Jinzhe Gong

Detection of Distributed Deterioration in Single Pipes Using Transient Reflections

A number of different methods that use signal processing of fluid transients (water hammer waves) for fault detection in pipes have been proposed in the past two decades. However, most of them focus solely on the detection of discrete deterioration, such as leaks or discrete blockages. Few studies have been conducted on the detection of distributed deterioration, such as extended sections of corrosion and extended blockages. This is despite the fact that they commonly exist and can have a severe negative impact on the operation of pipelines. The research reported here proposes a method of detecting distributed deterioration by investigating the time-domain water hammer response trace from a single pipe with a deteriorated section. Through wave analysis using a step pressure input, a theoretical square-shaped perturbation is found to exist in the transient pressure trace as a result of distributed deterioration. The hydraulic impedance of this section can be derived from the magnitude of the reflected pressure perturbation, while the location and length of the corresponding deteriorated section can be determined by using the arrival time and duration of the perturbation. The proposed method has been validated by analyzing experimental data measured from a pipe with a section of wall thickness change.

Single-Event Leak Detection in Pipeline Using First Three Resonant Responses

Hydraulic transients (water hammer waves) can be used to excite a pressurized pipeline, yielding the frequency response diagram (FRD) of the system. The FRD of a pipeline system is useful for condition assessment and fault detection, because it is closely related to the physical properties of the pipeline. Most previous FRD-based leak detection techniques use the sinusoidal leak-induced pattern recorded on the FRD, either shown on the resonant responses or the antiresonant responses. In contrast, the technique reported in the current paper only uses the responses at the first three resonant frequencies to determine the location and size of a leak. The bandwidth of the excitation only needs to be five times that of the fundamental frequency of the tested pipeline, which is much less than the requirement in conventional FRD-based techniques. Sensitivity analysis and numerical simulations are performed to assess the robustness and applicable range of the proposed leak location technique. The proposed leak location technique is verified by both numerical simulations and by using an experimental FRD obtained from a laboratory pipeline.

Frequency Response Diagram for Pipeline Leak Detection: Comparing the Odd and Even Harmonics

AbstractPipeline leak detection using hydraulic transient analysis is a relatively new detection technique. For single pipeline systems, recent work has led to two different approaches for determining leak parameters based on leak-induced patterns displayed in a pipeline’s frequency response diagram (FRD). The major difference between the two techniques is that one uses the leak-induced pattern within the odd harmonics of an FRD, while the other one uses the leak-induced pattern at the even harmonics. In order to compare and contrast the two approaches, the current research analyses the relationship between the characteristics of the leak-induced patterns and the parameters of the pipeline system. A dimensionless analysis, based on hydraulic impedance, is adopted to simplify the equations. The amplitudes of leak-induced patterns at both the odd and even harmonics in the FRD are found to be dependent on a critical parameter: the dimensionless steady-state valve impedance, ZV*. The value of ZV* is dependent...

Detection of Localized Deterioration Distributed along Single Pipelines by Reconstructive MOC Analysis

AbstractThe detection of localized deterioration that is distributed along pipelines, including wall thickness reduction caused by large scale corrosion, is essential for targeted pipeline maintenance and the prevention of pipe failure. This paper proposes a novel technique for the detection of distributed deterioration along a pipeline by estimating the distribution of pipeline properties using a measured pressure transient trace. The proposed technique is referred to as reconstructive method of characteristics (MOC) analysis, and it is an inverse process of the traditional forward MOC calculation. The reconstructive MOC analysis reconstructs the MOC grid and estimates the pipe parameters, such as impedance and wave speed, reach by reach from downstream to upstream. Numerical simulations are performed on a pipeline with three pipe sections of impedance changes. These deteriorated sections are accurately detected and located by using the new technique. Experimental verification is also performed by succes...

On-site non-invasive condition assessment for cement mortar–lined metallic pipelines by time-domain fluid transient analysis

Pipeline condition assessment is essential for targeted and cost-effective maintenance of aging water transmission and distribution systems. This article proposes a technique for fast and non-invasive assessment of the wall condition of cement mortar–lined metallic pipelines using fluid transient pressure waves (water hammer waves). A step transient pressure wave can be generated by shutting off a side-discharge valve in a pressurised pipeline. The wave propagates along the pipe and reflections occur when it encounters sections of pipe with changes in wall thickness. The wave reflections can be measured by pressure transducers as they are indicative of the location and severity of the wall deterioration. A numerical analysis is conducted to obtain the relationship between the degree of change in wall thickness in a cement mortar–lined pipe and the size of the corresponding pressure wave reflection. As a result, look-up charts are generated for any specific cement mortar–lined pipeline to map this relationship. The wall thickness of a deteriorated or distinct section can be determined directly and quickly from the charts using the size of the reflected wave, thus facilitating on-site pipeline condition assessment. The validity of this time-domain pipeline condition assessment technique is verified by numerical simulations and a case study using the field data measured in a mild steel cement mortar–lined water main in South Australia. The condition of the pipe as assessed by the proposed technique is generally consistent with ultrasonic measurements.

