Uneven thickness of anti-corrosion coating on spiral steel pipe and its treatment

Spiral steel pipe is mainly used as fluid pipe and piling pipe. After the steel pipe is made, if it is used for water transportation, it will generally be treated with anti-corrosion on the inner or outer surface. The general anti-corrosion includes 3PE anti-corrosion, epoxy coal tar anti-corrosion, epoxy powder anti-corrosion, etc. Since the epoxy powder dipping process is troubled by adhesion problems, the epoxy powder dipping process has never been promoted. At present, with the successful development of a special phosphating liquid for epoxy powder dipping, the adhesion problem of the epoxy powder dipping process has been overcome for the first time, and the emerging process of epoxy powder dipping has begun to appear.

Analysis of the uneven thickness of the anti-corrosion coating on spiral steel pipe. The uneven thickness of the 3PE spiral steel pipe coating is mainly manifested in the uneven thickness of the test points on each side distributed in the circumferential direction. The industry standard SY/T0413-2002 does not stipulate the uniformity of thickness, but only stipulates the thickness value of the coating, but requires that the thickness value of the coating cannot be lower than the thickness value of the point, rather than the average value of multiple test points.

If the coating thickness is uneven during the coating process of spiral steel pipe, it will inevitably cause waste of coating materials. This is because when the coating thickness at the thinnest part reaches the standard, the thickness of the thick part will be much greater than the coating standard thickness. Moreover, in the case of uneven coating, it is easy to cause the coating thickness at the thinnest part of the steel pipe to fail to meet the standard. The main reasons for uneven thickness during the production process are uneven material discharge at several places and bending of the steel pipe. An effective way to control the uneven coating of 3PE anti-corrosion pipelines is to adjust several extrusion dies to make the thickness of the anti-corrosion coating at several places as uniform as possible, and not to apply coating on unqualified steel pipes.

Wrinkles on the coating surface: The polyethylene material needs to be rolled by a silicone roller when it is extruded and wrapped on the steel pipe. Improper adjustment during this process may cause wrinkles on the coating surface. In addition, the rupture of the melt film when the polyethylene material leaves the outlet die during extrusion will also cause quality defects similar to wrinkles. The corresponding control methods for the causes of wrinkles include adjusting the hardness and pressure of the rubber roller and the angle of the pressure roller, and appropriately increasing the extrusion amount of polyethylene to control the rupture of the melt film.