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Ran gas line, won't hold pressure?

Post in 'DIY and General non-hearth advice' started by Badfish740, Mar 14, 2013.

  1. Badfish740

    Badfish740 Minister of Fire

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    Last weekend I ran a 1/2" gas line (black steel pipe) into my kitchen for the new gas range (we had all electric previously)-it's a pretty simple run. Starting from the kitchen there is a brass appliance shutoff which is connected to an 8" black nipple that goes down into the floor. At the end of that there is a 90 degree elbow connected to an 8' length of black pipe that runs through a joist bay straight out the back of the house. From there it 90s down to a 6" nipple, and then 90's along the wall using a tee with a plug in t the other end (for possible expansion one day) with a 10' length of pipe running along the side of the house to where the two 100lb propane tanks will be installed. All joints were sealed with the yellow teflon tape for gas lines.

    To test the system I rigged up a simple pressure test device consisting of a 1/2" black tee with a schrader valve (the kind you see on a tire), a ball valve (to seal off the pipe when pressurized), and a 0-30 psi pressure gauge. I closed the appliance shutoff in the house, went outside, connected my pressure tester, and used a hand pump to pressurize the line to 25 psi. I know that gas pressure is only about .5 psi, but schedule 40 black pipe is good to 150 psi, so i figured it wouldn't hurt to test it far beyond the normal working pressure just to be sure. I checked the gauge about 30 minutes later and the pressure had dropped from 25 to 20 psi. I then leak tested all of the joints with test solution. All joints checked out except for the joint between the 8" nipple coming up through the floor and the appliance shutoff-I got a lot of bubbles out of that one. I took it off, cleaned all of the old tape off, rewrapped it, and put it back on. At that point I repressurized the line to only 20 psi this time and retested the joint. No bubbles. I rechecked all other joints and again, no bubbles. I went to bed (11:00 p.m.) and rechecked the gauge this morning (7:00 a.m.-so about 8 hours) and the pressure had dropped to about 9 psi, but again, I had not seen any bubbles the night before when I checked the joints. What gives? Is the teflon no good? Should I be using pipe dope instead? I've seen plenty of shops where they use black pipe to run air lines that are holding 100-125 psi no problem so I can't see why my lines can't hold 20-25 psi?

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  2. stee6043

    stee6043 Minister of Fire

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    I doubt it's the tape. My first thought is crank it up to 50 psi, let it sit for a few hours, measure pressure, let it sit for a day, measure pressure again. I've been consistently surprised with how significantly air pressure changes with temperature. If you have a pipe that's both inside and outside the house you may well be seeing temp related pressure change (after your first leak fix).

    If you want a more stable test with instant results, use water!
  3. nate379

    nate379 Guest

    Yellow tape?

    I like Rector Seal, rare to use that and have leaks at the joints.
    PapaDave likes this.
  4. stee6043

    stee6043 Minister of Fire

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    And for what it's worth a whole slew of us guys from the boiler room are using black pipe for our systems. I used dope and rope on my pipe and it held pressure at 50psi without batting an eye.

    I used yellow tape only when I plumbed a CSST natural gas line to my garage and never had an issue.

    I think you are seeing temp issues or I suppose it's possible you have a warped fitting/nipple. You should see that with your leak test though.
  5. woodgeek

    woodgeek Minister of Fire

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    A 20% swing in pressure seems a bit large to explain with a temp swing, as it would correspond to a change in 80°F
  6. Lighting Up

    Lighting Up Feeling the Heat

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    I never used tape...always used pipe dope for black pipe and never had a leak.:)
    md
    fox9988 likes this.
  7. heat seeker

    heat seeker Minister of Fire

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    Some of your test equipment (gauge, etc.) may be sandbagging you, too. The pipe itself may have a defective spot in a wall, something a water test would easily show.

    And, be sure the ID of the pipe isn't larger that the OD of the pipe…….:p That causes a really large leak!
  8. Dune

    Dune Minister of Fire

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    Tape is kind of bogus for most things...I always use dope or dope and tape or thread, depending on the joint. I do a LOT of high pressure piping (3000 psi).
    Tape alone for me would be good for maybe air fittings or an emergency, if it was all I had.
    Now I know lots of people will bleat about how great tape is, but the bottom line is, tape without dope is a lot easier to screw up.
  9. Ehouse

    Ehouse Minister of Fire

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    I think if you had a leak at the brass shutoff joint initially, that's still the problem, even though you cleaned and reapplied it. You used less pressure and waited considerably longer on the second test. it's easy to crack or x-thread a fitting when going from brass to steel.

