一种钻杆累积疲劳的预测方法

钻杆在服役过程中承受着苛刻的工作环境和复杂的交变载荷,这些易导致钻杆的疲劳失效。在定向钻井中,累积疲劳是钻杆发生故障的常见形式。传统理论认为,钻杆疲劳破坏的主要原因是由于钻杆在弯曲井眼中旋转时发生周期性交变弯曲应力所致。在前人研究的基础上,分析了钻杆在交变弯曲应力和拉应力共同作用下的交变应力状态,并基于损伤容限设计的假设,结合Paris疲劳裂纹扩展模型和Miner累积损伤理论,提出了一种基于疲劳裂纹扩展的钻杆累积疲劳程度预测方法,并给出了算例,指出该预测方法在钻杆管理方面的作用。

A Method of Cumulative Fatigue Damage Calculation of Drill-pipe

The drill-pipe in service is suffered from rigorous working condition and complicated alterative loads,which trends to cause fatigue damage of a drill-pipe.And cumulative fatigue damage is the most popular form of drill-pipe damage in directional drilling.Therefore,the calculation of drill-pipe cumulative fatigue life can benefits the drill-pipe management and ensure the safety of oil production.A method of drill-pipe cumulative fatigue life calculation,based on the fatigue crack propagation,is presented.Paris fatigue crack propagation model and Miner cumulative damage theory were combined in this method under the hypothesis of defect-tolerant design philosophy which the concept of which that all structures or components posses defects,either from manufacture or from service.According to the traditional theory,fatigue damage of drill-pipe is mainly caused by the alternative bending stress while the drill-pipe is rotating in the crooked hole.On basis of previous researches,both bending stress and axial tensile load are considered in the analysis of alternative stress state of drill-pipe in this paper.Result of an example shows the effect of this method.