Mark L. Stephens

Field Tests for Leakage, Air Pocket, and Discrete Blockage Detection Using Inverse Transient Analysis in Water Distribution Pipes

Stephens, Mark Leslie; Lambert, Martin Francis; Simpson, Angus Ross; Vitkovsky, John; Nixon, John B. Field tests for leakage, air pocket, and discrete blockage detection using inverse transient analysis in water distribution pipes Critical transitions in water and environmental resources management [electronic resource] : proceedings of the World Water and Environmental Resources Congress : June 27-July 1, 2004, Salt Lake City, UT / sponsored by Environmental and Water Resources Institute (EWRI) of the American Society of Civil Engineers ; Gerald Sehlke, Donald F. Hayes, and David K. Stevens (eds.): pp. 1-10

Calibrating the Water-Hammer Response of a Field Pipe Network by Using a Mechanical Damping Model

Hydraulic transient field tests have been conducted in a water distribution network. Existing transient models are applied to model the measured responses, but poor matches are obtained apart from the estimation of the initial rise of pressure. Possible reasons for these discrepancies include the effects of demands, entrained air, unsteady friction, friction losses associated with small lateral pipes, and mechanical damping caused by the interaction of pipes and joints with surrounding soils (including the effects of vibration and different degrees of restraint). These effects are systematically investigated by inclusion of the previously mentioned phenomena in conceptual transient models and calibration to the measured field responses. A mechanical damping-based conceptual transient model is shown to be the only model that can be accurately calibrated to the measured field responses.

INTERNAL WALL CONDITION ASSESSMENT FOR WATER PIPELINES USING INVERSE TRANSIENT ANALYSIS

A methodology for determining the wall condition of water pipelines, by using an inverse transient model to interpret the measured response of the pipeline to deliberately induced controlled transients is presented. Changes in pipe wall lining and thickness theoretically give rise to reflections in measured transient responses and these can be interpreted to assess pipeline wall condition. The results of field tests on a 750mm diameter pipeline, containing reflections from a damaged section of pipeline, are presented. A distribution of known damage (determined from CCTV camera footage) and inferred damage is characterised in terms of four categories of wall deterioration. This distribution of damage is then included in a transient model of the pipeline and the measured and predicted reflection response are found to compare favourably. The transient model is then combined with a Genetic Algorithm and inverse transient analysis is performed using transient data generated from a distribution of known, inferred and arbitrary damage. The inverse transient analysis relatively accurately predicts the pre-determined distribution of damage along the pipeline.

Field Measurements of Unsteady Friction Effects in a Trunk Transmission Pipeline

The relative importance of unsteady friction effects in real pipelines remains a matter of debate. This paper presents the results of a set of field transient measurements on a 13.5 km long trunk transmission water pipeline located in regional South Australia. Modelling has been undertaken using efficient rough pipe turbulent weighting function methods to calculate the unsteady friction contribution. The relative importance of unsteady friction, for no-leak and leak cases, is assessed.

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.

Field Test Investigations into Distributed Fault Modeling in Water Distribution Systems Using Transient Testing

Current condition assessment techniques are focused on leakage, however this forms only part of the story with regard to the efficiency and condition of pipelines. The neglected phenomena are distributed faults including pipe wall deterioration and blockages, where blockage refers to any build up ranging from increased pipe roughness to complete obstruction that may be caused by debris, sedimentation, tuberculation, biofilms or valves. The objective of this research was to develop a non-invasive condition assessment technique for water distribution systems (WDS) that has the ability to detect distributed faults including blockages. Inverse Transient Analysis (ITA) has been identified as a potential method but requires developments in modeling techniques for distributed faults. Blockages can be caused by the build up of many different materials each with their own properties. Extended blockages also form complex flow routes, which cannot accurately be captured by the current approach unless extremely fine discretisation is incorporated, increasing computational effort very significantly. The current approach models extended blockages as reduced diameter sections of pipeline. While a blockage does reduce the diameter, the material properties of the blockage significantly differ from that of the pipeline. A viscoelastic element may be used to account for the change in pipe material and hence response due to the blockage material. Field tests have been conducted on the Adelaide metropolitan water distribution system in streets that have been identified as having significant potential to form blockages. The transient tests indicated that the complex response of the pipe to transient excitation suggests that they are indeed suffering from substantial problems with blockages. The location and identification of zones of differing condition to the remainder of the pipeline, and hence having the potential for distributed faults, have been determined using inverse transient analysis.

