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1. weld seam defects: weld seam defects are serious, and manual mechanical grinding is used to make up for them. the resulting grinding marks will cause uneven surfaces and affect the appearance. pickling and passivating only the weld seam also creates an uneven surface.
2. difficult to remove scratches: the overall pickling passivation can not remove all kinds of scratches generated during the processing, and can not remove the carbon steel and spatter adhered to the surface of plastic-coated steel pipe due to scratches and welding spatter. such impurities lead to chemical corrosion or electrochemical corrosion and rust in the presence of corrosive media.
3. uneven passivation of grinding and polishing: pickling and passivation treatment after manual grinding and polishing, it is difficult to achieve a uniform treatment effect for workpieces with large areas, and it is impossible to obtain an ideal uniform surface. and the cost of working hours and the cost of auxiliary materials are also higher.
4. limited pickling ability: pickling passivation paste is not a panacea, and it is difficult to remove the black oxide scale produced by plasma cutting and flame cutting.
5. the scratches caused by human factors are relatively serious: in the process of hoisting, transportation, and structural processing, the scratches caused by human factors such as bumping, dragging, and hammering are relatively serious, which makes the surface treatment more difficult, and also causes rust after treatment the main reason.
6. equipment factors: during the bending and bending process of profiles and plates, the scratches and creases caused are also the main reasons for the rust after treatment.
7. other factors: in the process of procurement and storage of plastic-coated steel pipe raw materials, bumps and scratches caused by hoisting and transportation are also relatively serious, which is also the cause of corrosion.