Is black gas pipe ever completely leak free?

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MJL

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After months of chasing down one tiny leak after another in my new LP gas piping installation, I have to wonder if anyone ever gets these things *completely* leak free? I have about 100ft of pipe overall and it can easily hold 10psi for 15 minutes, which seems to be the requirement for passing inspection in most places. Even 30, 50, or 70 psi for a day or two. But given a few days, the pressure always starts dropping. And I always find a tiny leak, fix it, and repeat again and again. I tore the whole system out and replumbed it a couple of weeks ago, meticulously cleaning every thread and joint with acetone, and using Hercules Block because it seems to be recommended everywhere for foolproof leak-free joints. Two days went by at 30psi with no problem. The following morning, one psi less. Now several days later I'm down to 20psi. There are no appliances attached, every outlet is capped, and I fill the system via schrader valve. The valve and gauge were originally part of the leakage problem, but have been fine since I resealed them.

So I'm just curious to hear from the professionals out there: what is reasonable/expected/acceptable? When it comes to gas, I would think that ANY leak would be unacceptable. And I understand that pipe which leaks at 10 psi or higher might not leak at all when subject to the much lower LP gas pressure. But what's the consensus here?
 

John Gayewski

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It shouldn't leak. It's the Schrader valve. Any gas pressure will change with temperature change. Air will defuse through certain materials. The reason not to test over long periods of time is because static pressure in a closed system can/ will change.
 

MJL

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The schrader valve isn't leaking, and the temperature hasn't changed enough to cause a 10psi drop. I'm actually finding leaks at joints (soap spray bubbles). I'm just curious what the threshold is for people who do this kind of work day in, day out. Do they do a 10psi test for 15 minutes and call it good, or do they ever monitor over days or weeks? If not, is it safe to assume that many of these systems would leak at 10psi+ over an extended period, but it's just not being caught because installers don't monitor for that long?
 

Fitter30

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Any of your black pipe system did u cut and thread any pipe? Did u check if the thread was the correct depth? 2.5 turns with no dope till it gets tight by hand with a 90*. What type of dope did u use? Most gas systems have very little volume any leak shows up quickly within 30 minutes or less. Any appliance needs to be valved off.
 

Reach4

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I am not a pro, but I suspect longer wrenches would help.

I would also comment that most residential gas lines carry about 1/4 psi.
 

jadnashua

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Put a good cap on your Schrader valve that has a nice O-ring in it, then test again...Schrader valves DO leak...a good cap can make a huge difference.

Unless the temperature of the whole system remains constant, pressure will change, too.
 

John Gayewski

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The temperature change can cause plenty of PSI change. It's based on the volume of air so the more pressure you put on the more volume will change, Which in turn changes the pressure. If you have a portion of gas piping outside there's no controlling the temp. If you are finding actual leaks your pipe is not threaded correctly, Or you don't have enough thread engagement.

Hydronic systems last 50 years plus, using black pipe and have no leaks.
 

MJL

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Any of your black pipe system did u cut and thread any pipe? Did u check if the thread was the correct depth? 2.5 turns with no dope till it gets tight by hand with a 90*. What type of dope did u use? Most gas systems have very little volume any leak shows up quickly within 30 minutes or less. Any appliance needs to be valved off.

Yes, I threaded some of it. To the correct depth, according to Ridgid instructions. I originally used Rectorseal yellow (#5, I think) for dope. This time around is was Hercules Block. No appliances connected. All outlets capped.
 

MJL

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Put a good cap on your Schrader valve that has a nice O-ring in it, then test again...Schrader valves DO leak...a good cap can make a huge difference.

Unless the temperature of the whole system remains constant, pressure will change, too.

I understand, but the valve is not leaking. No bubbles when sprayed. As noted before, I've found the leaks and they've all been at pipe joints. I have a thermometer in the basement and temperature has fluctuated maybe a couple of degrees. Definitely not enough for a 10psi drop. And the pressure just continues to drop. It never rises.
 

John Gayewski

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I understand, but the valve is not leaking. No bubbles when sprayed. As noted before, I've found the leaks and they've all been at pipe joints. I have a thermometer in the basement and temperature has fluctuated maybe a couple of degrees. Definitely not enough for a 10psi drop. And the pressure just continues to drop. It never rises.
To end this you either have a leak or you don't. To find that out test it with a 0-5 psi gauge for 15 min. You should loose nothing. Not even a 10th of a psi. If you do it's leaking.
 

MJL

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The temperature change can cause plenty of PSI change. It's based on the volume of air so the more pressure you put on the more volume will change, Which in turn changes the pressure. If you have a portion of gas piping outside there's no controlling the temp. If you are finding actual leaks your pipe is not threaded correctly, Or you don't have enough thread engagement.

Hydronic systems last 50 years plus, using black pipe and have no leaks.

I understand PV=nRT. But as I mentioned above, the couple of degrees change in temp wouldn't have made a 10psi drop. None of the piping is outside at this point. All in the basement, with a few stubouts through the floor. The temp is pretty consistent.

