钻井工具接头内螺纹牙型底部开裂原因

Causes of cracking at the bottom of internal screwed teeth in drilling tool joint

某钻井工具接头在短期使用后出现周向裂纹,采用化学成分分析、硬度测试、金相检验等方法对其开裂原因进行了分析。结果表明:该钻井工具接头的裂纹为疲劳裂纹,裂纹萌生于内螺纹接头与杆柱体最临近的螺纹牙型底部,在周期性疲劳载荷的作用下,裂纹沿螺纹牙型底部周向扩展,同时向外壁方向扩展,最终外壁发生开裂。

The circumferential cracks appeared in a drilling tool joint after short-term use.The cracking causes were analyzed by chemical composition analysis,hardness test and metallographic examination.The results show that the crack of the drilling tool joint was fatigue crack,and the crack initiated at the bottom of the thread tooth profile closest to the internal thread joint and the rod body.Under the action of periodic fatigue load,the crack extended circumferentially along the bottom of the thread tooth profile,and at the same time extended outward,and finally the outer wall cracked.