How to find leak

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New Member
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Santa Barbara, CA

I have added a room and a water heater and have put in a new black pipe gas line starting at 1 1/4" still capped near the gas meter gradually narrowing down to 3/4" where a new tankless water heater will be. I also put in a tee to run a line to where my other water heater is in case I wish to switch it to tankless some day since it currently only has a 1/2" pipe over there. Total length of pipe is about 140 feet with 14 elbows and one tee. I have pressurized it to 15 psi and passed my gas inspection. However, I have noticed that after passing inspection, it has been losing about 0.5 psi per week. A loss of less than 0.1 PSI per day when the inspector only had to see it hold for 15 minutes was never going to be something the inspector could have seen. At first I thought it might be the gauge but I put a shutoff valve between the majority of the pipe and the gauge and it does not appear the small stub with the gauge that is losing pressure. I have soaped all the joints with the soap specifically made for looking for leaks and cannot find any. I have confirmed it is not a temperature issue since the temp has been stable in the morning when I check it. I have determined there must be a miniscule leak somewhere in the system. I used pipe rectorseal T + 2 for all joints.

So, I need some advice. I talked to one guy who came into work who has a son who is a plumber and he used to help him out. He said, I shouldn't worry about it since the operating pressure is 0.5 psi or less and it would not leak at that pressure if I am leaking so little at 15 psi. Is he right? I could justify that the reason the inspector only needs to see the gauge hold for 15 minutes is since they know that if it can do that, then any miniscule leak would not be a problem at 0.5 psi.

However, I am still a bit nervous but don't know what else to do. Is there some compound I could put in the pipe, pressurize it and then try to see if I smell it at the joints? Is it fine as is?

Thanks for your input.


In the Trades
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Seattle. WA
A leak that can not be detected by the usual practical tests, does not exist for all practical purposes. Let it rest. If you start smelling
gas after the line is put into use, you can continue the investigation easily enough.


Retired Defense Industry Engineer xxx
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New England
After the meter, the gas pressure is normally in the 0.5# may not leak then verses when it has 15# in it. It's possible that there is a small pinhole in a fitting (sand casting fault) or something else that may not be at the threads.
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