Research of G105 drill pipe failure under loads of pure tension and pure twisting

Oil drill pipe is one of most important components for oil and natural gas exploration and development, which is liable to failure because of the poor service environment. In order to avoid the drill string failure, it is necessary to study the failure mechanism of drill string. So, based on the deformation theory of plastic mechanics, the mechanical model which can calculate the twisting strength of drill pipe has been established in this paper. According to this model, the torque of drill pipe can also be calculated in the elastic and plastic stage. Simultaneous, the full-scale tensile and torsion test of G105 drill pipe were conducted. The yield strength and tensile strength were obtained through the tensile test. The elastic and plastic limit torque were obtained through the torsion test. The results of torsion test are in excellent agreement with the calculation results. The research results can provide powerful new thoughts and some theoretical basis for the strength design and the further development of the study on the failure mechanism of fatigue for drill pipe respectively.