热熔焊接工艺参数对聚乙烯燃气管道焊接残余应力的影响

Effect of hot-melt welding process parameters on welding residual stress of polyethylene gas pipeline

高密度聚乙烯(PE-HD)管道具有韧性高、抗腐蚀等优点,广泛应用于输水输气、核工业和氢能等领域。受加工工艺和焊接技术的限制,PE-HD管道系统存在生产残余应力和焊接残余应力。残余应力的存在,会加速管道内部裂纹的萌生和扩展,显著降低了管道的使用寿命。因此,研究残余应力对准确评价PE-HD管道可靠性具有重要意义。分别采用开口圆环法和盲孔法测得了PE-HD管基材和热熔接头的环向残余应力,并基于弹塑性本构建立了温度-位移耦合的热熔焊接有限元模型,探究了热熔焊接接头残余应力的分布及焊接工艺参数对温度场和残余应力的影响。结果表明:盲孔法和开口圆环法测量结果近似相等;与传统的黏弹性模型相比,建立的弹塑性热熔焊接有限元模型计算结果更接近实验测量值;熔融层厚度随焊接温度和加热时间的增加而增大,延长加热时间可导致热熔接头长度增加;焊缝和熔合区的残余应力为拉应力,且内壁的拉应力大于外壁的拉应力,距离焊缝5 mm处残余应力由拉应力转变为压应力,焊接温度升高和加热时间延长会使残余应力数值增大。

Polyethylene(PE-HD)pipeline has the advantages of high toughness and corrosion resistance,and is widely used in the fields of water and gas transmission,nuclear industry and hydrogen energy.Due to the limitation of machining technology and welding technology,there are production residual stress and welding residual stress in PE-HD pipeline system.The existence of residual stress accelerate the initiation and expansion of cracks inside the pipeline,and significantly reduce the service life of the pipeline.Therefore,the study of residual stress is of great significance to accurately evaluate the reliability of PE-HD pipeline.The hoop residual stress of PE-HD pipe substrate and hot-melt joint was measured by open-ring method and blind hole method respectively.Based on the elastic-plastic constitutive model,the finite element model of hot-melt welding with temperature-displacement coupling was established.The distribution of residual stress in hot-melt welded joints and the influence of welding process parameters on temperature field and residual stress were investigated.The results measured by the blind hole method and the open ring method are approximately equal.Compared with the traditional viscoelastic model,the calculation results of the elastic-plastic hotmelt welding finite element model established are closer to the experimental measurements.The thickness of molten layer increases with the increase of welding temperature and heating time,and the length of hot-melt joint increases with the increase of heating time.The residual stress in the weld and fusion zone is tensile stress,and the tensile stress in the inner wall is greater than that in the outer wall.The increase of welding temperature and heating time will increase the residual stress value.