Questions about acid cleaning and passivation
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1. For the stainless steel surface, which area needs to be pickled and passivated: the inner surface (i.e., the side in contact with the medium), the outer surface, the inner surface of the welds, or the outer surface of the welds? Why? 2. If there is only one component in the equipment made of stainless steel, such as in a carbon steel heat exchanger where only the heat exchange tubes are made of stainless steel, is it necessary to carry out acid washing and passivation? How to pickle? Apply the acid cleaning paste, or soak it in the acid cleaning tank? 3. Stainless steel pipes are produced according to standards; has the pipe itself been pickled and passivated during its manufacturing process? If pickling and passivation have already been done, is it still necessary to carry out pickling and passivation again during container manufacturing?
1. The surface of the container in contact with the medium should be acid-washed and passivated; the requirements for corrosion protection and coating on the outer surface of the container vary. 2. This depends on the specific usage conditions; a passivated surface provides excellent corrosion resistance. Stainless steel heat exchange tubes must be individually passivated after pickling, with immersion being the common method used. 3. This is not necessarily the case; in some situations, negotiation between both parties is required. However, even for steel pipes that have been pickled and passivated, the passivation film is inevitably damaged during container manufacturing, and pickling and passivation should be carried out again after the containers are manufactured.
1. For stainless steel sheets, grade 1D should be selected; these sheets have already been passivated upon leaving the factory. If the surface of the sheet is not damaged during manufacturing, there is no need for acid washing or passivation. Conversely, if the original surface is damaged after polishing or processing, acid cleaning and passivation are required. Welds also need to be pickled and passivated.
2. The same is true for stainless steel pipes.
I saw that aluminum products are also passivated, with passivation before welding and manual polishing after welding
1. The inner and outer surfaces, as well as the welds, must be pickled. Impurity contamination is inevitable during the manufacturing process, and it can damage the passivation film of stainless steel. The interior is acid-washed and passivated to resist medium corrosion, while the exterior is acid-washed and passivated to resist atmospheric corrosion. Stainless steel generally does not have corrosion protection. 2. Heat exchange tube manufacturers will carry out pickling and passivation; if it is a separate component, pickling is not required. On the one hand, it can cause corrosion of carbon steel components; on the other hand, stainless steel has self-passivation capabilities, so as long as the contamination is not severe, there is no problem.
The outer half of the carbon steel container is made of stainless steel; is it necessary to carry out pickling and passivation?
The Environmental Protection Agency no longer allows manufacturers to carry out pickling processes