川渝地区某超深井钻铤外螺纹断裂失效分析

某Φ279.4 mm钢制钻铤在川渝地区某超深井服役过程中紧扣时，在距钻铤外螺纹端面2～4 cm处发生断裂。通过对断口进行宏观形貌观察及断口和台阶面特征、金相组织、硬度分析，并结合钻铤材料的力学性能试验，对失效钻铤外螺纹断裂原因进行试验分析。结果表明:钻铤螺纹齿牙之间附着大量沉积物，台肩处大量大尺寸磨损坑，多处裂纹源在齿根底部形成，集中在最末完全扣前3～5扣处，在拉伸应力以及扭矩交变载荷的共同作用下，裂纹缓慢扩展，形成初始断口，当钻铤断裂截面处不足以承载交变载荷以及扭矩作用时，发生断裂。

Fracture Failure Analysis of Drill Collar External Thread in Ultra-deep Well in Sichuan-Chongqing Region

During the service of a Φ279.4 mm steel drill collar in an ultra-deep well in Sichuan-Chongqing area, the drill collar broke 2~4 cm away from the end face of the external thread of the drill collar. Through the observation of the fracture morphology, and analysis of the characteristics of fracture and step surface, metallographic structure, hardness and mechanical properties test of drill collar material, the fracture reason of the failed drill collar external thread was analyzed. The results show that a large number of deposits are attached between the drill collar thread teeth, a large number of large-scale wear pits at the shoulder, and multiple crack sources are formed at the bottom of the tooth root, concentrated in the first 3~5 buckles of the last complete buckle. Under the action of tensile stress and torque alternating load, the crack expands slowly and forms initial fracture. When the fracture section of the drill collar is insufficient to bear the alternating load and torque, the fracture occurs.