Crevice corrosion is a form of localized corrosion that may occur in occluded metallic surfaces where a stagnant solution is developed. Pitting corrosion and crevice corrosion are essentially the same phenomena from an electrochemical viewpoint although there are geometrical differences between them. Ni-Cr-Mo alloys such as Alloy 22 may suffer crevice corrosion when in contact with chloride containing solutions. Chloride is the main aggressive species causing crevice corrosion of Ni-Cr-Mo alloys in industrial applications. The crevice corrosion susceptibility of the alloys is increased at higher temperatures and higher chloride concentrations.
Crevice corrosion inhibitors are able to mitigate or avoid the occurrence of localized attack. They may be commonly found in service environments or added on purpose to the environment. Crevice corrosion may occur only if the corrosion potential of the alloy (ECORR) is higher than its repassivation potential (ERCREV) in the field conditions. Cathodic inhibitors cause a shift of ECORR to more active potentials while anodic inhibitors cause a shift of ERCREV to more noble potentials.