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ACOUSTIC LOCATION OF LEAKS IN PRESSURIZED UNDER- GROUND PETROLEUM PIPELINES
Citation:
Eckert, E. G. AND J. W. Maresca. ACOUSTIC LOCATION OF LEAKS IN PRESSURIZED UNDER- GROUND PETROLEUM PIPELINES. U.S. Environmental Protection Agency, Washington, DC, EPA/600/SR-92/143, 1992.
Impact/Purpose:
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Description:
Experiments were conducted at the Underground Storage Tank (UST) Test Apparatus Pipeline in which three acoustic sensors separated by a maximum distance of 38.1 m (125 ft) were used to monitor signals produced by 11.4-, 5.7-, and 3.8-L/h (3.0-, 1.5-, and 1.0-gal/h) leaks in the wall of a 5-cm-(2-in.-) diameter pressurized petroleum pipeline. The line pressures and hole diameters used in the experiments ranged from 69 to 138 kPa (10 to 20 psi) and 0.4 to 0.7 mm (0.01 to 0.03 in.), respectively. Application of a leak location algorithm based on the technique of coherence function analysis resulted in mean differences between predicted and actual leak locations of approximately 10 cm. The standard deviations of the location estimates were approximately 30 cm. This is a significant improvement (i.e., smaller leaks over longer distances) over the cross-correlation-based techniques currently being used. Spectra computed from leak-on and leak-off time series indicate that the majority of acoustic energy received in the far field of the leak is concentrated in a frequency band from 1 to 4 kHz. The strength of the signal within this band was proportional to the leak flow rate and line pressure. Energy propagation from leak to sensor was observed via three types of wave motion: longitudinal waves in the product and longitudinal and transverse waves in the steel. The similarity between the measured wave speed and the nominal speed of sound in a gasoline suggests that longitudinal waves in the product dominate the spectrum of received acoustic energy. The effects of multiple-mode wave propagation and the reflection of acoustic signals within the pipeline were observed as non-random fluctuations in the measured phase difference between sensor pairs. Additional experiments with smaller holes and higher pressures (138 to 345 kPa [20 to 50 psi]) are required to determine the smallest leaks that can be located over distances of several hundred feet. The current experiments indicate that improved phase-unwrapping algorithms or lower noise instrumenta- tion, or both, are required to optimize system performance.