Role of bicarbonate in CO2 corrosion of carbon steel

This study investigates the dual role of bicarbonate in the CO2 corrosion of carbon steel through electrochemical measurements and immersion tests conducted in a CO2-saturated solution. The results show that the critical bicarbonate concentration for the aggressive/inhibitive transition is approximately 0.03–0.05 mol·L−1. Above this concentration, bicarbonate exhibits an inhibitory effect on the CO2 corrosion of X65 steel. The size of FeCO3 particles decreases as the bicarbonate concentration increases, leading to a denser FeCO3 film and enhanced passivation of the steel. However, at concentrations below 0.03 mol·L−1, bicarbonate enhances the CO2 corrosion of carbon steel owing to its participation in cathodic processes.