An Electrochemical Model for Prediction
of Corrosion of Mild Steel
in Aqueous Carbon Dioxide Solutions |
by |
S. Nesic,* J. Postlethwaite,** and S. Olsen*** |
Abstract |
A predictive model was developed for uniform carbon dioxide
(CO2) corrosion, based on modeling of individual electrochemical
reactions in a water-CO2 system. The model takes
into account the electrochemical reactions of hydrogen ion
(H+) reduction, carbonic acid (H2CO3) 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 CO2 (PCO2) = 0 bar to 1 bar (0 kPa to 100 kPa), and v =
0 rpm to 5,000 rpm (vp = 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 CO2 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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