压扁阻断对聚乙烯燃气管道力学性能的影响

Influence of squeeze-off on the mechanical properties of PE gas pipes

压扁阻断是基于聚乙烯(PE)管道良好的韧性而设计的专用管线施工及抢险维修技术,近年来得到了广泛的应用。但是不规范的压扁阻断会引起PE管道损伤,缩短其使用寿命,严重影响燃气管网的安全运行。为了创建安全高效的压扁阻断工艺流程、保证PE燃气管道的安全运行,采用实验室试验与有限元模拟相结合的方法,探究了压扁阻断对PE管道力学性能的影响规律,重点分析了挤压速度、管壁压缩率、挤压棒尺寸、管道和挤压棒之间摩擦系数等对管道最大应力和塑性应变的影响情况。研究结果表明:①压扁阻断后的PE管道耳朵处的弹性模量和屈服应力仅为初始值的17%和72%;②管道最大载荷、最大应力和最大塑性应变随挤压速度、管壁压缩率的增大而增大;③减小挤压棒尺寸虽然会降低最大挤压载荷,但却能明显增大管道最大应力和塑性应变;④降低管道和挤压棒之间的摩擦系数有利于减小管道最大应力和塑性应变。结论认为,压扁阻断会引起PE管道力学性能的衰退,建议给压扁阻断后的PE管道尤其是耳朵处施加必要的防护措施;同时,增大挤压工具尺寸、减小管道和挤压棒之间的摩擦系数,可以减小管道应力和塑性应变,有利于PE管道的安全运行。

Squeeze-off is a dedicated pipeline construction and rush repair technology which is designed on the basis of the good toughness of polythene(PE)pipes,and it has been extensively applied in recent years.However,non-standard squeeze-off can bring damage to PE pipes,shorten its service life and even severely impact the safe operation of gas pipes.In order to establish a safe and efficient squeeze-off process and ensure the safe operation of PE gas pipes,this paper investigates the influential laws of squeeze-off on the mechanical properties of PE pipes by means of laboratory experiments and finite element simulation.And the influences of extrusion speed,wall compressibility,size of extrusion rod and friction coefficient between pipe and extrusion rod on the maximum pipe stress and plastic strain are mainly analyzed.And the following research results were obtained.First,the elastic modulus and yield stress at the ear of PE pipes after the application of squeeze-off are only 17%and 72%of the original values.Second,maximum pipe load,stress and plastic strain increase with the increase of extrusion speed and wall compressibility.Third,as the size of the extrusion rod decreases,the maximum extrusion load decreases,but the maximum pipe stress and plastic strain increase significantly.Fourth,reducing the friction coefficient between pipe and extrusion rod is beneficial to the reduction of maximum pipe stress and plastic strain.In conclusion,the squeezeoff can deteriorate the mechanical properties of PE pipes,so it is suggested to apply some necessary protection measures to the squeezed off PE pipes and especially its ear.What's more,increasing the size of extrusion tool and reducing the friction coefficient between pipeline and extrusion rod can lead to the reduction of pipe stress and plastic strain,which is beneficial to the safe operation of PE pipe.