    Unrelated, but you didn't mention a drop leg or sediment trap beneath the shut off which is code here, so you might want to check on it before you hook everything up.
  10. Badfish740

    Badfish740 Minister of Fire

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    I'm just going to take it all apart and use dope-that Rectorseal stuff looks pretty good. Back when I had my truck running on WVO I built a pressurized heating device out of schedule 80 pipe that the oil would travel through on it's way to a centrifuge to be filtered. I used nothing but teflon tape for those joints and never had a leak at 90-120 psi with temperatures up to 160 degrees F. Of course, oil is a little thicker than air :p The other thing I'm going to do before I put it all back together is test each fitting (luckily there are only 4 in the system) by plugging one end and hooking up my pressure tester to the other and dunking the whole thing in water. I've read a lot of posts recently about plumbers cursing cheap Chinese sand-cast fittings as they have a tendency to have tiny pinholes in them :mad:
    scooby074 likes this.
  11. bmblank

    bmblank Minister of Fire

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    Most Teflon tape is actually contraindicated for use in gas lines. Most paste is ok for use in gas, but make sure to check the label, some are not. The gas actually degrades the tape. I believe there is a blue Teflon paste made just for gas lines.
  12. SmokinDiesel

    SmokinDiesel New Member

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    I work on gas systems everyday . I use only ProDope with no tape . Check the packing nut on the ball valve where the stem comes out for the handle , they usually leak . And yes the Chinese sand cast fittings are awful . Seen many with a little pin hole in them . Good Luck !
    ScotO likes this.
  13. stee6043

    stee6043 Minister of Fire

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    Ahh the internet...the land of misinformation.

    Yellow PTFE tape (Teflon) is widely (US, Canada, Europe) approved for use in gas lines of a certain size (1/2" to 2" I believe). You may want to double check your contraindicating list of plumbing does and don'ts.
  14. Badfish740

    Badfish740 Minister of Fire

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    Yep, yellow tape is what I was using-good tip on checking the packing nut on the appliance shutoff too-I'll be ticked if all this time it was just that leaking!!!
  15. bmblank

    bmblank Minister of Fire

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    Ok, i was unaware of any yellow tape. I've never seen or heard of it until now. Only kind I've seen in any of our stores is the standard white tape; that is usually contraindicated, but like i said, check labels.
    And a simple, "that's wrong, here's one that's made for it," would do.
  16. FanMan

    FanMan Feeling the Heat

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    When I ran the gas lines to my stove and heaters I used the yellow tape on all pipe threads (lots of brass fittings and dapters with flared copper tubing for the long runs) and didn't have any leaks at all. Tomorrow I'm replacing the electric clothes dryer with a gas one, so more new lines.
  17. Gary_602z

    Gary_602z Minister of Fire

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    Stupid question, but are you wrapping the tape in the right direction? That said I would only use paste on it rather then tape.

    Gary
  18. stee6043

    stee6043 Minister of Fire

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    Sorry there, bm. I wasn't trying to insult you. You were pretty firm in your position that most teflon is no good for gas. I was just trying to be equally firm in saying "umm, no, not quite right".
  19. yooperdave

    yooperdave Minister of Fire

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    Not only was I always told, but I was also taught to never use tape on gas line threads. It gives the potential of a piece of tape breaking loose and working its was to the gas control and lodging the control in the open position by not alowing the diaphram to seal completly when the control tries to shut off.
  20. xman23

    xman23 Minister of Fire

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    Did you cut and thread the pipe? What die did you use? They are not all water, gas tight.
  21. Badfish740

    Badfish740 Minister of Fire

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    Success! Last night I started pulling everything apart and this morning redid all of the piping with tape AND Rector Seal. When I got everything done I hooked my pressure tester up (after I had given it a good once over for leaks) and the pipes held 30 psi dead on the mark for four hours while I was out running errands with the wife. With that I hooked up the regulator, tank, got the stove in place, turned the gas on, bubble tested the lines, and wa'la... Turns out my high school teachers were wrong-there IS hope in dope ;lol I'll definitely never do gas piping again without it, that's for sure.
  22. tim1

    tim1 Member

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    I use a product called Leak lock. Tim
  23. MasterMech

    MasterMech Guest

    I work with high-vacuum plumbing (pressures down to about 1.0 x 10-6 torr) quite a bit. It's amazing what "leaks" and the statement that there is no such thing as a perfect seal is very true. Alcohol based pipe dope was the solution for me when I was trying to add fittings to a vacuum pump. The threads were exposed to oil and even though I knew the threads were good (drilled the caps and started the tap with the tailstock of our lathe, so I know the threads are straight. The fittings were extremely high-quality, SwageLok.) the damn things would leak even with tape, Pro-dope (which is good stuff BTW), or both applied. The alcohol based pipe dope was spec'd to be oil, LP and NG resistant and 3 years later all of those fittings are still vacuum tight. I still check 'em with a helium leak detector occasionally.

    Just because something is water tight does not mean it is air/gas tight as well. That's why we use helium to check for leaks on vacuum piping, small molecules find leaks that are absolutely miniscule.
  24. heat seeker

    heat seeker Minister of Fire

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    I used to love checking our EB welders for leaks with helium, still remember the old tester would squeal when it sensed the leak. (This was decades ago, technology has surely improved since then!)
  25. MasterMech

    MasterMech Guest

    Actually, not too much, leak detector has a remote display now but I can set it up to squeal like a pig. EB welders eh? These machines run EB guns as well, but they don't weld....

    http://en.wikipedia.org/wiki/Electron_beam_physical_vapor_deposition

    [​IMG]

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