welding onto existing gas pipe ? evacuate?

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I need to tie some gas pipe into existing lines.     Most tie ins are on the 3'', main.    There is a union we can break apart near main valve.     I then was going to a far end and run nitrogen through it to hopefully evacuate oxygen.     I dont think I'll be able to get flow through every branch of reduced down pipe,  that tees off main though.     Its probally 250 feet of main and two or three times that amount branching off.       I've done this once before w/ propane lines but they were alot simpler routed and I had a experienced helper.      Questions are:      Is nitrogen the choice thing to use.    Is nitrogen heavier or lighter than oxygen?     How much purging does it take?     Does natural gas soak into the inner walls of the pipe over time?       Any words of advice or precautions that I'm leaving out or got wrong?        Anyone know of any tests to perform to see if oxygen is at safe level for welding?           Also thought of running compressed air through lines for half a day to move gas out before using nitrogen, but would that make it more dangerous?    Anyone have experince w/ this?
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Reply:Anyone have experince w/ this?They are all gone now!
Reply:No experience of this BUT the answer is very simple...FOLLOW THE WPS!!!!If there is no WPS in place (anyone doing this sort of work would've followed one when testing out) then you shouldn't be going anywhere near the line!Whats next, DIY hot tapping on a wing and a prayer
Reply:There is a procedure for doing such a thing.  A tee connection is welded onto the outside of the pipe then a gate valve and boring attachment is mounted on the leg of the tee.  The hole is cut into the main with a cutter then the cutter is withdrawn back to the other side of the gate valve and the gate valve closed.  The cutter unit is operated through a shaft and stuffing box to prevent gas leakage.  I have no personal experience with this however I have read several articles on this procedure.
Reply:That explains what I have seen. I have seen the local gas co. use what looked like a saddle to tie into pipe like you described. I thought they were bolt on with sealant but maybe I was wrong. I'll have to pay closer attention.Not to be a smart @ss, but I would think the local gas co would have an exact procedure they want you to follow. They get kind of cranky when a main blows up and takes out a block, even if they marked the street wrong for some one digging.
Reply:Propane is heavier than air.Natural gas is lighter than air.I would not weld on a gas main at all.There must be some kind of threaded connection or something.I will look this up.
Reply:I looked around on the web... You can purchase a hot tapping procedure from Edison group for 12,000 US!!  If you can stop flow and purge and use a gas detector on the exhausting gas you still will have to have a proper weld procedure.  These things should be left to experts.  The fees to have consulting engineer approvals will be a major expense for a reason.
Reply:I'd purge it with steam, then test with the proper instruments.Patrick
Reply:I have done quite a few hot taps like lotechman describes. It works well.
Reply:this type of pipe welding is common. do a search on hot tapping. But, as others have mentioned, this should be left to experienced professionals.
Reply:Sounds like he may have to change his handle to 123Kaboom!At least he asked, sounds like a job for a gas company.
Reply:Maybe I didn't describe this clear enough.      The pipe I'm welding on isn't energized,   there is a union that we will disconnect on main.       It's in a building, it was recently being used.      I am able to get flow by purging nitogen in areas that I will be welding.    However smaller pipes branching off of it probally wont get flow through them.      Does this change anyones answer?       There is no wps and utility company isnt talking .
Reply:The origonal post was perfectly clear, doesn't change the answer thoughResponsible people DO NOT mess around making alterations to gas mains based on guesses and infomation gleaned from public forums!!Ignoring all the legal ramifications lets look at some of the other issues...How old is this gas main? How do you know what state the line is in? UT?I could go on for a quite a while...You say you've done similar work before yet are asking how to check the line is safe . Are you saying you didn't use an LEL meter last time or did you check the purge with a match
Reply:Sounded to me like you were doing a tie in at the street from your 1st post.When I do residential gas work, say a new gas dryer or hot water heater, it's all threaded work. I have never seen a welded pipe for gas in any building residential or commercial I have worked in. Turn off gas. clear line if possible. Disconnect union or cut pipe. Measure and rethread pipe. Screw it all back together. Check for leaks. We used to thread large pipe all the time doing compressor work. Just a question of having the right tools and know how.The new flex pipe in small sizes is even easier, but I haven't had the time to get certified on the material. I usually just work with someone who is.All said it's not a job for those that don't know and are unprepared for the consequences. When in doubt DON"T.Last edited by DSW; 06-04-2008 at 03:41 PM.
