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Carbon Dioxide as Shield Gas for Brazing

Is carbon dioxide effective as a shield gas to trickle in to refrigeration tubing while brazing? I can can justify buying a co2 tank and different regulator setups for carbonating and for leak testing and brazing but I can't quite justify a co2 and nitrogen setup for the different occasional uses.

Is my assumption that 99.90% pure beverage grade co2 has to be inherently dry correct?


    EBEBRATT-Ed Member Posts: 11,996
    I have been through this before. Most will say "no, dry nitrogen only" because that's what the books say.

    I have used Co2 for years with no issue. The tanks are a lot lighter to lug around and they hold way more gas than nitrogen. Go for it and don't look back.

    Now, I'll wait for the backlash LOL :)
  • Larry Weingarten
    Larry Weingarten Member Posts: 2,546
    Hi, Sometimes the right answer to a question is another question. So, my question: How about making a braze joint while purging with carbon dioxide, then cut the pipe open and see if any scale has formed? I'd be concerned about the 02 part of the gas affecting copper, but that's just a wild hypothetical guess. :p

    Yours, Larry
  • pecmsg
    pecmsg Member Posts: 2,887
    Just use N2
    EBEBRATT-Ed Member Posts: 11,996
    I have done some braze test joints while purging with Co2. It's not an issue. It's a lot cheaper and you get way more purging gas out of a bottle.

    If you want to stay with nitrogen it's fine with me
  • ratio
    ratio Member Posts: 3,174
    edited August 2021
    A better question would be "Does CO₂ decompose when passed across copper heated to a red hot temperature." I don't know for sure (my public school education ended last century!), but I wouldn't be a bit surprised if it does.

    We always just use N₂. Around here, an 80 CU FT bottle is like 12 bucks to exchange after you buy the first one.

    EBEBRATT-Ed Member Posts: 11,996
    Look on U tube "NathansHVAC Co2 brazing" he brazes tubing with and without Co2. See for yourself