Steels containing more than 11% Chromium are capable of forming an invisible, inert or passive, self-repairing oxide film on their surface. It is this passive layer that gives stainless steels their corrosion resistance. If a stainless steel surface is scratched, then more Chromium is exposed which reacts with oxygen allowing the passive layer to reform.
However, if a particle of carbon steel is embedded in the scratch or the piece is Welded then the passive layer cannot reform and corrosion will occur when the metal is wetted or exposed to a corrosive environment (Heated Oxalic Acid Vapor). This Will Happen if the Equipment is not treated this way causing rusting and corrosion of you Device.
Passivating stainless steel is the removal of exogenous iron or iron compounds from the surface by means of a chemical dissolution, most typically by a treatment with a concentrated nitric acid passivation solution that will remove the surface contamination but will not affect the stainless steel itself.
Passivation returns the surface to HIGH CORROSION RESISTANCE.
Professional Oxalic Acid Vaporizer