Keywords: double pipe system, pipe failure, pipe diameter resizing, total energy loss, network performance, single pipe system.

In the design of water supply networks, the looped network is the most usual configuration proposed. To take the maximum advantage of the redundancy of pipes in the looped network solution, the design procedure should include the analysis of both: (a) normal working scenario (steady design hydraulic demands) and; (b) the so-called abnormal situations, due to pipe failure, which will lead to flow patterns with higher head losses.

Pipe failure consequences on the looped network performance are mainly due to: (a) change of the flow pattern (in some cases with reverse flow); (b) decrease of the number of flow paths and (c) an increase of the length of the alternative paths. The present paper studies these consequences and suggests an alternative approach to design and maintenance of water supply looped networks. To reach this objective, a case study is presented and identified, as well as the successive steps followed to justify the suggested methodology.

The analysis covers the consequences of pipe failure in the flow pattern, in the flow distribution in the energy losses and in the resizing procedure to guarantee that previously defined values of maximum head loss (correlated with minimum pressure at the nodes) are achieved. The costs associated to such procedures are also quantified and presented.

The configurations studied are named as follows (a) the Single Pipe Looped Network (SP); (b) the Double Pipe Looped Network (DP); (c) the Partially Double Pipe Looped Network (two pipes) (PDP2); and (d) the Partially Double Pipe Looped Network (four pipes) (PDP4).

The four configurations were studied for normal working scenario (all pipes in good conditions) and single pipe failure scenarios. The sequence of the study was focused on the consequences of pipe failure in the flow pattern, the decrease of the number of paths between the source node and the demand nodes, the increase of the length of the alternative flow paths in these pipe failure scenarios and the possible ocurrence of reverse flow in some pipes in these failure scenarios.

The results of this study are presented in the paper using Tables and Figures with adimensional variables for head losses (ER), costs (CR) and maximum energy loss restrictions (NPFI). In a final stage, for comparison and for an overview of the studied and proposed methodology a "cause-effect grid" is also presented.

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