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  1. #27
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    Show me documentation where it states it is okay to use co2 as a brazing purge gas.

    Do a search "co2 corrosion carbon steel".

    CO2 is not an inert gas.

    Maybe my terminology was a little strong. Unless somethings have changed, I read in one of my books never to introduce co2 into refrig systems. Having pulled high vacuums on the shells of many large cryogenic vessels, I can verify that it is much easier & faster to remove nitrogen with a vacuum pump than it is co2, air or any gas with a moisture content. Boiling off moisture is what delays busting below 500mi. I needed to get below 100mi on perlite tanks, and 10mi on super insulated mylar tanks.

    CO2 will also react to high heat such as it does in the GMAW.
    Read about it here.
    http://en.wikipedia.org/wiki/Gas_metal_arc_welding

  2. #28
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    Quote Originally Posted by Capz View Post
    Show me documentation where it states it is okay to use co2 as a brazing purge gas.

    Do a search "co2 corrosion carbon steel".

    CO2 is not an inert gas.

    Maybe my terminology was a little strong. Unless somethings have changed, I read in one of my books never to introduce co2 into refrig systems. Having pulled high vacuums on the shells of many large cryogenic vessels, I can verify that it is much easier & faster to remove nitrogen with a vacuum pump than it is co2, air or any gas with a moisture content. Boiling off moisture is what delays busting below 500mi. I needed to get below 100mi on perlite tanks, and 10mi on super insulated mylar tanks.

    CO2 will also react to high heat such as it does in the GMAW.
    Read about it here.
    http://en.wikipedia.org/wiki/Gas_metal_arc_welding
    We're not dealing with carbon steel, now are we? We're also not reaching GMAW temperatures in a brazing process, are we?

    Nitrogen isn't a perfectly inert gas, either. It will react under certain conditions.

    http://www.bristolcompressors.com/fi...881/200022.pdf see page 4

  3. #29
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    http://lvhvac.com/cope_bulletins/1177.pdf

    This was posted in the tools forum by slctech

    Copland recommends CO2 as a pressure test gas and purge gas but they have nothing in there regarding purge while brazing.

  4. #30
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    CO2 inert or not.
    Well, it does break down with high heat, plasma for example and with free water (which you should not have in your system anyway)
    What about the moisture in CO2 (food grade), the majority of CO2 production processes bring the moisture dew point down to below -50C, (via a regenerative molecular sieve drier, very similar to what is in modern refrig driers) before compression and liquification.
    Depending upon CO2 source, the CO2 is likely to go through an oxidizing agent. to rid of the reactive components, and then some purification via activated carbon.
    Even in the storage tank, further purification occurs and parts of the CO2 evaporates and re-condenses, "distillation" leave non condensables at the top which are blown to atmosphere.
    So even food grade, is still 99.96 pure, and how much are you using for purging during brazing.
    Why do we purge, to remove oxygen, so we do not get the "black crap, (a good technical term), why do you use CO2 extinguisher, to remove the oxygen and put the fire out.
    your choice.

  5. #31
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    Quote Originally Posted by itsiceman View Post
    http://lvhvac.com/cope_bulletins/1177.pdf

    This was posted in the tools forum by slctech

    Copland recommends CO2 as a pressure test gas and purge gas but they have nothing in there regarding purge while brazing.

    nice one.

  6. #32
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    Quote Originally Posted by barbar View Post
    CO2 inert or not.
    Well, it does break down with high heat, plasma for example and with free water (which you should not have in your system anyway)
    What about the moisture in CO2 (food grade), the majority of CO2 production processes bring the moisture dew point down to below -50C, (via a regenerative molecular sieve drier, very similar to what is in modern refrig driers) before compression and liquification.
    Depending upon CO2 source, the CO2 is likely to go through an oxidizing agent. to rid of the reactive components, and then some purification via activated carbon.
    Even in the storage tank, further purification occurs and parts of the CO2 evaporates and re-condenses, "distillation" leave non condensables at the top which are blown to atmosphere.
    So even food grade, is still 99.96 pure, and how much are you using for purging during brazing.
    Why do we purge, to remove oxygen, so we do not get the "black crap, (a good technical term), why do you use CO2 extinguisher, to remove the oxygen and put the fire out.
    your choice.

