Find That Buried Plastic

These tips can help solve the challenge of locating and marking underground plastic pipe

Find That Buried Plastic

Matt Bellmann, owner of Sweetwater Utility Exploration, uses a RIDGID electromagnetic locator to map utilities outside Bank of America Stadium in Charlotte, North Carolina. (Jason Miczek photo) 

Plastic main and service tubing is now well accepted in the waterworks industry and has some advantages, but also has a major disadvantage compared to iron pipe or copper tubing. It can be difficult to find and detect once buried. However, there are ways to find it, and once found, mark it to make it easier to find the next time.

Look Beyond Pipe and Cable Locators

Iron pipe, steel and copper tubing is fairly easy to locate with traditional pipe locators and metal locators. We can use traditional electronic pipe locators to connect and send an AC current directly to the conductive pipe or send a signal by induction through the ground above the pipe. Since iron, steel or copper pipe is electromagnetically conductive, it can carry the signal, which can be detected by a receiver. However, plastic pipe is non-conductive, so this won't work unless a conductive tracer wire was installed along with the pipe. Often pipe was installed before tracer wire was commonly used, so another method must be used. We also see cases where tracer wire was not installed properly, sub-standard wire has deteriorated, was not repaired when broken, or the wire is no longer accessible to trace.

The Gen-Eye Hot Spot pipe locator from General Pipe Cleaners is designed to locate underground plastic pipe that includes tracer wire.
The Gen-Eye Hot Spot pipe locator from General Pipe Cleaners is designed to locate underground plastic pipe that includes tracer wire.


1. Tracer Wire - Tracer wire has been used for quite some time as a tool to help use a pipe locator 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 water proof is a potential to ground out and reduce the signal quality. A utility should also implement a policy that when a main break or tracer wire break occurs that the tracer wire system is fixed to the same quality that it was installed or better. If the tracer wire is attached to the pipe at the top or center line, it can be used to accurately locate the pipe depth as well as location. Contact me if you would like more information on suggested specifications for a quality tracer wire locating plan.

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 be detectable. There is also a non-detectable warning tape without the foil back. Detectable tape is generally buried above the pipe as a dig warning before hitting the pipe. A locator signal can be sent through and end of the tape or by induction using a transmitter on the ground above the tape using 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 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 non-metallic 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 if 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 not typical 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 tip of the probe with a sonde locator to locate the exact end of the probe. 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 knock on the pipe or tubing. The intensity and frequency are adjustable. It straps to the outside of the pipe, so it is non-invasive 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 alternate method must be used. Distance will vary based on depth and soil type, but 100 to 150 feet is achievable.


The Stopper on the item above is 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 then is 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 stopper creates. I have detected the sound and located pipe 300-500' 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 temporary 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 water line 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 if pipe direction, or at regular intervals such as at intersections or every 100 feet or so.

Real-time infraMAP Software from iWater is a mobile GIS program that allows seamless data collection, updates to a utility's asset management program, and pulls data from Neptune’s N_Sight Software.
Real-time infraMAP Software from iWater is a mobile GIS program that allows seamless data collection, updates to a utility's asset management program, and pulls data from Neptune’s N_Sight Software.


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. scaleable 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 and the markers located on the maps to be easier found by users and detected by with the marker locators precisely.

Summary

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.

Mark Beatty is CEO and Principal Owner at Utility Technologies, LLC. This article was originally posted on LinkedIn, and is being used with Mark's permission.



Discussion

Comments on this site are submitted by users and are not endorsed by nor do they reflect the views or opinions of COLE Publishing, Inc. Comments are moderated before being posted.