Leak Noise Research Articles

An Investigation into the Physical Mechanisms of Leak Noise Propagation in Buried Plastic Water Pipes: A Wave Dynamic Stiffness Approach

In buried plastic water pipes, the predominantly fluid-borne wave is of particular interest, as it plays a key role in the propagation of leak noise. Consequently, it has been studied by several researchers to determine the speed of wave propagation and its attenuation with distance. These features are encapsulated in the wavenumber. By examining the factors that govern the behaviour of this wavenumber, this paper presents an in-depth examination of the physical mechanisms of leak noise propagation. To achieve this, an alternative physics-based model for the wavenumber is developed, using the concept of the wave dynamic stiffnesses of the individual components within the pipe system, i.e., the water in the pipe, the pipe wall, and the surrounding medium. This facilitates a clear interpretation of the wave behaviour in terms of the physical properties of the system, especially the interface between the pipe and the surrounding medium, which can have a profound influence on the leakage of acoustic energy from the pipe wall into the external medium. Three systems with different types of surrounding medium are studied, and the factors that govern leak noise propagation in each case are identified. Experimental results on two distinct test sites from different parts of the world are provided to validate the approach using leak noise as an excitation mechanism.

Laboratory implementation of the noise correlation methodology for leak location in water distribution systems

Nowadays, reducing the loss of water resources is of primary concern in many countries worldwide. Different methodologies exist for the identification and localisation of leaks in water distribution networks, which can be applied simultaneously at a different scale, to improve success rate. Acoustic correlation has been employed for many years to localise such leakages, based on the post-processing of vibroacoustic signals acquired by two sensors placed on both sides of the pipe where the leakage is supposed to be located. The practical application of this methodology still presents some significant issues. The implementation of the noise correlation methodology was investigated through an experimental test rig by simulating leakages in different conditions of pressure and flow and investigating the effects of background noise. Hydrophonic measurements and recordings were performed, identifying the frequency range affected by the leak noise, and the signal to assess the accuracy of the noise correlation method. A pre-filtering of the signals to reduce the effect of background noise masking was also investigated. The accuracy of acoustic correlation in localising the leakage was assessed by computing the propagation velocity, which depends on the vibroacoustic fluid-structure interaction, through approximated analytical equations

Influence of noise masking on leak pinpointing: Experimental analysis on a laboratory test rig for leak noise correlation.

The efficient management of water distribution networks requires the detection and mitigation of leaks that result in significant water losses, economic costs, and potential health hazards. This experimental study focuses on the optimal frequency range for accurately locating a water leak in a distribution network using the noise correlation approach while mitigating the influence of background noise associated with water consumption from users. Through laboratory experimental tests, a digital bandpass filter was defined in order to pre-process signals and to improve cross-correlation analysis within the pertinent frequency range. This was done by characterising the frequency content of leak-induced noise, noise masking resulting from water consumption, and background noise. The analysed signals were recorded using hydrophones installed within the pipes of a laboratory test rig under different conditions of water flow rate. The spectra analysis assessed the influence of varying water flow rates on the acoustic sound field within the pipeline system. Additionally, the results of the analysis made it possible to discriminate clearly between noise generated by leaks and noise attributed to water consumption. This distinction is useful for implementing suitable filters, and also to establish a threshold ratio of leak flow rate to water consumption flow rate for effective pre-filtering. This study aims to establish a methodological framework that can effectively differentiate between acoustic signals stemming from leaks and noise generated by other sources within the system, to improve leak location accuracy through the noise correlation approach.

Comparative Study of Leak Detection in PVC Water Pipes Using Ceramic, Polymer, and Surface Acoustic Wave Sensors.

