Fracture Failure Analysis of the Thread of the P110 Casing Pipe

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.