Corrosion behaviour in simulated solutions within pits and crevices on carbon steel

Abstract

The corrosion behaviour of mild steel in simulated solution within pits and crevices was investigated using potentiodynamic polarisation. The results showed that the cathodic process was controlled by the diffusion of hydrogen ions at pH 2-4, and controlled by electrochemical processes at pH<2. The anodic dissolution may take place by Bockris’ pH dependent mechanism. A critical pH value or salt concentration was not observed for mild steel. The logarithm of corrosion rate was inversely proportional to the pH value: logV _c = −0·444pH + 0·968. This implies that a small change in pH value within pits and crevices would result in a significant change in corrosion rate. The enrichment of Cl⁻ anions within pits and crevices would result in a decrease in pH value, and it was found that the relationship between pH value and Cl⁻ concentration can be expressed by pH = −0·172[Cl⁻] + constant.