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    the environment from the adverse effects of corrosion.

General Attack Corrosion

Also referred to as "general corrosion" or " uniform corrosion," general attack corrosion proceeds more or less uniformly over an exposed surface without appreciable localization. This leads to relatively uniform thinning on sheet and plate materials and general thinning on one side or the other (or both) for pipe and tubing. It is recognized by a roughening of the surface and usually by the presence of corrosion products. The mechanism of the attack typically is an electrochemical process that takes place at the surface of the material. Differences in composition or orientation between small areas on the metal surface create anodes and cathodes that facilitate the corrosion process.

Most often caused by misapplying materials in corrosive environments, general corrosion often can be tolerated because the effect of metal loss is relatively easy to assess and allowances can be made in the initial design. Protective coatings are particularly effective in controlling uniform corrosion. Cathodic protection (CP)-an electrochemical technique used for corrosion control (see "Methods of Corrosion Control" later in this article)-can be used in underground or immersion situations.

Localized Corrosion

Unlike general attack corrosion, localized corrosion occurs at discrete sites on a metal surface. Types of localized corrosion include pitting, crevice, and filiform corrosion.