Pickling and Passivation

Pickling is a process used to remove the heat-affected zone from the surface of stainless steel after welding. It also removes a small amount of metal from the surface of the stainless steel.

Passivation is a non-electrolytic process that typically uses nitric or citric acid to remove free iron from the surface of stainless steel. The process forms an inert, protective oxide layer that renders the stainless steel more rust-resistant by eliminating iron that can react with the atmosphere.

During manufacturing processes such as machining, imperfections can occur on the surface of stainless steel parts due to iron being embedded or smeared onto the surface from machining tool steels. These free irons must be removed to prevent a corrosive reaction between the different metals.

The passivation process chemically removes these free irons and forms a passive oxide layer, which further improves corrosion resistance without altering the aesthetics of the part.