Pickling and Passivation are both acid chemical treatments for stainless steel, developed to remove contaminants, discolouration and scaling.

The two processes combined together result in a clean, chemically passive and corrosion resistant oxide surface film on stainless steel.

Stainless steels need to be pickled before they can be passivated, as the surface needs to be clean, free from contamination, and free from any scale resulting from previous welding operations.

Although two treatments are often performed together, they are not the same:

• Pickling is done first and removes scale via the application of strong acids. It usually involves nitric/hydrofluoric acid mixtures
• Passivation adds a passive outer coating to the metal via an oxidation process. using only nitric acid. Sometimes Nitric acid alone can also be used to remove any light surface iron contamination after which the acid facilitates the passivation of the cleaned steel surface.