Passivation is 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
How it works:
Passivation is the chemical treatment of a stainless steel with a mild oxidant, such as a nitric acid solution, for the purpose of enhancing the spontaneous formation of the protective passive metal oxide ﬁlm.
Descaling removes a buildup of oxide film caused by thermal action (welding, high temp baking etc). Descaling must be removed prior to passivation. Descaling methods are either chemical (Pickling) or mechanical (grinding, blasting).