Failure Analysis on Piercement of a 139.7 mm×10.54 mm G105 Drill Pipe

The reasons to the piercement of drill pipe with grade of G105 and size of 139.7 mm×10.54 mm were analyzed through morphology analysis, chemical components analysis, mechanical property test, microstructure examination, SEM analysis and energy spectrum analysis. The results show that the essence of drill pipe piercement was early fatigue failure, and the main reason of which was severe alternating stress induced by vibrations such as bit bouncing. Dissolved oxygen in drilling mud caused the pitting on the outer surface. Just those pits accelerated arising of fatigue crack. Moreover, direct transition from the drill collar to the drill pipe, the sudden change of the section led the exacerbation of the stress concentration which was also one reason causes for the occurrence of drill pipe fatigue failure. Scavenger and inhibitor were suggested to add in the drilling mud. In addition, a lower bit weight and optimum drilling parameters were good ways to avoid drill string vibration strenuously.