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1. Weld defects:

The weld defects of plastic-coated steel pipes 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. Hard to remove scratches:

The overall pickling and passivation can not remove all kinds of scratches generated during the processing, and can not remove carbon steel, spatter and other impurities adhered to the surface of the plastic-coated steel pipe due to scratches and welding spatter, resulting in corrosion in the corrosive medium Rust occurs due to chemical corrosion or electrochemical corrosion under existing conditions.

3. Uneven polishing and passivation:

Pickling and passivation treatment after manual grinding and polishing, it is difficult to achieve a uniform treatment effect for large-area workpieces, 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 capacity:

Pickling passivation paste is not a panacea, and it is difficult to remove the black scale produced by plasma cutting and flame cutting.

5. The scratches caused by human factors are more 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 surface treatment more difficult and is also the main reason for rust after treatment.

6. Equipment factors:

During the bending and bending of profiles and plates, scratches and creases are also the main reason for rust after treatment.

7. Other factors:

In the process of procurement and storage of plastic-coated steel pipe raw materials, the bumps and scratches caused by hoisting and transportation are also relatively serious, which is also the cause of corrosion.