Help Finding a gas leak

[Unofornaio]

Hey all,

I'm putting a new gas line in (under ground) to a bbg area at my house. I have pressure tested it at 16lbs with a gas gauge and air but I cannot seem to find the leak.

It is only 3 10' sticks, 1 30" piece and a stub up of 8" there are 2 couplings 2 elbows and one cap. This sounds like it should be easy but it is driving me NUTS. I have gas pipe dope on all the threads and the fittings are all nice and tight, I cannot figure out where I am loosing air. I almost bought a new gauge today but thought naa that cant be it the one I have is pretty new and I have only used it a couple of times after which I put it back in a zip lock bag for storage.

I have tried soap several times on all the joints and the gauge and there are NO BUBBLES that I can see. The leak is VERY small in that I'm loosing a little less than 1/2 lb over several hours. I have done my fair share of gas line and never had this much trouble, heck I redid this whole house and didn't have this much trouble. BTW everything is new, and the pipe is coated for underground use (green)

Any tips or tricks would be greatly appreciated.
Thanks.

[Les]

Uno,

You will pass inspection with that little of a loss. You won't even find that amount with fire I think I only had to hold pressure for 30 minutes. I know what you mean though - there are times when I swear I can smell gas but I can't find the source. I'm starting to think it is leaking from my BBQ valves.

Back to your problem; Do you have the line isolated from all the other pipe in the house? Applying that much pressure may cause any gas appliance to leak.

Les...

[Unofornaio]

Yea its a completely new run outside I haven't even tied it into the main yet. I wanted to test it first before I bury this section. I cant remember what I tested the rest of the house at but I didn't have any loss. I pumped this up to 16 because I figured why not thats how far the gauge goes I actually don't even know what psi a standard gas line runs at. Ill have to look it up. Didn't have the house part inspected nor will this be..shhhhh don't tell anyone.

thanks

[Les]

If I remember, the supply only runs at 4-6 lbs, not squat. I thought I had to pump mine up to 25. But as you are aware, every city and state has their own power trip.

Les...

[Unofornaio]

Sorry, I said 16 it was 15..

[Archena]

Hmmm, might not be worth the effort but maybe Teflon tape on all the connections? If there's no leak when pressurized then you know it's a connection and can strip the tape on one at a time until you locate the culprit.

[n2iko]

At my job we use an ultrasonic probe. Essentaily it is a an ampliphier attached
to a set of headphones that detects ultrasound and converts it into something we can hear with our ears. Picture a "radio" for sound. It tunes across the ultrasonic band and converts it into sound in the audible human ranges.
You can pick up a tiny leak this way. You heard it as a squealing in the headphones. Be prepared also to hear stuff you never thought possible like
air moving across the crass making a razzing type noise or the ants in the ground sort of singing and you can also hear bats' radar. Interesting stuff.

--mr.jim

[Unofornaio]

Thanks guys. I talked to the building inspector today and he told me that the code reads 10# for 15 min..or was it 10 min?.any way I have been holding 13 1/2 all day so I'm gonna back fill and move on.

I really do not like the idea of loosing air at all it just doesn't seem right but apparently this is acceptable.. I suppose that it makes sense that if the gas line runs at, I think he said 6 or 7 lbs that if I can hold over 13 but not 15 at 6 or 7 I shouldn't loose anything. Whatever...next project..I swear I cant see the day when I can come home and just sit out by the pool or on the patio and not have to be in the "thinking or planning mode" I cant even remember what that is like..

[mastergene]

I would back fill it too! But maybe just for the heck of it ..What if you took a heat gun A.K.A. blowdryer and while holding the 13.5psi ,you heated up the pipe and watched the guage? I am wondering if the compressed air is warm when its going in from the small oriface's its going thru and then as it cools the molecules shrink and thus the pressure drop. Isn't that the bernolli principle? just wondering way up here in the mountain.

[Unofornaio]

Thanks. yes the molecules defiantly expand and contract. During the night the pressure drops then gradually increases. Then when the pipe was in the sun the pressure went up.