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Abstract

A method for locating the joints and fractures of underground cast iron gas mains comprises connecting several sections of an underground cast iron gas main pipeline across a sixty watt signal generator with an audio-frequency signal output of 7800 hertz. The connections take advantage of service lines, valve boxes and drip access at the surface, otherwise holes are drilled to accommodate contact probes. The signal passes through the pipe sections and their joints in series. The centerline of the underground cast iron gas main pipeline is plotted directly above on the surface of the ground, e.g., along a surface centerline. The relatively higher impedance of the pipe joints compared to the pipes themselves, causes current fluxes to radiate from each joint. The relative linear positions and their corresponding signal power measurements are collected along the surface centerline. The locations of the joints of the underground cast iron gas main pipeline are estimated to be directly below points on the surface centerline that provide signal power peaks.

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First Claim