LEAK DETECTION - HELIUM METHOD
Helium can be used for detecting leaks in embedded or buried pipes where other detection methods fail. Not all broken tubes will make a sound, so acoustic detection is not 100% effective, and it has considerably lower sensitivity than helium. Heat sensors require enough hot water to leave the broken pipe to form a large enough area to detect a difference. Helium can exit any break in a pipe, rise to the surface and be detected. The helium method excels on very small breaks and broken tubes located under bath tubs, shower stalls, walls, cabinets, fireplace hearths or just about any place an installer might lay them in the slab. In most cases the location of the leak can be determined within a few inches, greatly reducing the area impacted by repairs.
Some facts on helium gas that make it a prime candidate for detection:
• Helium is non toxic, inert, and only 5 parts per million in the atmosphere. It will have virtually no affect on piping and its low concentration in atmosphere makes it easy to identify leaks.
• Helium is the second smallest molecule. It can escape through the smallest crack or fissure.
• Helium can permeate through concrete, carpet, carpet pad, tile floors, wood floors (sheet vinyl is a little more difficult but not impossible).
• It is relatively inexpensive and readily available from any specialty gas supplier.
To save a tremendous amount of time and to do a quality job it is necessary to have a piece of equipment that can detect less than 50 parts per million. Machines that can only detect down to 200 to 300 parts per million are considerably less expensive but will not be able to locate many of the broken tubes and require covering every square inch of floor space. Machines that can detect less than 50 ppm can cover 1,000ft2 in fewer than thirty minutes. This type of detector has a sampling pump which "sniffs" (draws in) the air and flows it over a permeable membrane that allows helium to pass through it and be detected. Other gasses cannot penetrate the membrane. The amount of helium detected is read out on a digital display in parts per million. Most helium leak detectors weigh over 100 pounds and require a 120VAC supply. However, there is also a lightweight (5.7 pounds), battery powered machine that has nearly the same sensitivity as expensive mass spectrometers. This instrument was originally developed for detecting leaks in gas-purged underground telecommunications cables.
Broken tubes are often found where concrete cracks; therefore, it is easy to pin point these types of breaks because the helium is able to travel up through the open crack. Pipes leaking due to electrolysis and corrosion can be anywhere in the slab; thereby, taking a little more time to locate because the helium has to work its way up through solid concrete.
1. Leak Test
Do a hydrostatic or pressure decay test to determine if there is a leak in the system.
2. Remove Water
Remove the water from the radiant floor tubing. Compressed nitrogen works best as air compressors can contaminate the piping with oil or debris.
3. Don't Rush
FROM THIS POINT ON DO NOT BE IN A RUSH! If you saturate under the slab and fill the building with helium gas, you will not be able to pin point leaks.
4. Fill with Helium
Fill the system with helium gas. Start small; do not pressurize the system to its working pressure. It is not necessary to maintain a constant pressure in the system, because the area around the broken tube will become saturated with helium and will take quite a while to dissipate.
5. Sniff for Leaks
Pass the detector over the floor while watching the LED indicator. A rapid increase in parts per million will indicate the location of a leak.
6. Fix Leak(s)
When a broken tube is located, stop and fix it. Then pressurize the system again and look for the next broken tube (always assume there is one more broken tube, it will save a lot of time in the long run).
7. Continue Search
As breaks in the tubes get smaller it may be necessary to increase the pressure to make them easier to detect. This is a judgment call since each system, floor, and building is different.
8. Leak Test
When all of the leaks have been repaired, do a pressure decay test before refilling the system with water to avoid having to fill the system with water and do a hydrostatic pressure test.
Courtesy of Agilent Technologies, Inc.