漠大线输油保温管道外护层开裂的热力耦合仿真与试验研究

摘要

With respect to the cracking problem of multilayer structure of oil transmission insulated piping in the Mohe-Daqing line between China and Russia,the cause of cracking under big dynamic temperature difference in cold area was researched in combination with thermal coupling dynamic simulation by ANSYS software and performance test of the low temperature material.Through the finite element modeling of multi-layer structure of insulated straight pipe and elbow pipe,the boundary condition and dynamic temperature load under stacking condition were determined,and then the stress field and strain field of polyethylene outer protective layer were obtained.The simulation analysis shows that the multilayer structure of the in-sulated pipe produces complex mechanical constraint effect due to the difference of linear expansion coef-ficient of the materials in different layers,resulting in presence of difference in stress and strain between the layers.Under the reciprocating dynamic influence of big temperature difference between day and night,this difference causes serious thermal fatigue effect of the polythene outer protective layer of the multilayer structure.On this basis and in combination with the performance test of low temperature materi-als,further researches were conducted on cracking and crack propagation of straight pipe and elbow pipe of multi structure under the effect of alternating temperature.The results show that both the values of stress and strain have exceeded the tensile fracture ultimate strength of polyethylene outer protective lay-er.The results of finite element simulation are consistent with the test results,which provides a new scien-tific basis for the improvement of insulated piping materials.%针对中俄漠大线输油保温管道多层结构开裂问题,结合ANSYS热力耦合动态仿真和低温材料性能试验研究寒地动态大温差下开裂原因.通过对保温直、弯管道多层结构进行有限元建模,确定堆放条件下的边界条件与动态温度载荷,得到聚乙烯外护层的应力场及应变场.仿真分析得出,保温管道多层结构因各层材料线膨胀系数差异而产生复杂的力学约束作用,造成各层之间存在着应力及应变差异,这种差异在昼夜大温差的往复动态影响下,使多层结构的聚乙烯外护层产生严重的热疲劳效应.在此基础上结合低温材料性能试验,进一步对交变温度影响下多层结构直管与弯管开裂与裂纹扩展进行了研究.结果表明,在大温差下,应力及应变值均已超越聚乙烯外护层拉伸断裂极限强度,有限元仿真结果与试验结果相吻合,为保温管道材料的改进提供一种新的科学依据.