Study Of Perfect Pipes On Ultimate Capacity Under Complex Loads

Submarine pipelines have been widely used as one of the most economical ways for transporting oil and gas over long distances. With the development of oil and gas industry, the pipelines, which serve as the lifeline of offshore oil and gas field, are playing a more and more important role in China. Meanwhile, oil leakage due to pipeline failure occurs occasionally worldwide, which results in huge environmental damage. Consequently, study of perfect pipelines on ultimate bearing capacity and buckling modes is vitally significant.Submarine pipelines are applied to complicated loads during operation, such as internal pressure induced by inner transportation medium; axial force induced by self-weight, supports from the surrounding soil, temperature change of inner medium and Poisson effect, bending moment induced by subsidence, landslide, earthquake, seabed deformation; drag and lifting force of free spanning submarine pipeline under waves and currents, and so on. The mechanical model of pipeline subject to environmental loads can be described as the combinations of internal ptessure, axial force and bending moment. The research focuses on the strain-based and stress-based analysis methods of pipelines subjected to joint loadings. The content of the paper includes:Using ABAQUS, the finite element method is adopted to study ultimate bearing capacity of pipeline under combined internal pressure, axial force and bending moment. Considering material nonlinearity and geometric nonlinearity, three-dimensional finite element models of the perfect pipe under complex loads are established. Compared with experimental results by scholars, the FE models established in this paper are validated.Numerical analysis of perfect pipes under combined internal pressure, axial force, and bending moment are carried out by the finite element method software. The effects of diameter to thickness ratio, internal pressure ratio, and material properties on critical buckling strains of the perfect pipes are studied. Based on the numerical results, a regression formula to predict critical buckling strains of perfect pipes under complex loads is proposed. Comparing with the experimental results, equations presented in the CAN/CSA-Z662(1996) and DNV-OS-F101(2000), the regression formula proposed in this paper is validated.Bending moment capacity of perfect pipes under complex loads was calculated for each load case. The effects of each parameter on moment capacity are analyzed, and compared with the theoretical method.