My background is with BOC Gases as a field service tech on medical, industrial & the food industry. Our trainers taught us not to use co2 for purging. This is what I go by. Commercial grade co2 is not a pure gas. The cylinder of co2 on your truck is likely a by-product of the oil & gas industry and other places unless you have spec gas. What's the moisture content in co2 vs nitrogen? I don't know. I'll keep using nitrogen from an Airgas cylinder. Or maybe I'll sweat some coupons with co2 purge for inspection and document the outcome for my own good.
And one more thing, go ahead and fill your refrig unit with co2 for pressure testing on a very cold day. Blow it out quick. What will happen to some of co2 inside the compressor? I guess a good vacuum will solve this issue but why bother using it in the first place? It's not a great gas for leak testing. Nitrogen is much lighter and a better gas for leak testing and easier to evacuate.
We aren't talking welding, friend, so that information, while interesting, isn't really pertinent to the discussion we're having about using CO2 to prevent oxidation within a copper line being heated to 12-1400 degrees F.
Please, do as you suggest and try a couple of joints with CO2 and post pictures showing us how different they are from one done with nitrogen.
I'll be very interested to see the difference.
In order for CO2 to flash-freeze to dry ice, you would have to have LIQUID CO2 in the system. Paying close attention to pressure/temperature relationship of CO2 would prevent that from happening.
Why not just use Nitrogen? Its a known gas that has no effect by heat,does not hold or transfer h20
And is simple to aquire,regulate,use...
just sayin... why not use pure argon or Halon they both displace oxygen, and are odorless an contain no moisture.