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Old 11-29-2011, 09:25 AM   #1
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Gas Pipe Pressure Testing?


What are the proper steps for pressure testing black iron pipe meant for natural gas? A step by step guide would be amazing! Thanks for any advice.

Some of the things I have already encountered right or wrong on this subject include:
I can't use my pressure gauges from the garage (needs to be 1/10psi increments)
Flex hoses for appliances need to be disconnected or the ball valve before them must be turned off and/or everything capped
Disconnect on the house side of the main meter (Don't go thru the METER!)
Suggestions of PSI and LENGTH of test recommended are different

Backdrop: I installed a new high efficiency furnace, replaced all the ductwork using proper software and installing dampers on each supply for further system balancing, sidenote: the house used to be one of my mother's rental properties and we had the ductwork cleaned between each tenant-> not worth a dime, absolutely disgusting . I piped all the new gas line, soapy water method passed flying colors. I bought a Extech ex40 combustible gas sniffer, an existing 1" union on the main line into the house failed the gas sniffer but not the soapy water test. Retightened, let the area air out, passed soapy water failed gas sniffer. Broke down cleaned everything replaced 1" union with new, turned gas on soapy water yes gas sniffer NO! Frustrated but have checked the gas sniffer against other gas lines that passed the soapy water method. So, taking the gas sniffer seriously, it seems to pinpoint the leak very well. I have worked on higher pressure gas line and high pressure city water lines, live taps etc. From what I read, it is more difficult to catch a residential small line leak due to the low psi around 2 or so? Frustrated but moving on to pressure test for piece of mind. Any tips on how to check the pressure would be amazing, I assume I have to evacuate the line of any gas before pressuring with air? When done testing with full lines of air, must the line be purged?

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Old 11-29-2011, 09:44 AM   #2
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Gas Pipe Pressure Testing?


Here in DC the building inspector needs to see a gauge, on the terminus of the line (where the flex line would be attached) that shows the line pressurized. I don't think the line needs to be purged before it is pressurized...gas is gas, a leak does not care whether it is natural gas or air.

This I think is a new requirement for close-in inspection because my plumber was not familiar with it. I don't recall what he psi he pressurized the line to and I can't find reference to it anywhere by Googling although I seem to recall seeing the gauge standing at 20 psi. But he left the gauge on for the inspector to see so it was there for at least 48 hours. He used a Husky bicycle pump to pressurize the line.


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Old 11-30-2011, 04:27 AM   #3
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Gas Pipe Pressure Testing?


Correct about meter. Disconnect flex and attach guage. You should use the correct fitting for this. Gauge is not special. The one I use is incremented in 2 psi increments. Any shut off valves at appliances should be disconnected and the pipe capped. Do not test through a shut off valve. After all of the new pipe is capped, with a test gauge at one end, pump it up to around 15 psi. It has to hold with no more than a few psi drop for ten minutes. Those numbers could vary with different areas, inspectors.
Basically, they want to see pressure holding steady for ten or fifteen minutes.
Remember, the pressure after the meter, going to appliances, is only a few ounces. Like 1/2 a pound. So if it holds 15 or 20 psi for ten minutes, it's good to go.
The inspector is going to check that the pipe is capped, that it has pressure, and holds it.

And that the pipe is properly supported, clamped.
Usually, he will look at gauge, release a pound or so of pressure to check that the gauge works, walk around and check everything is capped, come back to check pressure is where it was, put the green sticker on the pipe and you're done.
Make sure it is ready and pressurized when he gets there.
After, remove caps and hook up. Usually the gas company is then called by inspector and they will come turn gas on and check for leaks at flex lines (where you had caps on )
Did you put drip tubes in at each appliance?

No purging or evacuating of air required. When it is filled with gas and valve opened to appliance to light it, the air will come out.

Last edited by jammin06; 11-30-2011 at 04:30 AM.
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Old 11-30-2011, 04:44 AM   #4
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Gas Pipe Pressure Testing?


Reread your post. Unions are not recommended. Very hard to seal. You just have to reef on them. Use couplings if possible. Hope you didn't use teflon tape. Grey pipe dope better.
Go get a test fitting. 3/4" male pipe thread on one end. Schraeder valve ( like bicycle tube valve ) on the other end. Psi gauge threaded into top
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Old 11-30-2011, 07:27 AM   #5
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Gas Pipe Pressure Testing?


Thanks for the help, so I'm pretty sure I got the few answers I was looking for. I already picked up the gauge and such from the local plumbing supplier yesterday after posting, I'll give it a whirl today. Have a good one!

Yes, I use pipe dope, yes, each appliance has a sediment/drip trap, yes, I understand compression unions are not ideal and if I were to do the original install years and years ago I would've avoided it haha, but they didn't and I would've fought to get a regular coupler based on the other lines in the house.
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