Reply:I have done alot of hot taps in the refinaries...I hate them because its always old to new...and old usually means the pipe is now so worn out that it is now schedual 10...on something this small, you should try to thread the line...welding on gaslines without proper procedures is asking for trouble!!   If you are going to do it anyway...Steam the line...test for gas...Then purge,,,i like argon instead of Nitrogen...But either will work...Argon is heavier than air...Nitrogen is lighter...so vent properly!! At least when we do Hot Taps at the refinary...If I  screw up, I'll never know  it!!      Jonesy
Reply:just to add to jonesy70 with the old you'll typically have more arc blow issues.
Reply:Originally Posted by DSWThey get kind of cranky when a main blows up and takes out a block, even if they marked the street wrong for some one digging.
Reply:I work for a gas co so there are alot of things that have to be known.If you can blow out the 250' with air,fine and can you blow out any of the smaller braches at I'll assume where they go to appliances or machinery.A combustible gas indicator will tell you also what the gas level is in the pipe you are blowing out.5-15% is the explosive level.What the guys are talking about above is how are you tapping the header for the flow to the piece you are installing.Mandrels and stuffing boxes are for live tapping which I don't think your doing?Were you drilling or burning a hole in and going to add your fitting over it with the pipe dead?If we have to evacuate and weld in a situation with questionable branches we use an air mover that kind of vaccumms and purges with air and check it with the cgi mentioned above.As for our  gas mains we weld the taps on them live with 100% gas inside, we can't shut down and blow down miles of mains to add a service tee or new main line.If you burn through the main with 100% gas you won't have an explosion.See if you can talk to a local plumbing contractor who deals with welded pipe installs and he may  help you.The gas co probably doesn't want involved because we usually only come to the meter.I'm assuming this has to be welded because of the size of the pipe or delivery pressure inside.Hope this helps.Last edited by stevinator; 06-04-2008 at 11:45 PM.pro-level dumpster diver                                     Hobart 125EZ
Reply:thanks Stevinator for understanding and answering my question.    No, were not putting holes in pipe or using weldlets.       The plumbing contractor wants Tees put in.     Yes we are welding it because of the size more so than the pressure.       I like what you said about using vacuum.      I've been trying to think of something that I can use for vacuum,where motor would be clear of all gases or make no spark.       Now a couple other guys tried to help also.    One mentioned purging w/ argon.    Well it seems if I were to inject argon and nitrogen at same time,  argon being heavier than oxygen and nitogen being lighter( according to replys), it would be a more thourough purge( less place for oxygen to remain).     Anyone have any feelings on this.     Anyone know of any hazards the two combined might create?       Another guy or two suggested purging w/ steam, then followed by nitrogen.       I'm not familiar w/ that one.     What does steam do to help this?     Also what is used to make and induce the steam into line?        Hottrodder, I ask you not reply to anymore of my posts in future, and I won't comment on anything you write.      I consider advice from people who've had hands-on experience  w/ the subject.   Not solely on a piece of paper some white collered kid behind a desk handed down, especially when lives are at stake.
Reply:123 weld,I can't tell you about evacuating with nitrogen or argon because we use the air mover with compressed air or in something similar to yours, just air from a compressor blowing for awhile.We will put a slug of nitrogen in a long run of gas main to help shorten purge time with natural gas though.I don't want to sound like dangerous Dan here but if this has been dead awhile like you say and you are cutting a cylinder out of the pipe to put the tees in and opening more of it I know people that would run air through both sides for awhile and flash the pipe with something as simple as a propane torch.And always leave everything completely open that you can open.If you get a residual woof or rumble it will exhaust and have some where to go.And of course after that,problem solved.LOLpro-level dumpster diver                                     Hobart 125EZ
Reply:Okay 123 Weld, I have a definitive answer from the owner of CMAC refinery and pipeline construction. (I am remodeling his house!!) The proper way to do this is: purge the line with nitrogen. then, you will install either bladders, or dams to plug the pipe. For natural gas: Build the blockage with dry ice. You will need approx 2.5X the dia. in depth of block to do the job right, and the backside of the block will need a vent opening of some kind. When the weld is done, the dry ice evaporates, and you are done. If the line carries petroleum: You would purge with nitrogen. Then, build a blockage with benzoate clay, not dry ice. Same procedure. This is from a guy who has done nothing but pipelines since 1971. He does this all the time at the refineries near Los Angeles harbor area.Hope this helps you out. Paul.And then, after so much work...... you have it in your hand, and you look over to your side...... and the runner has run off. Leaving you holding the prize, wondering when the runner will return.
