The sulfide stress cracking resistance of steel oil country tubular goods (OCTG) is commonly correlated to the hydrogen sulfide (H2S) partial pressure, calculated by multiplying the mole fraction H2S by the total system pressure. However, sour gas mixtures exhibit non-ideal behaviors at high system pressure. Neglecting these non-ideal effects causes large over-conservatism at total system pressures above 5000 psi. It is important to compensate for non-ideal gas and solution behaviors in order to select representative laboratory test environments for sour service fit-for-purpose materials evaluations.

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