A crucial step after stainless steel pipes are pressed into shape is pickling. Industry experts say that only stainless steel pipes that have undergone the pickling and passivation process are qualified. So why do stainless steel pipes need to be pickled and passivated with a stainless steel pickling and passivation solution? What are the benefits of pickling and passivation?

One of the purposes of pickling is to create conditions for the passivation treatment and ensure the formation of a good passivation film. Pickling removes an average 10µm thick layer of the stainless steel surface. The chemical activity of the acid causes the dissolution rate of defective areas to be higher than that of other areas. Therefore, pickling evens out the entire surface, eliminating some of the potential corrosion hazards.

While room-temperature descaling processes are effective for removing thin oxide scale, they are less effective for thicker oxide scales, especially at welds, where black slag is virtually impossible to remove. Through pickling and passivation, iron and iron oxides dissolve preferentially over chromium and chromium oxides, removing the chromium-depleted layer and enriching the stainless steel surface with chromium. Oxidant passivation then creates a complete and stable passive film on the stainless steel surface. This chromium-rich passive film can reach a potential of +1.0V (SCE), approaching that of precious metals, enhancing the stainless steel's corrosion resistance.

Different passivation treatments also affect the film's composition and structure, thus affecting its stainless properties. For example, electrochemical modification can create a multilayered passive film, forming CrO₃ or Cr₂O₃ in the barrier layer, or a glassy oxide film, maximizing the stainless steel's corrosion resistance.

Stainless steel's corrosion resistance is primarily due to an extremely thin (approximately 1-15 nm) and dense passive film covering the surface. This film isolates the corrosive medium and serves as the primary protective barrier for stainless steel. Stainless steel passivation is a dynamic process and should not be considered a complete cessation of corrosion. Rather, it forms a diffusion barrier that significantly reduces the rate of the anodic reaction. Generally, the presence of reducing agents (such as chloride ions) tends to destroy the passive film, while the presence of oxidizing agents (such as air) can protect and repair it.

During the stainless steel production process, after rolling and welding the raw stainless steel plates, cracks may appear in the weld joints, and oil stains, scale, and weld spots may appear on the stainless steel surface. Therefore, the first benefit of a pickling reaction passivation solution is that it can remove surface oil stains, scale, and other such stains, making the product more aesthetically pleasing and competitive.

This method forms a dense oxide film on the workpiece surface through a chemical reaction. Its purpose is to form an oxide film or oxygen adsorption layer on the workpiece surface, thereby preventing electrochemical corrosion and improving the metal's corrosion resistance.