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Detect or find gas leaks in natural gas or LP gas / propane piping, fittings, & appliances:
This article describes how to find gas leaks on LP or natural gas piping, regulators, or appliances, and it provides free sample draft home inspection report language for reporting defects in oil and gas piping at residential properties. This article series provides descriptions and photographs of unsafe gas piping, indications of unsafe or improperly operating gas appliances, gas meters, and other gas installation defects are provided.
We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.
How to Test or Look for LP Gas System Leaks
Here we outline some common procedures used to test gas piping and fittings for leaks. These procedures should work equally well for both
LP gas (propane or bottled gas) systems and for natural gas (piped-in gas from a gas utility company) systems.
Watch out: improper installation and even improper inspection and testing methods involving natural or "LP" gas can involve
dangerous conditions and risk fire or explosion. If you smell gas you should leave the building immediately and should do so without doing anything that could create a spark such as operating a light switch or telephone. From a safe location, call your gas company's
emergency line and/or your fire department. The text provided here is a working draft and may be incomplete or inaccurate.
NOTICE: while example report language is provided here, reproduction of this or any of our web pages or their contents at other websites
or in printed documents for sale is prohibited.
Our photo at above left of an LP gas line shutoff shows black staining around the shutoff valve and flare fitting, with some of the black worn away - previously there had been an LP gas leak at this location.
General Safety Warnings for LP or "bottled" or "propane" Gas Installations & Inspections
Immediate LP or natural gas safety hazards: if there is evidence of an LP or natural gas leak at a building, gas odors, for example, you should:
Do not do anything that is likely to cause a gas explosion, such as lighting a match, operating an electrical switch, or even using a telephone in the building
Leave the building immediately and keep a safe distance away - 100 feet or more.
Notify other building occupants of the safety concern
Contact the local gas company and/or fire department
Heating equipment which the inspector (or building occupant or manager) judges to be an immediate life safety hazard should be shut down and appropriate emergency services called.
Pressure testing a gas piping system for evidence of gas leaks
These two methods are generally used to test a gas piping distribution system to see if leaks are present.
Low Pressure Method Gas leak tests by gas service technicians generally include the following steps:
All gas piping connections, valves, and appliance connections and valves are inspected visually for tightness and good condition
A gas pressure gauge [such as the Fisher™ Type 50P-2 gas pressure gauge] is connected to a burner orfice
The gas service valve is opened to permit gas to flow into the gas piping distribution system, and then the valve is closed again, securely
The gas pressure gauge should read eight inches of water column in pressure (previously 9 inches, earlier eleven inches of water column) and should hold steady.
The gas pressure at the point of testing, say a gas-fired heating appliance, is bled off slowly until the gas pressure test instrument gauge
indicates nine inches of water column.
The system is monitored for any pressure drop for at least three minutes. If no pressure drop is detected the system is considered not leaking.
High pressure gas leak method is also used by gas service technicians and includes steps similar to those above, using a special
fitting [such as the Fisher(TM) Type J600 test block] installed between the service valve outlet port at the LP gas tank. The service valve
is opened,as above, to pressurize the gas piping, and the system is bled down to a test pressure of 10 psig, then monitored for at least
three minutes to check for a pressure drop.
Our photo above shows Con Edison workers performing gas line replacement & repair work on Washington Avenue in Brooklyn, NY in April 2015. In 2015 the National Transportation Board found that in 2014 a large gas explosion in East Harlem in Brooklyn NY that destroyed two five-story buildings and killed eight people was probably caused by a poorly welded joint in a Con Edison gas line and a break in an old city sewer line. The NTSB previously noted a leaky cast iron gas main that had been installed in 1887.
Thanks to reader Tony Martinez for updating our data on the proper pressure for LP or Natural Gas leak testing. Thanks to another reader JR, an industry manager familiar with gas pressures, who adds that these two fuel gases operate at different pressures. In residential appliances
Natural Gas system pressure: Natural gas operates at a nominal pressure of 7” WC (about 0.253 psi)
LPG or Liquid Propage Gas system pressure: LP gas or propane operates at a nominal pressure of 11” WC (about 0.397 psi)
Actual NG or LPG gas pressures vary: [Note: the exact pressure you see in the building at an appliance may vary from these numbers depending on the gas distribution piping system size, diameter, number of appliances served, number of appliances operating, regulator adjustment, and other factors.
