New Gas Leak Detector Passes the Test in BellSouth

Article for Locating, Testing & Repairing Magazine
By Walt Dreyfus, BellSouth Communications

If you had bet me a few years ago that I’d be using hydrogen to safely and accurately locate pressurized cable leaks, I probably would have called your bluff. But today, nine months after a successful demonstration of the new hydrogen leak detector from System Studies Incorporated, my crew and I are enjoying the payoff from our initial wager of time and effort.

Until recently, the standard leak detection gas used in BellSouth was helium. And while helium is fairly effective for finding leaks in manholes and buried cables, there were always some leaks that we just couldn’t locate. So, when I heard about a new gas detection tool from Sweden at a System Studies Partners in Pressurization symposium in the spring of 1999, I was ready to give it a try.

The opportunity came last summer when Lynda Reep of System Studies Incorporated contacted me and set up a demonstration. Lynda arranged to have Rich Rethorn, System Studies’ Field Engineer in New York City, come down to Plantation, Florida and help to demonstrate their new 3708 Hydrogen Leak Detector. Since Rich had been working with one of the first field units available in the United States, he had the most experience. From the outset both he and Lynda were enthusiastic about the capabilities of the hydrogen method, and before long I could see why.

During our first attempt at leak locating with the new equipment in the field, we were able to find a number of tough leaks in a quarter mile-long section of buried cable—without even having to pound holes in the ground. This pretty much convinced me that the Hydrogen Leak Detector was worth pursuing for BellSouth. But I knew it would meet some resistance, primarily because it requires the use of hydrogen gas (remember the Hindenburg?).

Buffering the Hydrogen Concern
Sure enough, several people voiced fears about the use of hydrogen. That’s understandable—after all, isn’t hydrogen flammable and explosive? In some concentrations and mixtures, sure it is. But not the hydrogen tracer gas recommended for use with the new leak detection equipment. It uses a relatively dilute mixture of 5% hydrogen (H2) and 95% nitrogen (N2). In this mixture the hydrogen is traced by the detector, while the nitrogen acts as a buffer.

Unbuffered hydrogen in certain concentrations and conditions becomes flammable when mixed with air or oxygen. But as long as a commercially-available, green label mixture of not more than 5% hydrogen and 95% nitrogen is used, there is absolutely no risk involved. I have since learned that in Sweden they use an ever higher concentration of hydrogen in their gas mixture (10% H2 and 90% N2) without any problem, but the manufacturer recommends that the 5% hydrogen maximum be used here in the states.

Tracer Gas Characteristics
One of the reasons why hydrogen tracer gas is so effective for leak locating is because hydrogen is one of the smallest molecules and the lightest of all gasses (about 15 times lighter than air). Hydrogen has the ability to rise through surfaces even as dense as concrete. This saves valuable time when searching for those conduit leaks between manholes.

Hydrogen also provides nearly instantaneous readings. You can turn off the gas (take it off the cable), and in the matter of few seconds the Hydrogen Leak Detector will show a zero reading. In manholes, hydrogen is much better than helium in pinpointing a leak because helium has a tendency to swirl around some. You’ll pick up strong readings in numerous locations in the manhole. Conversely, if you saturate a manhole or area with the hydrogen tracer gas, you can wait a few minutes for it to clear and start again. This makes it possible to quickly identify and confirm the location of a leak.

Repeated Success
Once we got the word out about the capabilities of the new Hydrogen Leak Detector, we were able to generate considerable interest. In August of last year System Studies came back for another successful demonstration of the product—this time for members of our Air Pressure Advisory Board. Once again, the equipment worked beautifully, and we were able to locate several leaks in a buried cable outside of our meeting facilities.

This really started the ball rolling. By September, the product was approved in BellSouth, and in December we purchased our first Field Unit Hydrogen Leak Detector along with a Surface Probe. The Surface Probe is a rod with an attached two-speed vacuum pump and a rubber boot, which makes it possible to effectively seal off the surface area during the gas sampling process. The pump provides suction for the boot and helps to move the gas through an internal tube to the sensor located in the pump housing.

Shortly after we bought this equipment, Facility Technician, Jerry Frage, found a conduit leak under the concrete in a busy intersection in Ft. Lauderdale. Since the cable was not in alarm, we were not about to shut down traffic at this location for a dig. But shortly afterwards, we found another section leak that we had been trying to locate for well over a year. We dug this one up and fixed it.

