oxidation scale in copper tube and fittings

I would be interested in members views on the prevention of oxidation scale in copper tube whilst brazing and what they think is the best means of prevention. Our current method is to cap both ends of the tube. Both caps have a 1/4" copper tube brazed into the cap. Nitrogen is passed through a tube into the top capand allowed to bleed through the bottom cap as it is lighter than oxygen.Getting the flow rate right without wasting nitrogen seems to be a bit hit and miss. Any suggestions to flow rates, alternative methods etc?

Between 2 to 5 psig should do it, as to alternatives, sorry don't have one. ;)

I use propane, and at that temp it appears to all most consume any previous oxide. Allot trickier set up though.

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Originally Posted by The MG Pony

I use propane, and at that temp it appears to all most consume any previous oxide. Allot trickier set up though.

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Please explain how you can purge PROPANE through a pipe while you are brazing it? :eek:

hehe, I use a flash back arrester and a burn vent and use a low flow rate, it is only good for smaller Jobs where you can work in a ventilated area, not too practical for field stuff, but for in shop or at home it works great.

Helium would be another plausible alternative.

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Originally Posted by The MG Pony

I use propane, and at that temp it appears to all most consume any previous oxide. Allot trickier set up though.

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Since the propane is burning in the copper pipe you are introducing contamination into the system by doing this. The combustion by-products of the propane...

In a large system built on the customers site you would absolutely need a hot work permit, which someone might consider questionable for the process you are doing.

Not to mention the fact that you are reinventing the wheel and bypassing traditional methods of using an "inert" gas for the purging.

No the combustion is not happening any where inside the system, I use it only for my own stuff due to not having a good Nitrogen system, for a customers site I would not use such a method, I would use Helium or Nitrogen, technicaly Helium is better as it is a truly inert gas, but if time where absaluetly criticle and for some reason I could not aquier either of the aboce mentioned it will work as a fail safe.

Regarding internal cleanliness during soldering of interconnecting refrigeration copper pipework I recommend the following.
Employing Nitrogen as an inert gas to firstly purge the pipework of air, then maintain a flow rate based on the pipe diameter / length (read as internal volume) Note: if the flow rate is to high the nitrogen may cause the silver solder spit (causing holes) during the soldering process. this also wastes nitrogen. the correct flow rate for varied applications should be acheived through diligent experience.

Handy hint.
Manufacture a copper sleeves (at various pipe sizes for differing pipe applications) That are blanked off at one end. Drill a hole in the centre of the blanking end plate and solder a 1/4: Male Flare to solder fitting. Expand the other end of the tube to fit over the refrigeration copper tube you wish to solder. This fitting will assist in reducing wastage of Nitrogen (Innert gas) when brazing it will also stop any air being draw into the refrigeration lines (by a venturi effect) during brazing.

At the other end of the refrigeration pipework place a second copper sleeve the also has a blanking plate however the exhaust hole should be off set located at the top of the blanking disc, this will ensure that the refrigeration pipe work fills with dry nitrogen prior to soldering (minimising any internal oxydisation and scale.) and also improving the management of nitrogen during the soldering process.

we once discussed a nitrogen generator.
Seems nobody is using it.