The destruction of the metal due to the electrochemical and chemical effects on it of an aggressive external environment is called corrosion. Corrosion can be local, in which a small area of the surface is destroyed, as well as uniform. With it, the entire surface is destroyed. There is also corrosion along the boundaries of grains — this is inter -quristalline corrosion. The essence of corrosion is that the metal under the active and constant effect of oxygen and the aquatic environment changes the structure and becomes loose powdered substance of light brown.