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Up Topic Welding Industry / General Welding Discussion / gass line welding
- - By texarc (*) Date 05-11-2004 16:32

Heres the deal have a gass line lets say from a metter and valve to a boiler. need to weld a weldalet on the line so a guage can be put on. what I have seen happen is that the gass valve is shut and the line is opend up but there was no purge just cranked up the amps and burned a hole threw the pipe and let it burn off and then welded the weldalet.
Is this safe? or completly insane?
Parent - - By thcqci (***) Date 05-11-2004 16:51
I might be a rookie, but my vote is COMPLETELY INSANE!!!

In the shipyards, where I got my whole start in the welding industry, anytime there was to be welding on tanks or lines, they were filled with nitrogen. A marine chemist was ALWAYS involved to certify gas levels.
Parent - - By G.S.Crisi (****) Date 05-11-2004 19:18
It is also my vote: absolutely irregular and unsafe.
I don't know about AWS, but API (the American Petroleum Institute, www.api.org) has published recommended practices on how to cut and weld on tanks and pipelines that have contained flammable substances.
Giovanni S. Crisi
Sao Paulo - Brazil
Parent - By texarc (*) Date 05-11-2004 19:58

I would think that purgeing the line even with air would be better than letting the gas burn itself out of the opening of the pipe.
Parent - - By JTMcC (***) Date 05-12-2004 00:14
Live gas lines are welded on hundreds of times per day, it many times involves some amount of fire. All gas companies have strict procedures that govern the work.
People outside the gas industry usually find it appaling, but it's standard procedure on gas pipelines.

JTMcC.
Parent - By Diesel (*) Date 05-12-2004 00:38
Please! do not purge with air! Weld on the weld-o-let and then drill out the coupon. A 0.25 hole will be large enough for a gauge.
Parent - By texarc (*) Date 05-12-2004 10:19


THx for the replies, I was told that there was no danger because the line always had an opening for any combustion to escape. And that there would only be a problem if one of the cut off valves would
not completly close for that reson they are gressed before closeing.
JTMcC there are gass industry related people on these jobs, so I fell better after your post.
Parent - - By Bill A (**) Date 05-12-2004 13:11
Some of the previous comments were right on...weld on the fitting then tap the pipe with a drill and don't purge with air. You have to be aware of the possibility of ignition from gas getting around the drill and contacting an electric drill motor. I would use an air motor. It is very common to weld on pressurized gas lines but appropriately controlled welding procedures are used to avoid unexpected burnthrough from excessive heat input and cracking from inadequate heat input. If the owner doesn't provide you with a copy of a welding procedure to follow, or you don't have one of your own I think you are incurring a lot of liability if anything goes wrong, beside being in violation of just about any code that applies to that type of assembly.
Parent - - By JTMcC (***) Date 05-12-2004 16:17
Everyone that is saying don't purge with air are evidently unfamiliar with this work and the use of air handlers. There are several different methods that could be used to do your job, all used succesfully tens of thousands of times. People who have never done hot work on live gas lines may respond in horror, but it's an everyday occurence in the business.

A lot of work on live gas lines involve cutting into the pipe, and fire results. Fire, controlled, is not cause for panic.

JTMcC.
Parent - - By Bill A (**) Date 05-12-2004 18:31
I agree with you, but given the level of technical sophistication (or lack of) in the original question, I have to question their ability to do an air purge properly.
Parent - By Diesel (*) Date 05-12-2004 19:36
I have to say that I have never used air or seen its use. No companies we work for allow air in thier lines. There are even time limits on atmospheric exchange with a charged line. Additionally our safety procedure requires that 4" and larger pipe must have a constant source of ignition (arc or torch) until the stringer is placed. I must quallify my answer by saying that everything we do is high pressure transmission or gathering. Does this apply to a supply line for a boiler? Maybe but how expensive is N2, which I might add reguires no post purge.
Parent - - By texarc (*) Date 05-12-2004 21:17
BILL A