Reply:Thank you Rojodiablo.   Sounds like you went the extra yard to comment on this.     I'm not real educated on dry ice.     I always thought of it as liquid nitrogen in a liquid form.      However I'm going to try to study more about dry ice, and the benzoate clay you mentioned for petroleum.   Thanks again, hope the remodel goes well.    I used to live right below you in San Bernadino, I miss the climate the most.
Reply:123weld, the nitrogen and vac are the way to go. don't be suprised if you still get a little burn off when you start burning. there might be some residue that sticks to the inside of the pipe. i don't get why some guys feel they have to pipe in when they have no idea what they're talking about (weld gas pipe?).anything over 2" has to be welded here (if indoors). you have a good question here. that's what these sites are for.  just for info sake, i'm a fitter and cert.welder.
Reply:thanks pumahyvac,  today is going to be my first day on the job.Rojodiablo  Thankyou,   I was reading this thread and thinking dry ice will do the job nicely.I've used this myself on av gas/jet A1 lines and it worked great, push the ice as far down the line as you can and as high as you can and persto, one very well purged line.  When I used it we where doing tie in's at the local airport, empty the line, cold cut, then pack with ice and go for it.  One thing though, I like to have some gas on hand to do a post heat cause I don't like the speed the pipe is cooled with the ice.I'd rather be hunting........USE ENOUGH HEAT.......Drifting around Aussie welding more pipe up, for something different.....wanting to get home.
Reply:Hi, for future reference to all would be plumbers working on gas pipes, get up to date on procedures or get another job!  If you don't understand the  basic %5-%15 gas ratio what hope do you have, if your confused about inert gases  your in the wrong job!  why would you cut and weld in an equal tee when you can arc weld a tee on to your main live, call TD williamson and they will tap it for you at a cost. I have worked with natural gas for thirty years, where we are taught to oxy weld on live mains, or arc weld on live mains under stop off and by pass conditions. you dont just read up on the internet and then have a go!  A little bit of knowledge can be dangerous to yourself and the unsuspecting public! follow half the tips off the internet and then try and explain the result to the coroners court!
Reply:123 you say you are purging with nitrogen to evacuate  oxygen..this is a gas line..wheres the ox coming from????
Reply:Do you realize this thread has been dead and buried for over two years. Why is it that first time posters ALWAYS find a thread that's been dead and gone for making their first post on a forum? Millermatic 251Spectrum 300 PlasmaEverlast PowerTig 250EXEverlast PowerCool W300Harris / Victor OACraftsman 13 Speed Drill PressProTools Air/Hydraulic Bender48" BrakeCompressor, Notchers, Grinders, etc.
Reply:Originally Posted by lotechmanThere is a procedure for doing such a thing.  A tee connection is welded onto the outside of the pipe then a gate valve and boring attachment is mounted on the leg of the tee.  The hole is cut into the main with a cutter then the cutter is withdrawn back to the other side of the gate valve and the gate valve closed.  The cutter unit is operated through a shaft and stuffing box to prevent gas leakage.  I have no personal experience with this however I have read several articles on this procedure.
Reply:Here's a clue Rugar! You can never stop talking saftey no matter how old the topic is!
Reply:Originally Posted by Booger WelderThat is the same procedure that the water company here uses to connect a new tap and their pressure is up around 90 PSI.Gas pressure in local lines is usually somewhere down around 15 to 20 PSI, you can hold your hand over the end and nothing will come out.Here is a article that came to mind that happened about 20 miles from my house a week or so ago.  A good reason - why not to weld on pipe that has gas in it.http://www.wishtv.com/dpps/news/nati...t10-td_3505408