Gas line leak check

I installed a run of black pipe for a propane stove installation. I'm sort of ready to call for an inspection, but I think I have a problem. I ran a leak test @30 psi and found 3 leaks including the valve on the tester. After fixing all that I found, it's still dropping from 30 to 26 in 6 hours. I would really like to find the last little leak, but I haven't been able to. I'm not sure it isn't still in the schrader valve. I just replace the core with an automotive valve core. I had put this piping together in steps, and tested along the way, so I'm pretty sure the leak is in the last several joints. Ive been soaping the joints like mad, but I can't find that last leak. Is this overkill and should I live with the 4 psi in 6 hr drop? Or is there another, better way to find the leak? I was thinking of getting it pressurized with R22 or R134a and using one of those electronic sniffers. I was also wondering if there was a dye that could be used. What do you think?
Barry

 

Under no circumstances can you proceed without finding that leak!! Propane is one of the most unforgiving gases around, one small leak and you could create a bomb!

You can use any kind of dishwasher soap that makes a lot of bubbles for your testing, you have to start soaping up the fittings themselves, not just the threads, if that dosen't find the leak you will have to soap up the pipe. The schrader valve should have a cap on it.

Using refrigerant to check the lines doesn't seem like a good idea, it too can be a safety hazard.

 

i have never had a problem finding a leak with dish soap and water. with 30 psi on the line it shouldnt be hard to find the leak/s. you might even try pumping it up to 50psi and checking again. 3-4 little teeny tiny leaks could be your problem.

the only reason for a gas lie to loose any pressure at all is from the air cooling over night and then it would only be 1-2psi for about a 20 deg. drop in temp but should rise again as it warms up.

i once put 5 psi on a natural gas test in the morning and it was close to 10 psi by the time the inspector got there in the afternoon

 

So I gather typically one does not see any pressure loss for days. That was a question since the code reads that the test is to be run for 10 minutes minimum. Surely I wouldn't see any pressure loss in 10 minutes. I think I found another source of a leak. I put my tester on a short pipe with a cap and it lost 3 psi in half an hour. I don't think this equates to 4 psi in 6 hrs for the whole system, but I'll see. I thought to look at the tester since the gauge is one thing I didn't soap up. I've got another gauge, a 100psi one, so I'll replace the one on my tester and give it another go. I've got my fingers crossed.

 

i use a gauge that goes to 15 psi and if you have a leak you will know it in about 10 mins. it is a $100 gauge though

 

I should be OK witha a 100 psi gauge. I'm allowed to test at as little as 1/5th full scale or 20 psi, and I've been using 30 psi.

 

if the line is going to be inspected you need to check with your local code authority as to what they want for the test specifically. normally for gas tests they dont want a 100psi gauge ass it is harder to tell if there is a leak than with a smaller more precise one such as a 30 psi gauge.

 

Probably true, but I think I do meet the letter of the law. I may ask the inspector if he would be ok with it.

The good news is I finally found the leak. Soap didn't do it for me. I finally gave up on looking. I figured regardless of where the leak was, I would be doing the same thing. So I just started taking things apart, a couple fittings at a time, and pressure testing. The leak turned out to be a bad thread in a section of pipe I had custom cut for me. So here's the big question. Since I don't have a servicable thread cutter, is it better to buy pre-cut lengths and have a few extra joints, or should I try again to get a piece cut to length? I didn't think it was that tough to cut threads, but of three pieces I had cut, two had threads that were unusable and one was the wrong length. I guess the third option is buying a used pipe threader that dies are available for (unlike my antique). I don't think my local tool rental rents pipe threaders. I don't see it on their price list, but I didn't ask either. What do you think?

 

if you are getting them cut somewhere like a big box store then i would do everything to find a rental place that has them. their lists dont always show everything. the problem with bigbox stores is their employees are shown how to operrate their machines but they dont get very good training or much practice and dont really know what they are doing.


pre-cut might be the way to go but remember that the more fittings the more places and chances for a leak.

good luck with your project

 

I went to 2 big box stores. At one, the machine looked brand new. I found one guy who had used it one time before. I gave him some advice and encouragement and he actually did a pretty good job. The other one looked like they cut a lot of pipe. The guy there looked like he knew what he was doing. I trusted him. That was my mistake. He cut the threads too deep. Both the bix box stores do have some pretty impressive threading tools. With their power lube, I doubt any hand threader could do such a nice job. The problem is it is still operator dependent to set up the tool. I do know one DIY oriented plumbing supply that does cut and thread pipe. It's an hour away, but may be worth the trip.

 

yeah them big boxes can afford them $3000 - $5000 machines

 

Yeah..they can afford the machines when they build the store...but then they can't afford to replace the dies when needed. Or train the poor folks who work there to use the machine correctly. Luckily I was trained by a pipefitter with 30 yrs on the job.