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  • MIG welding pipe

    I'm a pipe welder with 23 yrs experience with TIG and Stick. My boss has a job coming up which involves welding 26" heavy wall pipe. We're talking something like 2" wall thickness. And has to be 100% x-ray. Normally we would TIG the root pass and then Stick weld the rest. A lot of welding! We are considering using the Pipe Worx 400 machine on this project to speed things up. I have run MIG quite a bit but never on pipe. Any suggestions on using this machine for that type of job. Should we use pure CO2 for gas or a mix? We can't have any lack of fusion anywhere in the joint. Thanks.

  • #2
    Where i work we make pressure vessels and they are 1" - 1 1/2" thick. We use solid .035 mig wire w/C02 for the root and .045 gas flux core with C02 for the next 15-25 passes. They are all 100% x rayed joints...Bob
    Bob Wright

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    • #3
      What would happen if we ran solid Mig wire all the way out instead of flux core? What does the flux core do for the weld?
      We are trying to eliminate chipping and wire wheeling of slag during the process. However, we can't sacrifice proper fusion and penetration either. Also, I believe this is going to be a "hot weld", requiring a constant pre-heat of 400 to 500 F. And welded in position. No rolling of pipe.

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      • #4
        Flux core with gas cleans up easily. You can run hot and fast.

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        • #5
          Thank you for the replies. Sounds like flux core is the way to go.

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          • #6
            [QUOTE=Welder Dean;277716]What would happen if we ran solid Mig wire all the way out instead of flux core? What does the flux core do for the weld?
            We are trying to eliminate chipping and wire wheeling of slag during the process. QUOTE]

            The people I know who fab pipe in a shop, and have used both, weld out with flux core for two reasons.
            One is fewer repairs due to LO sidewall fusion and cold lap.
            Two is they can carry more iron at higher heat out of position.

            Power brushing between passes doesn't offset the gains made with FC.

            JT

            A # three is you can run FC out in the yard and every setup doesn't have to be in the shop, that makes a difference if your pipe is large or you have a big gaggle of welders with limited fitting/welding space or a limited amount of inside equipment handling stuff like bridge cranes, etc.
            #4 is in hot weather the welders can run a large fan to remove fume and cool the poor welder with FC but not with anything using gas. Happy comfortable welders = productive welders.
            #5 is in cold weather the welder can run an agressive heater for the same reasons as #4 exept the opposite.
            Last edited by JTMcC; 01-02-2012, 10:57 AM.
            Some days you eat the bear. And some days the bear eats you.

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            • #7
              Pipe Worx 400

              Call your local Miller rep and tell them you're considering buying this unit for the upcoming job, ask if they can bring a demo unit into your shop and let them show you what it can do.
              Richard
              West coast of Florida

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              • #8
                I got quite an education back in the 70,s, pipe welding for off shore oil drilling, big pipe up to 30 inch dia with up to 3 inch wall, and all other sizes too, these were welded on rollers, when i first started, the root pass was by mig, there would be about 1/8" gap between the pipe and connector, they were tacked together, brought up to temp and then the mig was placed in the groove on the od of the joint and then the pipe would turn as needed to complete the weld, after a bedd was welded with 5/32 7018 over the joint from the inside, after that a sub arc filled it up. once i got the hang of it, the company stopped using the mig, due to lack of fusion, xray and ut was used on all welds, the new procedure was done by welding the root from the inside by stick, then back grind the outside of the root to get 100% fusion, then run a stick pass over the ground joint, then a sub arc to fill. if I had to do this job, i definetly would get a set of rollers, stick weld the root as i described, then fill it up with stick, 7018x 5/32" then go up to 3/16 and 1/4" rod when it opens up, with the rollers the weld is a down hand weld, the position of the rod is just shy of tdc, being closest to you and the pipe rolling away from you, good luck

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                • #9
                  did alot of stringer passes on jacket legs with mig but never did a filler and cap with it .we always ran the stringer with mig then flux cored it the rest of the way.

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                  • #10
                    [QUOTE=JTMcC;277799]
                    Originally posted by Welder Dean View Post
                    What would happen if we ran solid Mig wire all the way out instead of flux core? What does the flux core do for the weld?
                    We are trying to eliminate chipping and wire wheeling of slag during the process. QUOTE]

                    The people I know who fab pipe in a shop, and have used both, weld out with flux core for two reasons.
                    One is fewer repairs due to LO sidewall fusion and cold lap.
                    Two is they can carry more iron at higher heat out of position.

                    Power brushing between passes doesn't offset the gains made with FC.

                    JT

                    A # three is you can run FC out in the yard and every setup doesn't have to be in the shop, that makes a difference if your pipe is large or you have a big gaggle of welders with limited fitting/welding space or a limited amount of inside equipment handling stuff like bridge cranes, etc.
                    #4 is in hot weather the welders can run a large fan to remove fume and cool the poor welder with FC but not with anything using gas. Happy comfortable welders = productive welders.
                    #5 is in cold weather the welder can run an agressive heater for the same reasons as #4 exept the opposite.
                    we would just put tarps up to block the wind when we was outside and run our a/c tube up in the bottom of our shirts to keep us cool on the hot days.pretty good setup because that cold air blows right up through your shirt and into your shield . but like you said in the winter time that heat is nice. best way to stay warm is keep welding.

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