Natural gas line
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  1. #1
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    Apr 2011
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    Kansas City, Kansas
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    Natural gas line

    I've installed a lot of new gas line that was later treaded into the meter, but I haven't welded to any existing gas lines that have been in service I always turn them down. Is there a special procedure you should use before welding on existing line.

  2. #2
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    Apr 2008
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    NW ON Canada
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    Re: Natural gas line

    Are you certified to be welding on gas line?
    Around here, the gas companies use their own certified welders to do this type of work.
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  3. #3
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    Dec 2010
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    Re: Natural gas line

    First question id try to figure out , does your insurance cover it ? Mine restricts me from crane repairs and burglar bars, go figure rite , id check with your insurance to see if u can touch inservice lines before going any further. i know some people who do it around i could find out from them if ya want.
    I forgot how to change this.

  4. #4
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    Re: Natural gas line

    You know you can't just go welding on somebody's lines don't you

    And in some cases not even your own

    Better head these guys warning
    Backed my CATMA over your CARMA oops clusmy me

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  5. #5
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    Apr 2011
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    Re: Natural gas line

    Yes i'm certified to do it, and insurance is not a problem, I do new installations all the time. Around here everything in the building has to be welded but once it makes it outside it can be treaded. My question is about lines that have been shut off but need to be tied into, I've always turned these jobs down but I would like to know how it's done anyway. That way when I turn the customer down I can give an explanation.

  6. #6
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    Mar 2011
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    Bamberg Germany
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    Re: Natural gas line

    well if the line is off and it still has pressure its a pipe bomb, if the pressure has been bled off its a pipe bomb that "might" explode. i worked with a guy that tied in to the biulding main that had residual gas in the line, as soon as he burned thrugh with the torch the gas ignighted and shook the hole building and i had to change muh shorts. if you can purg it befor you do any thing.
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  7. #7
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    Feb 2010
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    Re: Natural gas line

    They do do hot taps where they weld onto a live gas line. The ones I have seen they weld a fitting onto the pipe where they are going to tie in and then pierce the pipe with a special tool and tie it into the new line going to the building. Im not really sure how it all works but I have seen it done.

  8. #8
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    Sep 2005
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    Cave Creek AZ
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    Re: Natural gas line

    If it is shut off, just purge the line and then treat it like a new install. If it is live, then the section you are welding on needs to be valved off then purged, or you need to use tapping equipment.

  9. #9
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    Jun 2009
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    TEXAS
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    398

    Re: Natural gas line

    i just got done with a gas company's "in service" testing. In Pa., gas companies are now going to 7018 when hot tapping onto high pressure gas line to eliminate hydrogen cracking. When you say, weld onto a line that has been shut off, do you mean onto a line that's open on one end ? As long as the gas company can convince me there is absolutely no gas in the line and none leaking out (b/c of a leaking valve), I 'll weld on it.

  10. #10
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    Mar 2011
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    red rock country
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    Re: Natural gas line

    The reason the hot taps work is because the concentration of natural gas in the pipe is high enough that it prevents ignition inside the pipe. I don't remember the exact concentrations but I believe it's somewhere around 15-24% natural gas that will ignite. a live line will be around 80 to 100 % natural gas. if the line is off you would have to purge it in order to get the concentration level way down.
    Remember it takes 4 things to start a fire ( yes 4) fuel, oxygen, heat AND chemical reaction (foams and powders extinguish fire by prohibiting the chemical reaction). call your local gas company and talk to a welder or the safety guy and they can explain it in much more detail.

  11. #11
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    Apr 2011
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    Kansas City, Kansas
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    Re: Natural gas line

    Thank's guys, I was hoping I could tell them something other than, I am a chicken, LOL

    I'll have to talk to the gas company, it sounds do able no cense in turning them down if it can be done safely.
    Last edited by woodweld1; 07-19-2011 at 03:14 PM.

  12. #12
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    May 2011
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    wisconsin
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    Re: Natural gas line

    Gotta say , atleast u were smart enough to ask before u went welding on the pipe bomb. Most would just pretend they know it all and end up hurting some one or them selves . ( ive read some threads on here , were people are just plain arogent ) . Never hurts to ask .
    >Innovations are what i leave behind for History<

  13. #13
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    Jun 2010
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    N.W.
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    42

    Re: Natural gas line

    I worked beside a mechanical contractor about 4 years ago in a insulation manufacturing plant doing retrofit work. That guy welded and "hot tapped" on 4" live natural gas line in 6 different spots for instrumentation ports. Made it look simple. Made me nervous as hell. Said it was pretty standard for him being a mechanical contractor.

