Effect of chloride and bicarbonate ions on corrosion behavior of carbon steel in anaerobic environment

This investigation was initiated to study the influence of chloride ions and bicarbonate ions on the corrosion behavior of Q345 carbon steel in anaerobic condition by electrochemical tests and surface characterizations. It was found that low concentration of Cl- tends to cause general corrosion of sample while high concentration of Cl- induces localized corrosion because of its migration to the corrosion defects, leading to the accelerated dissolution of matrix. The existence of individual HCO3- results in the passivation of sample. When Cl- co-exists in the solution, the increase concentration of HCO3- results in an overall decrease of corrosion pit depth and the disappearance of localized corrosion, revealing the inhibitory effect of HCO3- on corrosion due to the formation of dense FeCO3 film. This corrosion suppression behavior of HCO3- is opposite to its synergistic effect on pitting with Cl- in aerobic environment.