Predicting the Chemistry and Corrosion Rate of Steel in a Crevice of Variable Gap

A fundamental mathematical model is developed that allows for predicting the chemistry, corrosion potential and rate of steel in a crevice of variable and/or varying gap. The crevice gap may initially vary with distance from its mouth. It may also vary with time as the metal dissolves into solution by corrosion. The effect of this spatial and temporal variation of the crevice gap on the crevice chemistry and corrosion rate is traditionally not often treated for the simplicity of the experimental setup or mathematical modeling. This study is aimed at investigating into this effect through modeling. Although this model is here designed to simulate the crevice corrosion of underground steel pipelines: crevice formed due to a polymer coating disbonded from the pipe surface, the model itself is not limited to this specific application. Other types of crevice corrosion including the substrate being a passive alloy can also be modeled with the same governing equations. In this paper, the fundamental principles used for the model, some key model results and the implications of the results will be discussed.