Underwater oil and gas pipelines are prone to alignment differences and angle offsets during docking, and the spherical flange connector can address this problem. Its main function is to enable compensation of the different angles of the pipeline during docking and to apply a non-standard spherical sealing structure using O-rings to the connection. In this paper, the study of a spherical sealing structure using O-rings was based on a spherical structural model of the connector. The Mooney–Rivlin constitutive equation and material parameters of the O-ring were determined according to nonlinear theory. The structure of the non-standard spherical sealing groove was designed and analysed with reference to the standard sealing groove, the calculation expression of the spherical groove specific size was deduced, and the width and depth of the groove were determined. A finite element analysis of the non-standard O-ring sealing structure was carried out using ANSYS Workbench software; the effects of different pressures and compression ratios on the O-ring sealing performance were analysed and studied in terms of von Mises stress, contact pressure and contact width of different contact surfaces so as to determine a more reasonable compression ratio in the sealing structure. Finally, the theoretical analysis of the non-standard spherical sealing structure using O-rings was validated by testing, and it was proven that it could maintain a good seal under high pressure.

The sealing performance of the rubber packer is of vital importance for the subsea retractable connector, and the cross-sectional shape of the rubber packer is one of the most important factors affecting it. The compression distance of the rubber packer is increased by 19.54% utilizing the established two-dimensional numerical model. In addition, a new parameter called the anti-shoulder extrusion variable was defined in this paper. Shoulder extrusion will not occur when using this variable as a constraint during simulation. In general, the upper end and the lower end of a rubber packer are subject to different constraints, and the structural parameters of the rubber packer affect each other in terms of sealing performance. Therefore, the importance and originality of this study are exploring the optimization of the thickness and chamfer angles of the upper and lower ends of the rubber packer by use of a combination of the response surface optimization method and the multi-objective genetic algorithm, taking the thickness and chamfer angles of the upper and lower ends as design variables, and the stress on the inner side of the casing wall and the axial force of the compressed rubber packer as optimization objectives. Besides that, the anti-shoulder extrusion variables are also introduced as constraints to prevent shoulder extrusion. Ultimately, the cross-sectional shape of the rubber packer with a smaller-thickness and larger-angle upper end, and a larger-thickness and smaller-angle lower end can be obtained. The result to emerge from the test in this paper is that the pipe pressure that can be sealed by the optimized rubber packer structure is 25.61% higher than that before optimization. The anti-shoulder extrusion variable and the asymmetric cross-sectional shape of the rubber packer proposed in this paper shed new light on the finite element simulation of rubber and the research on similar seals.

Taking a subsea collet connector as an example, the contact characteristics of the sealing structure of the subsea connector under thermal–structural coupling were studied. Considering the heat transfer problem of the subsea connector in deep water, the heat transfer model of seawater layer between sealing structures was established, and the relationship between equivalent thermal conductivity, composite heat transfer coefficient, and temperature was determined. The steady-state temperature field distribution of the connector under the action of the internal high-temperature oil and gas and external low-temperature seawater was obtained. Considering the stress and deformation of the subsea connector under the thermal load, the thermal–structural coupling analysis model of the steady-state temperature field was established, and the thermal stress theoretical analysis and numerical simulation of the key sealing structures of the connector were compared and verified. Analysis of coupled stress calculation, for example, under a steady-state temperature field, was carried out on the sealing structure of the subsea connector. At the same time, the pressure shock mode under a steady temperature field was analyzed, which showed that the lenticular sealing gasket is sensitive to high pressure under high-temperature conditions.

With regard to the sealing structure characteristics of the underwater clamp connector, based on the Hertz contact theory, this article studies the method of solving the extreme value of the radius of curvature on the two curved surfaces at the sealing contact point; first, the method of calculating the extreme value of the radius of curvature at any surface point of the rotary part is obtained, and then the equivalent radius of curvature is solved. Using finite element simulation to study the contact sealing characteristics without considering the edge thickness and width of the sealing gasket, it is verified that the Hertz contact theory is applicable to the metal contact theory of underwater clamp connectors. Then, the sealing simulation with the influence of the detailed dimensions of the sealing gasket is compared with the theoretical result of the direct application of the Hertz contact theory in the underwater clamp connector contact, and the theoretical correction coefficient of metal contact seal for underwater clamp connectors is introduced to solve the errors. The pressure sealing experiment is carried out on six-inch flange and metal sealing gasket, which proves that the coefficient can greatly enhance the theoretical calculation accuracy of the contact sealing of the underwater clamp connector.

A complete subsea production system (SPS) is assembled by interconnecting subsea manufacturing facilities through subsea connectors. To ensure the reliability and longevity of the SPS, it is imperative to thoroughly investigate the mechanical behavior and sealing performance of the subsea connector’s core-sealing components. In this study, the loading conditions of the subsea clamp connector are examined to analyze the load transfer relationship between its components under different modes. A mathematical model for the load transfer between locking torque and sealing contact pressure is developed for the preloading mode, and the concept of mechanical transfer efficiency is introduced. Another mathematical model for the load transfer between the locking torque and the design pressure is developed for the operation mode. Furthermore, a three-dimensional full-size finite element model of the subsea clamp connector is established to analyze the effects of complex loads on the mechanical behavior and sealing performance of its core-sealing components. The simulation results indicate that internal pressure loading positively affects the sealing of the subsea connector, and that the stress distribution in the core-sealing components under bending moment loading exhibits significant asymmetric characteristics. Additionally, the superposition of axial tensile loads reduces the effect of the bending moment on the strength of the core seal member but further weakens the seal. Finally, an experimental system is designed to validate the simulation results.

Taking the subsea collect connector as an example, the sealing characteristics of the sealing structure of the subsea connector under transient thermal–structural coupling were studied. Based on Airy’s thermal stress function, the mathematical model was established, the complex stress function was used to solve the problem, and a three-dimensional transient thermal stress model of the core sealing parts was obtained. The transient thermal–structural coupling stress model of the core seal was obtained by linear superposition principle. The transient temperature field of the subsea collet connector under different working conditions was analyzed. It was found that the larger the temperature difference between the components was, the greater the difference of expansion rate was, and the greater the impact on the sealing performance of LSG was in the process of temperature variation from transient to steady distribution. Numerical simulations of various working conditions under the transient temperature field were carried out. The results showed that sudden change of the temperature and oil–gas pressure will bring about large fluctuations of the maximum contact stress and equivalent stress of the seal, which was easy to fatigue wear, and thus affect the reliability of the sealing performance. Finally, the experiment proves that the sealing ring can maintain sealing performance under the conditions of temperature-cyclic loading. The coupled mathematical model proposed in this paper could be used for the transient thermal–structural coupling theoretical analysis of similar subsea equipment.