Investigation on Parameters Affecting the Performance of Negative Pressure Wave Leak Detection Systems

The Negative Pressure Wave (NPW) methodology of leak detection has potential advantages over other pipeline leak detection technologies in terms of leak location accuracy and detection speed. This paper investigates the parameters affecting the uncertainty of the leak location inferred by the NPW methodology. Numerical tests based on data sets generated by an offline hydraulic simulation tool with different leak scenarios are applied to investigate the impact of various parameters on the prediction of the leak location, including noise level, data acquisition scanning rate, transient period of the leakage and wave speed. Based on the analysis of these parameters, this paper further studies how the leak location uncertainty is affected by two non-dimensional variables: Signal to Noise Ratio (SNR) and Transient-period to Scan-rate Ratio (TSR). Numerical tests containing random perturbations of these two variables are performed to evaluate their influence on the leak location uncertainty. This paper then discusses how leak characteristics and pipeline conditions are related to SNR and TSR, and how these affect the minimum detectable leak size. Through the investigation, this paper finds that the leak location uncertainty of the negative pressure wave system is affected significantly by the uncertainty of the wave speed estimation and the event time of detecting the pressure wave at the pressure sensor. The event time uncertainty is mainly determined by two factors: SNR and TSR. This investigation also suggests that the percentage of nominal flow rate is not sufficient for defining the minimum detectable leak size for a negative pressure wave system. It is more reasonable to define the minimum detectable leak size as the actual leak flow rate with respect to leak transient period, the pipe diameter, the type of fluid transferred by the pipeline and pressure noise level.