Research Of Collapse Resistance Design And Experimental Verification For Marine Unbonded Flexible Pipe

Unbonded flexible pipe is one of the most important equipments for the exploitation of offshore oil and gas resources. It’s made of structural layers of metalic materials and functional layers of polymer materials through the composite non-adhesive form, allowing the relative sliding between layers. For the double affects of the harsh marine environment and the complexity of the structure, the failure modes of this pipe are very complex. Among them, collapse is the local buckling when the external hydrostatic pressure is greater than the design value, leading to the pipe scrap, resulting in huge economic losses.For the specific requirements of the marine environment which the pipe used, considering the development of water depth, installation load and the pipe through the tensioner, the collapse resistance design for unbonded flexible pipe is necessary in order to enhance the ability to resist radial deformation of the pipe. The key point is that the pipe designed achieve sufficient radial stiffness provided by the innermost carcass. On the basis of the structural design idea based on failure mode analysis, beginning with the basic concepts and principles of structural stability, the paper expounds the general flow of structural stability design based on failure mode dominated. Refering to the theoretical model used in the collapse resistance design for the marine steel pipe, some reasonable equivalent method is adopted for flexible pipe design. However, the theoretical analysis, only considering regular structure, is based on some hypothesis, such as isotropy, small deformation and plane section assumption. The numerical simulation of non-continuum is also difficult. The method of experimental verification is very important and indispensable.Crushing test is used to research the radial stiffness of the carcass layer, and compared with theoretical model and numerical model, the essence of the capacity for resistance to radial deformation is revealed. In order to research the integrated capacity of collapse resistance for unbonded flexible pipe, preliminary design of collapse simulation experimental set-up is presented. The force analysis upon the pipe is also presented, so as to provide a useful guidance to carry out an in-depth research of unbonded flexible pipe collapse.