Asymmetric collapse of offshore pipelines under external pressure

There exists inevitably various geometric imperfections in offshore pipelines in the manufacturing process. In deep waters, the pipes have to withstand high external hydrostatic pressure, in general, which is a dominant parameter for the design of such structures. A 2D theoretical formulation is presented to predict the collapse pressure of elasticplastic tubes with arbitrary initial geometric imperfections represented by the ovality and wall thickness variations. In addition, numerical simulations are also carried out using a 3D finite-element model within the framework of ABAQUS. Close agreement between the results validates the effectiveness of this theoretical method. Then, the theoretical model is applied to study the effects of some important parameters such as diameter-to-thickness ratio, initial ovality, wall thickness variations and material properties, etc., on the collapse pressure of the pipes. Based upon extensive parametric studies, a few significant conclusions are drawn, which aim to provide the theoretical basis for design of offshore pipelines with various initial geometric imperfections and material properties.