Large diameter steel pipe coating stress crack welding defects

In order to guarantee the quality of the extruded polyethylene coating, the large-diameter steel pipe specified in this standard shall be welded to ≤ 2.5 mm, and the weld shall be smoothly transitioned. For some steel pipes entering the factory, if there are burr surface welds at high standards or welds, sharp bump welding, welding wave scales, craters, splashes, undercuts and other defects, because these defects can be apparent in the plastic surface layer The disability, cooling contraction residual stress will further concentrate on the disability and lead to the initial crack of the plastic layer. At this point, the two tips that form cracks with only a small compressive stress (converted from residual stress) can develop rapidly. Regardless of the cause of the crack, once formed, it will continue to develop until the residual stress within the plastic buildup relaxes to less than the required crack stress development.