Non-Faraday material loss in flowing corrosive solution

The weight loss of carbon steel in flowing 0.1 M Na2SO4 solution was investigated under galvanostatic condition. It was found that in corrosive solution even without solid particles, the mass loss rate of sample experimentally measured with the traditional weight loss method was higher than that calculated with Faraday's law as the flowing velocity of solution was high enough. The extra mass loss is regarded as non-Faraday material loss because it cannot be predicted with Faraday's law. According to the experimental observations, the non-Faraday material loss increases with flow velocity but decreases with surface hardness of the target, indicating a role of mechanical force. However, the non-Faraday material loss increases with the anodic current density and is inhibited under the cathodic protected condition, suggesting it is not solely caused by a mechanical force. Upon comparison with the experimental results in flowing slurry, it was found that the dependence of the non-Faraday wastage on anodic current density follows analogous trend with the corrosion-enhanced erosion observed in flowing slurries. It implies that the non-Faraday material loss may result from certain interaction between electrochemical and mechanical processes, i.e. corrosion-induced erosion.