How to maximize the corrosion resistance of stainless steel strips

Surface cleaning, pickling and passivation of stainless steel seamless pipes not only maximizes corrosion resistance, but also prevents product contamination and achieves beautiful appearance. According to GBl50-1998 "Steel Pressure Vessels", "the surface of containers made of stainless steel and composite steel plates with anti-corrosion requirements should be pickled and passivated." This regulation is for pressure vessels used in the petrochemical industry. Because these equipment are used in situations where they are in direct contact with corrosive media, pickling and passivation are necessary to ensure corrosion resistance. For other industrial sectors, if it is not for anti-corrosion purposes and is only based on cleanliness and aesthetic requirements, pickling and passivation are not required for stainless steel materials. However, the welds of stainless steel equipment also need to be pickled and passivated. For nuclear engineering, certain chemical equipment and other applications with strict requirements, in addition to pickling and passivation, high-purity media must be used for final fine cleaning or finishing treatments such as mechanical, chemical and electrolytic polishing.

Stainless steel workpieces will form an oxide film when placed in the air, but the protection of this film is not perfect enough. Usually, thorough cleaning, including alkali washing and pickling, and then passivation with oxidants are required to ensure the integrity and stability of the passivation film. One of the purposes of pickling is to create favorable conditions for passivation treatment and ensure the formation of a high-quality passivation film. Because an average of 10 μm thick layer on the surface of stainless steel is corroded through pickling, the chemical activity of the acid makes the dissolution rate of defective parts higher than other parts on the surface, so pickling can make the entire surface even and balanced, some of the original Hidden hazards that could easily cause corrosion are eliminated. But more importantly, through pickling and passivation, iron and iron oxides are dissolved preferentially than chromium and chromium oxides, and the chromium-poor layer is removed, causing chromium to be enriched on the surface of stainless steel. This chromium-rich passivation film The potential can reach +1.0V (SCE), which is close to the potential of precious metals, improving the stability of anti-corrosion. Different passivation treatments will also affect the composition and structure of the film, thereby affecting the rust resistance. For example, through electrochemical modification treatment, the passivation film can have a multi-layer structure, forming CrO3 or Cr2O3 in the barrier layer, or forming a glassy state. The oxide film enables the stainless steel strip to exert maximum corrosion resistance.