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Welding ferrules to tanks with no access to the inside?

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  • Welding ferrules to tanks with no access to the inside?

    Wondering if anyone has had success adding 1.5" or 2" ferrules to tanks that lack easy access to the inside? I am considering trying to alter the attached tank into a uni, by either adding a couple of smaller ferrule or a larger 8" ferrule (with two smaller ferrules in the end cap) for racking and carbonation. The 8" option would allow (constricted) access to the inside for clean up, but it's pricey. Talking to local welders, it seems like adding smaller ferrules with clean welds would be impossible. Does anyone have any experience that counters this? If so, how did you go about doing it?Click image for larger version

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  • #2
    I used to work for a company that manufactured ultra high purity gas purification equipment, and many of the smaller vessels were made from pipe, with a similar access problem. The way those guys would do it would be to cut the ID of the tank wall opening just slightly smaller than the ID of the ferrule (a short ferrule is easiest, if it's 2" tube). Then grind or cut a saddle in the end of the ferrule, tack it to the opening, and then fusion weld from the inside of the ferrule where it meets the vessel wall. It requires a very close fit, because you don't want to add filler. It's very hard to control the arc when you're welding on the outside where it meets the wall, because it will drift to one surface or the other, and have poor penetration where it counts. So you weld from the inside of the ferrule, reaching through from the outside. But if your welders say it's not possible, I'd probably have to believe them.

    This company would also weld long tubes to a custom machined valve body which also has to be done on the outside, but in that case they cut a small groove around the opening, leaving a small plateau around it, sort of like a super-short section of tubing sticking out of the solid block. Then they fusion weld as normal from the outside, since this is essentially a simple fusion butt weld and you can get a smooth surface on the back side. But in your case, the tank is pressurized, so even if the wall is thick, you probably couldn't do it that way. Maybe if you then filled the groove with filler rod...

    But wouldn't it be very nice with a real manway installed?

    Mike Sharp


    • #3
      Thanks, Mike. An idea, anyway. I've only talked with one company so far. I work at a university, with an adjacent college with a welding program, so I am going to chat with the instructors to see if they can be give me a more definitive answer.

      A real manway would be fantastic, but sadly at that point--which is probably the point I am at--I might as well just buy an actual uni/brite.



      • #4
        It can be done, and we have done similar things in the past, but it would be very difficult to get a weld sufficiently smooth on the inside for CIP.

        The fitting must be perfect--no filler rod. The poster above describes the fit very well, but I'd go for an ID-ID fit--the ferrule resting perfectly on the outside of the tank. You'll need to fill the tank with an inert gas--we usually use Argon for TIG welding. A slight pressure on the tank will insure that no O2 can infiltrate, and will help support the weld, which must have 100% penetration and will sag if the pressure is too low, or bulge if it's too high. The weld must be perfectly flush with the inside of the tank for good CIP. We use tape to cover an opening, then punch a few small holes--using the tip of the tungsten--to control the pressure.

        You would want to run a few practice welds using tubing of the same thicknesses as the ferrule and tank walls first, which could be cut open to reveal the quality of the welds.

        If you go with the 8" ferrule, this gets much easier, as the weld can be made from the inside.

        In the end, unless you hire a certified pressure-vessel welder and have the welds inspected--probably using x-rays--you will not have a legal pressure vessel.

        Finding a good cylindro-conical fermenter and using this tank for something else would probably be the best way to go.
        Last edited by TGTimm; 07-31-2015, 10:16 AM.
        Timm Turrentine

        Terminal Gravity Brewing,
        Enterprise. Oregon.