某定向井在钻井作业时发生钻杆接头刺漏事件，采用显微组织、断口形貌观察，化学成分、力学性能测试等方法分析了刺漏原因。结果表明：钻杆在服役过程中受到较大的弯曲应力，其内螺纹接头18°吊卡台肩根部产生应力集中，同时台肩根部存在周向划痕，导致疲劳裂纹萌生并扩展；钻杆钻进过程中，弯曲应力增大，裂纹扩展速率加快，刺穿整个壁厚导致刺漏。建议优化钻杆结构，并严格控制钻杆加工工艺，避免产生划痕，同时减缓台肩根部的应力集中。

A drill pipe joint puncture event occurred during drilling in a directional well. The cause of the puncture was analyzed by microstructure and fracture morphology observation, chemical composition and mechanical properties test. The results show that the drill pipe was subjected to great bending stresses during the service, leading to stress concentration at the root of the 18° elevator shoulder of the drill pipe internal thread joint. Moreover, there were circumferential scratches at the root of the shoulder. Therefore fatigue cracks were originated and propagated. During the drilling of the drill pipe, the bending stress increased, resulting in the increase of the crack growth rate. The propagated cracks pierced the entire wall thickness, resulting in the puncture. It was suggested that optimizing the drill pipe structure and strictly controling the drill pipe processing technique to avoid scratches and reduce the stress concentration at the root of the shoulder.