  14. #14
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    Mar 2011
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    red rock country
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    Re: Natural gas line

    The biggest thing to do it safely is to have the tools to test the gas concentration. Like I said natural gas can only ignite in the right concentrations so if the pipe is completely full or completely empty, you'll be fine.

    I learned about all that stuff at my last job. I got to be in the ditch for lots of hot taps. the first was on a 30" mainline (running at 550 psi) my boss explained the procedure to me and said I was going to be the fire watch in the ditch, and to not worry that they did it "all the time". I called my wife, told her I loved her and to remember me if anything happened. Then I climbed into the ditch and handed the welder the torch end.
    I still find the whole thing slightly unsettling, even though I've been around dozens of them.

    I found this chart online about explosive concentrations Natural Gas is primarily methane.
    http://www.engineeringtoolbox.com/ex...its-d_423.html
    Last edited by Birdwell4; 07-19-2011 at 09:43 PM. Reason: added link

  15. #15
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    Dec 2009
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    Houston, Texas
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    Re: Natural gas line

    Quote Originally Posted by ironmangq View Post
    They do do hot taps where they weld onto a live gas line. The ones I have seen they weld a fitting onto the pipe where they are going to tie in and then pierce the pipe with a special tool and tie it into the new line going to the building. Im not really sure how it all works but I have seen it done.
    Like this?

    http://www.tdwilliamson.com/Document...P_Brochure.pdf

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  16. #16
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    Apr 2011
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    Re: Natural gas line

    Quote Originally Posted by BTD View Post
    Like this?

    http://www.tdwilliamson.com/Document...P_Brochure.pdf

    At least that's the service I've used on past projects.
    Thanks for the info. You have to admit that guy on that brocure looks a little stressed out. LOL

  17. #17
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    Sep 2010
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    eastern u.s.
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    Re: Natural gas line

    I have lots of experience making hot welds on main line pipelines up to 42" in diameter, but no experience making hot welds on gas lines inside houses, but I can imagine the dangers of such work, because I fully understand the dangers of making hot welds on loaded gas pipelines.

    Making hot welds are different than making tie-in welds on open existing gas lines. You should know the difference already.

    On tie-in work the thing that will save you is the purge. A good purge and its a pretty safe operation. A bad purge and somethings going to blow up.

    Without what we call "a sniffer" I don't think I'd attempt such work as you describe because I couldn't do it safely without one. Without a sniffer I could only guess that it was safe to actually weld on, where using a sniffer would tell me it was safe to do so. So I could not do this job safely even with all my experience welding on as many loaded and open gas pipelines as I have over the years. lol

    A gas sniffer is a gas concentration detector (?) that reads parts per million. Get the parts per million wrong and you're going to hear a large boom when you arc up your welder.

    Getting a good enough purge is a skill and it also depends on the situation at hand on how you go about doing it. Knowing how gas works helps but nothing takes the place of experience IMO. Handle the situation wrongly when a home is involved and you could easily burn it completely down to the ground I would think.

    Tapping into an existing (been in service) home gas line with an arc welder is nothing to take all that lightly IMO.

    Good luck
    Last edited by slowhand; 07-20-2011 at 08:24 PM.

  18. #18
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    Jan 2008
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    3,422

    Re: Natural gas line

    Quote Originally Posted by Birdwell4 View Post
    he time". I called my wife, told her I loved her and to remember me if anything happened. Then I climbed into the ditch and handed the welder the torch end.
    sounds like they gas welded it?

  19. #19
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    Oct 2007
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    Yuba City, CA
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    Re: Natural gas line

    In purging with inert gas-the purpose is to take to O2 level ideally to zero---no O2 inside-no bang.
    LEL meters will still show HC vapor content in a good purge outflow.

    With the heat of welding, more HC vapor is released and this can make LEL go kRAZY.....doesn't
    matter as long a O2 is zero.

    Positive pressure purge outflow can have enough HC vapor
    to create combustion and ignition is sometimes seen directly around the torch--
    ---which can be a rush.
    Doesn't matter--if O2's at zero and positive purge pressure.

    This sounds simple--the practice of it-isn't. As others have said, studying the situation,
    isolating the line (ideally with blockoffs, locking out any inlet valves), creating a repair
    plan and a purge plan, then monitoring the purge is all part of the deal.

    I'm surprised there haven't been any suggestions to fill it with water, use exhaust gas,
    or wave a lit torch over the open to make it bang......fools rush in, where angels fear to tread
    Blackbird

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