Corrosion of Iron in an H2S-CO2-H2O System Composition and Protectiveness of the Sulfide Film as a Function of pH

Abstract

Composition and protectiveness of the iron sulfide film, formed as a result of the liquid phase H2S-CO2-H2O corrosion of Armco iron, have been related to the initial pH of the solution. Composition of the film was determined by electron diffraction analysis. Protectiveness of the film was determined by measuring the weight loss of iron specimens previously corroded and covered by sulfide films formed in H2S-CO2-H2O solutions of different pH values. Composition and the protectiveness of the iron sulfide film were affected by the initial pH of the H2S-CO2-H2O solution. The film was least protective in the pH region of about 6.5 to 8.8. The film that was least protective contained essentially kansite, whereas the film that was most protective contained pyrite and troilite along with kansite. Because the HS– anion is the predominant species in the pH region of about 6.5 to 8.8, it is indicated that the HS– was at least partially responsible for the film being less protective.