Durability of Syntactic Foams for Deep Offshore Insulation: Modelling of Water Uptake under Representative Ageing Conditions in Order to Predict the Evolution of Buoyancy and Thermal Conductivity

Abstract : Three different syntactic foams were aged under various conditions of both temperature (from 4°C to 130°C) and pressure (from 1 bar to 300 bar) in renewed sea water. Some functional properties were measured during aging. First, the link between water uptake and both buoyancy and thermal conductivity evolutions was established for each syntactic material under any ageing conditions. Then a finite element model was developed in order to compute water uptake in the materials. The model, based on the description of three hydration mechanisms, each mechanism being linked to a part of the microstructure of the foam, gives a satisfactory agreement with experimental results for all aging conditions and specimen sizes. The model was finally used to simulate the evolution of some functional properties that would experience a structure immersed in real conditions over 20 years. Furthermore, the thickness of the insulation material affected by water ingress after 20 years of aging can be estimated, and this value can be used at the time of design as a sacrificial thickness.