The detection of pipeline blockages using transients in the field

Abstract

Over periods of time deposits build up on the inside of pipes in water distribution systems through a process called tuberculation and, once large enough, may become blockages. Blockages significantly affect both the operational efficiency and the water quality in water distribution systems. Inadvertently closed or partially closed valves can also cause blockages. They can be difficult to detect, particularly in networks, using existing telemetry records or steady state analyses. To date, customer complaints have been one of the primary mechanisms for the detection of blockages. Unfortunately, by the time such complaints are recorded, the blockage is usually in a highly evolved state and difficult to remove. The potential application of transient and inverse transient techniques to the problem of water distribution system analysis has been explored theoretically and in the laboratory since the mid-1990s. In 1994, Liggett and Chen proposed leak detection and calibration techniques based on transient conditions in pipelines and pipe networks. These techniques apply equally to the problem of blockage detection in pipelines. Controlled pressure transients can be used to infer information about the status of pipelines and pipe networks (including blockages). Transient techniques have advantages over steady techniques because of the additional information contained in transient pressure waves that propagate throughout pipe networks. Numerical analysis using an inverse transient model called NETFIT, together with an iterative threshold technique for the selection of likely blockage candidates, has been undertaken. A branch pipeline, representative of those encountered in the field, was numerically simulated. The results revealed that multiple blockages could be successfully located and sized after a limited number of iterations of the combined inverse transient analysis and threshold technique. The paper concludes by presenting the development of a practical method, based upon the inverse transient technique, for the detection and location of blockages, and/or closed and partially closed valves, in field networks. A case study area at Willunga (to the south of Adelaide) is being instrumented and studied. Preliminary field results have demonstrated that pressure transients are susceptible to accurate measurement in the field. That said, the collection of "real" field data has revealed sensitivities associated with the model parameters (including the discretization and physical geometry of the Willunga network). Future work will involve the development of improved models and the application of inverse transient analysis to measured transient responses to detect blockages in 'real' networks. This research is a collaborative project between the University of Adelaide and United Water International.