Silvia Meniconi

In-Line Pipe Device Checking by Short-Period Analysis of Transient Tests

In this paper, the results of laboratory transient tests concerning the interaction between a pressure wave and an in-line device are discussed. Transients are generated by means of a fast and complete closing of an end valve, and pressure measurements are carried out just upstream of the maneuver valve. The main effect of the device on the pressure time-history—hereafter referred to as pressure signal—is a sharp increase caused by the pressure wave reflection. Three experimental setups are considered, in which different in-line devices are installed (i.e., a ball valve, a butterfly valve, and different-sized orifices). The pressure signal is analyzed in the time domain, and a reliable evaluation of the device location is obtained by means of wavelet functions. Furthermore, on the basis of the value of the pressure increase, the status of the device can be determined; experimental results are synthesized in a dimensionless diagram. Finally, criteria for using the obtained results in other pipe systems are...

Experimental Evidence of Hysteresis in the Head-Discharge Relationship for a Leak in a Polyethylene Pipe

The relationship between leak outflow from a damaged pipe and flow condition inside the pipe plays a crucial role in pressurized pipe systems management. As an example, this relationship is used in leakage reduction techniques based on pressure control and in leak detection techniques based on inverse analysis. To explore the relationship between total head inside the pipe and leak outflow for a single leak in a polyethylene pipe, tests were carried out at the Water Engineering Laboratory of the University of Perugia. These tests point out that the viscoelastic nature of the pipe material gives rise to a hysteretic behavior of the investigated relationship, i.e., the outflow depends not only on the synchronous total head but also on the total head time history and variation rate.

Experimental Investigation of Coupled Frequency and Time-Domain Transient Test–Based Techniques for Partial Blockage Detection in Pipelines

AbstractPartial blockages commonly exist in pressurized pipeline systems, and the rapid remediation of such faults is required to reduce the wastage of energy as well as to maintain the serviceability of the pipe network. Numerous transient test–based techniques (TTBT) have been developed for detecting pipe defects, with each technique providing different advantages. Two previously developed techniques—pressure signal analysis (PSA) and frequency response analysis (FRA)—are experimentally tested in this study on systems of different pipe material and characteristics. Each method is validated using the experimental data, and the results show that PSA is most accurate for locating the blockage while FRA is most accurate for determining the radial constriction and length of the blockage section. To take advantage of the different strengths of the techniques, a coupling of the two methods is proposed. Experimental application results reveal that both detection accuracy and calculation efficiency are improved ...

Potential of Transient Tests to Diagnose Real Supply Pipe Systems: What Can Be Done with a Single Extemporary Test

In this paper, the reliability of a transient test-based technique as a powerful tool in the management of real supply pipe systems is shown. The pressure signal acquired during the first phase of the single completed test has been analyzed on the basis of extensive research activity performed in the previous years in the field of transient test-based techniques and refined on the basis of numerical and laboratory tests. Specifically, the wavelet transform, which allows the automatic detection of singularities in noisy pressure signals, and a Lagrangian model, which evaluates the causes of discontinuities, are efficiently coupled for analyzing the pressure signal acquired in the described pipe system. As a result, the topology of such a system has been checked, and its functioning conditions have been determined. Moreover, the unwanted status of an in-line valve—certified by the manager as fully open but actually partially closed—has been pointed out.

Is the leak head–discharge relationship in polyethylene pipes a bijective function?

Traditional characterization of the leak head–discharge relationship in pipeline systems relies on the use of power law functions to explain the increase in leakage rate with pressure when network and laboratory data are analysed. However, recent studies addressed that the leak behaviour is complex and influenced by pipe material and leak geometry. The experimental tests, carried out at Water Engineering Laboratory of the University of Perugia (WEL), Italy, show that the leak head–discharge relationship on polyethylene pipes is not a bijective function since it gives rise to different discharge values with respect to one value of the pressure. To explore this issue, two viscoelastic models of a leak in a polyethylene pipe are introduced and compared with other leakage models. The results show that the viscoelastic behaviour reflects the leak head–discharge relationship, and care should be taken in the use of bijective relationships.

