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root pass/cap pass ?

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  • root pass/cap pass ?

    I've read several posts here and read in several welding manuals I've got about welding a root pass then welding a cap pass (or passes if necessary). I understand the theory behind what is to be done but since I've never seen anyone do it. I don't understand when you would need to do this root pass/cap pass.

    Perhaps my ignorance comes from only welding thin metals (mostly 3/16-1/4" stuff) and you do this type thing on thick metals ??

    In the context of root pass with cap pass (or passes), most reference using a 60 series rod then capping with a 70 series rod. why this choice of rods ?

    thanks ... just trying to learn something new.

    - jack

  • #2
    Generally speaking this scenario will come into play on pipe when no backing ring is used. You install the root pass with E6010 or GTAW because they do much better on an open root than low hydrogen. You then put a hot pass in with E7018 within a couple of minutes of the root (don't let it cool before putting in the hot pass), then you put in cover passes, the cap is the last cover pass.
    Respectfully,
    Mike Sherman
    Shermans Welding

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    • #3
      thanks Mike.

      why do you not want it to cool ?

      how thick would the pipe be at a minimum before this procedure was used ? I thought I read something similar to this from the guy who worked on big mining equipment ?

      - jack

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      • #4
        Hey Bro. In my trade (Union Ironworker), we use a 60 series root and 70 series cap for plates 3/8" to just under 1" thick. If I'm not mistaken, thats with about a 22.5 degree bevel and 1/8" gap between plates. For plate 1" and larger, we use a backing strip and 1/4" gap between the plate, with a 30 degree bevel. Always grind the millscale back about an inch and completely clean the backing strip. I cant help you on the pipe, thats for pipefitters, the "Professional Welders". Anyway, I hope this helps. Good Luck!
        Buy Union, Buy American, the job you save may be your own.

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        • #5
          thanks for the info spud. any more info out there ?

          - jack

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          • #6
            Hey spud. I was working for AB in Miami and got sent your way to go on the Skyway Bridge. I drug about 5 mins after showing up. You guys must have got it finished.
            http://www.facebook.com/cary.urka.urkafarms

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            • #7
              root

              I'm a downhill pipeliner , root also called stringer is first pass, for thin wall pipe dime space and dime landing for thicker pipe .219 and greater use penny space and landing , next comes hot pass which cleans out stringer and ties sides together, filler if needed to make it flat and then cap . For schedule 40 pipe we use 6010 all the way out , the only thing we use 7018 on is hottaps on x60 or greater pipe

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              • #8
                Dano, Ever hear the saying; "nickel wide and a dime high"?

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                • #9
                  Jack: Root pass or passes are the first pass in a v-groove joint or any joint shaped like one(t joint ect.) cover passes are just what it says. Usually means the last welding for finished product. Revpol. P.S. to spud Righty tighty lefty loosey from a boilermaker buddy

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