Leak Detection in a Branched System by Inverse Transient Analysis with the Admittance Matrix Method

The diagnosis of water distribution systems by means of the inverse transient analysis requires efficient and reliable numerical models. In the network admittance matrix method (NAMM) the 1-D waterhammer governing equations are integrated in the frequency domain and organized in a laplacian matrix form. The NAMM is particularly suitable for complex systems because of this structure and can be used for the system diagnosis, including leak sizing and location. In this paper a damaged branched system is considered and the diagnosis is performed by means of the NAMM using experimental data from laboratory transient tests. Two different boundary conditions are used in the implementation of the NAMM and the leak is located and sized with a reasonable approximation. An extended numerical investigation is also presented and allows confirmation of the results for different leak locations. The use of the NAMM for the leak detection and the validation using experimental data on a branched system are the main original contributions of this work. The successful diagnosis indicates promising results for applications in more complex systems.

Experimental verification of pipeline frequency response extraction and leak detection using the inverse repeat signal

ABSTRACT This paper presents the original design of a side-discharge valve based transient generator that can produce two types of pseudorandom binary signals: a maximum length binary signal and an inverse repeat signal. These two signals are both wide bandwidth, persistent and periodic, but the inverse repeat signal has the advantageous property that it is antisymmetric within each period. The two signals are used to extract the frequency response function of a single water pipeline in the laboratory. The experimental results demonstrate that the frequency response function extracted by the inverse repeat signal is closer to the theoretical linear results as obtained from the transfer matrix method due to it being able to cancel the effect of even-order nonlinearities. The customized transient generator is then applied to a pipeline with a leak. The location of the leak is successfully determined using the first three resonant peaks as extracted by the inverse repeat signal.

Determination of the Creep Function of Viscoelastic Pipelines Using System Resonant Frequencies with Hydraulic Transient Analysis

AbstractThe determination of the creep (compliance) function of viscoelastic pipelines is essential for modeling their hydraulic behavior and accurately predicting pressure responses under transient events. This paper proposes a novel frequency-domain technique for the determination of the creep function of viscoelastic pipelines using hydraulic transients. A viscoelastic pipeline system, when compared with a frictionless elastic pipeline under the same system configuration, has nonuniformly shifted resonant frequencies. Analytical analysis shows that the shift in the resonant frequencies of a viscoelastic pipeline system is related to both the pipe wall viscoelastic compliance effects and the unsteady wall shear stress effects. A technique is developed to determine the elastic wave speed and the viscoelastic creep compliances based on the shifted system resonant frequencies. To improve the accuracy of the calibration for the viscoelastic parameters, an approach is proposed to correct the shifting in the ...

Field study on non-invasive and non-destructive condition assessment for asbestos cement pipelines by time-domain fluid transient analysis

Asbestos cement pipelines constitute a significant portion of the potable and waste water systems in many countries in the world, including Australia. Most of the asbestos cement pipes in the developed countries were installed before 1980, and many utilities are observing that the breakage rate is increasing with the ageing of the pipe. Condition assessment for asbestos cement pipes is of important necessity for prioritising rehabilitation and preventing catastrophic pipe failure; however, few techniques are available for direct assessment of the condition of asbestos cement pipes and most of them are localised and destructive. This article outlines a pilot field study of the non-invasive and non-destructive condition assessment of asbestos cement pipelines using fluid transient pressure waves. Fluid transient analysis previously conducted by the authors for metallic pipelines is further developed and adapted to asbestos cement pipes for the detection of localised defects. A new sub-sectional condition assessment technique is proposed for determining the effective wall thicknesses of asbestos cement sub-sections within a section of pipe bounded by two measurement points. A field trial is conducted in Australia on an asbestos cement water main (which has class changes with varying wall thicknesses) to verify the proposed techniques. The wave speeds, lengths and wall thicknesses of sub-sections in different classes are determined and the results are consistent with the information in the design drawings provided by the water utility. This field study, for the first time, verifies that controlled fluid transient waves can be used as a tool for non-invasive and non-destructive condition assessment of asbestos cement pipelines.

Experimental validation of the admittance matrix method on a Y-system

ABSTRACT This paper presents the first experimental validation of the network admittance matrix method (NAMM) using experimental data collected from a branched pipeline system during hydraulic transient events. The branched pipeline model is formulated for two model scenarios with different nodal boundary control conditions, namely demand- and pressure-controlled boundary nodes, describing different forms of hydraulic transient excitation for the system. The matrix expressions for these two cases are derived and the effects of these different boundary control conditions, in terms of model structure and simulation accuracy, are investigated. The simulated results are compared with the measured experimental data acquired in the Y-system. The small differences indicate that the admittance matrix method is able to reproduce the experimental data with a good agreement in both the time and frequency domains.