How to handle uneven coating thickness on spiral welded steel pipes

Spiral welded steel pipes are mainly used as fluid pipes and piling pipes. After the pipes are manufactured, if they are used for water transport, they are generally treated with anti-corrosion coatings on the inner or outer surface. Common anti-corrosion treatments include 3PE anti-corrosion, epoxy coal tar anti-corrosion, and epoxy powder anti-corrosion. Due to adhesion problems, epoxy powder coating has not been widely adopted. However, with the successful development of a special phosphating solution for epoxy powder coating, the adhesion problem of epoxy powder coating has been overcome for the first time, leading to the emergence of epoxy powder coating as a new process.

Analysis of the causes of uneven coating thickness on spiral welded steel pipes: The uneven coating thickness of 3PE spiral welded steel pipes is primarily manifested in the uneven thickness of the test points distributed along the circumference. The industry standard SY/T0413-2002 does not specify uniformity of thickness, only the coating thickness value, but requires that the coating thickness value cannot be lower than the thickness value of a single point, not the average of multiple test points.

Uneven coating thickness during the application of coatings on spiral steel pipes will inevitably lead to material waste. This is because while ensuring the thinnest part of the coating meets the standard thickness, the thickest parts will be significantly thicker than the standard coating thickness. Furthermore, uneven coating can easily result in the thinnest part of the steel pipe failing to meet the standard thickness. The main reasons for uneven thickness during production are uneven material extrusion at several points and pipe bending. Effective methods to control uneven 3PE anti-corrosion pipe coatings include adjusting the extrusion dies to ensure the coating thickness is as uniform as possible at several points, and refraining from coating substandard steel pipes.

Surface wrinkles in spiral steel pipe coatings: The extrusion and winding of polyethylene material onto the steel pipe requires the use of silicone rollers for pressing. Improper adjustments during this process can cause wrinkles to be squeezed out of the coating surface. In addition, the cracking of the melt film when the polyethylene material leaves the exit die during extrusion can also cause quality defects similar to wrinkles. The corresponding control measures for the cause 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 melt film cracking.