Leak detection

[mariomp]

Hi all,
I'm building an addition to my house with extensive natural gas piping for furnaces, pool, drier & BBQ.
I've installed a bunch of black pipe, closed all my valves, pressurized the system and guess what...
Yea, you guessed it, I've got a leak.
I found and fixed couple on few fittings and one on the valve.
I also found that my pressure gauge is leaking.
Addressed all those but its still leaking, what's worst, it’s leaking slowly.
I'm loosing about 10psi a day, when pressurized to 100psi.
So far I've used the simple soapy water and some stuff to put on the outside that’s supposed to hold bubbles longer. What makes the process more difficult is that I've ran the piped thru trussed (BTWn 1st & 2nd floor)
Do U know of anything that I can use to put on the inside with detector on the outside? I can't spend too much on it, but I obviously can't have leaks either.

Any help would be great,
Thanks,
Mario P.

[jrejre]

I'm not a pro. That said, nearly every time I have had this problem, it's been the valves. The inspectors have just had me take the valves off and screw in a plug for the test. That's certainly a cheap thing to try.

I hate to ask, but I assume you used the proper joint compound at each joint, right?

[Terry]

Many valves won't hold a 100 psi air test.

I would pull the valves and use caps instead for the test.
Make sure you have no leaks before you put the valves back in, and then soap test them.

[Gary Swart]

I prefer the old fashioned pipe compound over teflon tape. Used both, but the goop is easier to put on, and I've never had a leak using it. But, as noted earlier, the problem is very likely with the valves. Also, I've used the commercial fluid for testing, but I've had very good luck with using dishwashing detergent straight out of the bottle, not diluted. Use a small flat container like a margarine tub for the detergent, and an old toothbrush or small paint brush to apply it, then a good light so that you can get a good look it the valve/joint.

[hj]

Gas systems are tested at 10psi, unless they are medium/high pressure systsems then it is 60 psi. If you are using regular gas valves, not ball valves, they are probably marked, or tagged, for 10 psi maximum. Even after you get the main system tight, the inspectors should require a second test before approving it for the utility to turn on the meter. This one would be a 10 psi with all the valves installed, and turned to the "open" position, and the appliance flexible connectors attached and capped. So if you have bad valves that will not hold 10 psi now, they will not hold it then either.

[mariomp]

Thanks for your help.
So I used joint compound and it said that it had teflon but its white, I've seen the one used on my existing house (only 2 years old) was yellow, what's that all about?
Also, since I did put 100psi on the valves, I used all ball valves, do I have to replace them now or will they still be OK at the 10psi range?
Finally, how long should I let pressure sit at 10-12 psi to be satisfied that all it good?
Again, great forum.
Thanks,
Mario P.

[RioHyde]

Here we test gaslines at 30psi for 15 minutes. If you used ballvalves, check the packing nuts on them. On a system pumped up to 100psi that loses 10psi after 24 hrs (you said "a day" I'm assuming 24 hrs) I'd suspect a packing nut needed tightening.

[Gary Swart]

Yellow teflon tape is a bit thicker and is for use with gas, the thinner white is for water. My personal preference is the gooey stuff, but I know some plumber use both together, and some use just tape. I suppose it's a matter of personal preference, I don't know if there have been any scientific studies on the topic.

[mariomp]

Yellow teflon tape is a bit thicker and is for use with gas, the thinner white is for water. My personal preference is the gooey stuff, but I know some plumber use both together, and some use just tape. I suppose it's a matter of personal preference, I don't know if there have been any scientific studies on the topic.

I was asking about gooey stuff that looked yellow to me. Is there a diff between yellow and white plumber's putty? I always thought it was yellow contained Teflon and that's how U could tell it apart, but I have white stuff and it says "... with Teflon".

Again, Thanks for all the replies.

[RioHyde]

There are many different colors of pipe dope out there. I use ProDope (gray), Megalock (blue) or Gasoila (yellow) for gaslines. Most of the pipe dopes I've seen that are white contain teflon...not all are, but most. I usually use the white teflon pipe dope on anything water related for its ease of cleanup. They all serve the same purpose; to help create a gastight seal. What you used is fine for a gasline. I'd still check packing nuts.

just a little edit: some pipe dopes shouldnt be used on pvc (not that this is related to this gasline). Check the label to be sure its ok to use in your particular application.