φ139.7mm钻杆内螺纹接头纵向开裂失效分析

Longitudinal-cracking Failure Analysis of Box

通过力学性能测试、化学分析、金相组织和断口分析,并结合受力状态,对某井φ139.7 mm钻杆内螺纹接头纵向开裂原因进了行分析。结果表明,钻杆接头纵向开裂失效的原因是内外旋合螺纹之间发生剧烈的摩擦作用导致内螺纹牙顶形成"马氏体"白亮层组织,裂纹从白亮层内萌生,由于材料的横向冲击功明显小于纵向冲击功,裂纹沿纵向脆性扩展,最终导致钻杆接头发生纵向开裂失效。

Failure reason of vertically-cracking box of φ139.7 mm drilling pipe was studied through visual inspection, mechanical testing, metallographic examination, fracture surface analysis and considering loads added on it. Results showed that reason of failure was the ＂Martensite＂ layer caused by screw thread pair＇s severe friction. During drilling process, cracks were initiated from ＂mansensite＂ layer on the thread crest and brittle-vertically developed by the reason of its lateral absorbed-energy was much lower than longitudinal absorbed-energy. In the end, they lead box of drilling pipe to longitudinal-cracking failure.