Weld geometry mutations on stress corrosion cracking of the main floor has two. First, because the high weld stay more than the same width, same height when molten plastic extruded film on steel cladding, coating the inevitable formation of the weld zone and thin compared to steel area, if the weld reinforcement than the standard provides more severe than this thickness. As we all know, when the plastic wall thickness is uneven, not only led to the plastic layer to form a ring body strength is poor, Tiny Zone
resulting in stress cracking caused by the weak link, the more serious is forming in its cooling process, will lead to shrinkage of residual stresses in thin cooling zone accumulation, in other words, the residual stress concentration in the weld zone coating body. Second, due to the geometry of the weld bead formed mutation weld reinforcement, under the same heating conditions, different thickness of the steel substrate different heat storage capacity, resulting in the formation of the weld zone area and the pipe heat tolerance, heat tolerance, if not in such effectively eliminated under cooling conditions, weld bead zone stress cracking corrosion layer also has a serious impact. As mentioned before, in the same frequency heating conditions, due to the presence of weld reinforcement, heat storage capacity greater than steel weld zone, if the weld reinforcement exceed standards, this is more serious heat tolerance. The effect of water cooling process mainly in the steel pipe weld zone and the formation of different residual heat pipe area. Because of the large heat storage capacity weld area, under the same cooling conditions, if the molding production line water cooling parameters insufficient cooling of residual heat after forming the weld zone is greater than the accumulated steel area, the residual heat by heat conduction with the weld area the second plastic layer is heat capacity, resulting in a temperature region higher than the plastic layer plastic pipe layer region, in other words, causes the strength of the plastic layer is less than the area of Plastic pipe layer