A Calculation Method of Ultimate Torsional Strength for Subsea Collet Connector Based on Finite Element Method

Subsea connector is an important connection facility in subsea production system. Once destroyed, it will cause sealing failure which could lead to leakage accident, so the connectors must have high degree of damage-resistance capacity. Ultimate bearing capacity is composed of a set of important parameters measuring subsea connectors’ damage-resistance capacity, such as ultimate bending strength, ultimate torsional strength, etc. However, these data are usually obtained by carrying out destructive tests, which will bring heavy cost to subsea connector products in order to obtain the required technical data. Considering reducing the cost of destructive testing, a theoretical calculation method is needed to be developed. In addition, during the stage of product design, it is also necessary to estimate ultimate bearing capacity to verify whether the structural design parameters meet the anticipated requirements. In this paper, only the ultimate torsional strength of subsea connectors was studied, and based on finite element analysis, a calculation method of ultimate torque was put forward, which consists of using finite element software to build the 3D subsea connector model, loading different pure torsional moment, analyzing the calculation results and establishing torsional failure criteria to determine ultimate torsional strength. The results show that sealing failure will be ahead of structural strength failure under the pure torsional loads, and traditional strength failure criterion is not suitable for determining ultimate torsional strength of subsea connectors; the numerical solution of ultimate torque is 60KN·m based on the sealing failure criterion in this paper. In the end, a simplified mechanical model of subsea connector was established, the limit state equation of sealing failure was built in the action of pure torsional load, and the analytical solution of ultimate torque was calculated. The calculation method of ultimate torsional strength established in this paper was verified through comparative analysis.