Φ139.7 mm加重钻杆内螺纹接头断裂失效分析

Failure Analysis of Box Joint of aΦ139.7 mm Heavy Weight Drilling Pipe

通过断口宏观和微观分析,材料化学成分分析、力学性能试验和金相分析,明确了Φ139.7mm加重钻杆内螺纹接头的断裂原因。结果表明:加重钻杆内螺纹接头断裂属于疲劳断裂;断裂的主要原因是加重钻杆内螺纹接头外径小于标准规定值,降低了加重钻杆的抗拉强度和抗扭强度。在交变载荷的作用下,裂纹首先从内螺纹接头危险截面处的螺纹牙底萌生并扩展,直至发生断裂。

A fracturedΦ139.7 mm heavy weight drilling pipe was analyzed through chemical composition analysis,mechanical property test,metallography analysis,Scanning Electron Microscope(SEM)and Energy Dispersive Spectrometer(EDS).The results show that the failure of the heavy weight drilling pipe was belong to fatigue fracture.The main reason for the fatigue fracture lies in the fact that the decreased outside diameter of the box joint led to the reduction of the torsion and tensile strength.Under alternating load,fatigue crack first appeared at the bottom of inner thread which was the dangerous section part of the box joint,and then propagated until the final fracture occurred.