随钻仪器钻铤的断裂失效分析

利用光学显微镜、扫描电镜进行组织观察,通过力学性能测试、微动磨损测试等试验方法,对一种随钻仪器无磁钻铤的断裂失效原因进行了分析。结果表明,该随钻仪器钻铤在使用过程中发生了微动磨损,在工件过渡锥角根部形成了环形磨损凹槽。环形磨损不仅使钻铤有效直径减小,而且在带有弯曲的复杂载荷下,易在环形磨损处造成很强的应力集中,最终导致工件的断裂。环形磨损的产生是由于工件装配结构所致,但钻铤取材于原材料锻件半径的1/2位置偏内,此处晶粒较为粗大,硬度低,在同等工况下磨损相对严重。

Fracture failure analysis of logging while drilling instrument drill collar

The fracture failure reason of non-magnetic drill collar for drilling instrument was analyzed by means of optical microscope, scanning electron microscope, mechanical properties test and fretting wear test. The results show that fretting wear occurs on the logging while drilling (LWD) instrument drill collars during operation, and the annular wear groove is formed at the root of transition cone angle of workpiece. Annular wear not only reduces the effective diameter of drill collar drive shaft, but also causes strong stress concentration in the annular wear area under the complex load with bending, which eventually leads to the fracture of workpiece. Annular wear is caused by the assembly structure of workpiece, but because the driving shaft is taken within half of raw material forgings radius, where the grain is relatively coarser, hardness is lower, thus, the wear is relatively serious under the same working conditions.