Tailored local design of deep sea FRP composite risers

Abstract

The use of fibre reinforced polymer (FRP) composite materials in offshore engineering for deep sea riser systems has drawn considerable interest due to the potential weight savings and improvement in durability that can be achieved. The design of FRP composite risers consists of two stages: (1) preliminary local design based on critical local load cases (LCs) and (2) global analysis of the full length composite riser under global loads including platform motion, hydrostatic pressure, gravity, buoyancy, wave and current loads to determine and assess critical locations. The preliminary local design stage is necessary to obtain a first estimate of the laminate configuration – fibre orientations and layer thicknesses of the tube wall, since the deformations and hence the forces and bending moments due to the global loads, depend on the geometric configuration. This paper describes the methodology, LCs, analysis procedure and results of the first stage, the local design of the composite riser. The local design is conducted using five different LCs as prescribed by the standards. In this study, geometric configurations of eight different composite body and liner combinations were optimised to provide minimum structural weight. Previous composite riser designs have mainly focused on axial and hoop reinforcements; in the present study, fibre reinforcements at other orientations are included. The highlight of the current study is that it shows that the use of off angle fibre orientations in addition to axial and hoop reinforcements offer substantial weight savings.