Monitoring composite tanks
The need for further reductions in polluting emissions urged the automotive industry to promote cleaner vehicles, such as the Fuel Cell and Natural Gas Vehicles (NVGs). Apart from the environmental savings, a lighter storage technology would also improve the energy consumption. Both environmental and energy savings should not compromise the structural safety of the vehicle. Until now, most of the control methods used for composite natural gas cylinders in service involved hydrostatic testing at around 300bars. This method requires dismantling of the cylinders from the vehicle. To avoid this dismantling, a visual inspection method could alternatively be used, yet both methods provide information only on whether the cylinders pass the pressure test or not. The ZEM project resulted in a new inspection method that offers information about the behaviour of the pressure vessel on a permanent basis. The new method employs an optic fibre sensor system that is embedded in the cylinder providing information continuously either at refuelling or at inspection stages. Thereby, it would be easy to determine the existence of any deformation that could further develop into a failure. The monitoring system uses a threshold deformation value specified by the nominal and the first test deformation values. When this is exceeded, re-inspection is necessary. The new, optical fibre method was tested and found successful in the detection of any overpressure and artificial damages as cuts, flaws, shocks, impacts and delamination. The novel inspection system is expected to improve both the safety of vehicles and the service process.
