indenting

Through failure analysis of a fractured tubing in Daqing oil fields, we have concluded that it is a fatigue fracture of the tubing, and what led to the cracks in the bottom of the tubing threads is the original cutting marks.

油管螺纹齿底的原始加工刀痕是造成裂纹萌生的主要原因，萌生的裂纹在油管承受的拉－拉脉动载菏作用下发生疲劳扩展，最后导致油管断裂失效。