Development and integration of innovative glass fibre sensors into advanced composites for applications in hostile environments

Glass reinforced polymer composites (GRPs) are increasingly used in the petrochemical industry, but there is a reluctance to use them in extreme conditions due to unknown long term stability. They are cheaper, lighter and easier to install than traditional steel pipes. However it must be possible to give accurate, non-invasive data on degradation rate during component lifetimes of up to 30 years. This research was focussed on the development and integration of innovative glass fibre sensors into glass reinforced polymer composites for applications in hostile environments. The diffusion and absorption of water into a vinyl ester resin in in simulated seawater, at 120°C in pressurised steel vessels, was measured using optical fibre sensors. Low cost evanescent field sensors were prepared from a standard multimode fibre and compared to commercially available fibre Bragg gratings. It was found that both sensors were capable of detecting the ingress of water into the resin through different mechanisms. The fibre Bragg gratings showed a 1.02±0.24nm peak shift due to the swelling of the resin after 48hrs, whilst the evanescent field sensors showed a progressive reduction in transmitted power due to a change in the environment surrounding the sensor starting from the very early stage of the water diffusion through the thickness of the GRP.