I would like to ask whether stainless steel containers should be acid-washed and passivated on both the inside and outside
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I would like to ask whether stainless steel containers should be acid-washed and passivated on both the inside and outside Is there a standard specifying that the inner surface should also be pickled and passivated?
Is it necessary to acid wash and passivate stainless steel containers? Not necessarily. For applications with requirements for corrosion resistance and cleanliness (such as in the pharmaceutical industry), acid washing and passivation are necessary; however, if it is to be used only for heat resistance, such acid washing and passivation are not required. Is it necessary to acid-wash and passivate both the inner and outer surfaces? Not necessarily. For example, when corrosion resistance is required, some drawings specify that the stainless steel parts in contact with the medium must be pickled and passivated. However, many manufacturers also carry out pickling and passivation on the outer surfaces for aesthetic reasons.
The inner and outer surfaces should be pickled and passivated, so that a passivation film is formed on the surface, which provides corrosion resistance against various media; moreover, it also enhances the aesthetic appearance of the outer surface. Therefore, for stainless steel equipment, our corrosion allowance is 0. In ordinary situations or with general media, it is sufficient to perform acid cleaning to remove oils and other impurities; passivation is not necessary.
The standard only specifies the surface of the stainless steel; the inner surface is not specified because cleaning many tanks in a sealed environment is unbearable! So often, there is no pickling! I’m not sure if there are any standards that explicitly state the need for pickling and passivation internally
The surface in contact with the corrosive medium needs to be pickled, while other surfaces do not.
This can only be due to substandard facilities in the factory; small tanks or areas that are inaccessible can be fully submerged in acid wash solution, as there is a dedicated area in the workshop where an acid washing tank is installed. Large equipment has manholes, which shouldn’t prevent internal pickling, right?
It depends on the situation, the customer’s requirements, and the medium. Generally, hot-rolled sheet containers are acid-washed and passivated, while cold-rolled sheet containers are polished