See LP or Natural Gas Pressures for a table showing the range of variation
in LP gas pressure in the tank at various temperatures. - Ed.]
Watch out: Extinguish gas pilot lights - in order to perform pressure-testing methods for LP or natural gas leak detection as discussed above, you will need to extinguish the pilot lights on all gas-fired appliances in the building, and the pilot lights will need to be re-lit again after testing is complete.
Methods used to find and identify points of gas leaks in a gas piping distribution system or at a gas appliance
Visual Inspection for Evidence of Gas Leaks in fuel gas lines and appliances:
Our photograph at below left shows black stains on copper tubing at the flare fitting connecting an LP gas line to a shutoff valve and at below right stains inside of a flare fitting on LPG piping.
Some service technicians
point to these stains on piping as an evidence of a possible chronic leak in the gas line at this point.
Indeed on disassembly of a 15-year old LP gas cooktop installed in a New York home I [DF] found this black-stained flare fitting at the connection to the gas inlet nipple of the cooktop. Owners had occasionally smelled a whiff of LP gas but had been unable to find its source, thinking perhaps it was coming from the burners themselves. It wasn't .
See GAS COOKTOP INSTALLATION for photos of the old and new gas appliances involved.
Protracted leakage of fuel gas from a fitting can eventually leave black stains such as shown on the exterior of the flare fitting at above left and the interior of the flare fitting shown at above right.
Gas odors observed during gas piping inspection: The mercaptan put into LP gas and natural gas is inserted there by the
gas company as a safety feature so that people may notice that they have a dangerous (explosive) gas leak in
their home. Some people may confuse this odor with a septic tank gas odor.
See Diagnosing and Curing Sewer Gas Smells and Septic Tank Odors for a discussion of
sewer gas odors.
"Soap solution" bubble tests for gas leaks: a solution of soapy water (some technicians use dish soap and a brush or rag) is the most
common method used to test for gas leaks. As we noted earlier, Readers who are interested in gas leak detection equipment should review our article and gas testing warnings
Recommendations for gas measurement instruments & gas detector tubes
for indoor gas level tests which includes our description of use of the TIF8800 and similar gas detectors.
Soap solution is applied at every piping joint or connection (or the test instrument may be used carefully at and around every
connection or other suspect point) and the technician watches the soaped connection to see if soap bubbles are formed. Experts warn
that this method requires some experience and care. For example, a large gas leak may blow away the solution without forming
a soap bubble, or bubbles may be forming in a location which is physically hard to see.(Sometimes we can "see" around a corner
or to the back side of a pipe using our TIF 8800 combustible gas detector in these cases.)
Soap solution is applied along gas piping to lengths of piping to test for pinholes or mechanical damage if no leaks are found at threaded
or flared connectors but when gas leaks are evident in the system.
Gas leaks at gas valves: we very often find very small gas leaks at the seamed sides of some gas valves, such as those commonly
found on gas-fired domestic water heaters, especially when using the TIF 8800.
These leaks can be so miniscule that they do not show up
during a bubble test, and they are often present even on new valves. This may be a source of some disagreement between a home inspector,
building owner, and the gas service technician, and need to be handled with some judgment, experience, and reason.
Identifying Sources of Leaks at Brass Flare Fittings on LP Gas Piping Systems
Here are two brass flare fittings. One of them had a gouge that gave us a gas leak that was a bit tough to find until
we disassembled and inspected the leaky joint.
If tightening flared copper tubing connections does not easily correct a leak
at that joint, do not just over-tighten the joint (you may break the flare and cause a still larger leak), and do not
rely on pipe sealant inside of flared copper tubing fittings.
Open and inspect the flare fitting joint, and replace the flare fittings or
make a new copper tubing flared end if necessary.
