Subsea production systems have become critical with the rapid increase in oil and gas production from deepwater offshore fields. These systems consist of connectors, pipelines, risers and other equipment and facilities required to operate the wells. Unfortunately, the applicability of these systems in deeper and remote oil fields like those located in arctic areas remains a big engineering challenge, especially in ensuring the connectors’ reliability, safety, and long service life. Therefore, developing effective subsea oil production technologies will be of great benefit in maximizing production, reducing environmental effects and reducing the associated capital and operational expenditures.
Subsea connector plays a vital role in subsea production systems as they ensure sealing and locking between the two subsea facilities. Failure of these connectors might lead to oil and gas leakages that might impact not only the safe operation of the systems but also the environment. Due to the increasing amount of studies on the sealing working principle of subsea connectors, theoretical designs of different components of subsea connectors, such as gaskets, have been presented. Another key connector component that has recently drawn research attention is the hub because it works with the gasket to achieve the desired sealing performance. Thus, studying the design of the hub structure, including its geometric dimensions, marks an important step toward improving the locking and sealing performance of subsea production systems.
ASME-VIII design method is one of the most used methods in designing flanges and various connector components. Though it provides an easy solution to the mechanics analytical model, it is not suitable for designing hubs due to the inadequacies in the analytical model approximations that might result in erroneous deviations. Other methods such as flange stress analysis are also not suitable due to several limitations. It is worth noting that addressing these difficulties associated with the design of the thick-walled hub structure for the connectors requires a feasible and robust method for solving the axisymmetric bending deformation problem.
Herein, Professor Menglan Duan and Dr. Kang Zhang from China University of Petroleum in collaboration with Professor Carlos Soares from the University of Lisbon and Professor Jeom Paik from Pusan National University conducted a detailed theoretical investigation of the design problems of the parameters of the hub structure of the subsea. In particular, a novel analytical model named the stress analytical method was developed. The hub structure was divided into two: a hollow annular plate and a thick-walled cylinder, and the axisymmetric bending deformation of the thick-walled cylinder was proposed. Finally, the feasibility of the analytical method was validated through a finite element method, and a case study was carried out to compare the stress results with the ASME design method. The work is currently published in the research journal, Thin-Walled Structures.
The research team established the deformation continuity relationships between the hollow annular plate and the thick-walled cylinder as well as the analytical solutions of the displacements, stress components, internal forces and rotational angles with high precision using the present method. This was attributed to the effective development of the geometric, constitutive, physical and equilibrium equations to determine the displacement analytical solution of the thick-walled cylinder structure of the hub considering the effects of the wall thickness. Consequently, the axisymmetric bending deformation problem of the thick-walled structures was solved under the action of edges. Compared with the ASME design method, the presented method obtained more detailed results and could inspect the weak points of a certain section by determining the stresses along the entire section.
In summary, the study reported an analytical model to solve the axisymmetric bending deformation problems of connector’s thick-walled hub structure under the action of edge shear and bending forces. Using the hoop and axial stresses as comparison indexes, the stress value of the weak point calculated by the proposed analytical method was in good agreement with the finite element method results when the ratio of the outer and inner diameter of the thick-walled cylinder ranged between 1.5 to 1.8. In addition, this model was more accurate in predicting the hoop and axial stresses. In a statement to Advances in Engineering, Professor Menglan Duan said the study findings would significantly enhance the operation reliability and safety of offshore oil and gas production.
Duan, M., Zhang, K., Soares, C., & Paik, J. (2021). Theoretical investigation on hub structure design of subsea connectors. Thin-Walled Structures, 159, 107036.