Electropolishing and Passivation

Passivation of corrosion resisting steel, sometimes referred to as stainless steel, is a chemical process whereby the surface of the metal is rendered chemically inactive, or passivated, to certain corrosive environments.

The primary reason that un-passivated surfaces are susceptible to corrosion is that foreign material, primarily iron, becomes embedded in the surface during machining or forming processes. The source of these contaminants is the tooling used for these operations. The embedded material oxidizes and forms “rust”.

Other than being aesthetically unappealing, these corrosion sites in some rare cases can expand and cause mechanical failure of the component, or in the case of food contact surfaces, contaminate the food product. The passivation process is used to remove these contaminants.

To passivate stainless steel parts, they must be submerged in a chemical solution of citric acid or nitric acid for a certain period of time and at a certain temperature. This removes foreign matter like free iron from the surface, but does not remove the heat tint or oxide scale that may be left behind by welding or heat treating. The passivation process improves corrosion resistance and leaves a clean finish, but ultimately does not change a part’s appearance or make it visibly brighter.