For many of their intended applications, guided wave structural health monitoring systems are expected to be able to perform well over periods of many years. The results from a system attached to a steel water tank for over 3 years are analysed. From measuring individual parameters of the collected signals including the first arrival time, maximum amplitude, centre frequency and bandwidth, it appeared that no notable long term changes were occurring. When baseline subtraction based data processing algorithms were applied to the dataset, the value of the post subtraction residual increased to values where only gross damage would be detected over a period of weeks. This means that changes, not highlighted by the measured parameters, are occurring over relatively short time scales which would prevent the successful operation of such a system. This demonstrates the need for the long term performance of guided wave structural health monitoring systems to be investigated further.
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