The detection and location of pipeline leakage can be deduced from the time arrival leak signals measured by acoustic sensors placed at the pipe. Ongoing research in this field is primarily focused on refining techniques for accurately estimating the time delays. This enhancement predominantly revolves around the application of advanced signal processing methods. Additionally, researchers are actively immersed in the utilization of machine learning approaches on vibro-acoustic data files, to determine the presence or absence of leaks. Less attention has been given to evaluating the sensitivity, performance, and overall effectiveness of these sensors in leak detection; although acoustic methods have been successfully used for leak detection in metallic pipes, they are less effective in plastic pipes due to the high attenuation of leak noise signals. The primary thrust of this research centers on identifying sensors that not only possess sensitivity but also exhibit high efficiency. To accomplish this goal, we conducted an exhaustive evaluation of the performance of three distinct categories of acoustic sensors employed for detecting water leaks in plastic pipes: specifically, lead zirconate titanate (PZT) sensors, polyvinylidene fluoride (PVDF) sensors, and surface acoustic wave (SAW) sensors. Our evaluation encompassed the performance of PVDF and SAW sensors in leak detection, comparing them to PZT sensors under a variety of conditions, including different leak sizes, flow rates, and distances from the leak. The results showed that all three sensors, when they were placed in the same position, were able to detect water leaks in plastic pipes with different sensitivities. For small leaks (1 mm, 2 mm), the PVDF sensor showed the greatest sensitivity (0.4 dB/L/h, 0.33 dB/L/h), followed by the SAW sensor (0.16 dB/L/h, 0.14 dB/L/h), and finally the PZT (0.13 dB/L/h, 0.12 dB/L/h). Similarly, for larger leaks (4 mm, 10 mm), the PVDF sensor continued to show superior sensitivity (0.2 dB/L/h, 0.17 dB/L/h), followed by the SAW sensor (0.13 dB/L/h, 0.11), and finally the PZT sensor (0.12 dB/L/h, 0.1 dB/L/h), outperforming the PZT sensor. This suggests that SAW and PVDF sensors, have the potential to serve as valuable, cost-effective alternatives to traditional commercial leak noise transducers. The outcomes of this comparative study involving three acoustic sensors hold the potential to advance the development of robust and dependable systems for the detection of water leaks in plastic pipelines.

Plumbing defects in residential buildings: analysis of anomalies and their causes

PurposeMost residential building owners often report problems associated with the plumbing systems. If identified at the early stages, plumbing-related defects can be easily repaired. However, if unnoticed for a long period of time, they could lead to major damages and incur a significant cost to repair. Despite the problems, studies investigating plumbing anomalies and their root causes in residential buildings are limited. This study aims to explore plumbing defects and their potential causes, diagnosis methods and repair techniques in residential buildings.Design/methodology/approachThis research used data collected through an extensive survey of both academic and grey literature. Through the content analysis, plumbing defects and the associated causes have been identified and presented in tabular format.FindingsThe study investigated the anomalies and causes in the residential plumbing system under five key sub-systems: water supply system; sanitary plumbing system; roof drainage system; heating, ventilation, air conditioning and gas system; and swimming pool. Accordingly, some of the identified plumbing defects include leakages, corrosion, water penetration, slow drainage and cracks. Damaged pipes, faulty equipment and installations are some of the common causes of the anomalies. Visual inspection, hydrostatic pressure test, thermography, high-tech pipe cameras, infrared cameras, leak noise correlators and leak loggers are techniques used for diagnosing anomalies. Reactive, preventive, predictive and reliability-centred maintenance strategies are identified to control or prevent anomalies.Originality/valueThe findings of this research can be used as a useful tool or guideline for contractors, plumbers, facilities managers and building surveyors to identify and rectify plumbing system-related defects in residential buildings.

Analysis of phase data from ground vibration measurements above a leaking plastic water pipe

One way to locate a buried plastic water pipe is to measure the surface vibration due to a leak in the region above the pipe, and to process the data to infer the pipe location. This paper investigates the physical mechanisms that propagate leak noise through the pipe and the surrounding soil to the ground surface. An analysis is carried out of the relative phase between vertical ground vibration measurements at points in a grid above the pipe. The study involves experimental measurements from a site in the UK with a more realistic leak mechanism compared to recent research, a simplified analytical model to gain insight into the underlying physics, and a numerical model to validate some of the assumptions made in the derivation of the analytical model. Three waves are principally involved in propagating leak noise to the ground surface from the pipe, namely the predominantly fluid-borne wave in the pipe, and the shear and compressional waves in the soil radiating from the pipe. Their influence on the ground surface vibration is investigated through measured and simulated phase contours over a rectangular grid of surface velocity measurements. It is shown how shear and compressional waves combine to affect the shape of the lines of constant phase on the ground. The results demonstrate the potential of the proposed analytical and numerical models to investigate wave radiation from buried water pipes, and possible pipe location strategies using phase data from surface vibration measurements.

