Thermal vertical buckling of surface-laid submarine pipelines on a sunken seabed

Abstract

Submarine pipelines are the most viable way for transporting offshore oil and gas worldwide. However, it is easy to cause the vertical buckling in the process of work under the high temperature and high pressure. In this paper, the energy method was used to analyze and derive the relationship between the temperature and the buckling height during the thermal vertical buckling of the third-order mode of pipeline. Additionally, the finite element method was utilized to model and simulate the pipeline on submarine pit and trench respectively. From this investigation, it is found that the maximum circumferential stress and strain in mid-section of pipelines are larger than in left-section on submarine pit. On submarine trench, the maximum circumferential stress in mid-section is larger than in left-section but the maximum circumferential strain in mid-section is smaller than in left-section. The buckling height and length sharply increases with the increase of temperature or pressure whether on submarine pit or trench. With the increase of temperature, the stress of pipelines increases first and then decreases on pit but always enlarges on trench. With the increase of pressure, the stress of pipelines increases on trench, and the stress of pipelines in left-section increases but in the mid-section decreases. The length and depth of submarine pit and trench directly affect the shape of pipelines and size of the initial sunken imperfection. The friction coefficient has little effect on the buckling length, height and stress and the buckling deformation changes from third-order mode to fifth-order because the axial friction cannot balance the thermal axial force if the friction coefficient is too small. The buckling height, length and stress enlarges accompanied by the increase of diameter-thick ratio of pipelines and reducing the diameter-thick ratio in practice can effectively strengthen the ability of pipeline to resist buckling.