CREVICE CORROSION OCCURS in regions of a metal that are not directly exposed to an environment such as flanged joints, lap joints, and under corrosion deposits. The metals that undergo crevice corrosion are otherwise protected by a surface film. Alloys that are not protected by a surface film tend to corrode outside the crevice region where there is greater access to cathodic reduction reactions. In this regard, there are many similarities between pitting and crevice corrosion. Indeed, for some classes of materials, a case can be made that the same mechanism operates both phenomena. It must be emphasized that the crevice corrosion tendency is not the property of a particular alloy class; rather it is a function of the alloy's response to a given environmental condition. For example, carbon steels do not suffer crevice corrosion in acidic solutions because of the absence of a passive film, but do suffer crevice corrosion in alkaline solutions when there is a passive film. Similarly, some alloys suffer crevice corrosion in the presence of a corrosion inhibitor, whereas corrosion occurs outside the crevice in the absence of the inhibitor.