Uniform corrosion

Corrosion of metals by uniform chemical attack is the simplest and most common form of corrosion, and it occurs in the atmosphere, in liquids, and in soil, frequently under normal service conditions. The rate of attack can be rapid or slow, and the metal surface can either be clean or covered with corrosion products. Selection of a metal that has a suitable resistance to the environment in which the specific part is used and the application of paints and other types of protective coatings are two common methods used to control uniform corrosion.
Uniform corrosion commonly occurs on metal surfaces having a homogeneity of chemical composition and of microstructure. Access to the metal by the attacking environment is generally unrestricted and uniform. In uniform corrosion, electrochemical reaction between adjacent closely spaced microanode and microcathode areas is involved; consequently, uniform corrosion might be considered as localized electrolytic attack occurring consistently and evenly over the surface of a metal.
All metals are affected by this form of attack in some environments; the rusting of steel and the tarnishing of silver are typical examples of uniform corrosion. In some metals, such as steel, uniform corrosion produces a somewhat rough surface by removing a substantial amount of metal, which either dissolves in the environment or reacts with it to produce a loosely adherent, porous coating of corrosion products. In such reactions as the tarnishing of silver in air or the attack on lead in sulfate-containing environments, thin, tightly adherent protective films are produced, and the metal surface remains smooth.
Corrosion rate and expected servite life can be calculated from measurements of the general thinning produced by uniform corrosion. 
Sigla.com - Internet Partner