Failure Analysis of Horizontal Directional Drilling Crossing Drill Pipe Fracture

The fractured directional drilling crossing drill pipe was investigated by means of non-destructive test, chemistry component analysis, material mechanical property testing, optical microscope and SEM inspection of fracture. The results indicated that the diameter of crossing hole was greater than out-diameter of drill pipe, while rotary drilling, drill pipe not only rotated around its own axis, but also revolved along the axis of crossing hole. Therefore, high alternating stress occurred on the outside surface of drill pipe, which was nearby the reamer. Consequently fatigue crack was initiated from outside the surface of drill pipe and extended to fracture.