Failure Analysis for Drill Pipe Upset Transition Area

Cases concerning failures of drill pipe upset transition area are investigated,and thus the characteristic,mechanism and causes of the failure are identified,resulting in the theoretic ground and technical basis for possible prevention of such failure.Based on the analysis the following conclusions are made.The failure characteristic is through-piercing of the drill pipe body,while the failure mechanism is corrosion fatigue.And the failure is caused in such a process,i.e.,owing to stress concentration and corrosion concentration in the drill pipe body,corrosion fatigue-caused cracking develops on both the inner and outer surfaces in the run-out point section in the upset transition area,and then along with the gradually expanding of the cracking,the wall thickness of the cracking area is reduced gradually till it becomes too thin to stand with the inner wall pressure,which eventually leads to the end,i.e.,the high pressure liquid filling the inside of the drill pipe thrusts through the wall remainder,and thus forms pierced holes on the drill pipe body.