Key Factors That Influence the Frequency Range of Measured Leak Noise in Buried Plastic Water Pipes: Theory and Experiment

The frequency range of the leak noise in buried water pipes, measured using acoustic correlators, depends significantly on the type of pipe and its location as well as the type of sensors used. Having a rough idea of this frequency range can be beneficial for operators prior to conducting tests; however, there is currently no method of predicting it except through practical experience, and no model-based approach yet exists. This issue is addressed in the present paper by using a concise and relatively simple analytical model of the water-pipe–soil system combined with the sensors’ frequency response. The influence of the various physical parameters of the system, such as the pipe and soil properties and the sensor type, on the cross-power spectral density (CPSD) of leak noise signals and, furthermore, the frequency range are investigated. The main factors that affect the bandwidth are the distance between the sensors, wave speed of the predominantly fluid-borne wave in the pipe and the attenuation of this wave. It is shown that the external medium has a profound effect on the propagation and, in turn, on the bandwidth. The approach to predicting this bandwidth is validated using experimental data from three different test sites.

Risk assessment and leakage prediction system of the water distribution system of Changzhou, China

ABSTRACT In order to improve the application efficiency of intelligent monitoring equipment, leakage early warning system and water loss estimation methods under flow monitoring in different water supply areas are explored. Pressure monitoring provides risk alerts regarding unusual activity in the water distribution system in an effort to lessen or prevent catastrophic pipe bursting incidents. The location of leak points can be more accurately identified with the help of hydrophones or leak noise loggers. Furthermore, on the basis of the continuous improvement of hydraulic monitoring, a technical way to predict water quality changes through hydraulic monitoring is being developed.

Towards applicability of wavelet-based cross-correlation in locating leaks in steel water supply pipes

The paper discussed the application of wavelet-based cross-correlation analysis to the processing of the leak noise signals acquired in the field. Nine recordings produced with the commercial leak noise correlator are considered in this study. All the cases are considered as classified as challenging for signal interpretation. For most of the cases, the basic correlation technique proved to be insufficient to measure the time lag with the required confidence. We implemented a wavelet cross-correlation algorithm for time lag estimation. At least in five cases out of nine, it managed to estimate time lag accurately. In three of the remaining cases, it failed. Unfortunately, due to a lack of information on field studies when records were produced, we are not able to investigate the reason of failures. We concluded that the proposed solution is practical and can be implemented in the software of leak noise correlators.

Experimental Investigation on Characteristics of Leak Noise in Gas Pipeline Systems

AbstractPipelines are essential elements in the daily operation of modern cities, but significant economic loss and environmental damage commonly occur because of pipeline leakage. The acoustic met...

Study on leak localization for buried gas pipelines based on an acoustic method

As an important part of a city’s “lifeline,” an urban underground natural gas pipeline network is an integral part of the infrastructure, facilitating energy transmission. If the source of a leak is not located accurately, explosive incidents may occur owing to the highly flammable nature of natural gas, causing casualties and property damage. Thus, this study presents a new method of leak identification in buried natural gas pipelines. The proposed method achieves this goal through leak noise in the soil, and this is verified through experiments conducted as part of this research. The surrounding soil of the buried pipeline was considered as the propagation medium of the noise associated with leaks. For four microphones, placed in detection holes, were used to capture leak noise within the soil. Multi-layer wavelet packet decomposition was performed on the collected time domain signal of leak noise and was reconstructed on the characteristic frequency band of 0–200 Hz. Leak localization was completed by estimating the time difference of arrival between each pair of microphones on the buried natural gas pipeline. In the experimental scenario, the leak location error of the buried gas pipeline was 8 %–12 %. Therefore, the proposed method can successfully be applied to realize leak localization for buried natural gas pipelines.

Limits for leak noise detection in gas pipes using cross correlation

The cross correlation method is widely used in leak detection and location for pipes. The model of the cross correlation function of the leak noise for water pipes has been established in an earlier study, while there is no such model for gas pipes. In this study, a model of the correlation function of the leak noise in gas pipes is developed. The characteristics of wave propagation in gas pipes, combined with the leak noise spectrum, are incorporated into the model to consider the effects of physical parameters, i.e., turbulence parameters, pipe parameters and flow parameters, on the cross correlation function. This model is capable of describing the main features of the correlation results in gas pipes. Moreover, the model gives an estimation of the detection limits of the leak noise in the absence of noise, which is crucial to the deployment of sensors in real gas pipelines. The findings of this study provide theoretical insight and experimental evidence for optimizing the cross correlation method when conducting leak detection and location in gas pipes.

