This form of localized attack can occur at crevices where material is meet in such a way that the environment can enter the joint between them but the flow of material into and out of the joint is restricted.

• A. Pitting
• B. Fretting
• C. Crevice corrosion
• D. Uniform

Answer: (C)

Crevice corrosion is a localized attack that happens in confined spaces where fluid exchange is limited, such as the gap between mating surfaces, under gaskets, or where debris or deposits keep the environment in contact but prevent normal flow. In these crevices, fresh oxygen from the bulk solution cannot reach the interior, so the solution becomes stagnant and oxygen-depleted. This differential aeration sets up a corrosion cell: the metal inside the crevice acts anodically and dissolves, while the more oxygen-rich exterior surface remains relatively protected by its passive film. The confined solution also becomes slightly acidic as metal ions hydrolyze and, if chlorides are present, this acidity and ion concentration accelerate metal dissolution. The result is a focused, localized attack that advances within the crevice boundaries.

Pitting involves small pits from localized breakdown of the protective film but isn’t specifically tied to a restricted-flow crevice. Fretting is wear-related corrosion from micromotions at contact surfaces, and uniform corrosion is spread evenly across a surface rather than concentrated in a crevice.