Issues related to acidic passivation and polishing of stainless steel mixing equipment
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I would like to ask those of you who design and manufacture stainless steel mixing equipment: for the inner and outer surfaces of the equipment, should acid passivation and polishing be done only one of them, or both? If both are to be carried out, should polishing be done first and then acid washing and passivation?
It depends on the purpose of your device; generally, polishing is followed by pickling and passivation. Once pickling and passivation are complete, no further operations should be carried out, as the passivation layer can easily get oxidized if damaged.
The polishing requirements are designed to meet the needs of the material and are located inside the equipment. Pickling and passivation are generally performed on both the inner and outer surfaces. Polishing should be done first, followed by pickling and passivation. Of course, polishing equipment is required, and it’s best to purchase stainless steel plates that are suitable for polishing.
The original poster just needs to understand the respective purposes of polishing and pickling/passivation, and then it will be easy to figure out when polishing is needed and when pickling/passivation is required.
Generally, the inner surface is pickled and passivated, while the outer surface is polished. Just do one of them. Think about it: if polishing is followed by pickling and passivation, then what is the purpose of polishing? Similarly, if polishing is done after pickling and passivation, then what is the purpose of pickling and passivation?
The purpose of pickling is to remove oil, rust, and oxidation-induced discoloration on the surface; passivation is intended to form a dense passivation film on the stainless steel surface to provide some degree of corrosion protection; polishing involves bringing the surface of stainless steel to a smooth or mirror-like finish. After polishing, the surface of stainless steel becomes quite clean; the chromium in stainless steel combines with oxygen to form a passivation film on its own. If polished, it is possible to remove oil stains, rust, and the oxidation colors resulting from welding from the surface. So, as for how to carry out pickling, passivation, and polishing, it depends on the actual requirements. Pickling and passivation are two treatment processes.
If corrosion resistance is required, pickling and passivation are carried out; if the viscosity of the medium is high to prevent it from sticking to the inner walls of the equipment, polishing is performed.