Electrical resistance tomography to detect leaks from buried pipes

Abstract

This paper describes a non-invasive method for detecting leaks in buried pipes, which uses a surface linear electrode array perpendicular to the axis of the pipe. Two electrodes inject current and the remaining electrodes detect the drop in voltage on the ground surface using both the dipole-dipole array and a modified Schlumberger array. A single-step reconstruction algorithm based on the sensitivity theorem yields two-dimensional images of the cross section. A personal computer controls current injection, electrode switching and voltage detection, which allows us to easily test various arrays of electrodes and speed up the process of measurement. The system was first tested in the laboratory using a stainless steel tube immersed in water and covered by a rubber sleeve to simulate a non-conductive leak. By taking reference measurements with the immersed bare pipe, it is possible to reconstruct images showing the simulated leak using only 16 electrodes and even as few as eight electrodes, albeit with reduced resolution. Field measurements have involved simulated leaks of water from a plastic tube 1 m long and 8 cm in radius buried at a depth of about 24 cm in a farm field. The hardware system injected 1 kHz, 20 V peak-to-valley square waveforms, thus avoiding electrode polarization effects. The simulated leak was unmistakably distinguished.