Predicting Carbon Dioxide Corrosion of Bare Steel Under an Aqueous Boundary Layer Available to Purchase

The corrosion of bare steel under an aqueous boundary layer with dissolved carbon dioxide (CO₂) was modeled to investigate the effect of CO₂. The model incorporated the coupled effect of CO₂ diffusion, hydration, local ionic equilibria, ferrous carbonate (FeCO₃) precipitation, and steel corrosion. The model was verified against published experimental data under both FeCO₃-saturated and unsaturated boundary layers. Good agreement was shown under a variety of conditions. For saturated boundary layers, the results show that the corrosion rate in carbonic acid (H₂CO₃) is greater than in hydrochloric acid (HCl) for a given pH and that H₂CO₃ reduction is the cause for the increase of corrosion rate in H₂CO₃. Increasing temperature was found to increase corrosion rate substantially. This work provides further understanding of the CO₂ corrosion mechanism and is a reliable, convenient, and practical tool for predicting the rate of CO₂ corrosion.