The effect that even small concentrations of H2S can have upon CO2 corrosion has been recognized since at least the 1940's. Early studies showed that the FeS corrosion products that were formed had an impact, but disagreed whether the impact was beneficial or not. Although H2S corrosion has not received the level of attention given to CO2 corrosion, the literature has shown that there are a number of different forms of FeS that can form as corrosion products, depending upon the exposure conditions. Between the corrosion, geochemical and thermodynamics literature, a great deal is known about the corrosion chemistry involved with the formation of the various FeS species as well as the impact that each has upon further corrosion. However, there is still a great deal that is not known. For example, there are currently no generally accepted prediction algorithms for any form of H2S corrosion. There are also still a number of unknowns about the corrosion reactions that lead to pitting, which is the most common mode of sour service equipment failure. This paper reviews a sampling of the H2S corrosion literature over the past 60 years and describes some of the areas of research that remain.
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