| Summary: | A predictive model was developed for uniform carbon dioxide (CO) corrosion, based on modeling of individual electrochemical reactions in a water-CO system. The model takes into account the electrochemical reactions of hydrogen ion (H) reduction, carbonic acid (HCO) reduction, direct water reduction, oxygen reduction, and anodic dissolution of iron. The required electrochemical parameters (e.g., exchange current densities and Tafel slopes) for different reactions were determined from experiments conducted in glass cells. The corrosion process was monitored using polarization resistance, potentiodynamic sweep, electrochemical impedance, and weight-loss measurements. The model was calibrated for two mild steels over a range of parameters: temperature (t) = 20°C to 80°C, pH = 3 to 6, partial pressure of CO (P) = 0 bar to 1 bar (0 κPa to 100 κPa), and ω = 0 rpm to 5,000 rpm (ν = 0 m/s to 2.5 m/s). The model was applicable for uniform corrosion with no protective films present. Performance of the model was validated by comparing predictions to results from independent loop experiments. Predictions also were compared to those of other CO corrosion prediction models. Compared to the previous largely empirical models, the model gave a clearer picture of the corrosion mechanisms by considering the effects of pH, temperature, and solution flow rate on the participating anodic and cathodic reactions.
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