A Mechanistic Model of H2s Corrosion of Mild Steel

Glass cell experiments were conducted to investigate the mechanism and kinetics of mild steel corrosion in H2S environments which is accompanied by iron sulfide scale formation. By using the weight change method, the rates of corrosion and scale formation were found. It was also concluded that mackinawite is the predominant type of iron sulfide that formed on the steel surface under the test conditions studied, probably by a direct reaction of H2S with the underlying steel. Based on the experimental results, a mechanistic model of uniform H2S corrosion of mild steel is presented that is able to predict the rate of corrosion with time. In the model, the corrosion rate of mild steel in H2S corrosion is a function of H2S gas concentration, temperature, velocity, and the protectiveness of the mackinawite scale. The amount of scale retained on the steel surface depends on the scale formation rate as well as the scale damage rate. The scale formation may occur by corrosion and/or precipitation, while the scale damage can be by mechanical or chemical means.