Deterministic Modeling of the Effect of Acetic Acid in the Corrosion of Low-Carbon Steel by Carbon Dioxide

CO₂ corrosion has been a recognized problem in oil and gas production for many years and it is becoming more common with the extensive use of CO₂-flooding as an oil recovery technique. Along with the CO₂, the presence of acetic acid is systematic in oil fields, however, its role has not been well recognized and it is still unknown whether it can serve as corrosion inhibitor or a corrosion promoter. 

The present work is carried out focusing on an understanding on CO₂ corrosion of low-carbon steel that includes the effect of acetic acid. This understanding is achieved by mean of experimental data and developing a deterministic model that explains and accounts for the observations. The interaction of acetic acid and inhibitor with the corrosion-products layer is studied and the system is modelled by considering protective film formation and its breakdown.
According to Electrochemical Impedance Spectroscopy, acetic acid effect is markedly dependent upon the pH, showing a decrease in the charge transfer resistance at pH=4, and an increase of this parameter at pH=6. Ellipsometry measurements define the nature of the surface films formed and the impedance model based on the Point Defect Model represents a good account for the film development.