The composition and some of the physical properties of the sulfide film which formed when iron was corroded in the system H2S-CO2-H2O have been related to the concentration of the H2S in the H2S-CO2 gas (in equilibrium with the solutions). At H2S concentrations below 0.1 psia, a protective sulfide film consisting of FeS2 (marcasite or pyrite), troilite and some kansite formed. Due to the protective nature of the film, at H2S concentrations between 0.0009 and 0.1 psia, the corrosion rate of the specimen and the surface area of the film were relatively low and independent of the H2S concentration. At H2S concentrations greater than 0.1 psia, a nonprotective film was formed, composed mainly of troilite, pyrite and a predominating amount of kansite. In the region 0.1 to 4.0 psia, the surface area of the film and the corrosion rate increased rapidly with an increase in H2S, indicating a nonprotective, porous film.

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© 1963 National Association of Corrosion Engineers
1963
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