In a project funded by the U.S. Department of Transportation’s Pipeline and Hazardous Material Safety Administration, NETL partnered with the Colorado School of Mines and the U.S. Army Corps of Engineers to identify the best methods for locating buried plastic pipelines.

According to the Plastic Pipe and Fittings Association, plastic piping systems obtained wide acceptance in the late 1950s and early 1960s. Underground plastic pipe use has increased significantly every year since. Plastic piping has become a popular choice for underground use in water mains, hot and cold-water distribution systems, sewers, gas distribution networks, irrigation systems, conduits, fire sprinkler systems, and process piping throughout the world.

Plastic piping systems also enable many important sustainable and green technologies for new building construction. In addition to its low installation costs, plastic pipe is attractive for non-pressure applications because the smooth inner walls assure high gravity flow rates that minimize chances of developing stoppages. In addition, plastic pipes have adequate strength for earth loads and high chemical resistance.

A drawback to the growing popularity and use of underground plastic pipe is that they are difficult to find when utility companies need to perform maintenance or new construction projects require lines to be relocated. That is where the NETL/Colorado School of Mines/Corps of Engineers project comes in.

“Plastic pipelines are not conductive or magnetic, which prevents them from being located using methods available to utility location contractors,” NETL’s Rick Hammack explained. “This study evaluated ground penetrating radar, seismic, direct current resistivity, gravity gradiometry, and photoacoustic methods by modeling their response to plastic pipelines of various diameters when buried beneath geologic materials typical of U.S. soils.”

The project results suggest that a towed land streamer that can simultaneously acquire geophysical data types using multi-offset ground penetrating radar, multi-channel resistivity, seismic geophone and/or distributed acoustic sensing, and potentially photoacoustic/thermoacoustic data would be an appropriate platform for locating buried plastic pipeline.

Hammack explained that a land streamer for plastic pipe location would be an integrated array of multiple geophysical instruments designed to be towed along the ground. The concept is based on marine streamers — arrays of hydrophones that are towed behind ships. Geophysicists borrowed the concept and applied it to land uses. Land streamer surveys are low cost and easy to move, deploy and collect.

The land streamer arrays that the study suggests can be effective in locating underground plastic pipes include:

• Ground-penetrating radar — A noninvasive geophysical method that uses the reflection of electromagnetic energy to produce images of subsurface interfaces and features. It provides a continuous real-time profile of subsurface features in soil and geologic deposits.
• Multi-channel resistivity — A method for determining the electrical properties of the ground using current injection and volt­age measurement at different locations.
• Geophones — Used in seismic investigations to transform vibrations in the ground into a voltage.
• Distributed Acoustic Sensing — Optical fiber cable that uses laser pulses to measure ground vibration at different positions along its length.
• Thermoacoustic and photoacoustic effects — A new method that uses microwave or laser irradiation to induce ground vibrations that are detected by sensitive ultrasonic transducers.       

NETL is a DOE national laboratory that drives innovation and delivers technological solutions for an environmentally sustainable and prosperous energy future. By using its world-class talent and research facilities, NETL is ensuring affordable, abundant, and reliable energy that drives a robust economy and national security, while developing technologies to manage carbon across the full life cycle, enabling environmental sustainability for all Americans.