某油田开采井使用的P110钢级套管在使用过程中出现断裂失效。使用宏观形貌分析、化学成分分析、金相检验、力学性能测试的方法，结合现场施工过程中失效套管的使用、维护及螺纹端部的使用状况分析，详细分析了套管螺纹断裂失效的原因并提出预防措施。结果表明：该套管断裂性质属于疲劳断裂；套管上卸扣过程中的不规范操作增大了螺纹端局部接触应力，装配过程中套管与接箍螺纹的轴线偏斜导致螺纹间存在间隙，局部接触应力过大导致螺纹面上的金属产生变形和磨损；螺纹旋进阻力增大、下井前仅部分旋入，是造成套管螺纹断裂失效的主要原因。

Fracture failure occurred to a P110 grade casing pipe used in an oil extraction well during the using process. By methods of macroscopic morphology analysis, chemical composition analysis, metallographic examination and mechanical property test, the reasons for the fracture failure of the casing thread were analyzed in detail and the preventive measures were put forward combined with the use, maintenance of failure casing and the behavior in service of the end of the thread in the field of construction process analysis. The results show that:the failure mode of the casing pipe was fatigue fracture; non-standard operation during the shackle process of the casing pipe increased the stress of local contact threaded end; during the assembly process of the casing pipe and the coupling thread, the axis deviation led to the gap between the threads; the excessive local contact stress caused the deformation and wear of the metal on the threaded surface; the main reasons of the fracture failure of the casing thread were that the resistance of the screw thread increased and only a part of the thread screwed in before down well.