Etude du comportement des systèmes d'isolation thermique pour les grandes profondeurs d'eau

This work deals with the study of the thermomechanical behaviour of multilayered thermal insulation systems protecting subsea pipelines, used in the context of deep sea offshore exploitation (down to 3000 m water depth). The first step of this work consisted in obtaining experimental data on the thermal, mechanical and water diffusion behaviour of insulation materials, particularly of syntactic foams (polymer matrix reinforced with hollow glass microspheres), which are widely used in the thermal insulation of pipelines. The development of experimental tests on industrial multilayered coated structures under representative deep sea conditions (until 300 bar external hydrostatic pressure) represented one of the major aims of this work. The global heat transfer coefficient of the structure which is representative of the thermal performances of the multilayered structure has been determined for several thermal gradients, without and under hydrostatic pressure. Moreover, the study of the stationary and transient thermal states allowed the apparent thermal properties of the syntactic foam to be determined, first without additional pressure then under hydrostatic pressure. In parallel, numerical modelling of the thermomechanical behaviour of the industrial multilayered structure, based on the experimental data obtained at a "laboratory scale" on small samples, has been developed with the software Comsol Multiphysics®. This work underlined the importance of the mechanical stress on the damage evolution of the insulation material. The correlation between model prediction and experimental data obtained on structures has contributed to establishing the validity of the models.