i am a welder not a gas technition, it is there job to say if the line is safe to work on, after that I weld. My technical sophistication is none of your buiznes! And as for the air purge that is also handeled by the gas guys not the welder. You shouldent slam people for asking questions, didnt any one tell you thats how you learn?
Parent - - By jwright650 (*****) Date 05-13-2004 10:26
Tex,
I would feel uneasy about tackling a job like yours too, if I'd never done it before. Some of these guys that do this regularly know the risks and how to handle them. I don't, I've never done anything like this before. If I were you I would get comfortable with the idea before you tackle this one. You are asking because, like you stated, you aren't familiar and you want to learn. Nobody can fault you for that, besides, it's safer that way. Please ask questions, at least satisfy, in your own mind, the doubts you have about this. I don't think Bill A meant anything by his statement, he was just stating the facts or the lack of. I'm sure he would not want anything to happen to you or anyone else while tackling this without being armed with all the information to do this safely.
How long before you have to strike an arc on this one?
John Wright
Parent - By texarc (*) Date 05-13-2004 11:26


I am working with guys that have done this for years. JUst recently starting to deal with this work, I still questioned it. Got the answers I needed here. And the welding is going fine, now that I know the guys im with know what there talking about.

Thx.
Parent - By Bill A (**) Date 05-13-2004 18:36
jwright650 is correct. Notice I didn't reference you specifically in my response. Obviously the welder on jobs like these is under the supervision of the owner/operator/or primary contractor and the welders don't often conjure up these practices by themselves. My concern was the apparent total lack of safety awareness exhibited by whomever was responsible on this job, (although they may have taken some safety-related steps that were not referenced in your e-mail.) Failure to provide the welder with a welding procedure further supports my point of view that the supervision was not following practices consistent with best practice or with most common codes and standards. Therefore, in view of the many ways a purging can go wrong, and not thinking this to be the correct forum to provide a detailed dissertation on purging, I elected to not support purging in my original response. Unfortunately, it may have been better to say I supported PROPER purging and leave it at that. So don't get your leathers is such a wad.
Parent - - By TimGary (****) Date 05-13-2004 11:50
I have a crazy friend, who works for the city of New Orleans, that does hot taps on 6", 150 psi gas mains frequently. He prefers the oxy/fuel welding process for this application. He says that every once in a while, he blows through the pipe wall and the rush of escaping gas will extinguish his torch. Thats when the tricky part comes in. He can't just let it go, he has to relight the torch and fill in the hole with filler metal, while the gas is still escaping, before the gas can settle in his bell hole and ignite.
That's a little bit of a too high stress work environment for me.

Tim
Parent - - By james1 (*) Date 05-19-2004 21:36
tim i think your friend is full of gas
Parent - - By Michael Sherman (***) Date 05-19-2004 21:46
I do hot taps by welding a weld-o-let on, put a valve in place, screw my hot tap drill with a hole saw on the end, turn by hand a few cranks, pull the shaft with the slug back thru the valve, close the valve, vent the hot tap drill, remove it and your done. It is far safer (and much faster) to have the gas moving thru the pipe than to try and evacuate it. That's just the way I do it.

Mike Sherman
Shermans Welding
Parent - - By james1 (*) Date 05-19-2004 21:56
Mike have you ever thought of a D5 (muellercompany,com)
Parent - - By Michael Sherman (***) Date 05-20-2004 13:53
That is very similiar to my Rigid RT3422. It is the fastest way to do a hot tap that I have ever found.

Mike Sherman
Parent - - By james1 (*) Date 05-21-2004 00:05
Mike sort of reminds me of the t18 or the newer t101a willaimson looks like a nice drilling machine didnt know ridgid was in that business..jim
Parent - By pgeweldor (*) Date 05-21-2004 20:17
Just for some info. Mueller and Continental make self cutting tees. You weld them on the line and tap them with an allen wrench or a half-inch socket extension. They are usually good for pipe up to and including 4inch. Bigger pipe there are fittings(tees), that get welded on and tapped with the E-5 or D-5 drilling machines made by mueller that had been mentioned previously. Paul
Up Topic Welding Industry / General Welding Discussion / gass line welding

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