Three-dimensional mechanical properties analysis and fatigue life prediction of G105 drill pipe

Abstract

G105 drill pipe has been widely used in drilling construction, such as mine exploration, water exploration, and gas extraction. However, the service life of the drill pipe is lower than its de-sign life. The drill pipe is the most vulnerable component within the overall structure of the drilling tool due to its exposure to cyclic axial tension, torsion, and bending forces. Taking the G105 drill pipe as the research object, the mechanical property parameters and fatigue S-N curve of drill pipe material were tested by tensile test and tension-torsion multi-axis fatigue test. The geometric expression of the cross-section profile perpendicular to the drill pipe is derived, and a parametric three-dimensional finite element modeling method for the drill pipe is proposed. According to the relationship between the element and the node, a parametric three-dimensional hexahedral mesh modeling program for the drill pipe is developed. In con-clusion, an examination is conducted on the mechanical characteristics of the drill pipe when subjected to various loads, including make-up torque, compression-torsion, and compression-bending-torsion. Additionally, a prediction is made regarding the fatigue life of the drill pipe under these multi-axial conditions. The results show that the maximum stress of the drill pipe under the combined load appears on the inner and outer surfaces of the drill pipe, and is most significant at the intersection of the transition section and the pipe body under the influ-ence of stress concentration. The fatigue life of the pipe body is positively correlated with the wall thickness, and the minimum value of the multi-axial fatigue life of the drill pipe occurs in the vicinity of the interface between the transition section and the pipe body, so in order to im-prove the fatigue life of the drill pipe, it is preferred to give priority to the optimization of the structure or the surface reinforcement treatment in this place.