A Mechanistic Model of Uniform Hydrogen Sulfide/Carbon Dioxide Corrosion of Mild Steel

A mechanistic model of uniform hydrogen sulfide (H₂S) and hydrogen sulfide/carbon dioxide (H₂S/CO₂) 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 is primarily affected by H₂S concentration, temperature, velocity, and the protectiveness of the mackinawite surface layer. The amount of mackinawite retained on the steel surface changes with time and depends on the layer formation rate as well as the layer damage rate. The layer formation may occur by corrosion and/or precipitation, while the layer damage can be by mechanical or chemical means. The model predictions were compared with a very broad set of experimental results and good agreement was found. The current version of the model does not yet include iron sulfide precipitation effects, nor hydrodynamic effects on film damage, which will be addressed in future work.