Pressure-Based Leakage Characterisation of Water Pipes

Abstract

A significant amount of research has been done on the behaviour of leakage from water pipes with changes in pressure. It is now widely accepted that the areas of most leaks are not fixed, as is assumed in the orifice equation, but vary with pressure. In addition, the variation in leakage area has been shown to be a linear function of pressure in all cases where the pressure in a pipe is reduced. Consequently, a modified orifice equation has been proposed for more realistic modelling of leakage behaviour. In this study a method was developed to identify the size and type of leaks present in real water supply pipes. The method uses a device consisting of a storage tank, pump, pipework, valves and instrumentation to pressurize an isolated section of pipe at different pressure levels. The leakage flow rate is measured at each pressure, which allows the respective leakage areas to be determined. Fitting a straight line to this relationship allows the initial leakage area and the head-area slope (and thus the type of leak) to be estimated. This paper demonstrates this process based on a field test conducted on a 1 km long, 300 mm diameter asbestos cement pipe. A few behaviours from other tests are shown that may be used in future to identify pipe problems.