Pipe System Characteristics vs. Reliability of Transient Test-Based Techniques for Pipe Inspection

In drinkable water pipe systems, transmission mains (TMs) convey the whole discharge. As a consequence, even a small percentage of losses in TMs implies a large volume of non revenue water. However, until a few years ago, TMs were excluded from leak detection programs and in most cases the only action was to measure the inflow and outflow discharge. The two main reasons of such a behavior were: i) the unjustified conviction that leakage in TMs is negligible, and ii) the larger cost of inspection with respect to distribution networks. Nowadays things have changed radically: several technologies have been proposed for fault detection in TMs and experiments are in progress to test them. Roughly speaking, such technologies can be classified in two main families: the inline-type (ITT) and the transient test-based (TTBT) ones. To explore TMs, within the ITTs, sensors are inserted (e.g., puretechltd.com; echologics.com) whereas in TTBTs pressure waves are injected into the pipelines (e.g., [1]). This paper clearly places in the research activity aiming the evaluation of the merits and drawbacks of TTBTs. Specifically, for given pipe system characteristics, the role played by the place where the pressure waves are injected with respect to the transient response of TMs is explored. The analysis is based on the field tests executed in a real TM with transients generated by means of two quite different methodologies: pump shutdown ([3]) and the Portable Pressure Wave Maker ([4]).