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　　Chemical corrosion

　　1. Surface pollution of welded steel pipes: oil, dust, acid, alkali, salt, etc. attached to the surface of the workpiece are transformed into corrosive media under certain conditions, and react with certain chemicals in the stainless steel parts to produce chemical corrosion and corrosion.

　　2. Surface scratches on welded steel pipes: Various scratches damage the passivation film, reducing the protective ability of stainless steel, and it is easy to react with chemical media, resulting in chemical corrosion and corrosion.

　　3. Welded steel pipe cleaning: after pickling and passivation, the remaining liquid will remain and the stainless steel will directly corrode (chemical corrosion).

　　Electrochemical corrosion

　　1. Carbon steel pollution: scratches and corrosive media caused by contact with carbon steel parts form a galvanic cell and produce electrochemical corrosion.

　　2. Cutting: The adhesion of slag, splash and other easily meltable substances and corrosive media form galvanic cells and produce electrochemical corrosion.

　　3. Roasting: The composition and metallographic structure of the flame heating area change unevenly, and form a galvanic cell with the corrosive medium to produce electrochemical corrosion.

　　4. Welding: physical defects (undercuts, pores, cracks, lack of fusion, incomplete penetration, etc.) and chemical defects (large grains, poor chromium at grain boundaries, segregation, etc.) in the welding area and corrosive media form galvanic cells to generate electricity Chemical corrosion.

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