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  1. #1
    Join Date
    May 2013
    Posts
    2

    Default 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. #2
    Join Date
    Jul 2009
    Location
    Australia
    Posts
    1,031

    Default

    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

  3. #3
    Join Date
    May 2013
    Posts
    2

    Default

    Quote 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.

  4. #4
    Join Date
    Feb 2013
    Location
    Canada
    Posts
    81

    Default 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...

  5. #5
    Join Date
    Sep 2005
    Location
    northern NJ
    Posts
    1,825

    Default

    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. #6
    Join Date
    Dec 2011
    Posts
    385

    Default

    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

  7. #7
    Join Date
    Sep 2005
    Location
    northern NJ
    Posts
    1,825

    Default

    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 at 05:46 PM.
    MM250
    Trailblazer 250g
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    MM200 black face
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    Miller spectrum 875
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    RCCS-14

  8. #8
    Join Date
    Dec 2011
    Posts
    385

    Default

    Quote 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 at 05:36 PM. Reason: Spelled my name wrong!Ha.

  9. #9
    Join Date
    May 2013
    Location
    Cincinnati
    Posts
    1

    Default 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

  10. #10
    Join Date
    Aug 2010
    Location
    Los Angeles
    Posts
    1,163

    Default

    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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