An Electrochemical Model For Prediction Of CO2 Corrosion
S.Nesic, J. Postlethwaite and S. Olsen

A Predictive model of CO2 corrosion , based on modeling of individual electrochemical reactions occuring in a water - CO2 system, is presented. The model takes into account the following electrochemical reactions: hydrogen ion reduction, carbonic reduction, direct water reduction, such as: exchange current densities and tafel slopes for different reactions are determined from experiments conducted in glass celss. In those experiments the corrosion process was monitored with the folloing electrochemical measuring techniques: polarisation resistance, potentiodynamic sweep, electrochemical impedance in addition to weight loss measurements. The model has been calibrated for two different mild steels over a wide range of parameters: t = 20 - 80 C, pH 3 - 6, p(CO2)=0 - 1bar, w= 0 - 5000rpm. In its present stage of development the model applies for the case of uniform corrosion with no protective films present.

Performance of the model is validated by comparing the predictions with results from independent loop experiments. The predictions made with the present model were also compared with performance of other CO2 corrosion prediction models. Compared to the previous largely emperical models, the present model gives a much clearer picture of the corrosion mechanisms and of the effect of key parameters.

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