The corrosion resistance of stainless steel and nickel alloy is dependent on a thin invisible film on the steel surface, the passive film. There are, however, environments that cause permanent breakdown of the passive layer. Under circumstances where the passive layer cannot be rebuilt, corrosion occurs on the unprotected surface. Different media can cause different types of corrosion attack that may vary in nature and appearance. Several forms of corrosion can occur on stainless steels and nickel alloy plates.