What is Passivation?

According to ASTM A 380, passivation is “the removal of exogenous iron or iron compounds from the surface of a stainless steel by means of a chemical dissolution, most typically by a treatment with an acid solution that will remove the surface contamination but will not significantly affect the stainless steel itself.” In addition, it also describes Passivation as “the chemical treatment of a stainless steel with a  mild oxidant, such as anitric acid solution, for the purpose of enhancing the spontaneous formation of the protective passive film.”

In layman's terms, the passivation process removes “free iron” contamination left behind on the surface of the stainless steel as a result of machining and fabricating processes. These contaminants are potential corrosion sites which, if not removed, result in premature corrosion and ultimately result in deterioration of the component. In addition, the passivation process facilitates the formation of a very thin, transparent oxide film, which protects the stainless steel from corrosion. So the Passivation process is a combination of cleaning and protecting.