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(Oct 24, 2014) cyndi said:
The gas company said there must be leaking gas pipes in the ceiling because it won't hold pressure. Do you know how the plumbers I hired to fix the issue will be able to know which pipes to fix so they dont break my ceiling and replace every pipe when it could just be one pipe? not sure how it works
(Nov 15, 2014) finding a leak said:
If the plumbers do not know a gas pipe from a water line then you definitely have the wrong plumbers. Gas lines that are supply lines should be black iron with threaded fittings. There should never be galvanized lines for gas. The gas will dissolve the oil in the galvanizing. If the ceiling is drywall and not readily accessible, the plumbers should make sure the leak is not in an exposed line first before tearing out ceiling. It may just be a flare nut that needs tightening or a leaky regulator on an appliance. The only thing you can do is hire people that are know to have a good reputation and not Joe Blow that is an expert on everything. Ask for references. For myself, I can give a homeowner the names of many many people I have worked for. If they cannot do that, tell them to have a nice day: you think you want to check some more.
(Jan 14, 2015) Anonymous said:
Help! We smell gas and gas company came out and confirmed there was a leak in system. They didn't identify where but they turned off gas valve and said to have a heating professional find & fix it. TWO visits by plumber and heating specialist failed to find a leak with both a pressure test and a gas meter. However we still smell gas in the heater area but it appears to be intermittent. Is this possible? I'm concerned about the safety of my family. Should we be in the home? What steps can we take?
Sounds as if you need to get the gas company back to perform more testing using combustible gas analyzers not just a pressure test. How those instruments are used and how carefully and how thoroughly makes a lot of difference in reliability of the result.
Intermittent odors could be due to intermittent leaks such as when equipment operates, or due to variations in building ventilation when a leak is constant.
Very small trace leaks do not necessarily cause an explosion but NO gas leak should go unrepaired. The risks are too serious.
Question: how can I fix a leak in an old lever type gas shutoff valve?
(July 22, 2015) Steve Kohan said:
I have a gas leak at the shutoff valve were the knob enters the pipe. How do I fix this small leak on a old lever type shutoff valve?
Unless the gas leak is due to an improperly-tightened fitting or a poorly-made flange on gas piping that can be corrected, you'll have to replace the valve. Sorry. NO external fix such as a patch, tape, or goop would be safe.
Question: repair a line breakage a foot from tank at the bottom
(Sept 11, 2015) Tim said:
can you repair a line breakage a foot from tank at the bottom, right before it goes into the ground, without replacing whole line that goes to the house?
What are we discussing here? A leak in a tank, in gas piping, or in some other type of piping.
Any piping or gas line can be repaired using proper fittings and safety measures (like turning off the gas supply and testing the repair for leaks), but the question of how much line needs replacement should be decided *after* an assessment of the condition of the rest of the piping; if it's deteriorated it's unsafe and thence patching an immediate leak is inadequate and also unsafe.
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Questions & answers or comments about troubleshooting LP gas or natural gas leaks in gas piping or appliances .
Try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
National Fuel Gas Code, 1988 articles 2.6.2, 2.6.3, & 3.4.2 "Piping in Partitions". Also NFPA 58 Code. See ANSI Z223.1-NFPA 54.
Residential Gas Hot Water Heater Pocket Partner - Testing and Trouble Shooting, State Corp., Ashland City, TN 37015
U.S. Energy Information Administration - eia.doe.gov/
U.S. Environmental Protection Agency - epa.gov/solar/energy-and-you/affect/natural-gas.html
At Natural Gas.Org www.naturalgas.org/environment/naturalgas.asp#emission you’ll find a table of combustion products
At geocities.com/rainforest/6847/report1.html is an interesting and detailed though not “neutral” report on the components and contaminants in the combustion of natural gas. You’ll see a long long list of emissions products, but look again – most of the contaminant levels listed are in the picograms.
apvgn.pt/documentacao/iangv_rep_part1.pdf lists the components in natural gas exhaust from vehicles
The Need Project, Manassas, VA: need.org/needpdf/infobook_activities/SecInfo/NGasS.pdf
Kroschwitz, Jacqueline I., and Mary Howe-Grant (eds.). "Gas, Natural." In Encyclopedia of Chemical Technology. 4th ed., vol. 12. New York: John Wiley and Sons, Inc., 1993.
Tussing, Arlon R., & Bob Tippee. The Natural Gas Industry: Evolution, Structure, and Economics. 2nd ed. Tulsa, OK: PennWell Publishing, 1995.
Thanks to reader Tony Martinez for technical editing regarding the test pressures for gas leak evaluation - 3/19/2010.
Thanks to reader JR for discussing LP and natural gas operating pressures and leak detection safety, October 2010.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
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