Reversing Time To Spot Cracks In Gas Pipes

His team will present the latest simulations and experimental evidence showing the detectors are feasible.

Detecting problems in buried pipes using ultrasound is tricky because they tend to disperse broadcast waves of sound. But this scattering is an ideal property for a technique called time reversal, where rich patterns created by dispersion can be analyzed to spot changes in a material. O'Donoughue's idea is send a wideband ultrasonic signal from one detector to another, through the walls of the pipe. When the signal bounces back and retraces its steps to the first detector, any structural imperfections show up as a disturbance in the combination of forwards and backwards waves. "If there is a crack or corrosion, the waves will not retrace their steps," says O'Donoughue.

The team is designing rings of these sensors to attach to the outside of pipes. The idea is to space out the rings, each which will eventually contain between four and eight sensors, 200 meters apart from each other. Simulations suggest a single sensor in each ring doubles the power output, that multiple sensors should further improve the performance, and that this configuration can detect a change in mass. The data from preliminary experiments show that time reversal should work in buried pipes.

The talk "Detection of structural faults in pipelines with time reversal" by Nicholas O'Donoughue et al will be presented at the 157th  Acoustical Society of America Meeting to be held May 18-22 in Portland, Ore.