Corrosion of Iron in an H₂S-CO₂-H₂O System: Corrosion Film Properties on Pure Iron

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.