What factors cause corrosion on the surface of welded steel pipes

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

　　2. Surface scratches: Various scratches damage the passivation film, which reduces the protective ability of stainless steel. It is easy to react with chemical media and cause chemical corrosion to damage the welded steel pipe.

　　3. Cleaning: After pickling and passivation, the remaining liquid will remain, which will directly corrode the welded steel pipe.

　　Second, electrochemical corrosion

　　1. Carbon steel pollution: the scratches and corrosive media caused by contact with carbon steel parts form galvanic cells and produce electrochemical corrosion of welded steel pipes.

　　2. Cutting: the adhesion of slag, splash and other easily meltable substances and corrosive media form a galvanic cell and produce electrochemical corrosion to corrode the welded steel pipe.

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

　　4. Welding: The physical and chemical defects in the welding area form a galvanic cell with the corrosive medium and cause electrochemical corrosion.