PALSPALSPipeline Advanced Leak Location SystemWhen a leak detection test indicates a breach in a pressurized underground pipeline, the PALS offers the latest-generation technology for locating the leak. OverviewLeak detection methods— techniques that determine whether underground piping systems are in fact leaking—have been around commercially for some time, and the number of methods is increasing annually. Reliable leak location methods are equally important, yet scarcer in the marketplace. Many users of leak detection systems face a dilemma if a leak is actually detected—how to accurately and reliably determine the location of the leak while minimizing both the disruption of service and the need for excavating buried piping. The acoustic signal produced by a leak can be masked by background noise, and signal-processing techniques must be applied that allow the detection of the signal amid the noise. Vista Research, long recognized as a leader in signal processing, specializes in separating meaningful signals from the background noise that has been the bane of other acoustic methods. Vista's PALS system uses a unique approach to signal processing that is based on coherence analysis. The PALS, which is gaining great commercial recognition, has regularly outperformed other acoustic methods by a wide margin. The PALS is a portable passive-acoustic system comprised of three acoustic sensors, three small pre-amplifiers, and a portable computer equipped with a data acquisition card. Each sensor measures the acoustic signal generated by the turbulent flow through a hole in the pipeline. The diagram at right shows how leaks are located. The acoustic signal generated by any leak that might be present between the "Ref" (reference) and "Pos" (position) sensors is picked up and transmitted to the computer via the pre-amplifiers; the speed at which the acoustic signal is propagating through the pipeline is measured in the region between the "Vel" (velocity) and Ref sensors, which—unlike Ref and Pos—do not bracket the leak. For the leak to be correctly located, the distances between the sensors must be known, since the measurement made by the PALS determines the location of the leak relative to the reference sensor. A leak location measurement can be made in as little as 2 to 5 minutes. BenefitsAccurate within Several FeetThe PALS locates leaks quickly and accurately, to within 1.5% or better of the distance between sensors, depending on that distance—usually a matter of several feet. Almost No Down TimeA PALS measurement can be made in a few minutes. Minimal Need for ExcavationBecause the PALS can place a leak within several feet of its actual location, the scope of the necessary excavation work is vastly reduced—it is limited, essentially, to repair-related digging. Easily Installed at Routine Access PointsThe PALS can be used on any underground pipeline system that can accommodate the placement of sensors at intervals along its length. Points of access to the pipeline, such as valve pits or aboveground manifolds, can be as far apart as 500 linear feet, and there is no need to remove anti-corrosive coatings. The PALS has been used on transfer lines at bulk storage facilities and on airport hydrant fuel systems. Noisy, active environments do not impact the performance of the PALS. PerformanceThe PALS performs well over a wide range of leak rates, pipeline configurations, backfill materials and backfill conditions—that is, under any condition encountered in an operational setting. Further- more, it is impervious to back- ground noise, even in settings as inhospitable as a jet aircraft flight line. When the sensors are spaced less than 200 feet apart, the accuracy of the PALS is within 3 feet. When the sensors are spaced further apart, its accuracy remains at or better than 1.5% of the sensor interval. Even in field tests where the distance between sensors exceeded 500 feet, the PALS routinely achieved the same high performance. PracticalityThe PALS excels in operational practicality. On most bulk and hydrant lines, sensors can be mounted at available access points without the need for excavation. Furthermore, sensors can be mounted on the ends or sides of a flange connection without sacrificing performance —meaning that the coating used to protect the pipe from corrosion does not have to be removed in order to conduct a leak location test. |
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