Fracture Failure Analysis on a Drill Pipe in Directional Drilling

This paper addresses fracture failures for drill pipes in a directional drilling construction project for an oil and gas pipeline. The authors analyzed failed drill pipe samples through fracture macro analysis, nondestructive testing for micro-cracks, mechanical properties testing on drill pipe material, microscopic microstructure analysis, the cross-section morphology analysis, and the service conditions analysis. This study determined that drill pipe failure is caused by a repeated overload thrust applied to a drill string for the purpose of freeing a stuck drill, resulting in a bent drill string and a drill pipe fatigue crack initiated on the outer surface of the bent drill pipe and propagated rapidly. Theoretical calculation and finite element simulation based on the drill string service condition showed a helical buckling deformation before fracture, leading to the conclusion that it was the repeated overload thrust that caused the drill pipe fatigue fracture.