凹坑缺陷参数对连续管疲劳失效的影响研究

The Effect of Pit Defect Parameters on Fatigue Failure of Coiled Tubing

为了探究凹坑缺陷参数与连续管疲劳失效的关系,建立了含缺陷连续管有限元模型,并利用试验对有限元模型进行了验证,分析了缺陷深度、缺陷轴向角度、缺陷长度、缺陷宽度和缺陷分布数量对连续管疲劳失效的影响,并与完整连续管进行了对比。研究结果表明:连续管在带压弯直循环过程中,缺陷处会产生明显的应力集中现象,最后发生疲劳失效;在一定角度的凹坑缺陷处,径向两个角落的塑性应变最大,连续管会沿着这两个位置发生断裂;5个因素对连续管疲劳失效的影响程度不同,缺陷深度和缺陷宽度对连续管的疲劳失效影响最为显著;在含缺陷连续管疲劳寿命理论模型建立过程中,应把缺陷深度和缺陷宽度作为主要考虑因素。所得结论为连续管疲劳寿命理论模型的建立提供了参考。

To study the relationship between pit defect parameters and fatigue failure of coiled tubing,a finite element model of coiled tubing with defects was established,and was verified by tests.The effect of the depth,axial angle,length,width of defect and defect distributions on the fatigue failure of coiled tubing is analyzed and compared with that of intact coiled tubing.The results of the study show that:during repeat bending and straightening of coiled tubing,there will be obvious stress concentration at the defects,and finally fatigue failure will occur.At the pit defects with a certain angle,the two radial corners have the largest plastic strain,where coiled tubing will break along.The five factors have different effects on the fatigue failure of coiled tubing.Defect depth and defect width have the most significant influence.During the establishment of the theoretical model of fatigue life of coiled tubing with defects,the depth and width of defects should be treated as the main considerations.The study could provide references for the establishment of the theoretical model of fatigue life of coiled tubing.