Stainless steel relies on the naturally forming chromium oxide film, commonly referred as a passive film, for its corrosion resistance. However, if there is surface contamination then that can lead to deterioration of the materials performance in service.
There are various sources of surface contamination on stainless steel, such as welding, which can produce a colored oxide layer known as heat tint, forming or working operations which can introduce iron or carbon contamination, and storage or adhesive labeling which can be a source for dirt and other contaminants on the surface.
The heat input to the surface during the welding process can result in a formation of an oxide layer. Beneath this layer, there can be a depletion of chromium Since a lower chromium content in the passive film can deteriorate the performance of a material in corrosive solution, it is often necessary to clean stainless steel equipment after fabrication and before placing it into service. Pickling and passivation are chemical treatments applied to remove contaminants and assist in the formation of a continuous passive film.
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