Research on Fretting Wear and Seal Structure Optimization of Premium Threaded Connections for Deepwater Gas Production String

Abstract

To address the susceptibility of premium threaded connections in deepwater gas production strings to fretting wear and seal failure under long-term cyclic loading, a numerical simulation method for fretting wear was developed based on the Archard wear model. A UMESHMOTION wear subroutine was written in Fortran and combined with ALE adaptive technique. This approach dynamically updated the seal surface profile and accumulated the wear depth. A correlation formula relating the main seal surface contact pressure to the structural parameters was derived based on thick-walled cylinder theory. The influence of the main seal taper angle and the torque shoulder reverse angle on the sealing performance was systematically investigated via orthogonal tests combined with range analysis and analysis of variance (ANOVA). A multi-objective comprehensive evaluation model using the Analytic Hierarchy Process (AHP) was then built. The model considered sealing performance, mechanical safety, and wear resistance and selected the optimal combination of structural parameters. The results show the following: When the main seal taper angle increased from 5° to 20°, the wear depth first decreased and then increased, while the contact pressure first rose and then dropped. The main seal contact pressure peaks at 882 MPa at a main seal taper angle of 15°. The Von Mises stress in the connection decreased monotonically. The main seal contact pressure and the seal index increased monotonically with the torque shoulder reverse angle, whereas the torque shoulder contact pressure showed a V-shaped change. The torque shoulder reverse angle significantly influenced the sealing performance and was the main factor. Considering the three performance aspects, the optimal combination was a main seal taper angle of 15° and a torque shoulder reverse angle of 15°. These results provide a theoretical reference and technical support for designing anti-fretting structures, improving sealing performance, and guiding field selection of premium threaded connections under deepwater gas well conditions.