Author(s): Jeffrey Tuck; Pedro J. Lee; Mark Davidson; Mohamed S. Ghidaoui
Keywords: Cross-section reduction; extended blockage; pressure wave; transient analysis; water pipelines
Abstract: This paper investigates the effect that an extended blockage has on a transient signal by examining numerical and experimental results in the time and frequency domains. Extended blockages can develop in pipelines via the processes of tuberculation, scaling, bio film growth, sediment deposition or through designed reductions in pipe diameter. It is identified that consideration of the gradual formation of these faults is important in pipeline design as they can significantly change the fundamental period of a pipelines transient response, maximum and minimum transient pressure heads and the evolution of the transient signal, thus potentially increasing a systems susceptibility to failure. Analysis of transient signals affected by a blockage provides information on the property and location of the extended blockage. In this paper, comparisons between discrete and extended blockage models are made and the effects of changes in blockage diameter, length and wave speed on the transient response are investigated. Furthermore, the ability of existing models to represent extended pipeline faults under transient conditions is evaluated through comparisons of numerical transient responses with new experimental results from the laboratory. Results show that the transient behaviour is modelled with a good level of accuracy over the first few periods of oscillation and that the level of accuracy decays with time. A periodic Fourier analysis of the data demonstrates that the damping rates of the experimental response are higher than the numerical predictions. Applying this new method of signal analysis has shown that the transient signal exhibits larger damping rates in the higher frequency components of the response.