Is pickling and passivation still necessary when painting the surface of 304 stainless steel containers?
Thread Content
There are 3 containers made of 304 stainless steel, 1 tank for storing a medium containing 20% ammonia, 1 tank for process water, and an ammonia evaporator. Since the project is located in a marine environment, the client requires that the stainless steel exterior surface be painted, with the surface treated by sandblasting or manual texturing. Question: Is it still necessary to carry out the stainless steel pickling and passivation process?
Stainless steel pickling and passivation treatment is required. Although painting and sanding or manual texturing can protect the outer surface of stainless steel, acid washing and passivation are still required for the interior of storage tanks and ammonia evaporators to prevent rust and corrosion. Moreover, the pickling and passivation process for stainless steel is a standard anti-corrosion treatment method that can effectively extend the service life of stainless steel containers and enhance their safety. -
It is necessary; the function of acid washing and passivation is to remove oils, particles, and other impurities from the surface of the equipment during the manufacturing process, thereby enhancing the adhesion of paint to that surface.
It is needed both inside and outside. Sandblasting cannot remove iron ion contamination and the like ； Of course, it depends on what the purpose of your company is; generally, company owners don’t require sandblasting unless it’s necessary, as profit comes first.
Thank you for the answer. Sanding or manual texturing is a surface treatment required by the client before painting; does such treatment damage the passivation film formed after pickling of the outer surface? Does the inner surface just need to be pickled and passivated?
Sandblasting or manual texturing only treats the outer surface of stainless steel, without damaging the passivation film that has been formed through pickling and passivation. Doing this can improve the adhesion of the coating and, to a certain extent, enhance the corrosion resistance of the outer surface. For the inner surface of stainless steel, acid washing and passivation are indeed sufficient to protect it from corrosion and contamination. The acid washing and passivation process for stainless steel removes impurities such as rust and oxides from within the steel, forming a passivation layer that enhances the steel’s corrosion resistance and durability, thereby ensuring the safety and cleanliness inside stainless steel containers. -
You’re welcome, wish you all the best! -
Painting the outer surface is primarily to prevent salt spray corrosion, while painting the inner surface is to prevent corrosion by process media; there is no inherent connection between the two. Treat them separately.