Reasons Analysis on Fracture of φ102 mm×9.19 mm DZ55 Geological Drill Pipe Body

Fracture reasons of a geological drill pipe with grade of DZ55 and size of φ102 mm×9.19 mm were analyzed through macro observation, metallographic examination, chemical compositions analysis, mechanical property test and SEM analysis. The results show that there were a lot of spiral scribes and scratches on outer surface of the drill pipe body, which caused stress concentration. At the same time, and material toughness of the drill pipe body was rather low. So cracks generated at the damage positions and finally brittle fracture happened during drilling process of the drill pipe.