A Mechanistic Model for Carbon Dioxide Corrosion of Mild Steel in the Presence of Protective Iron Carbonate Films—Part 3: Film Growth Model

A model of iron carbonate (FeCO3) film growth is proposed, which is an extension of the recent mechanistic model of car-bon dioxide (CO2) corrosion by Nesic, et al. In the present model, the film growth occurs by precipitation of iron carbon-ate once saturation is exceeded. The kinetics of precipitation is dependent on temperature and local species concentra-tions that are calculated by solving the coupled species transport equations. Precipitation tends to build up a layer of FeCO3 on the surface of the steel and reduce the corrosion rate. On the other hand, the corrosion process induces voids under the precipitated film, thus increasing the porosity and leading to a higher corrosion rate. Depending on the environ-mental parameters such as temperature, pH, CO2 partial pressure, velocity, etc., the balance of the two processes ca