The corrosion resistance of stainless steel is mainly because the high content of CR element is added to the steel, the CR element is easy to oxidize, the dense Cr2O3 oxide film can be formed rapidly on the surface of steel, so that the electrode electricity of steel and the corrosion resistance of the oxidation medium are improved. Corrosion resistance of stainless steel mainly depends on the surface covering this very thin (about 1mm) dense passivation film, this layer of passivation film and corrosive media isolation, is the basic barrier of stainless steel protection, if the passivation film is incomplete or defective, Stainless steel will still be corroded. Stainless steel can also rust the lifting, assembling, welding, weld inspection (such as coloring flaw detection, pressure test) and the surface oil pollution, scratches, rust, impurities, low melting point metal pollutants in the machining process. Paints, solder slag, spatter, etc., these substances affect the surface quality of stainless steel, destroy the passivation film, reduce the surface corrosion resistance, but also easy to contact with the chemicals in the corrosion of the media in the joint action, triggering pitting, intergranular corrosion, and even lead to stress corrosion cracking. The principle of pickling passivation in GBl50-1998 "Steel Pressure vessel" stipulates that "anti-corrosion requirements of stainless steel containers made of surface should be pickling passivation."
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