PICKLING & PASSIVATION
Pickling is the removal of a thin layer of the stainless steel surface in order to remove all impurities from stainless steel surfaces with the objective of preserving a pure metal surface. The protective passive layer can only be formed on such pure metal surfaces. During the process iron particles and chromium carbides - which are present in the material - are removed by using an acid mixture of nitric acid and hydrofluoric acid.
Passivation means forming the protective passive layer. This can 'grow' the natural way with humidity and oxygen or with demineralized (oxygen-rich) water. However, as there is a risk of corrosion until the formation of the passive layer is restored, it is recommended that passivation is done by using chemicals as this process will only take a few minutes instead of days.