为查明某定向钻穿越S135钢级钻杆断裂的原因, 对失效钻杆的断口形貌、化学成分、力学性能和微观组织进行了分析, 并运用断裂力学理论进行了相关计算。结果表明: 失效钻杆的断裂性质属于脆性断裂; 钻杆在生产过程中, 管体加厚过渡带外表面存在横向淬火裂纹, 使用时裂纹尖端形成了较大的应力集中, 当裂纹尖端实际受到的应力大于裂纹发生失稳扩展的临界应力时, 钻杆便发生断裂失效。

To find out the failure causes of S135 drill pipe in directional drilling crossing, the fracure morphology, chemical composition, mechanical properties and microstructure were analyzed and correspomding calculations were performed using fracture mechanics theory. The results show that the fracture style of the failed drill pipe was brittle fracture. The lateral quenching cracks were found on the outwall of upset section during the drill pipe manufacture,great stress concentration was formed at the crack tip during using. When the practical stress at the crack tip was larger than the critical stress of making cracks unstable propagation, the drill pipe failed.