Strength limit of titanium alloy drill pipe under combined tension and torsion load

Abstract

With a focus on the issue of drill pipe failure brought on by the interaction of tension and torsion in deep and ultra-deep wells, the yield limit curve of the pipe body and joints under the combination of tension and torsion was drawn. According to the practice of DNV-RP-F201, it was investigated how temperature affected drill pipe strength. The findings demonstrate that as temperature increases, both yield and tensile strength decrease linearly, and the decreasing range gradually decreases when temperature exceeds 140°C, and yield strength decreases by 31.91% in 140°C. Under the conditions of the same yield strength and outer diameter, the larger the thickness of the drill pipe body is, the higher its tensile strength and torsional strength are. The resulting yield limit curve covers a wider range. As the temperature increases, the yield limit elliptic curves of titanium alloy drill pipes with various wall thicknesses gradually shrink. This work presents the foundation for the strength research of titanium alloy drill pipe under tension and torsion load.