Buckling Behaviour Analysis Of Sandwich Pipes Under Hydrostatic Pressure

The recent substantial increase in world demand for energy and raw material resources has accelerated oil and gas exploration and production. At the same time, the depletion of onshore and shallow water oil resources presents a challenge to engineers to develop new means of harvesting and transporting oil and gas from harsh and remote areas. Sandwich Pipe (SP) is a relatively new design concept developed to address the transportation of oil in deep and ultra-deep waters as well as in cold environments. The main focus of this thesis is on the characterization of the buckling behaviour of these novel systems.Deep and ultra-deep water offshore pipelines are subjected to excessive hydrostatic external pressure during installation and operation. In this study, based on a series of assumption, an analytical solution is developed to evaluate the external pressure capacity of SPs by calculating the smallest eigenvalues of the characteristic equations of the system. As a result, it is found that two different buckling phenomena can occur with changes of structural parameters. Two simplified solutions are introduced in this study, and the accuracy of the two simplified solutions is discussed.As the analytical solution is based on the elastic material assumption and ignores the plastic deformation of the material, this method would have a lot of limit when used in the pratical design. In order to improve the accuracy, a numerical model of sandwich pipes under hydrostatic pressure is established by using the finite element method. In addition, the buckling behaviour of SPs is investigated by a case study. Compared with the single-walled pipes, it is found that SPs have a greater increase on buckling pressure and deformation ability and they have distinct characteristic paths.On the basis of extensive parameter analysis, the influencing mechanisms of various structural parameters on SP’s stucture behaviour are illustrated. The changes of parameters would have a great influence on system’s buckling capacity and deformation ability and would even change the pipe’s characteristic path. Moreover, based on the results of FE method, a simplified practical solution to evaluate the buckling capacity is obtained. Comparing the results of this solution with FE simulation and experimental results, the error produced by this method is relative small. It can be concluded that the proposed equation in this study could predict the pressure capacity of SPs with acceptable accuracy.