1155Crevice Corrosion

Crevice corrosion is a type of intense localized corrosion, which occurs within crevices and other shielded areas on the metal surface. This form of corrosion is often associated with the presence of Cl- ions and small volumes of stagnant solution caused by holes, lap joints, and crevices under bolt and rivet heads (Fig. 11.9). The cathodic reaction (often oxygen reduction) occurs on the metal surface outside the crevice. Inside the crevice metal dissolution and acidification reactions occur that result in further oxygen depletion creating conditions that allow corrosion to continue. The rate of crevice corrosion is dependent upon the crevice geometry, which in turn influences the local solution chemistry, that is, pH, and O2 concentration. Oldfield and Sutton [22] proposed the following mechanism for crevice corrosion: (i) deoxygenation of the solution in the crevice, (ii) accumulation of positive metal ions in the crevice, (iii) diffusion of Cl- into the crevice, and (iv) increase in aggressivity of the crevice solution.

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