Study on three-dimensional stress characteristics and torsional performance of titanium-steel tool joints

Abstract

Abstract Titanium alloy has promising applications in the ultra-deep well drilling field. When using titanium alloy drill pipes in composite drill strings, using titanium-steel tool joints becomes inevitable. However, the mechanical properties of such titanium-steel tool joints are not fully understood. This paper develops a three-dimensional elastic-plastic finite element model to analyze the loading characteristics of API standard tool joints with different material combinations. The analysis shows that the torsional performance of titanium-steel tool joints is significantly reduced compared to traditional steel tool joints. Based on these findings, a titanium-steel double-shoulder tool joint was designed. Its model accuracy was verified through experimental testing, and its mechanical behavior was analyzed. Results indicate that incorporating a secondary shoulder structure and adjusting the clearance of the secondary shoulder can effectively enhance the torsional performance of the tool joint. Specifically, the ultimate working torque of the titanium-steel double-shoulder tool joint (DS50-H) is 84.6 kN·m, 39.15% higher than the 60.8 kN·m torque of the titanium-steel single-shoulder tool joint (NC50). This improvement significantly enhances the tool joint’s stability under complex geological conditions.