Structural Health Monitoring Using Percolation Sensors—New User Cases from Operational Airliners and Chemical Plants

Abstract

Materials that are prone to corrosion are normally protected from a wet environment, and this can be achieved by isolations, such as casings, coatings or seals. However, as a result of the intensive use of engineering structures, those isolations can be damaged and aqueous liquids arising from spillage, condensation or rain can enter those confined spaces. An interesting tool to detect the underlying structural damage of sealings would be offered by the detection of hidden harmful liquids by appropriate sensor networks. Percolation sensors for detecting harmful liquids can be considered as bioinspired sensors. Their specific performance is in analogy to the swelling of organic materials after the uptake of water. It is well-known that all living organisms require aqueous liquids for enabling all sorts of biological functions, and the regulation of the respective water content is therefore essential. In analogy with the interaction of water with biomaterial, the swelling of organic compounds can be used to develop a group of sensors that are proven to be useful in various SHM applications. For this purpose, different percolation sensors were developed, and since two years, three operational airliners from Lufthansa were equipped with percolation sensor networks (Boeing 737-500, 2 x Boeing 747-400) protecting the floor structure below the galley, the lavatory and the service doors areas. Moreover, a couple of percolation sensors were installed in the isolations of outdoor pipelines in chemical installations of BASF Antwerp. The results obtained are very promising in all cases, and they show that the presence of corrosive liquids is indicated in a very reliable way proving the presence of structural damage of casings, coatings and seals.