某井随钻扩眼器接头外螺纹断裂原因分析

Fracture Analysis of External Thread of Reamer Joint While Drilling

针对某井随钻扩眼器接头外螺纹断裂失效,结合扩眼器现场工作情况,通过对扩眼器设备工作原理调研、接头材料的理化性能检测、外螺纹断口微观形貌分析及弯曲强度比计算,分析了扩眼器断裂失效的原因。结果表明,由于扩眼器接头外螺纹牙底部位不是平滑过渡的圆弧形状,导致该部位存在较高程度的应力集中;另外扩眼作业时扩眼幅度较大,使随钻扩眼器接头承受了较大的交变应力,从而在其外螺纹牙底部位萌生了疲劳裂纹并在使用中逐渐扩展,最后导致其外螺纹断裂。建议通过加工应力分散槽或在外螺纹牙根部进行冷滚压以提高其疲劳寿命。

Aiming at a failed well drilling reamer joint external thread,considering field work conditions,the reason of fracture failure was analyzed based on investigation of reamer working principle,test of physical and chemical properties of the joint material,microstructure analysis of the fracture of failed external thread and calculation of flexural strength ratio.The results show that there is a high degree of stress concentration at the bottom of the external thread of the reamer joint due to unsmooth transition of arc shape.In addition,the reaming range is large during operation,which makes the joint of reamer while drilling bear large alternating stress,resulting in fatigue cracks at the bottom of its external thread,which gradually expand in use,and finally lead to the fracture of external thread.It is suggested that the fatigue life should be improved by machining stress dispersion groove or cold rolling at the root of external thread.