Tracer Wire System Importance for HDD

The wire must be strongly attachedHorizontal directional drilling (HDD) has commonly been used to install telecommunications duct, conduits, water, sewer and gas lines for many years. There are many things to consider when performing an HDD job. Construction site holes or pits, size of equipment, drilling fluid systems, drilling head design, back reamers, pipe type and numerous other basic construction requirements are all important.

One often overlooked item is the tracer wire requirements to ensure that a good and accurate locate can be done when required long after the project is completed and the pipe or duct is in service.

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The types of piping material that are used for most HDD jobs are non-metallic. Polyethylene and PVC, both joint restraint and fusible, are the most prevalent for HDD projects. Since these types of material do not allow for a locator to send a signal on, it is necessary to add a metallic component with them when performing a drill. Tracer wire is the preferred product to install along with the piping. If the correct tracer wire type is used and installed properly, the pipe will be easily located when required in the future.

Unfortunately, there are times that the choice of tracer wire type and installation of the tracer wire with the pipe is not properly completed. There are several types and sizes of tracer wire available to the piping industry today. Some are designed for small open-cut projects and at the other end of the spectrum for violent pipe bursting projects. HDD falls toward the more difficult, violent end of the spectrum for tracer wire. Soil and rock conditions, length of pullback, power required to make the pull and properly connecting to the existing tracer wire after leaving the drilled section are all very important.

Past Tracer Wire

In the past, the most common type of tracer wire being used for HDD was solid copper with a coating to protect the wire. At times larger diameter wires were used; some as large as 6AWG. Another option was to use multiple copper wires, hoping one of them makes it through the bore. Both large sizes of wire and multiple wires being used are sometimes the case even today. Broken tracer wires during the process are very costly to the installer doing the job.

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There are also some stainless steel stranded tracer wires used due their strength, but the low conductivity of stainless steel makes it more difficult to locate accurately with the best pinpoint frequencies of today’s locating equipment.

In 2004 Copperhead Industries introduced a copper clad steel (CCS) tracer wire that was as much as six times the strength of the same size of solid copper wire. The method of using this CCS wire for HDD operations was patented in 2008. CCS wire is stronger, less costly than solid copper wire and volatility of copper prices is also eliminated. This wire greatly increases the success rate of getting the tracer wire to come through an HDD project in good shape. CCS tracer wire with the proper HDPE coating is also protected from the abrasive elements in the pullback process. CCS tracer wire has become the preferred wire for many HDD projects

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Another consideration for HDD project success is the proper attachment of the tracer wire to the pulling head of the pipe. If the wire is not strongly attached and protected in some manner, it is possible the wire may be removed from the pulling head, leaving the driller to try and find the end of the wire or perform a costly re-bore. There are techniques that have proven to be successful in tracer wire attachment, such as welding a short chain section to the pulling head and attaching the tracer to the trailing end of that chain. This better guides and protects the tracer wire during the pull back. Another good option is to attach the wire under the expander to protect the leading segment from being damaged or tearing off.

It is also important to install tracer wire that has the proper coating to eliminate or minimize any damage to the wire during the pipe installation.  A very durable high density polyethylene (HDPE) coating of 45 mil thickness on the wire is important. Smaller thicknesses or low density, high molecular weight polyethylene (HMWPE) or other lesser materials can more easily result in the coating being damaged during the pullback process. THHN wire should never be used for tracer wire in any application, HDD or open ditch. Also, the correct APWA color coating for the wire is important. This readily identifies the usage of the pipe being installed.

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Once the drill has been completed with the proper tracer wire installed, it is important to perform continuity or locate check on the installed tracer wire. This will find damage in the wire installed or lack of signal for future locating needs. If the signal is not present or continuity is not found, the wire must be re-installed. This means performing a re-bore. Typically this only happens if the correct wire is not used and breaks during the pullback or wire with the incorrect or thin coating is used and is scrapped off during the process. HDPE coating prevents this from happening.

Ground level test stationProper Connectors
In addition to having the right tracer wire for the job, connectors for the wire outside of the HDD operation to the tracer wire are important. Connectors that are rated for direct burial, have a dielectric gel and are sealed must be used.  This prevents any potential corrosion of the wire and ensures that continuity of the locate signal is good. Connectors not designed for direct burial should not be used. It is never recommended to have any wire connection of the wire being used during the pull.

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It is also important that proper test stations for connecting the tracer wire and protecting the ends when brought above-ground to attach the locator are installed. There are numerous types of test stations available. The preferred type is ground level with a locking lid to prevent vandalism or damage by mowing or traffic. These are color coated with the correct APWA color and usually note what utility type the pipe is being used for. Other types of test stations include posts and short tubing with condulet terminals. Simply bringing the wire above ground, leaving it exposed to the elements, vandalism, theft and grass trimmers is not acceptable.
The final part of the tracer wire system is the far-end ground on the wire. This further ensures a good strong locate signal to precisely locate the tracer wire. Grounding anodes for this purpose are a good investment, providing the locate technician an advantage compared to locating tracer wire without a good far-end ground, completing the locate circuit.

Lee Dester is vice president of sales for Copperhead Industries Inc., based in Monticello, Minn.

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