A model has been developed for calculating the rates of general corrosion of carbon steel and 13%Cr steel in aqueous systems containing carbon dioxide, hydrogen sulfide and other components.
The model combines a comprehensive thermodynamic speciation module with electrochemical computations based on the mixed-potential theory. The electrochemical calculations recognize the effects of various partial cathodic and anodic processes and incorporate a model for the active-passive transition and the effect of solution species on passivity. The model has been verified by comparing calculated corrosion rates with experimental data over substantial ranges of temperature, pressure and solution composition. In particular, the effects of salinity, hydrogen sulfide and acetic acid on CO2 corrosion can be simulated. Very good agreement with experimental data has been obtained. The model has been implemented in a program that makes it possible to analyze the effects of various environmental variables on the rates of general corrosion.
KEY WORDS: Modeling, thermodynamics, electrochemical kinetics, carbon steel, 13%Cr steel, CO2/H2S corrosion