Theoretical Analysis And Numerical Simulation Of Pipe Buckling During Deepwater Installation

The submarine pipeline is an important part of oil and gas exploitation projects in the deep waters. The uniqueness of environmental conditions and design needs determines the unforeseeable risks and challenges during the laying of pipeline. Pipes inevitably encounter combined tension, bending and high external pressure no matter the installation method is S-lay, J-lay or reeling-lay. Deepwater pipelines are vulnerable to local buckling, which will, in turn, have the potential of initiating a propagating buckle. The propagating buckle will lead to catastrophic flattening and failure of the whole pipeline, causing huge economic loss. Therefore, the researches focusing on the buckle responses and load-carrying capacity of pipes are of significant importance to promote the design ability and calculation technique for the laying of deepwater pipelines, and at the same time these researches play a very important role in the aspects of safety in the practical engineering.Based on extensive studies of loads acted on the pipeline and corresponding possible limit states for each installation method, a series of investigations on load-carrying capacity and buckling response of pipes under different loading combinations and various types of loading paths were carried out. The research work done in this paper can be summarized into five aspects listed as follows.(1) Based upon nonlinear ring theory, elastic-plastic material constitutive model and principle of virtual work, as well as Newton-Raphson method, a theory, which could effectively predict the nonlinear buckling response of pipe, was proposed capturing the practical loading characteristics of deepwater installation.(2) The buckling mode and the load-carrying capacity of pipes under bending in the presence of tension as well as those under combined external hydrostatic pressure, axial tension and bending were investigated respectively. Besides, the corresponding calculation analysis program was developed, which can accommodate the analyses of different installation methods, including S-lay, J-lay and reeling lay.(3) Adopting finite element code ABAQUS, a three-dimension pipe model was established to analyze the mechanical behavior and buckle response under axial tension and bending as well as the case of combined hydrostatic pressure, tension and bending. The results of the numerical model and the theoretical method agree well with each other, which prove the relative effectiveness of the theory.(4) A series of parametric studies, such as loading path, diameter to thickness ratio, material properties etc., were carried out in detail. Upon these studies several conclusions were made, which could provide the deepwater pipeline design with theoretical basis and references.(5) A set of software mainly used in S-lay method and a database system of the installation vessel were developed in this paper. The software was based on the catenary theory, and it can successfully analyze the S-lay configuration and associated stress state of pipe section, especially the case of deep waters. In addition, a database system was also developed in order to facilitate the selection of installation vessel.This study is partly sponsored by the National 863 High Technology Research and Development Program of China with its title as "Technique of deepwater pipe-laying". And it is an important part of the subject titled as "Investigation on technological design and computational analysis for deepwater pipe-laying" (Grant No. 2006AA09A105-1).