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  • Need expert advice

    Good afternoon to all.

    I have a project going through my shop that is driving my welders and me crazy. We are TIG welding 11 ga(.115) type 304 SS water tanks and can't get nice flat ripple/distortion free weld seams on the side walls. The tanks are 60" in diameter, have a dished head on the bottom, 48" deep and open on the top. The weld around the dished head comes out nice, no problem. The 48" seam weld is where we are having the problem. It's a butt weld and we have tried weld preps, chill plates, weld one side and then the other, various amperages, various filler diameters,tungsten diameters gas flows, back gassing etc,etc,etc and the 48" seam is rippled and in some cases has peaked outward or inward. Bottom line is we don't know how to get this right. Any help would be greatly appreciated.

  • #2
    Have you tried back step welding?
    Can you place and extra strip on the inside that is thicker and weld to it?

    Ji
    Grip it and Rip it

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    • #3
      Originally posted by Jigantor View Post
      Have you tried back step welding?
      Can you place and extra strip on the inside that is thicker and weld to it?

      Ji
      Ji, thank you for responding.
      I don't know what "back step welding" is, will you explain it to me?
      I should have mentioned we have to grind and polish the interior weld to a sanitary finish so we cant have a backing plate there.

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      • #4
        Need expert advice

        Back step is weld from the inside towards the outside and small weld,so let say ,3 inches from the end of the joint ,you start welding till end of joint,then you start over again 3 inches from the start of that weld towards the initial weld....and keep ongoing till you done!
        I would pulse to 33%on time33%background...

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        • #5
          Hammer & dolly to stretch the metal back to it's before welded state. When you weld it the haz shrinks. This makes it warp/distort. Think of it like a body panel. If done correctly you will have a nice, distortion free seem to sand/polish out.
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          • #6
            It's way outside my area of expertise but maybe you need to build a heavy duty clamp though the tube before you install the top or bottom to hold that sucker straight. I'd try clamping maybe an inch on either side of the weld.-- Meltedmetal

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            • #7
              Weld the rolled section first, clean up any high spots on the seam, Then clamp a 1" x 2" flatbar to the inside & hammer it carefully on the outside. This lets the flatbar act as a dolly. It can also be reversed but be extra careful not to get big hammer marks where you need to polish.

              Flatbar should be stainless.

              You may need to repeat the hammer/flatbar & sanding as needed.
              Last edited by MMW; 05-01-2013, 05:46 PM.
              MM250
              Trailblazer 250g
              22a feeder
              Lincoln ac/dc 225
              Victor O/A
              MM200 black face
              Whitney 30 ton hydraulic punch
              Lown 1/8x 36" power roller
              Arco roto-phase model M
              Vectrax 7x12 band saw
              Miller spectrum 875
              30a spoolgun w/wc-24
              Syncrowave 250
              RCCS-14

              Comment


              • #8
                Originally posted by MMW View Post
                Weld the rolled section first, clean up any high spots on the seam, Then clamp a 1" x 2" flatbar to the inside & hammer it carefully on the outside. This lets the flatbar act as a dolly. It can also be reversed but be extra careful not to get big hammer marks where you need to polish.

                Flatbar should be stainless.
                Sounds like the voice of experience, listen to MMW not me.--Meltedmetal
                Last edited by Meltedmetal; 05-01-2013, 05:36 PM. Reason: Spelled my name wrong!Ha.

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                • #9
                  Just did this same weld

                  I just built an altitude chamber out of 5/16 thick 304 stainless. Back welding the seems was a necessity, the welds are over 8ft long. I also use an aluminum heat sink on the root side of the weld. It really helps

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                  • #10
                    I have the same situation with alum cylinders. The best way I found in most cases is to.roll the barrel, weld, and reroll. Then grind the seams and add the ends.
                    Nothing welded, Nothing gained

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