The role of acetate (Ac”) ion on the rate of C02 corrosion has been investigated. The presence of Ac- in oilfield brines can significantly increase the rate of corrosion of carbon steel. In the presence of Ac”, the corrosion rate can increase even if the pH increases. Many corrosion prediction models cannot accommodate this observation. On a ppm basis, Ac- increases the corrosion rate more than the HC03- decreases it. The presence of Ac- only affects the corrosion rate and not the corrosion mechanism. The mechanism by which HAc increases the corrosion rate may be explained by its ability to both decrease the pH and solubilise Fe2+, thus reducing the iron carbonate film thickness.
Keywords: Carbon dioxide, acetic acid, acetate, bicarbonate, corrosion prediction, inhibition, mechanism.