Acoustic monitor

In-Depth

A new, lightweight device that detects leaks in natural gas pipelines has been successfully tested on a transmission main owned and operated by Dominion Transmission in Morgantown, W.Va.

The test was conducted by the US Department of Energy’s National Energy Technology Laboratory (NETL) and West Virginia University, which has worked with NETL for the past two years to develop the detection system.

Known as the Portable Acoustic Monitor Package (PAMP), the device -14 inches long, 18 inches tall, and weighing only five pounds - uses a variety of tools to capture and record sound waves that are transmitted by natural gas.

Computer software included in the package analyses and interprets the recorded signals to detect possible leaks. Natural gas compressor stations, which pump gas from one station to another, have a distinct sound, as does natural gas flowing normally through fittings and valves. Variations to these and other background sounds alert operators that a leak may exist.

The so-called PAMP system interests the natural gas transportation industry because it could enable companies to spot leaks faster than they do now, and it may be useful in preventive maintenance. It could also detect "third party" damage. Operators using a back hoe to perform pipeline maintenance, for example, may dig deep enough to strike a pipe, carrying sound waves within the pipe to a PAMP unit. Alerted pipeline operators would be able to locate the source of the sound waves and the pipeline intrusion.

For the field test, two PAMP units were attached aboveground to a 12 inch pipeline operating at a pressure of 200 pounds per square inch. Both units were able to detect simulated strikes on the pipe and leaks in real time. The two units were able to pick up sound anomalies when a one inch steel ball was dropped one inch above the pipeline approximately a half a mile away. Location of leaks can be determined by measuring the time difference as a signal arrives at two PAMP units.

The PAMP prototype is rugged and versatile, and it costs less than $1,000. In addition, it can be connected to any pipe through a half-inch-wide fitting at operating pressures up to 1,000 pounds per square inch.

West Virginia University is now working on categorising background sounds of natural gas pipelines. The university is also developing a sound generator to pull out real signals above the background noise of the pipe to determine how sensitive it is in pinpointing leaks.