Pickling & Passivation
Pickling and Passivation are chemical treatments which remove any surface contaminants and help to reestablish the passive layer. This is generally a requirement for fabrications used in process engineering and water treatment plant, but can also have applications in construction.
Welding stainless steel produces a coloured oxide layer and a depleted chromium layer. This can be removed by the use of pickling pastes which remove this surface layer.
The colour can also be removed by mechanical methods, however this can also introduce other ferrous contaminants.
For some fabricated components it may be appropriate to immerse the entire fabrication in a pickling solution. These are usually solutions of nitric (HNO3) or hydrofluoric acid (HF). The solution removes any weld colour, scale, the depleted chromium layer and any other iron contaminants. It restores the fabrication to a uniform condition.
Passivation aids the development of the passive film on the surface of stainless steel. This is usually a nitric acid solution (HNO3).
Both pickling and passivation use dangerous acid solutions and this process is usually undertaken by a specialist subcontractor. Talk to your sales contact about your requirements.