Study on simulated-crevice corrosion mechanism of X70 steel in bicarbonate solution

A detailed study on the crevice corrosion mechanism of X70 steel has been carried out by using a wedge-shaped crevice model. The results showed that the corrosion potential decreased differently within the crevice and there existed a maximum negative at the bottom side;Along with pH value reduced, the dissolved oxygen was nearly exhausted in the crevice. When the opening side of the coupons was coupled with each other the crevice corrosion in the crevice might be accelerated and the pH value gradually reduced, however, the oxygen was not completely exhausted. The unbalanced current density between anodic and cathode is the main cause of blocked self-catalysis effect in the crevice. The corrosion mechanism of the steel in the simulated crevice is identical in two different HCO₃^- concentration solutions. But the corrosion was severer in high concentration HCO₃^- solution.