Welding Schedule 40
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  1. #1
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    Apr 2006
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    Welding Schedule 40

    Would you use a Miller Matic 251 Mig welder to weld schedule 40 pipe for a low pressure steam system? This would be for 3 and 4 inch pipe.

  2. #2
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    Jan 2005
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    I would not. Id use smaw or gtaw
    IF it Catches...Let it Burn

  3. #3
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    Nov 2005
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    TxRedneck,
    sorry in advance, but I need to harass you a bit.
    I wonder if you would expand on your reply to RonL?
    Why would you not us a Miller Matic 251?
    Why would you perfer smaw or gtaw?
    Are there technical issues, or skill level issues, metallurgical issues?
    Do you have a personal experience you would like to relate?
    If I were someone trying to learn something about welding, I would want to know why you have your opinion.
    If all of us on this forum don't try to provide a reason for our opinion, whether its based on technical data or personal preference, we may as well just suggest seeking out a "seasoned welder" to "learn the secrets" of welding.
    This is a Professional Welding Forum.
    There, I think the bug is out of my axx.

  4. #4
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    Apr 2006
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    41
    The drop header for the near boiler piping will probably be shop fabbed with gtaw. This will be 4 inch piping. There will be 3 or 4 fittings that will need to be made on site. These will be 3 inch fittings. In a perfect world I would like to gtaw them but getting the equipment on site is not practical.

  5. #5
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    I have to agree with Tx Red about the tech. side of all I read, and it does't matter where I read it. I really like facts based upon science or personal experence.

  6. #6
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    California
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    I have read that the problem with GMAW in pipe welding is the issue of getting a good root pass. GTAW is preferred for this purpose. Here's an article that discusses it a bit but doesn't really provide a lot of detail:

    http://www.millerwelds.com/education...articles9.html
    -Heath

  7. #7
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    Well the supporting reasons have to do witht he fact that statiscally the GMAW process has a much higher rate of failure on pipeline welding. The shielded metal arc welding process has a much higher sucess rate. Being steam line, I would not want to take any chances. MIG there is a tendency to look like a good weld, and its not. Penetration is more difficult to obtain using GMAW than SMAW. Most importantly if youve got GTAW, you have SMAW. Just change the torch to a stinger and reverse the polarity.
    I do have personal experience welding pipe and I personally feel after having destructive and non-destructive testing done on welds from all three processes. I feel the GMAW is much more difficult to produce a sound weld for a visual a radiograph wont tear to pieces. There are no secrets to withold, the question was merely would you use this process for this application I said no, I dint have a lot of time when I posted so I merely asked the question. It is true that pipe is going semi-automatic, and in some areas automatic. HOwever, the repair rates are astounding. I would rather weld this with a process you know if it looks right it is.
    IF it Catches...Let it Burn

  8. #8
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    Heath

    Interesting article. The author seems to be advocating mig for pipe welding but recomends stick for the root pass.

  9. #9
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    I'm probably one of the firmest adherents of the GMAW process on this forum. I have a fondness for efficiency and in terms of deposition rate, nothing beats wire-fed welding processes, either GMAW, FCAW, or SAW (submerged arc). However, everything that I've read suggests that none of these processes work very well for the root pass on pipe applications. The author of the article suggests that GTAW (TIG) is preferred for the root pass while wire-fed processes can be used for fill and cap. I personally wonder if folks are using GTAW orbital welding technology for pipeline applications or if the root pass is done manually. I have little doubt that eventually, wire-fed processes will be dominant in pipeline welding as well. There's too much to gain in terms of productivity and efficiency for it not to, but I don't think that's the case now.
    -Heath

  10. #10
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    Feb 2006
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    Back in HB, close to my boys!!
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    Quote Originally Posted by RonL
    Would you use a Miller Matic 251 Mig welder to weld schedule 40 pipe for a low pressure steam system? This would be for 3 and 4 inch pipe.
    Nah. For schedule 40, use the purple primer, and Red hot blue glue!!!

  11. #11
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    Orbital is used extensively in clean room stainess. Its expensive and the set up takes time. I hardly see this being a practical alternative to manual arc welding. However, perhaps time will only tell. They used tig for a large titanium pipeline over in china some several years back. Seemed to work. Perhaps with higher strength metals the need for gtaw will be there. For now even with gtaw its better toi have a man do the welding though
    IF it Catches...Let it Burn

  12. #12
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    Jun 2005
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    New Zealand/Australia
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    Leave the wire in the workshop, that's where it work's best with roller's and all the other toy's. I know of job's where they don't what to stick weld the pipe because it's to fast, better to make the job last longer with the wire

    For the size pipe that's been talked about here I wouldn't even bother sticking the cap, just tig it all the way. By the time you swap the lead's you could be finished with the tig.

    Stephen
    I'd rather be hunting........
    USE ENOUGH HEAT.......

    Drifting around Aussie welding more pipe up, for something different.....wanting to get home.

  13. #13
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    Aug 2005
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    Lebanon, Oregon
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    Ron, ............ Most all of the pipe trade fab shops that I have ever worked in have all gone to wire or mig welding for pipe. Speed and productivity were the reason. If you have the shop set up correctly, with pipe positioners and other equipment, this is the fastest and most protifable way to weld pipe. Field work is another story. Many of the shops and jobs I've worked also required that all the welds be x-rayed, due to customers job specs. There is really no trick involved except for having the right heat, speed and watching what is happening in the puddle.

