Crevice corrosion cathodic reactions and crevice scaling laws

A numerical model that predicts the rates of metal dissolution and electrolyte composition along the length of a metallic crevice was used to simulate the crevice corrosion of AISI 304 stainless steel. The model considers both the forward and reverse electrochemical reactions that might take place during the corrosion process. The environment exterior to the crevice, where a net cathodic current is produced, was simultaneously modeled. It was found that cathodic reactions are likely to occur towards the tip of the crevice. For the case when the hydrogen evolution reaction was considered as a possible cathodic reaction in the crevice, it is shown how the delayed instigation of this reaction may be the cause of an experimentally observed increase in pH at the crevice tip. Two critical crevice scaling laws were examined using model predictions and one scaling law fit the model predictions very well. This scaling law differentiates between crevices that will undergo active corrosion and those that will remain indefinitely passive.