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  • Convotherm C4 cracks, yet again.

    Posted by olivero on February 3, 2021 at 10:20 am

    Howdy everyone,

    Had the top burner on our C4 unit develop a crack in the exact same place the one I mentioned about 2 weeks ago did, this one didnt’t completely seperate like that one did but a decent crack was forming.

    I wonder why this happens, I spoke to Convotherm they mentioned if the Spritzer is overspraying that could be part of the problem.

    Main thing I see when I pulled it out is where the burner sits, that section is warped way down and is not straight at all, which makes me thing it’s just super stressed.

    As you can see in the photots, the wall was also messed up again, so we had to cut a section of it out and replace it with a new piece of sheet and weld it in, then finish it and so on. Pretty big piece.

    I wonder if anyone else has as much trouble with this unit as I do.

    olivero replied 3 years, 1 month ago 4 Members · 21 Replies
  • 21 Replies
  • fixbear

    Member
    February 3, 2021 at 11:10 am

    What’s the ph of your water?

  • olivero

    Member
    February 3, 2021 at 12:34 pm

    Not sure, I guess i’d have to check. We have a test kit somewhere.

  • fixbear

    Member
    February 3, 2021 at 4:32 pm

    Something is causing the erosion of metal adjacent to the weld. Dissimilar metal?, Oxidizers, HAZ zone change? Or heat differential. Does the spritzer have droplets that hit there? Causes steam erosion. As well as hardening from the quick surface temp change.

    The weld will normally be thicker than the base metal. It will there-fore be slower to change from cooling and get brittle at the edges.

    Do you know the base metal alloy? Are you using TIG for this? What filler wire are you using?

    With heat exchangers, assumptions as to the alloy and what to use for a filler wire can be dangerous and bite you in the butt. Been there, done that. (Franklin aircraft cabin heater jacket in a Maule rocket.) I know it’s considered a stainless alloy, But there are hundreds and multiple welding wires and methods. And God help you if it has Magnesium or Titanium in the alloy.

  • olivero

    Member
    February 4, 2021 at 12:36 pm

    It’s true, definetley something.

    to me it seems the original weld got too hot and it damaged the crystaline structure of the metal and created some weak points, that’s the only reason I can imagine.

    It’s all 308 as far as I know or some variant of stainless, I TIG it with 308L and 316L depending on the hole size and what not, never had it rust or crack when cooled so I don’t think they are incompatible. I use pure Argon as a shielding gas.

  • fixbear

    Member
    February 4, 2021 at 3:19 pm

    I’m thinking more like a 430 stainless. Is it at all magnetic?

  • fixbear

    Member
    February 4, 2021 at 3:24 pm

    You may also want to ask you utility company for a gas analysis. With some high temp stainless chambers, sulfides will cause cracking of welds.

  • olivero

    Member
    February 5, 2021 at 10:42 am

    I don’t think it’s 400 series, I don’t remember it being magnetic, my watch strap is magnetic so it tends to stick to everything that’s magnetic and I don’t recall the heat exchanger doing that, but I could check.

    Not a bad idea, I know these burners were calibrated some years ago with a flue analyzer, perhaps we need to do it again.

  • GalvTexGuy

    Member
    February 10, 2021 at 11:51 am

    I had one blow about a quarter sized hole right after the cone. Mine was an OGS10.10.

    • olivero

      Member
      February 10, 2021 at 11:54 am

      Really? Blew an actual hole in it or a crack?

      • GalvTexGuy

        Member
        February 10, 2021 at 11:59 am

        An actual hole.

        IMG 4841
        • olivero

          Member
          February 10, 2021 at 12:04 pm

          Wow, that’s crazy.Looks like that transition joint, same place where mine cracked.

          What did you do to fix it? Replace it or get it repaired?

  • Convoserviceman

    Member
    February 10, 2021 at 12:12 pm

    OGS10.10 heat exchangers are titanium enriched stainless so welding them hasn’t worked well. If the combustion is correct, and I don’t know how old the unit is, it will last many years. OGS models were discontinued in 2014.

    • GalvTexGuy

      Member
      February 10, 2021 at 12:21 pm

      Yeah, we must have gotten the last of the OGS10.10 units before they were discontinued. We bought three in March 2014. It’s a long story, but there was a combustion issue, related to the combustion blower, which I’m pretty sure caused that hole. The combustion issue was solved. I won’t go into how the heat exchanger was repaired, but let’s just say it was “patched”.

      • olivero

        Member
        February 10, 2021 at 12:25 pm

        Interesting.

        Cmooon! I wanna know how you did it, as you can see above, I just welded ours, But yours got a big hole in it.

        I’m just curious though.

        • GalvTexGuy

          Member
          February 10, 2021 at 2:01 pm

          We are a small school district. The Nutrition Department, who I work for, has a limited parts budget. At the time, we did not have the funds to purchase a $2,600 heat exchanger for this combi-oven.

          Often times, I have to improvise to get equipment back online. Some of the things I’ve had to do to make repairs might rub some people the wrong way, especially if they are “by the book types”. Don’t get me wrong, I generally am one of those by the book types, but sometimes you have to do things that you wouldn’t ordinarily do. I do keep safety as my top priority, so I would never do anything that would cause an unsafe condition.

          The repair I made to the heat exchanger involved custom fabricating a piece of 14-gauge stainless sheet metal, some stainless steel hose clamps and some high temperature sealant. That’s all I will say.

          • olivero

            Member
            February 10, 2021 at 2:52 pm

            Okay, that makes sense, on the full size combi’s the heat exchanger runs upwards of 5K, so I understand.

            I know what you mean, I think we all run into these things to an extent, you are pushed a little out of your comfort zone but stuffs gotta run or someone is not eating. I Get that 100%, I do keep safety on the top priority as well.

            Cool, that sounds like a good way to do it, nothing wrong with that.

            I just have welding gear and can do it, which is the only reason I went that route, otherwise I would’ve had to figure something else out.

            • GalvTexGuy

              Member
              February 10, 2021 at 4:19 pm

              It’s good you know how to weld. All I know is oxygen/acetylene brazing. BTW, you hang out over in HVAC-Talk forum, don’t you?

              • olivero

                Member
                February 10, 2021 at 6:42 pm

                That’s good to though, I’ve never done oxy acetylene.

                Haha, yeah I do.

                Do you?

  • olivero

    Member
    February 10, 2021 at 12:15 pm

    Interesting, how come? To handle the burn better it has to be alloyed with titanium?

    Do you work for Cleveland or Rationale or one of these companies or you just specialize in combis?

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