Corrosion is the name of the damage which chemical or electrochemical, physical and biological action causes to materials starting at their surfaces. Almost always several corrosive factors act simultaneously on the attacked material. In general usage corrosion is understood to be the corrosion of metals, which in DIN 50 900, T1 (April 1982) is defined as: "The reaction of a metallic material with its environment, producing a measurable change of the material and leading possibly to an impairment of the function of a metal component or entire system. In most cases, this reaction is electrochemical in nature, but in a few cases it can also be of a chemical (non-electrochemical) or metal-physical character."