NACE MR0175 / ISO 15156 · Engineering tool
Sour service check (NACE MR0175)
p_H₂S = y · P
Determine whether a service is sour per NACE MR0175 / ISO 15156 from the H2S partial pressure.
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H₂S partial pressure
5.000psia
- Threshold
- 0.05psia
- p_H₂S / threshold
- 100.00
How it works
NACE MR0175 / ISO 15156 defines “sour service” by the partial pressure of H2S in the gas phase. For a gas system the partial pressure is p_H2S = y_H2S × P_total, where y_H2S is the H2S mole fraction and P_total the absolute total pressure.
The screening threshold is p_H2S ≥ 0.3 kPa (≈0.05 psia); at or above it, sour-service material selection (sulfide stress cracking resistance) applies. The standard also defines regions where total pressure or H2S content shift the boundary below that line.
This tool computes p_H2S from a total pressure and an H2S mol% (or ppmv) and flags the screening classification. The final materials decision also depends on chloride, temperature, and the specific equipment — confirm against the current standard edition.
Assumptions & limitations
- Single gas phase; p_H2S = y_H2S × P_total (y as mole fraction, P absolute).
- Screening threshold 0.3 kPa (0.05 psia) per the NACE MR0175 / ISO 15156 sour-service definition.
- Does not resolve the multi-phase / containment-region subtleties (very low total pressure with low H2S) — confirm against the standard diagram for borderline cases.
- Materials selection also depends on H2S, chloride, temperature, CO2, and stress — this is a screening flag, not a material selection.
Related reading
Companion articles
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