Monitoring of GFRP pipelines in Power Plants using active acoustic methods

In coal-fired power plants, the flue gas is transported through fibreglass-reinforced pipelines to cooling towers during the combustion of the respective raw material. These glass-fibre reinforced pipelines are usually located at great heights and can have very large diameters of several meters. Up to now, testing has been carried out as part of inspections during planned shutdowns and is associated with corresponding costs. The article is discussing the application of elastic wave measurement methods in hindsight of a 4-month field test at the power plants in Niederaussem and Neurath in Germany. The active measurement method, based on evaluation of guided elastic waves, was used to investigate the relationship between elastic material characteristics of the aged laminates and the phase velocities of guided waves. For this purpose, various sample panels were extracted from the cleaned gas channels and material parameters were determined by destructive testing methods afterwards. These material parameters were then compared with experimentally determined phase velocities of different wave modes, which were excited by piezoelectric transducers and recorded using a laser Doppler vibrometer. Furthermore, the influence of residual deposits in the gas channels on guided waves was also investigated as this would give an opportunity to detect liquid or solid residuals during operation non-destructively. Therefore, laboratory tests were conducted with varying filling levels to find suitable excitation frequencies and configurations. Based on the previous results a 4-month field test at Neurath was carried out, with additional focus on the influence of changing environmental conditions on the measurement results.