The pickling process is designed to remove resistant oxide residues formed as a result of high-temperature heating during hot rolling, heat treatments, or welding operations. Chemical pickling involves the use of acid baths based on sulfuric or nitric acid, heated to temperatures above ambient level. The time the metal remains in the pickling solution depends on the type of scale to be removed, its thickness, and its adhesion to the base metal.
After pickling, a passivation treatment must be carried out to rapidly and controllably restore the natural passive layer of stainless steels, while eliminating any residual surface contamination. The process is typically performed in passivating baths using solutions that are less aggressive than those employed during pickling. The purpose of this treatment is to dissolve any surface contaminants and rebuild the protective passive film, thereby accelerating the natural passivation process of stainless steel.