连续油管卷曲低周疲劳寿命预测

弯曲和内压作用下产生的疲劳是造成连续油管失效的主要原因,在疲劳曲线上按其破坏的循环数N划分,属于典型的低周疲劳问题。以三参数幂函数能量法(3SE)和梁弯曲理论为基础,结合连续油管的承载状态,考察其疲劳寿命及影响因素。实例分析表明,连续油管循环次数随卷绕半径的增大而增大,但基于材料本身特征,存在一个卷绕半径极限,超过该值时通过增大卷绕半径的方法来提高连续油管循环寿命无太大意义;3SE方法在寿命预测精度上优于传统Manson-Coffin方法,对于连续油管作业过程中涉及的低周疲劳问题及寿命预测具有一定的借鉴作用。

Prediction of low cycle fatigue life of curling coiled tubing

The fatigue under bending and inward press is the main reason for coiled tubing failure, which belongs to typical low cycle fatigue problem according to cycle number N at fatigue curve. Based on three-parameter exponential function energy method and beam bending theory, in combination with the bearing condition of coiled tubing, the fatigue life and affecting factors are investigated. The case study shows that the cycle times of coiled tubing increases with the increase of coiling radius. However, there exists a coiling radius limit due to material behavior. When the limit is exceeded, improving the coiled tubing cycle life by increasing coiling radius is of little significance. The 3SE method is superior to traditional Manson Coffin method in terms of life prediction accuracy, which has a certain reference in low cycle fatigue and life prediction regarding coiled tubing operation.