The Right Tool for the Job
In addition to the 3708 Field Unit Hydrogen Leak Detector that we purchased, System Studies also sells a smaller, more portable version. This model, called the 3707 Hand-held Hydrogen Leak Detector, works as well as the larger unit, but it is does not accept the Surface Probe attachment or any of the accessories that are available for the larger unit.

While either tool can be used to locate leaks successfully in a manhole environment, the hand-held model is more practical in these locations. For one thing it is much lighter and, when it is not being used, it can be worn comfortably on the hip using its belt-mounted clip. Having two hands free makes it much easier to climb in and out of manholes. The larger unit weighs a few pounds more and is meant to be worn over the shoulder. Consequently, it can be a little more cumbersome, but not enough to make it impractical.

Both units provide an audible ticking sound, similar to a Geiger counter, that increases in frequency as you zero in on a leak. So, in congested, dimly lit manholes, you don’t even need to reference the detector’s LED display (hand-held detector) or meter (larger field unit) when “sniffing” for a leak. Both units start clicking faster as you near the leak, eventually reaching a more frantic pace to indicate that you have found the leak.

By the way, you can continue to use the audible reference for leak locating outside the manhole in noisy outdoor environments because headphones are available for both units. This capability is especially important in the busy Ft. Lauderdale area.

Advantages Over Other Leak Detection Methods
One of the things I like most about the new Hydrogen Leak Detector, compared with other leak locating methods, such as an ultrasonic leak detector, for example, is its ability to find the big leaks (see sidebar). These are the ones that cannot be heard using the ultrasonic.

Also with the hydrogen method, the entire leak locating process is much faster. For example, when looking for high flowing cables, we first compare air pipe manifold flow rates with optimum air usage information to determine where to start. Then we visit the manhole location and identify the highest flowing cable. Before we leave, we place hydrogen/nitrogen tracer gas on the cable, set the flow rate between 10 and 15 standard cubic feet per hour (SCFH), and check the manhole and/or adjacent manholes thoroughly for leaks. In most situations, we’ll find the high flowing leak within a few hours—unless it’s located in a section between manholes.

If this is the case, we’ll adjust the flow rate of the tracer gas down to about 4 SCFH, and leave it on overnight. The next morning, we can go after the leak right away with the Field Unit and Surface Probe. This equipment makes it possible to save valuable leak locating time by not having to drill or pound holes in the ground surface—even if that surface is concrete or asphalt. Once we find the leak, we then confirm the location quickly by turning the gas off, waiting ten or fifteen minutes, and checking again.

I’ve even heard of some people placing the tracer gas in an air pipe to see if the pipe is leaking. With this technique, it is possible not only to track system damaging leaks in the air pipe, but also to check for multiple cable leaks as the gas works its way through the air pipe manifolds into the cables.

A Safe Bet on Improved Performance
There are numerous leak locating situations where the hydrogen detector can be used successfully. The fastest and most effective application is with direct buried cables, but as we become more familiar with the equipment and the hydrogen gas method, we’re seeing how it can be used in variety of applications, particularly for leak locating in manholes.

Helium may have its applications, and the ultrasonic leak detector is certainly not ready for the junk yard, but I’m willing to put my money on the hydrogen leak detection method. It’s a safe bet for improved leak locating and a guaranteed return on investment. I don’t know if I would have made the same wager a few years ago, but in the Ft. Lauderdale area we’ve to realize that our #1 leak locating tool is the Hydrogen Leak Detector.


Hydrogen Leak Detection – The Big Leak FinderWhen searching for those high flowing leaks, don’t mistake sound for substance. As the saying goes, “If you can hear it, that ain’t it.” Some people mistakenly believe that the louder the noise, the bigger the leak. Well, it just isn’t so. One of the biggest leak indicators, other than a manhole filled with water, just might be the Hydrogen Leak Detector. It can help you find those high flowing leaks at or near air pipe manifolds, in the central office at equipment panels, and in the CO vault at plug locations. And once you’ve found one or two of these leaks, you’ve already paid for the new equipment.


About the Author: Mr. Walt Dreyfus, currently in charge of Air Pressure for South Broward County, Florida, has been with BellSouth Communications for 41 years. His responsibilities include proactive maintenance
 

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