Research On Mechanical Behavior Of Unbonded Flexible Fibre Reinforced Pipe

Unbonded flexible fibre reinforced pipe is a flexible structure composed ofseveral composite layers. As an important component in the ocean and gas exploration,it can link up the subsea wellheads and the floating production facilities. With lowerbending stiffness, high strength, high resistance to fatigue and to corrosion, and easyinstallation, this kind of pipe is is particularly suitable for deepwater offshore oilexploitation. Research on mechanical behavior of unbonded flexible fibre reinforcedpipe is a significant key to the engineering design of the flexible pipe, it can help usknow over the structure property of the flexible pipe. This paper is based on thesubject “Development of Flexible Fibre Reinforced Pipe for Deepwater Offshore OilExploitation” of the marine technology field of the “863” High Technology Researchand Development Program of China.This paper presents a detailed finite-element analysis of unbonded FFRP usingABAQUS, which includes geometrical nonlinearity and frictional contact between alllayers as well as all adjacent tendons. First, The finite-element model computestension stiffness under axial tension, which is compared with an analytical modelobtained in literature. As a result, a very good agreement is obtained which validatesthe effectiveness of the proposed finite-element method. Next, this paper analysesstress characteristics and bearing property of FFRP subjected to tension, internalpressure, external pressure, torsion, bending by using the proposed finite-elementmodel. The results validates that choosing GFRP as spirally wound tendons can makefull use of typical anisotropism of the composite and take advantages of the highstrength of the tendons in fibre direction. The research achievements can providereferences for structure design of the flexible pipe and significant data for the designof end fitting.Unbonded flexible fibre reinforced pipe must be connected to a device namedend fitting. Using Orcaflex software, this paper gets the loads of the flexible pipe where it connects to the end fitting in specific sea state, based which, the proposedABAQUS finite-element model is used to give the stress characteristics and bearingproperty of all pipe layers at the joint. The analysis results can provide significant datafor design of the end fitting, and be used with strength evaluation of the FFRP.