全尺寸钻柱弯曲疲劳损伤试验研究

Test on Bending Fatigue Damage of Full-size Drill String

以往有关钻具疲劳损伤的研究多为模型模拟或小尺寸试验,不能准确反映全尺寸钻柱的疲劳损伤。为此,在四点弯曲疲劳试验的基础上,采用全尺寸钻柱作为试验试件,通过磁记忆检测技术对试件的应力状况进行检测分析,以此来描述钻柱损伤的演变过程。分析结果表明:在全尺寸钻柱四点弯曲疲劳试验过程中,循环加载后在中间段管体位置发生断裂,断裂过程中,不同的循环次数对应的磁记忆信号梯度峰值呈现出稳定阶段、裂纹萌生阶段和裂纹扩展失效断裂阶段。当循环82 000次时,管体部位信号梯度最大值达到1.14 V/mm,之后随着循环次数的增加,磁记忆信号梯度峰值迅速增大,当循环85 000次时,钻杆发生完全断裂。研究结果对预防钻柱断裂具有一定的参考作用。

In the past, the study on the fatigue damage of drill string was mostly modeling or small-scale test, which could not accurately represent the fatigue damage of full-bore drill string. Based on the four-point bending fa-tigue test, taking the full-size drill string as the test specimen, magnetic memory detection technofogy has been used to detect and analyze and the stress condition of the specimen, so that to describe the evofution process of drill string damage. The results show that,during the four-point bending fatigue test of the full-size drill string,the pipe cracks at the middle of the pipe body after cyclic loading. During cracking,the peak value of the magnetic memory signal gradient corresponding to the number of cycles showed stable stage,crack initiation stage and crack propaga-tion failure fracture stage. When the cycle times are 82 000,the maximum signal gradient of the pipe body reaches 1. 14 V/mm. Then,the peak value of the magnetic memory signal gradient increases rapidly with the number of cy-cles. When the cycle is 85 000,the drill pipe is completely broken. The conclusion could provide a certain refer-ence on the prevention of drill string crack.