Non-linear bending behaviour of offshore flexible pipes

Comparatively straightforward analytical formulations are given for determining the bending moment - curvature relationship for offshore flexible pipes experiencing combined bending and pressure loading. The approach takes into account the non-linear behaviour of a pipe, influenced largely by the relative sliding of individual layers. The stiffness is found to be a function of bending curvature, interlayer friction coefficients, and the pressures on the layer interfaces. The analysis presented here is based on the Coulomb friction model and is derived using energy methods. The interlayer pressures are found from existing theoretical models of the unbonded flexible pipe response to axisymmetric loading. Theoretical results for a typical flexible pipe are compared with experimental data from other sources. Encouraging correlations have been found.