A laboratory-based leak noise simulator for buried water pipes

Acoustic correlators are often used to pinpoint leaks in water distribution systems. Generally, these devices are tested for their efficacy in bespoke test rigs that are also used for training purposes. However, this can be problematic as it is difficult to expose the correlators to identical conditions, and only a limited number of situations is possible. An alternative approach is described in this paper, in which a bench-top device, called a leak noise simulator (LNS), is used to generate pipe vibration representative of measured leak noise. The LNS comprises a computer to generate and supply the signals, a dual channel power amplifier and two electrodynamic shakers and accelerometers to generate and measure the vibrations. There are two modes of operation. One involves the generation of leak noise signals using a theoretical model of the buried water pipe implemented in the computer, and the other replicates measured signals from the field that are stored in the computer. To faithfully replicate the pipe vibration due to leak noise, the dynamic effects of the power amplifier and shakers are compensated for by using a filter implemented in the computer. The design and testing of the LNS in both modes are reported in detail, demonstrating the potential of the device.

Using a geophone as an actuator to estimate the velocity of leak noise propagation in buried water pipes

A common way to pinpoint a leak in a buried plastic water pipe is to use a leak noise correlator. This is performed by using the time delay between two measured signals and the velocity at which such signals travel along the pipe. In this paper, an investigation is carried out into the use of a geophone in reverse, driven by an oscillating voltage. It then acts as a tapping device, exciting the wave responsible for leak noise propagation, when it is attached to an access point to estimate leak noise velocity. Two different ways of exciting the geophone were investigated. Initial tests were conducted in the laboratory to determine the effectiveness of the device in generating a force over a wide frequency range. Field tests were then carried out on a buried pipe test rig and the predominantly fluid-borne wave was generated by the tapping device, that travelled at least 7 m.

Experimental investigation of vibro-acoustic techniques to detect and locate leakages in gas pipelines

Leak detection and location are critical for the safety management of gas pipelines. Vibro-acoustic techniques have been proven to be effective. However, no single study exists, which examined the performance of different kinds of sensors in buried large-diameter gas pipelines. This paper presents an experimental investigation that concerns the feasibility of vibro-acoustic techniques in buried large-diameter gas pipelines for leak detection and location. A test rig was set up, and acoustic sensors and accelerometers were employed to measure the leak noise. This experiment confirmed that both acoustic sensors and accelerometers can be applied to detect and locate leakages in unburied gas pipelines under certain conditions. However, the acceleration responses were quickly corrupted by the existence of backfill soil, while acoustic sensors achieved satisfactory results. The evidence from this study suggests that the acoustic sensor is more suitable for buried large-diameter gas pipelines and this is encouraging for the development of a long-distance monitoring system.

A stochastic model for the speed of leak noise propagation in plastic water pipes

A good estimate of the speed of leak noise propagation is necessary to pinpoint the location of a leak using acoustic correlators. Models currently exist for this purpose, but they do not consider uncertainties in the pipe geometry and the properties of the pipe and soil. Using the fact that leak noise propagates as a predominantly fluid-borne wave, this paper develops a stochastic model of the speed of leak noise propagation in plastic water distribution pipes that can account for these uncertainties. The model provides confidence limits for the estimate of this wave speed. It is based on the mean and standard deviation of the pipe geometry as well as the pipe and soil material properties, which have strong influence on the speed at which the leak noise propagates in the pipe. Numerical examples, using parameters from water supply systems found in the field, in which the pipe is made from Medium-Density Polyethylene (MDPE) and Polyvinyl Chloride (PVC) are presented to validate the model. Monte Carlo simulations for both in-air and buried pipes are presented to check the 99.7% confidence interval. To verify that the predictions from the stochastic models give realistic results, they are compared with some measurements from different sites, in which nominal properties and tolerances for the pipe and soil properties are assumed.

