Weld Defect on Stress Cracking of Large Diameter Steel Pipe Coating

    In order to ensure the quality of extruded polyethylene coating, the standard stipulates the large diameter steel pipe weld I ≤ 2.5mm, and the weld should be smooth transition. For some steel pipe into the plant, if the weld over the high standard or weld surface there are burr, sharp bump welding, scaly welding wave, arc crater, splash, undercut and other defects, because such defects can be in the plastic surface layer left significant disability, the cooling shrinkage residual stress will be further concentrated in the disability, and lead to the plastic layer of the initial crack. At this point, only a small amount of the compressive stress (converted from the residual stress) at the two tips of the formed crack can be developed rapidly. Regardless of the factors that cause the crack, once formed will continue to develop until the accumulation of plastic within the residual stress relaxation to less than the crack stress required for the development.