This paper discusses the influence of different fluid temperatures on the creep behaviour of the polymer barrier inside unbonded flexible pipes. The creep behaviour of the polymer material is generally time-dependent and associated with larger, nonlinear deformation. Excessive creep deformation may lead to structural failure, due to the over-reduction of the barrier layer thickness, and is therefore an important design consideration in ensuring the structural integrity of this layer.
Creep behaviour in polymer material is complex, as it is governed by a number of variables, such as the stress/strain state, temperature, and pressure for example. This paper deals with the influence of different fluid temperatures on the creep behaviour of the polymer barrier layer under pipe design pressures, particularly in high temperature fluid transportation pipelines for deep or ultra-deep sea applications.
The analysis model was established using commercial finite element software ANSYS, where an implicit time hardening creep model, based on the Maxwell viscoelastic model, was selected to represent the creep behaviour of the polymer materials. The coefficients of the implemented polymer material gap span creep model are calibrated to represent the worst case of the small-scale sample gap span creep tests performed in-house.
A comparison is made between the simulation results of the calibrated gap span creep model and the corresponding small-scale creep test measurements. The experimental test results and the finite element modelling results show good correlation. This demonstrates that the creep model predictions are conservative for the polymer material of the barrier layer inside an unbonded flexible pipe.