One way to ensure that pipelines are accurately detected when planning a trenchless construction project is using tracer wires during the installation process so that they can be detected at a later date, either for geotechnical investigation reports requiring utility location or for pipeline maintenance. (For more on utility detection, see Effectively Using Utility Detecting Devices.)
Infrastructure assets under the ground are vital to a thriving society. To keep these assets in working condition, it is necessary that they be periodically inspected and maintained. In order to maintain them, it is necessary that they be accurately located when maintenance is due. Locating underground infrastructure is essential not only when maintenance is required but also when new pipelines are to be installed.
Drilling blindly can be disastrous in more ways than one, because other than damaging infrastructure, it can cause physical harm to workers and escalate direct and indirect costs associated with a pipeline project.
The Need for Tracer Wire
The installation of utility lines is performed using trenchless methods such as horizontal directional drilling (HDD), auger boring, microtunneling and pipe jacking. Tracer wire is very important while installing pipelines using these methods because the pipe materials used for HDD are nonmetallic such as high density polyethylene (HDPE), polyvinyl chloride (PVC) and polyethylene (PE).
This makes it difficult to be traced using utility locating devices since these materials do not respond to signals. Adding a metallic component such as a tracer wire makes it easier to be located when needed in the future.
A tracer wire, also known as locating wire, is placed along the length of the pipe during installation and can be traced using a locating device. When the wire is located, the location of the pipe can be established by potholing at regular intervals.
Installation of Tracer Wire in HDD
Coated solid copper wire was the most common tracer wire used for installation with HDD. Sometimes larger diameter wires and multiple copper wires are used in the hope that at least one will make it through the installation process. However these wires often break and are lost during the rough installation conditions that the wire is subjected to, sometimes requiring costly re-bore.
Copperhead industries introduced a copper-clad steel (CCS) tracer wire in 2004, with six times more strength than the coated solid copper wire, greatly increasing the probability of successfully completing the installation in good condition. The proper APWA color code for coating tracer wire should be used so that the pipes’ usage can be easily identified.
CCS tracer wire is also coated with HDPE of 45 mil thickness to create a durable wire, resistant to breakage and damage due to abrasion during the pullback process. A continuous length of tracer wire is installed by attaching the tracer wire to the pipe’s pulling head. The tracer wire should be attached properly to the pulling head so that it does not get lost during the pullback process. A lost tracer wire can mean a costly re-boring process and waste of project time.
To prevent losing the wire, a short chain section can be welded to the pulling head, and the tracer wire attached to the trailing end of the chain. The leading portion of the tracer wire can also be attached under the expander to protect from damage and tearing.
Once the tracer wire is installed, a continuity check is conducted on the tracer wire to find out if there has been any breakage or damage to the wire during the installation. Continuity is a type of electrical test conducted to determine the resistance between two points.
Low resistance implies that the points are connected electrically, while a high resistance indicates that the circuit is not connected or is open. Continuity is crucial to determine if the tracer wire system has been installed correctly. If continuity is found, it means that the tracer wire is installed correctly, and if not found, the tracer wire must be reinstalled.
Benefits of Tracer Wire
The prime benefit of tracer wire is that it makes locating utilities much, much easier than locating pipes not installed with tracer wires, even if they are metallic. The tracer wire helps provide accurate location of utility lines during geotechnical investigation, and reduces the cost and time of locating pipelines without tracer wire. Furthermore, the color coding as per APWA standard provides details about exact usage of the pipe, which helps prevent mishaps with workers due to incorrect handling during pipeline maintenance.
Nonmetallic pipes such as HDPE, PVC and PE that cannot be easily located under normal conditions are easily found when installed with tracer wires. The tracer wire is thin and flexible enough to allow installation along with pipe installation, and well installed, HDPE-coated tracer wires that are corrosion and abrasion resistant ensure that the wire remains in service as long as the utility pipe is in service. (For more on utility location, check out The Science of Getting it Right: Locating Underground Utilities.)
Installing tracer wire systems along with HDD and other trenchless pipeline installation methods is very important. The underground network of sewer pipelines, water pipelines, gas lines, telecommunication ducts, electric cables and signal lines are extensive.
Locating them is a challenge when it comes to installing new pipelines or finding old ones for maintenance or repairs through the crisscrossing maze. Tracer wires can make it easier not only to locate without digging, but also to trace the entire length of the pipeline as well as other lines passing through the vicinity.
Tracer wires greatly reduce chances of mishaps and cross-boring issues due to the clarity provided by color coding and traceability of the entire pipeline length.