A model-based health indicator for leak detection in gas pipeline systems

Leakage in gas pipelines is becoming a significant issue and has attracted much attention in recent years. This paper is concerned with the development of a robust health indicator for identifying the leakage in gas pipeline systems. A spectral exponent indicator is proposed based on a theoretical leak noise spectrum model. Measurements of the leak acoustic signals are also presented from a pipe rig with air under pressure. Then, a feature selection technique is employed to select properly desired features. Three data-driven approaches, artificial neural networks (ANNs), support vector machine (SVM), and random forest (RF) are trained with the most discriminative features. The proposed methodology showed to achieve 99.4%, 99.6% and 99.4% accuracies for ANN, SVM and RF respectively. Furthermore, the proposed indicator showed to be robust under different conditions illustrating its ability for applications in the field.

Water leak location based on improved dual-tree complex wavelet transform with soft thresholding de-noising

Water leakage control emerges as a prime concern among researchers and water utility companies due to ever-increasing water loss level. Acoustic leak detection technique is a promising and widely used approach. Unfavorably, the deficiency of this method is that acoustic waves are interfered by undesirable noise and presence of multi-modal dispersive wave. The conventional correlation-based method assumes leak noise propagates as a single non-dispersive wave and this leads to unreliable detection method. This paper concerns on noise reduction through an improved de-noising method and leak localization by considering wave dispersion. Wavelet de-noising is a common de-noising method used in past leak detection works. But it has shortcomings of frequency aliasing and shift-variant due to DWT decomposition. Therefore, a shift-invariant Dual Tree Complex Wavelet Transform (DTCWT) is introduced here to substitute DWT for wavelet de-noising. DTCWT will decompose the signal into several bandwidths then soft thresholding is applied to remove noise by eliminating the irrelevant signals. Multilevel DTCWT decomposition aids to tackle the problem encountered by basic localization method because the wave velocity is evaluated based on the dominant frequency and dispersion curve. Experimental results show that the proposed de-noising method outperforms ordinary wavelet de-noising. Besides, the method effectively removes noise and makes the peak of cross-correlation function more pronounced and hence it is achievable to increase leak localization accuracy. The proposed method outweighs other methods by offering the lowest false trips occurrence and minimal localization error of 3.33%. A field test result proved that the method is able to locate the leak in a 235-meter-long, underground buried pipe with a minimal error of 2.63% which is 57% lower than the conventional method.

Theoretical Investigation on the Characteristics of Leak Noise for Natural Gas Pipelines

This paper is concerned with the spectral characteristics of leak noise at the source relevant to fluid dynamics for natural gas pipelines. Comparison is made between the flow field characteristics for the buried and above-ground pipelines to demonstrate the differences in aero-acoustics generation mechanism. The fundamental spectral parameters including the sound pressure level (SPL) and power spectral density (PSD), are extracted to characterize the leak noise under different pipeline conditions of operation pressure and leak orifice diameter. Numerical results show that the leak noise of buried pipelines has less energy and are more concentrated at lower frequencies, compared with that of above-ground pipelines. It is demonstrated that leak noise is predominantly governed by the dipole and the quadrupole sources, generated from the gas–solid interaction and turbulent disturbance, respectively. It is shown that the dipole source is attenuated and the quadrupole source is amplified with the leak orifice diameter for buried pipelines whereas both are amplified for above-ground pipelines. Moreover, it is suggested that the feature parameters of fluid dynamics, such as the average dynamic pressure and turbulent kinetic energy, can be used to characterize the leak noise mechanism for natural gas pipelines.

The leak noise spectrum in gas pipeline systems: Theoretical and experimental investigation

This paper is concerned with a theoretical and experimental investigation into the pressure spectrum in a pressurised fluid-filled pipe containing a leak. A general theoretical framework for predicting the leak noise spectrum is derived. A simple relationship is developed between the leak noise pressure spectrum in the pipe and the velocity spectrum at the leak orifice. Measurements of the leak noise spectrum are also presented from a pipe rig with air under pressure. The variation in noise spectrum is investigated for various leak orifice diameters and pipe pressures and compared against predictions from the theoretical model. The model is shown to predict the general shape of the pressure spectrum when the turbulence quantities are appropriately chosen. The variation in overall noise with leak orifice radius and exit velocity is also well-captured by the theoretical model.