Locating Pipes with Acoustics and Mapping Software

When a contractor hits a buried line, damage to the line inevitably costs firms valuable time and money. But over the past decade, technology companies have introduced new software and tools that enable workers to more accurately locate water lines, gas lines, and sewer lines before they're hit. These technologies utilize electromagnetic locators, ground penetrating radar, Lidar and microwave technologies, sensor-based systems, acoustic systems, and geographic information systems (GIS) to locate and map underground pipelines.

Electromagnetic Locators

Electromagnetic-based tools consist of transmitters that apply specific active frequency signals to non-insulated or insulated metallic lines, as well as a receiver tuned to the same active signal. In addition to scanning for the active signal, receivers also scan for passive 60 Hz signals and broad-spectrum radio frequencies. Using this approach, an operator can accurately locate and trace metallic lines.

When checking for buried lines, operators can use direct connection techniques that place the transmitter near an access point and use the receiver to trace the target line. If an operator cannot find an access point, an alternative method called “ring clamp induction” connects a ring clamp around the pipe or cable and transmits the signal through a coil in the clamp onto the target line. A third method places the transmitter on the ground surface above the assumed location of a line for an inductive search.

Electromagnetic locators can find many types of metallic lines, including CATV and telephone lines, steel or ductile iron pipes, metal tanks, and electrical instrumentation lines. The locators also work if an operator can place a flexible and detectable rod inside a non-pressurized line such as a drain, conduit, or sewer line. Attaching a locating beacon to the rod allows the receiver to trace the line. However, electromagnetic locators do not locate non-metallic lines, such as PVC or thermoplastic pipes. Broken lines or poor conductors will also evade the locator system.

Ground Penetrating Radar, GPS, LIDAR, and Microwave Technologies

Ground Penetrating Radar (GPR) units scan for the location of pipes by transmitting continuous electromagnetic signal pulses through the earth or other structures and receiving reflected signals from any subsurface materials. The initial GPR image consists of a two-dimensional cross-section of buried metallic and non-metallic objects; processing software then converts the two-dimensional image into a three-dimensional image map, showing the location of lines, conduits, and pipes. Soil conditions and the smaller diameter of some lines may limit the effectiveness of a GPR system, however.

Newer solutions use a combination of global positioning systems (GPS), Light Detection and Ranging (LIDAR), and microwave technologies to locate underground lines, detect voids, and find leaks. GPS mapping and locating technologies have the capability to store, retrieve, and update accurate records of subsurface lines; software allows the addition of notes as work progresses. LIDAR uses light from a pulsed laser to measure ranges, while microwave technologies use ultra-high frequencies to locate sub-surface materials. These technologies can deploy from a push-type device, ATV, helicopter, fixed-wing aircraft, or drone. Given the combination of technologies and deployment options, operators can collect accurate data about underground lines over large geographical areas at depths up to 15 feet.

Sensor-Based Technologies

Sensor-based technologies avoid soil condition problems by deploying magnetic field sensors and geospatial mapping to develop a 3D vector map of a surveyed location. The vector map provides the exact 3D coordinates of underground piping objects with an accuracy of 4 inches. Sensor-based geospatial technologies can locate and map metallic, HDPE, PVC, and other composite pipelines at maximum depths of 50 feet. Detection of non-metallic pipes with this system requires the insertion of a detectable rod. Data obtained from the use of sensors can download into a GIS database and map to provide a detailed, dimensional picture of a piping system.

Acoustic Systems

Acoustic systems induce sound into the ground and use a receiver to listen for reflected sound. Acoustic systems can locate metallic, concrete, or plastic gas, water, and sewer laterals that have broken or missing tracer wires and that are buried at minimal depths. These systems can also pinpoint the source of leaks.

Sensors attach to contact points to triangulate the signal; accelerometers work with other circuitry and software in the receiver to measure the speed and strength of the reflected sound wave. From there, the receiver provides a digital display of the results. As a receiver scans a location, it uses 6-to-7-second-long linear slices of reflected sound to build a full scan. Contour mapping and pipe mapping software allows an operator to view the collected data in 2D or 3D formats. Acoustic systems have limitations that include the depth of detection and accuracy; for example, multiple pipes installed near one another can generate inaccurate readings. While an acoustic system can detect any type of pipe or conduit, it cannot indicate the type or size of the pipe, unlike some of the technologies listed above.