These tips can help solve the challenge of locating and marking underground plastic pipe
Plastic main and service pipe is well accepted in the industry and has some advantages. But it also has a major disadvantage compared to iron pipe or copper tubing: It is difficult to find and detect once buried.
Plastic pipe is nonconductive, unlike iron, steel and copper, which can be located fairly easily with traditional pipe locators and metal locators.
Here are some tips.
1. Tracer wire — Tracer wire has been used for quite some time as a tool to allow a traditional pipe locator to work on plastic pipe. However, in the early years, there was no special wire, and most engineers just specified standard electrical wire. This worked well for a while, but eventually the insulation used in homes above ground was found to deteriorate underground. The degradation or loss of insulation from abrasion or cracking shortens the distance the locating signal can go. Full breaks may even be a dead end for the signal.
New tracer wire designed specifically for underground use is no longer solid copper, but copper-clad steel for better strength to prevent breakage. The coating is normally polyethylene, the same polymer used to make underground water tubing, and can withstand harsh, wet conditions. The combination extends the life of the tracer wire system.
To optimize the distance a locator signal can travel, new tracer wire should also be installed with waterproof connectors and grounding anodes. Every connection that is not waterproof has a potential to ground out and reduce the signal quality.
Utilities should also implement a policy that when a main break or tracer wire break occurs that the tracer wire system be fixed to the same quality that it was installed at or better. If the tracer wire is attached to the pipe at the top or centerline, it can be used to accurately locate the pipe depth as well as location.
2. Detectable tape — Another way of marking the location of plastic pipe is with detectable tape. This tape comes in rolls about 2 inches wide and has an aluminum foil backing to allow it to be detectable. There is also a nondetectable warning tape without the foil back.
Detectable tape is generally buried above the pipe to serve as a warning before diggers hit the pipe. A locator signal can be sent through the end of the tape or by induction using a transmitter on the ground above the tape with a standard pipe locator. However, locating is less precise than a true tracer wire system and the signal can bleed over onto other underground objects for false positives.
Detectable tape is also typically above the pipe as an early warning to diggers, so depth-indicating pipe locators will be locating the tape depth rather than the pipe depth. Detectable tape can be buried shallow as an easier retrofit than tracer wire attached to the pipe itself.
3. Fiberglass probes — Another method of locating nonmetallic pipe is to push a fiberglass probe down the pipe. The probe has a copper wire core that can have a signal sent from a standard pipe locator transmitter similar to a tracer wire. With a sluice installed, the probe can even be inserted to a service line that is under pressure. This can be helpful when trying to locate both a leak and a pipe at the same time.
This is practical for service lines or lines that can be taken out of service, but it is not typically well suited for a larger water main. It could be done on a larger main if the line is taken out of service temporarily. A sonde transmitter can also be installed on the end to locate the exact tip of the probe with a sonde locator. The distance is limited by the length of the probe, typically about 200 to 325 feet.
4. Acoustic pipe locating — Plastic pipe can often be located when it has a leak by using traditional leak noise locators. Most who have used an acoustic leak locator can find the pipe by the leak sound. The leak locator will show peak sound when directly over the leaking pipe. Moving it perpendicular to the pipe can help find the pipe location.
It is possible to artificially induce a sound on plastic pipe and then use an acoustic leak detector to locate the pipe. On small-diameter service tubing, a mechanical knocker can do the job. It is a device that makes a controllable solenoid with repeated knocking on the pipe or tubing. The intensity and frequency are adjustable. It straps to the outside of the pipe, so it is noninvasive and does not require turning off water or removing the water meter. However the knocking is not loud enough to go very far on large-diameter pipe, so an alternate method must be used. Distance will vary based on depth and soil type, but 100 to 150 feet is achievable.
There is also a device with a valve that attaches to a fire hydrant. The hydrant is turned on and the valve pulsates water to create an acoustic pressure wave. The audio profile of the water main becomes much like a heartbeat. This sound can be followed on plastic pipe for hundreds of feet to accurately locate the pipe with an acoustic locator. There are acoustic pipe locators optimized to detect and locate the specific frequencies the device creates. I have detected the sound and located pipe 300 to 500 feet with a locator optimized for this purpose. Distance will vary depending on the depth, soil type and quality of your acoustic pipe/leak locator.
5. Marking plastic pipe locations — All too often, utility staff go to the trouble to locate pipe and only mark it temporarily for the job at hand with marking flags or paint. However, if you are going to the trouble to locate it, why not mark it more permanently, but with something more eye-pleasing and more permanent than wire flags or paint on the ground or sidewalk?
It is generally not practical to retrofit a plastic waterline with tracer wire. However, the pipe can be marked at regular intervals, and locations of bends and fittings, with 3M RFID markers. The markers can then be found later with a simple easy-to-use marker locator. Markers can be installed deep with the pipe as disks, shallower as marker balls, or very near the surface as marker pegs. Each utility can be determined separately, since markers are both color-coded and frequency coded by the type of service buried underneath.
RFID markers can also be used when a tracer wire system fails. Markers are typically located at major fittings, changes of pipe direction, or at regular intervals such as at intersections or about every 100 feet.
6. GIS mapping — Most utilities either have or are thinking about implementing a GIS mapping system. A GIS system uses GPS to locate pipe and then accurately plot it on a map. Scalable dimensions, satellite images, local photos and notes can all indicate the location of the pipe in relation to a GPS receiver or surrounding objects.
GIS mapping can be combined with RFID to mark locations more precisely.
A final word
Plastic pipe can be more difficult to locate than metallic pipe. However, there are tools on the market to detect and mark the pipe to make future locating easier. The key is finding the right mix of technology and equipment for locating and marking plastic pipe and tubing in your particular water, wastewater, stormwater or gas distribution system.
About the author
Mark Beatty is CEO and principal owner at Utility Technologies LLC. This article was originally posted on LinkedIn, and is being used with Beatty’s permission.
Do you have any tips or tricks on locating those hard-to-find utilities? Comment below or email firstname.lastname@example.org with suggestions for other contractors.