During the past decade or so, there has been an increase in the use of a rule-of-thumb that there is a dividing line between CO2 and H2S corrosion where the CO2/H2S gas partial pressure is 500. Most users of this ratio are familiar with neither the origins of the ratio, the assumptions that it implies nor of its practical limits. This work investigated both the history and the basis for the ratio. In doing so, it was determined that although there is a sound scientific basis for the ratio, the error band produced by variations in thermodynamic data inputs is so large as to make the ratio’s use impractical as an engineering guideline.

Subject
Mackinawite, Thermodynamics, Reaction products, Iron sulfides, Dissolution, Solubility, Siderite, Partial pressures, Ionization, Constants, Free energy, Risk reduction, Chemical reactions
Keywords:
CO2, H2S Ratio, H2S Corrosion, Mackinawite, Siderite
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2011
Association for Materials Protection and Performance (AMPP)
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