V150高强度钻杆断裂失效分析

Failure analysis of V150 high strength drill pipe fracture

某超深井在下套管过程中发生V150钻杆断裂事故,为查明断裂原因,采用宏观及显微组织分析、硬度测试、线弹性断裂力学分析等方法对断裂样品进行了失效分析。结果表明,该钻杆为脆性断裂,裂纹起源于摩擦对焊焊缝外表面附近的灰斑缺陷。由于钻杆焊缝热处理回火时超温,在较快冷却速度下形成了硬脆相组织,降低了焊缝断裂韧性及裂纹临界尺寸,在裂纹深度达到临界尺寸时,裂纹迅速失稳扩展,导致钻杆脆性断裂。

A V150 drill pipe broke down in the process of tripping casing in ultradeep well. In order to find out the cause of the drill pipe failure,the macro and microstructure analysis,hardness test and linear elastic fracture mechanics survey were carried out. The results show that the failure type of the pipe is brittle fracture. The fracture originates from the gray spot near the outside surface of the welding zone.Meanwhile,the weld line fracture toughness and critical crack size are decreased due to the hard and brittle phases in welding zone which forme due to over tempering and too fast cooling rate. When the source crack depth reaches the critical size,the crack propagates rapidly and finally leads to brittle failure.