Corrosion Resistance

the capacity of a metal or alloy to resist the corrosive action of a medium. It is determined by the rate of corrosion under given conditions.

The rate of corrosion is characterized by qualitative and quantitative indexes. Among the qualitative indexes are changes in the surface appearance and microstructure of a metal. Quantitative indexes include the time required for the appearance of the first corrosion site or the number of corrosion sites appearing over a given time period, the reduction in thickness of the metal per unit time, change in the weight of the metal per unit area and time, the volume of gas released (hydrogen) or absorbed (oxygen) in the course of corrosion per unit area and unit time, the current density corresponding to the rate of the given corrosion process, and the percentage change in any mechanical property, electric resistance, and reflectivity of the metal over a given period. A number of scales have been proposed for evaluating the corrosion resistance of metals. The most widely used and recom-mended is the ten-point scale.