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Pipe network analysis calculates fluid flows and pressure drops in complex piping systems, important for utilities supplying water or gas. It uses iterative methods and software packages to modify and upgrade systems, with the Hardy Cross method as a traditional calculation method.
Pipe network analysis is a calculation of fluid flows and pressure drops in complex piping systems. Pipe system analysis is important for utilities that supply water to consumers, natural gas distribution planning, or any piping system where constant supply pressures and flow rates are important. It is unlikely that a supplier knows specific demands and flow rates throughout the network, so pipe network analysis provides a method in which system loops are chosen and calculations are made.
The calculations required for pipe network analysis are available in commercial software packages, but the fundamental equations can also be calculated manually. The analysis uses a relaxation method in which piping loops are chosen, pressure drops and delivery points are estimated. The amount of material passing through the system is then determined and a series of calculations are performed.
At this point, corrections are made to the estimates and the calculations are repeated when necessary. This is known as an iterative method. The process continues with smaller and smaller changes in the assumptions, until the conservation of mass and energy is satisfied. Conservation of mass and energy means that the inlet pressures and flows at the supply point are equal to the system pressure drops and the customer’s required delivery flows and pressures.
Pipe network analysis uses the same iterative method regardless of the fluid being dispensed. The importance and complexity of these calculations increases as a pipe network grows and customers expect uninterrupted delivery. Fluid dynamics and pressure drops can be measured experimentally, but laboratory measurements don’t always translate well to real systems of overlapping loops, many delivery points, and an ever-changing piping network.
Utility planners can use the results of a pipe network analysis to modify and upgrade their systems. New customer requests may require additional pump stations or compressors to provide adequate flows. Growing subdivisions or neighborhoods may require a reanalysis of the network, as adding new pipe loops changes the calculation assumptions.
Water pipes can develop internal scale, or roughness, as they age. This may require additional pumping energy to overcome. Pipe network analysis typically needs to be a dynamic process with ever-changing variables, rather than a single analysis with no potential for change over time.
A calculation method traditionally used to manually calculate a pipe network analysis is the Hardy Cross method. This method assumes that all pipe sizes and lengths are fixed variables. The Hardy Cross method becomes less accurate as the piping system becomes more complex. The results of a Hardy Cross calculation may be less accurate than from software applications, but the results can be used as a guess for more complex software calculations.
