损伤钻杆断裂的有限元仿真分析

Finite Element Simulation Analysis in Fracture of Damaged Drill Pipe

钻杆在作业过程中,需要通过卡瓦夹持,才能顺利作业,但卡瓦在钻杆表面会留下作业损伤。为了防止损伤导致的钻杆断裂,影响结构安全性,以某深井作业钻杆实际工况为例,创建含横向半椭圆形表面裂纹的钻杆有限元模型,数值研究拉扭复合载荷下,3种类型的形状因子沿裂纹前缘的变化规律;通过多项式拟合得到形状因子表达式中对应的系数,进而推导出等效应力强度因子的表达式。仿真计算结果表明,在(0.6~0.8)之间存在一临界形状比,裂纹最深点和边界相邻点处的等效应力强度因子值在此处相等。拟合得到的等效应力强度因子表达式,为进一步研究损伤钻杆表面裂纹扩展和寿命预测提供参考。

During the drill pipe operation,the drill pipe needs to be clamped by slips to work smoothly,but slips will leave work damage on the surface of the drill pipe.In order to prevent the fracture of drill pipe caused by damage and affect the safety of structure,a finite element model of drill pipe with transverse semi-elliptic surface crack was established by taking the actual working condition of drill pipe in a deep well as an example.The corresponding coefficients in the shape factor expression are obtained by polynomial fitting,and then the expression of equivalent stress intensity factor is deduced.The simulation results show that there is a critical shape ratio between 0.6 and 0.8.The equivalent stress intensity factor values at the deepest crack point and the adjacent boundary point are equal here.The expression of equivalent stress intensity factor obtained by fitting provides reference for further research on crack propagation and life prediction of damaged drill pipe.