    If using a positioner, which I highly recommend for doing this, you also have to know at what position you need to be welding from the top of the top. Using 12 o'clock as the top, I usually always am running the bead at about 1 to 1:30 from the top. Sometimes I will drop down to around 2 or 2:30 to speed things up. Any further up, the root bead will build up inside and any further down the root bead will be very narrow, flatter and you stand a chance of getting lack of fusion and penetration. The gap is usually set narrower (3/32" max.) than when welding with stick and there is no land on the bevel, just a knife edge. Always point the wire up into the puddle, approx. 40 to 45 degrees, and keep the wire at the very front edge of the puddle, in the small key hole that the puddle is making. Keeping the wire in the middle of the puddle, instead of the front edge, will result in poor penetration and lack of fusion. At times I have been on the front edge of the puddle so far that you could see the wire was actually melting on the inside of the pipe, underneath the front edge of the puddle, through the key hole, not on the outside front edge of the puddle. Most all of the time, using this setup, you will get a even root bead that is approx. 3/16" to 1/4" wide, on the inside, and about 1/8" buildup on the inside of the pipe. With practice, you can manipulate the speed of the positioner and gun to get the bead inside the pipe the way you want, i.e. wide, narrow, thick, thin, built up or flat, but it does take some practice. Once the root bead is complete, you move the mig gun up near the top of the pipe (approx. 12:30), keeping the mig gun pointed into the puddle at about 40 to 45 degrees, and the wire at the front of the puddle, to make the fill and cap pass. Doing this will result in rotating the pipe a little slower, in the positioner, but more wire being deposited in the next pass, resulting in a heavier bead. If you use .045 wire to weld the size pipe you are talking about (3" to 4" sch. 40) you can make the root bead in one pass and the fill and cap, combined, in the second pass. Weaving or lacing the wire back and forth across the puddle, never let the wire go past the top outside edge of the bevel. Use the top edge of each bevel as your guideline, as to how far to weave or lace. Doing this will create a nice even bead that will consume the entire outer edge of each bevel and will have a cap buildup of about 1/8" and no undercut, on the outer edges of the cap. Make sure that you clean each pass good with a wire wheel on a small grinder.

    Since I built my own positioner, for my shop, I'd be glad to go out and run you a weld, but the only problem is that I haven't purchased a Miller 251 machine yet. However, I will be purchasing one in about 2 months, because of some piping work that I'll be doing.

    The specs on the 251 verses the 210 say the maximum thickness material for 1 pass is 1/2" for the 251, 3/8" for the 210. The 251 setup with the right gas and wire, running maximum heat range, which I don't recommend, because you'd be pushing the outer limits of the machine, you can actually spray weld with it. A friend of mine does this every once in awhile, with his 251, but I wouldn't put that kind of pressure on my equipment.

    I've made many x-rayable welds over the years and haven't had any problems using the above mentioned setup and process. I'm sure that the 251 will be more than enough to handle the job you mentioned.

    The most important thing to remember is to make sure each joint is extra clean (shinny metal) and you wire brush each pass real good.

    BTW, something an old welder passed on to me when I was starting out in the trade was, depending on the size of pipe (up to 12") and the wall thickness (sch.40), if the bevels are made correctly (37 degrees) and the gap is right, if your cap is more than a dime wide and a nickel high, then you are wasting time and welding material. I've used this method to check my welds every so often, while welding over the years and have passed this on to the apprentices that I teach in school, and it does work. Try it sometime. It's just another gauge that I use to check myself by.

    Hope this has helped and sorry this took so long, but I don't have any pics to explain it faster.

    Just my .02 cents.



  14. #14
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    Nov 2005
    Location
    utcia michigan
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    well just to add my $0.02 if you know how to MIG weld then do it if not then stick WHY well its harder to put down a bad stick weld that looks good but has no hold ,for MIG i would use .035 wire 70-6 and 80/20 Ar/co2 put in the root turn it up and run your cap
    this is just my thought's

    Chuck
    ASME Pressure Vessel welder

  15. #15
    Join Date
    Apr 2006
    Posts
    70
    first off, i would tig it, and if you cant tig it, a 6010 root, stick away from mig, thats more for structrual then for pressurized pipes and boilers (not saying it doesnt happen)

    Quote Originally Posted by halbritt

    I personally wonder if folks are using GTAW orbital welding technology for pipeline applications or if the root pass is done manually.

    I have little doubt that eventually, wire-fed processes will be dominant in pipeline welding as well. There's too much to gain in terms of productivity and efficiency for it not to, but I don't think that's the case now.
    root pass is done manually

    only wire feed is on the subarc, thats it, other then that is straight arc. cant change, and wont change

  16. #16
    Join Date
    Dec 2005
    Location
    South Central KY
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    84
    Due to the thermal expanison of steam pipe we use 6010 root and 7018 filler and cap. When we are dealing with over 350psi and using 5% chrome fittings we tig the root and 7018 filler and cap. We use mig on other types of process piping but never steam!

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