What are the problems and solutions for uneven anti-corrosion coating thickness in spiral welded steel pipes

Spiral steel pipes are mainly used as fluid pipelines and piling pipes. After manufacturing, if the pipes are used for water transport, anti-corrosion treatment is generally applied to the inner or outer surface. Common anti-corrosion treatments include 3PE, epoxy coal tar, and epoxy powder coating. However, due to adhesion issues, epoxy powder coating has not been widely adopted. Recently, with the successful development of a special phosphating solution for epoxy powder coating, the adhesion problem 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 in spiral steel pipes: The uneven coating thickness of 3PE spiral steel pipes is primarily manifested in the uneven thickness at test points distributed along the circumference. The industry standard SY/T0413-2002 does not specify uniformity of thickness, only a coating thickness value, but requires that the coating thickness value cannot be lower than the thickness value at a single point, not the average of multiple test points.

Uneven coating thickness during the coating process of spiral steel pipes will inevitably lead to a waste of coating material. This is because while ensuring the thinnest part of the coating reaches 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 not meeting the standard coating thickness. The main reasons for uneven thickness during production are uneven material extrusion at several dies and pipe bending. Effective methods to control uneven 3PE anti-corrosion pipe coating include adjusting the extrusion dies to make the anti-corrosion coating thickness as uniform as possible at several points, and refraining from coating unqualified steel pipes.

Coating surface wrinkles: Polyethylene extrusion and winding onto the steel pipe requires the pressure of silicone rollers. Improper adjustment during this process may cause wrinkles to be squeezed out of the coating surface. Additionally, the rupture of the melt film when the polyethylene exits the exit die during extrusion can also cause quality defects similar to wrinkles. Corresponding control measures for wrinkle formation include adjusting the hardness and pressure of the rubber rollers and the angle of the pressure rollers, and appropriately increasing the polyethylene extrusion amount to control melt film rupture.