Pipeline &
Gas Journal
April issue 2000:
Location Tool
Providence Gas Finds
Answer To Help Find Plastic Pipe
by Michael McGuire,
Manager of Engineering Design & Facility Locating,
Providence Gas, Providence, RI
Providence Gas has been installing plastic pipe since the mid 1970s but until the late 1990s, we’ve not been using tracing wire. All of our plastic pipe, prior to the late 1990s, was installed using a metallic marking tape. This warning tape had a foil backing which was to be used to trace the plastic pipe. Special tabs were required to connect sections of tape to ensure conductivity. These clasps were not always used. Now this tape has also deteriorated over time. Another problem is that other contractors as well as our own crews have dug into this tape over the years without always splicing it back together properly.
Due to this installation procedure, we have very little, if any, success tracing our older plastic installations with conventional pipe-locating equipment. There are cases where our records are no longer accurate due to road reconstruction, road name changes, 911 address changes and many other factors. When a facility locator notices that the records may be incorrect, our first recourse is to locate the line with our tracing equipment. With our plastic pipe installations, our only alternative to tracing out these facilities is to perform a test hole excavation. These are expensive and usually needed on very short notice.
Rhode Island’s one-call system, Dig Safe, allows us just 48 hours to locate our facilities. Test holes only give you a location at the one spot excavated if you’re locating plastic pipe without tracing wire. In the last few years, there has been an exceptional number of sewer installations in coastal communities. These generally take place in congested areas with dense population. We’ve been performing many more test holes because of this activity.
Providence Gas has been investigating available technologies to help locate plastic mains and services without using tracing wire. We’ve held demonstrations using instruments that detect sound waves through the gas stream but that technology did not work well for us. The product seemed to need an experienced field technician who could develop a feel for the signals and outputs that this unit received. The equipment also required a power source that consisted of a 12-volt car battery which needed to be carried to a point of entry in the gas stream such as a service riser. We found that it worked marginally on services and worse on mains.
We’ve also attended demonstrations for ground-penetrating radar locating. These machines are quite costly, require some training in interpreting underground facilities, and the data collection process can become cumbersome. Some of the other technologies such as the 3M locators cannot help us with pipe that’s been previously installed. Of all the available technologies, the E-line locator seemed to fit best.
Continental Industries approached us with the E-line locator last summer. This product allows you to enter a plastic main through a mechanical fitting similar to a tapping tee without the outlet branch. The cutter is extracted under no blow conditions. A steel locating cable is then introduced into the gas main. The unit holds 200 feet of cable. You can also introduce the cable in either direction, allowing you to trace up to 400 feet of main through one test hole. We’ve only been able to insert approximately 175 feet. Once the cable has been introduced into the gas main, you’re able to use your own conventional locating equipment. The unit that holds the cable has a counter in case you run into an unknown obstruction. The counter allows you to determine how far away the obstruction is located.
We first tried this unit at a juvenile prison complex. We have a 2-inch, 90# line installed throughout the complex. This main meanders throughout the facility and our records do not appear to match up with what we can visually examine above ground. They’ve been renovating this location in recent years, adding buildings, relocating utilities and excavating extensively on the property. As a result, we could not trace our existing warning tape. We brought in the two vendors previously mentioned and asked them to help us locate our pipe.
The E-Line locator and its simple technology worked best for this application as our locators felt comfortable using this system with little training. The installation of the saddle uses common techniques similar to installing a mechanical tapping tee for a residential service. The extraction as well as the completion of the cutter is very similar to using any conventional hot tapping machine where you work through a valve to perform this task. The actual locating was achieved by using our own Metrotech 810 machines. Our linewalkers felt comfortable with their readings and findings because they were using the same locating equipment that they use on a daily basis.
There is no need to learn a new form of locating and tracing; you’re just locating a metal snake instead of tracing wire or steel pipe. We had an experience where we thought we were receiving bad information. On one occasion we traced our service and the signal jumped off the cable and we started to trace an invisible perimeter dog fence.
After this demonstration and some additional research, we bought one of these units. We’ve since modified the unit so that we can insert the locating cable in plastic services. It’s also been modified so it can enter through the meter cock of services. The leading edge of the cable was too large to fit through a three-quarter-inch meter cock. We had a smaller entry ball made to accommodate installing the snake through such valves. Although we need to disrupt the customer to insert through the service line, we eliminate the need to dig test holes.
We typically have more difficulty locating our services and because of this, we have been using the E-Line locator primarily on service. The unit allows us to enter through the riser under no-blow conditions. This relatively low-tech solution has already saved our company from digging test holes on services in the short time that we have acquired this product. It will also limit the amount of test holes required on mains because we can trace up to 400 feet per test hole. The information we’re gaining on our facilities has been routed back to our Records Department, which has become more reliable.
This simple solution to an ever-increasing problem helps us locate our facilities without performing test holes. We view this piece of equipment as another device in our locating toolbox. Of course, nothing can compare to accurate and maintained records other than properly installed tracing wire. But when these aren’t available, we attempt to use our E-Line locator. P&GJ
The author has been with Providence Gas for 12 years, holding various positions in the Engineering De-partment. He is on the New England Gas Association Pilot Development Team for Opera-tor Qualification of Damage Pre-vention and is also the vice chairman of the Operations School Distribution subcommittee. He received his Engineering Degree at Lafayette College in Easton, PA.