Natural gas line

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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.
Reply: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.JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply: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.
Reply:You know you can't just go welding on somebody's lines don't youAnd in some cases not even your ownBetter head these guys warningBacked my CATMA over your CARMA oops clusmy me  What would SATAN do ?? Miller Trailblazer 302 AirPakMiller Digital Elite  Optrel Welding HatArcair K4000Suitcase 12RC / 12 VSHypertherm PM-45Rage 3 sawRusty old Truck
Reply: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.
Reply: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.WELD TO LIVE LIVE TO RIDEA bad welder blames his equipment, a good weldor can lay a perfect bead on any thing
Reply: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.
Reply: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.
Reply: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.
Reply: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.
Reply:Thank's guys, I was hoping I could tell them something  other than, I am a chicken, LOLI'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.
Reply: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
Reply: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.
Reply: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.htmlLast edited by Birdwell4; 07-19-2011 at 09:43 PM.Reason: added link
Reply:Originally Posted by ironmangqThey 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.
Reply:Originally Posted by BTDLike this?http://www.tdwilliamson.com/Document...P_Brochure.pdfAt least that's the service I've used on past projects.
Reply: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. lolA 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 luckLast edited by slowhand; 07-20-2011 at 08:24 PM.
Reply:Originally Posted by Birdwell4he 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.
Reply: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'tmatter as long a O2 is zero. Positive pressure purge outflow can have enough HC vaporto 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 repairplan 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 treadBlackbird