Two-Dimensional Features of Viscoelastic Models of Pipe Transients

AbstractTransients in pressurized polymeric pipes are analyzed by means of a two-dimensional (2D) Kelvin-Voigt viscoelastic model, calibrated by means of a microgenetic algorithm on the basis of pressure traces. The reliability of the proposed model is then tested by comparing numerical and experimental profiles of the axial component of the local velocity, the latter measured by means of an ultrasonic Doppler velocimeter. Differences between transients in viscoelastic and elastic pipes are pointed out by considering a 2D model in which an elastic behavior is assumed for pipe material. The comparison between the two 2D models allows attribution of the faster decay of pressure oscillations and velocity profiles to viscoelasticity because of the time-shift between pressure oscillation and retarded circumferential strain. The 2D analysis shows that the viscoelastic model generally presents flatter velocity profiles with respect to the elastic model.

Leak Size, Detectability and Test Conditions in Pressurized Pipe Systems

The relationships between leak geometry and detectability are explored with a distinction between steady- and unsteady-state based techniques. Various criteria to evaluate the size and detectability of a leak are first discussed. These criteria can be useful for the benchmarking and the comparison of different techniques. Since the test conditions play a crucial rule in leak detectability, the proposed criteria take this effect into account. Furthermore, they show that while in steady-state conditions increases in system pressure enhance leak detectability, in transient state, by contrast, higher pressures tend to decrease detectability. This effect is also confirmed by experimental tests carried out at the Water Engineering Laboratory of the University of Perugia.

Local and Global Leak Laws

The relationship between the functioning conditions of pipe systems and the leakage, or leak law, can be used at two different scales. At a local scale, i.e. for a single leak, it is derived from the classical orifice equation and, basing on experimental data, is modified to take into account all the relevant parameters it depends on (e.g., leak shape, pipe material and thickness, …). At a global scale, for a whole district or a part of a pressurized pipe system with several leaks, the same relationship is often used, basing on the assumption that the combination of local leak laws produces a similar global leak law.In this paper the effects of the spatial variation of the leak law parameters at the local scale on the leak law at a global scale are analyzed. Two leak laws derived from the orifice equation, the power law and the linear law, are considered. Results suggest that the global leak law exponent is larger than the corresponding mean local leak law exponent since it takes into account the spatial variability of the quantities affecting leakage.

Diagnosis of Pipe Systems by means of a Stochastic Successive Linear Estimator

Environmental concerns and legislation of the water industry have recently drawn the attention of many researchers to the management, calibration and power cost reduction of water pipeline systems. Effective water system management rests upon the knowledge of the current state of a water pipeline system. For example, leakages, unknown status of in-line valves, and partial blockages are often a source of management costs. These anomalies must be detected and corrected as early as possible. In this paper a diagnosis tool is presented able to detect leaks, partially closed in-line valves and partial blockages by means of transient head measurements. The algorithm introduced is a Stochastic successive Linear Estimator [SLE] (Yeh et al. Water Resour Res 32: 2757–2766, 1996a) which provides statistically best unbiased estimate of these anomalies and quantifies the uncertainty associated with these estimates via assimilation of available information. Therefore, the information from common diagnosis techniques e.g., inspection methods, and head measurements available at different locations of the system, obtained by different transient tests are fused to provide the most accurate and reliable diagnosis.

In-line partially closed valves: how to detect by transient tests

Reliable and quick techniques are needed to locate and estimate the asset of in-line partially closed valves in pressurised pipes. The methodology considered in this paper is based on the analysis of transient tests. As a matter of fact, singularities (e.g., junctions, partial blockages, partially closed in-line valves, leaks) give rise to reflected waves whose arrival time and amplitude ‐ recorded in one or more sections of the pipe ‐ allow their detection. Transients are generated by means of a total and fast closure of an end valve and the pressure time-history ‐ referred to as pressure signal ‐ is measured at a section immediately upstream the end valve. In the paper, first some numerical simulated signals show that this kind of analysis can be useful for locating the valve and determining its asset, also by means of two simplified numerical models. Then some results of an extensive laboratory campaign carried out at the Water Engineering Laboratory ( WEL) of the University of Perugia, Italy, are reported.