X80油气管道焊缝双裂纹干涉效应多场耦合数值模拟方法

Multi-field Coupling Numerical Simulation Method for Interference Effect of Double Cracks in X80 Oil and Gas Pipeline Weld

基于漏磁法检测管道焊缝理论,应用虚拟裂纹闭合法(Virtual crack closure technique,VCCT)提出一种流固磁多场耦合方法。以解决工程问题为例,由于实际管道中裂纹多以裂纹群的形式存在,因而应用该方法研究了X80管道焊缝共线双裂纹、环向对称双裂纹扩展问题。通过对管道焊缝内壁动态施加流体压力载荷,每完成一次裂纹增量扩展,重构网格,计算裂纹扩展进程中的特征量,包括管道内流体压力载荷P、裂纹尖端能量释放率GⅠ、扩展长度L、裂纹尖端张开角度CTOA、磁感应强度分量峰值Bx p,循环进行裂纹扩展和磁场分析。数值算例结果表明:共线双裂纹的干涉效应加速了裂纹扩展进程;环向对称双裂纹间距较大时,加速了裂纹扩展进程,当环向间距小于或等于0.5倍的焊缝环向弧长的双裂纹时,由于双裂纹干涉效应,双裂纹的存在抑制了裂纹的扩展。该方法的实现可为指导实际X80管道安全评估提供理论依据。

Based on the theory of magnetic flux leakage(MFL)method for detecting pipeline weld,a fluid-solid magnetic multi-field coupling method is proposed by applying the virtual crack closure technique(VCCT).Taking solving engineering problems as an example,because the cracks in actual pipelines mostly exist in the form of crack groups,this method is applied to study the crack propagation problems of co-linear double cracks and circumferentially symmetric double cracks of X80 pipeline weld.By dynamically applying fluid pressure load on the inner wall of pipeline weld,each time the crack incremental growth is completed,the mesh is reconstructed,and the characteristic parameters in the process of crack propagation,such as fluid pressure load P in pipeline,energy release rate GⅠat crack tip,propagation length L,crack-tip-opening angle CTOA,magnetic induction component Bx p,are calculated.Crack propagation and magnetic field analysis are carried out cyclically.The numerical results show that the interference effect of collinear double cracks accelerate the process of crack propagation,and the process of crack propagation is accelerated when the distance between circular symmetric double cracks is large.When the annular distance is less than or equal to 0.5 times of the annular arc length of the weld,the existence of the double crack inhibits the growth of the crack due to the interference effect of the double crack.The realization of this method can provide theoretical basis for practical X80 pipeline safety evaluation.