Tension and torsion distributions in tapered threaded connections

Abstract

Tapered threaded connections are widely used in casing and tubing applications. The load distribution in these connections is crucial for their strength and sealing performance. In this paper, we develop a tension–torsion coupling model for tapered thread connections for the first time. In the proposed model, the main structures of the connections are described as tension–torsion bars with variable properties, while the threads are modeled as modified cantilever beams fixed on the bars. By introducing the compatibility conditions and constitutive relations for thread contact, the contact force can be analytically obtained, and the tension–torsion coupling equilibrium equations for the connection are derived. The validation of the proposed model is confirmed through finite element analysis. While the finite element simulations require more than 1.6 h, the proposed model can instantaneously provide the load distributions. Based on the proposed model, the influence of geometrical and material parameters on load distribution is investigated. The comprehensive simulations demonstrate that the maximum tension and torsion loads are located at the cross-section where the external load is applied and where the connection is fixed. As the tapered angle increases and the thread angle decreases, both the maximum contact force and torque increase. The results obtained from the proposed model provide valuable insights for the design of sealing mechanisms in casing and tubing applications.