Time Dependent Carcass-Liner Interface Load Model

Flexible risers in operation may experience large forces between the carcass and the polymer liner. Especially, cool-down of a pressurized riser results in thermal shrinkage of the liner layer and will transfer tensile loading of the carcass at the end fixation. Two aspects are then important to explore; the structural load capacity of the carcass structure and the balancing load effects acting on the carcass and liner. The current paper addresses the latter: the carcass load model. This has been presented in a previous publication in form of closed form expression for the long term quasi-static axial loading [1]. The model is extended to include the time dependent evolution of the carcass-liner interface force taking account of the time dependent material behavior in the liner and the time variation of the driving forces acting on the carcass and liner. The extension expresses the axial force as a convolution integral. In all but for the simplest cases the integral needs to be evaluated through appropriate quadrature rules. The closed form solution represents a reduced, efficient and robust scheme for evaluating the critical load level of a newly discovered failure mode. Further, the model enables identification of the critical parameters driving this failure mode.