My question really was: how often do the pros go beyond the 10psi for 15 minutes code requirement? Do they ever test for longer?

Some of the pipe was bought threaded. Other pieces were threaded with a Ridgid 00R with brand new dies. Certainly some of the threads weren't perfect, but they will all hold 10psi for 15 minutes, no problem at all. It's the longer durations that leaks become apparent.
 

John Gayewski

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I understand PV=nRT. But as I mentioned above, the couple of degrees change in temp wouldn't have made a 10psi drop. None of the piping is outside at this point. All in the basement, with a few stubouts through the floor. The temp is pretty consistent.

My question really was: how often do the pros go beyond the 10psi for 15 minutes code requirement? Do they ever test for longer?

Some of the pipe was bought threaded. Other pieces were threaded with a Ridgid 00R with brand new dies. Certainly some of the threads weren't perfect, but they will all hold 10psi for 15 minutes, no problem at all. It's the longer durations that leaks become apparent.
Is there moisture in the air your using to test? I'm going bet that's a yes.

I usually try to test in the morning (while the climate is warming up for the day), then I check it on 15. If I can I let it set while I do other things and periodically check it. It always rises (due to the warmth) unless there's a leak.

The gauge your using isn't sensitive enough. Use a 0-5 lb. gauge. Or a 0-15 at most.
 

jadnashua

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We're getting a lot of pipe out of China...they don't always keep their threading tools sharp or keep the taper correct, or the length, so the interference fit on the taper may not wedge as tight as it should with the same effect. You may need a really good coat of pipe dope. With in-spec threads, it isn't that hard to make a tight joint. If the treads are torn or incorrect from dull dies, all bets are off. Worst case, a fitting has a pinhole in it.
 

MJL

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We're getting a lot of pipe out of China...they don't always keep their threading tools sharp or keep the taper correct, or the length, so the interference fit on the taper may not wedge as tight as it should with the same effect. You may need a really good coat of pipe dope. With in-spec threads, it isn't that hard to make a tight joint. If the treads are torn or incorrect from dull dies, all bets are off. Worst case, a fitting has a pinhole in it.

The pipe I've been using is from Indonesia. And it comes with threads from the factory that are unusable. But I've been unable to cut perfect threads in it, either. Always get at least some minor defect. None of the local supply houses even carry US pipe. All of it is overseas, and all of it has defects right off the shelf. Seems like everyone is getting around this problem by doubling up tape and dope. Which apparently does the job, but it seems like such a hack. How on earth does anyone do a competent job anymore with this stuff?
 

Jeff H Young

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2 days at 30 psi
We're getting a lot of pipe out of China...they don't always keep their threading tools sharp or keep the taper correct, or the length, so the interference fit on the taper may not wedge as tight as it should with the same effect. You may need a really good coat of pipe dope. With in-spec threads, it isn't that hard to make a tight joint. If the treads are torn or incorrect from dull dies, all bets are off. Worst case, a fitting has a pinhole in it.
Worst case still is a pin hole on the middle of a run of pipe! Had it happen on several occasions its tough to find because we usually concentrate only at fittings but sand holes on the fittings happen as well.
If it holds 20 or 30 psi with no drop for days there's no holes , or leaks on threads . My last threaded pipe job was over 5000 foot of 2 inch pipe . Not many leaks but we had some a few split fittings , some threads leaked . Did my best but between me and another guy we had 4 or 5 leaks. A lot of joints tons of offsets some places hard to get into . Gotta be on your toes try to look at every thread and fitting but so many variations things get missed but you will catch problems too so when you have 5 seconds to look at that fitting or thread closer. But a lot of times you know the fit isn't quite right and a judgement needs to be made whether to cut new threads , adjust dies, switch out the fitting, or put a couple more wraps of Teflon tape and some more dope on it. Or just push on and chance that the fit is good
 

Mr tee

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Testing at 30, 50 or 70 psi is overkill. 10 psi for 15 minutes is fine.
 

MJL

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Just wanted to follow up on this in case anyone is having similar problems. After reinstalling the system for a third time, this time with tape AND dope, the leaks appear to have resolved. I've had it pressurized at 15psi for a week now, and due to temp fluctuations the pressure has actually gone up slightly. I noticed that the tape/dope combo allowed the pipe to easily thread much deeper into the fittings, so this alone might be responsible for the better seal -- actually seems that it goes deeper than it should with maybe 1 or 2 threads showing in some cases, but whatever.
 

jadnashua

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There's a spec on how to thread tapered pipe, but that doesn't mean it's always followed or that the die or tap is sharp and the threads cut cleanly! The thing that won't work, is if the pipe bottoms out in the fitting, but as long as that's not happening, it should be able to get leak free. PTFE tape has less friction, so makes it easier to tighten things up. Throw pipe dope on top of it, and it can get slick. Works, though!
 
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