Impact of Failure Mode, Crack Area, and Pressure on Leakage Outflow

Abstract

The calculation of leakage outflow is of interest for several tasks in water distribution system analysis, e.g., investigation of pipe burst consequences, efficiency estimations of pressure management, or model-based leakage localization. Several studies on pressure-leakage dependencies have shown that this dependency can be much higher than defined with the orifice equation of Torricelli. The findings of these studies differ significantly, even for the same pipe material, failure modes, and sizes. In this paper, we describe the influence of uncertainties on assumptions of emitter exponents and crack areas on discharge rates for different failure modes. An approach for modeling elastically deforming leaks in water distribution pipes was implemented into systematic discharge rate calculations with EPANET2 by the means of an iterative estimation of the emitter exponent. For a partial pipe network of the city of Vienna, the results of the original EPANET2 and the extended emitter approach were compared. The largest differences in leakage outflow and hence in the amount of pipes with potential high failure consequences were found for longitudinal cracks. For this failure mode material, crack size and dimensions have a significant influence on the emitter exponent. Consequently, it is recommended for systematic discharge rate calculations to gather historic data about typical failure modes and failure dimensions of the investigated system. Further, if failure modes with a high sensitivity on the emitter exponent (like longitudinal crack or spiral crack) are relevant for the investigated system, a detailed calculation of the discharge rate is suggested.