INVESTIGATION OF THE RESPONSE OF PLASTIC WATER PIPES TO LEAKS USING DIFFERENT TRANSDUCERS

Leak detection is a major concern for large urban centres and water utilities. Various techniques are applied to detect and locate leaks at an early stage, with vibro-acoustic methods being among the most widely used. These techniques rely on the pipe's response to a leak to determine its position. One of the most effective approaches, leak noise correlation, utilizes two transducers to measure pipe vibrations at different positions, estimating the time delay between signals and using the leak velocity to calculate the leak location. However, leak velocity depends on the mechanisms through which leak noise propagates along the pipe. Recent studies have identified two possible mechanisms responsible for leak energy propagation in plastic pipes. However, these findings were based on different test rigs and boundary conditions. This paper aims to investigate the mechanisms governing leak energy propagation in plastic water pipes used in the interior of São Paulo state under consistent boundary conditions, including leak excitation and the type of flooring beneath the pipe. Multiple transducers will be used to measure the pipe's response: hydrophones, which measure sound pressure in water (invasive measurement); geophones and accelerometers, which are placed on the pipe wall (non-invasive); and laser vibrometers, which are non-contact sensors for measuring pipe wall vibrations. Classic signal processing techniques will be applied to analyse the pipe response and confirm the presence of these mechanisms, including Power Spectral Density (PSD), the modulus and phase of the Cross-Power Spectral Density (CPSD), coherence, and the Cross-Correlation Coefficient (CCF). Finally, actual leak velocity values will be compared to those estimated using analytical equations from the literature, based on wave models associated with leak-induced excitation. This comparison aims to support the hypothesis that multiple propagation mechanisms contribute to leak noise transmission.