Hydraulic Transient Analysis and Leak Detection on Transmission Pipelines: Field Tests, Model Calibration, and Inverse Modeling

The use of hydraulic transients for leak detection is theoretically possible assuming that water pipelines respond elastically and that current transient models are capable of replicating measured responses from real pipelines. This paper presents results for tests using hydraulic transients with and without a leak on a typical transmission main in South Australia. The size of the leak artificially introduced to the pipeline was set at the maximum limit of interest to South Australian Water Corporation operators. Based on the results of the field tests and modelling performed using a quasi-steady friction transient numerical model it was found that it was difficult to model the response of the pipeline, without and with the introduced leak, because of unsteady friction and mechanical dispersion and damping of the transient waveforms. Inverse analysis was performed using the quasi-steady friction transient model and it was found that leak could not be successfully detected. The transient model was improved by including unsteady friction and a viscous damping mechanism that was calibrated for inelastic mechanical effects using no-leak measured responses. Inverse transient analysis was performed using this improved model focussed on reflection information over 2L/a seconds of the measured leak responses and over an extended period. The small size of the direct reflections from the artificial leak made them difficult to discern amongst other reflections from elements not related to the leak. The inverse transient analysis performed over an extended period made use of leak damping information but was also affected by sources of damping not related to the leak. It was found that the improved forward transient model, in combination with prior information regarding the leak discharge (commonly available for flow monitored transmission pipelines), gave the best estimate of the location and size of the leak. However, the true leak was not identified as the optimal candidate following the inverse transient analysis because of persistent inadequacies in the replication of all the physical complexities affecting the measured transient responses.

Using field measured transient responses in a water distribution system to assess valve status and network topology

1 ABSTRACT Uncertainty about the status of valves in a water distribution system, or the existence of total blockages, is not uncommon. This paper presents an approach for determining topological changes using transient response analysis. Precise information is not available regarding all the physical elements contributing to the transient response of a water distribution system. Thus a parameterised model is developed and calibrated to represent “real” transient responses from a field water distribution system. The robustness of this model, and the methodology for diagnosing topological changes, are confirmed when used to successfully identify closed valves in the field.

Hydraulic Transient Analysis and Discrete Blockage Detection on Distribution Pipelines: Field Tests, Model Calibration, and Inverse Modeling

The use of hydraulic transients for blockage detection has been suggested based on the results of numerical and laboratory based experiments using transient models in both the time and frequency domains. The use of hydraulic transients for block detection is attractive because other investigative techniques are limited to steady state pressure and flow (C-Factor) tests and CCTV camera investigation. However, the practical application of hydraulic transient based techniques to water distribution (and other pipelines) requires demonstration. This paper presents the results of transient tests performed on a water distribution pipeline in South Australia both without and with an artificially introduced discrete blockage (created using an in-situ in-line gate valve). The tests revealed that the laboratory systems investigated thus far do not replicate the effects of topological complexity and uncertainty, inelastic and mechanical losses at joints and soil/pipe interaction, regardless of whether a discrete blockage is present. It was found that blockage detection could not be successfully undertaken using inverse transient analysis using a traditional transient model that did not take the non-blockage related physical complexities into account. A novel transient model has been developed using Kelvin-Voigt viscoelastic mechanical elements to incorporate the effects of dispersion and damping by introducing (and calibrating) equivalent viscous damping through calibration to no-blockage measured responses. This new model required spatially distributed viscous elements to replicate the physical variability along the distribution pipeline that was tested. The location and size of the constriction formed using the in-line gated valve was able to be successfully determined using the new calibrated transient model and inverse analysis for a range of discrete blockages. In contrast to steady pressure and flow investigations, the use of hydraulic transients provided information regarding both the specific location and nature of the artificial discrete blockages with little extra practical effort required to conduct the tests relative to C-Factor tests.