction of H2S in the gas.” Does the word “may” permit other methods, such as incorporating the effects of non-ideal gas behavior, to calculate partial pressure for determining material selection?


Yes. Please note: Annex C as a whole is “informative” rather than “normative” and is therefore not mandatory.

This question is in relation to NACE MR0175/ISO 15156-2 Annex C

Reference: ISO 15156 Maintenance Panel Inquiry #2004-08

At Oil & Gas Corrosion we see many enquiries related to the partial pressure of H2S. We have the expertise to support you selecting materials where ideal gas behaviour deviated such as High Pressure and High Temperature wells (HPHT). We do this by evaluating the production conditions (pressure, temperature, produced water etc) and evaluating the risks and consequences. Let us help you with the materials selection and partial pressure calculations.


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