    Excellent observations, barbar.

  7. #33
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    Quote Originally Posted by jpsmith1cm View Post
    We're not dealing with carbon steel, now are we? We're also not reaching GMAW temperatures in a brazing process, are we?

    Nitrogen isn't a perfectly inert gas, either. It will react under certain conditions.

    http://www.bristolcompressors.com/fi...881/200022.pdf see page 4
    Pg 4 BRAZE ON SUCTION AND DISCHARGE LINES. Flow an inert gas, such as nitrogen or CO2, through the system
    at approximately 1/4 to 1 psig. This will reduce the possibility of oxidation inside the tubing. Braze on the
    suction and discharge lines and braze the process tube shut following the recommendation listed below.
    co2 is inert at room temperature. But the question that needs answering, is at what temperature does it become reactive? I don't have the answer to this question. see pg12
    http://www.lincolnelectric.com/asset...ture/C4200.pdf

    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.

  8. #34
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    Quote Originally Posted by barbar View Post
    CO2 inert or not.
    Well, it does break down with high heat, plasma for example and with free water (which you should not have in your system anyway)
    What about the moisture in CO2 (food grade), the majority of CO2 production processes bring the moisture dew point down to below -50C, (via a regenerative molecular sieve drier, very similar to what is in modern refrig driers) before compression and liquification.
    Depending upon CO2 source, the CO2 is likely to go through an oxidizing agent. to rid of the reactive components, and then some purification via activated carbon.
    Even in the storage tank, further purification occurs and parts of the CO2 evaporates and re-condenses, "distillation" leave non condensables at the top which are blown to atmosphere.
    So even food grade, is still 99.96 pure, and how much are you using for purging during brazing.
    Why do we purge, to remove oxygen, so we do not get the "black crap, (a good technical term), why do you use CO2 extinguisher, to remove the oxygen and put the fire out.
    your choice.
    Where are you buying food grade or premium co2 pumped into a 20lb cylinder? Maybe New Z but not here. Premium co2 goes to Coca Cola & Pepsi. There is usually a shortage of the good stuff which comes from the mid-west every year. That's right. It's railed into the east and tested before it's unloaded into the tankers for delivery to soda bottlers. Never sees a welding supply house storage tank. I think it's a by-product of the wheat production. Commercial grade for welding, not so clean. But now we are way off topic.

  9. #35
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    Quote Originally Posted by Capz View Post
    co2 is inert at room temperature. But the question that needs answering, is at what temperature does it become reactive? I don't have the answer to this question. see pg12
    http://www.lincolnelectric.com/asset...ture/C4200.pdf

    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.
    Food grade moisture content at 99.96 purity if all impurity was water would 400 parts per million (most refrigerants come from the manufacturer at around 60-80 ppm) Most refrig systems require under 30ppm (hence a drier even on new systems)
    Nitrogen or what you should be using is Oxygen free Nitrogen, has dew point close to -194C (-310f) and PPM is very low. (this need not apply to a pressure swing nitrogen as used in CA stores or at the local garage for tyre pumping)
    Industrial grade CO2 not sure about.
    It is very unlikely because I have not done the numbers, than you would get sublimation (vapour to solid) by reducing pressure of CO2 vapour only at standard temps..

  10. #36
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    Quote Originally Posted by Capz View Post
    Where are you buying food grade or premium co2 pumped into a 20lb cylinder? Maybe New Z but not here. Premium co2 goes to Coca Cola & Pepsi. There is usually a shortage of the good stuff which comes from the mid-west every year. That's right. It's railed into the east and tested before it's unloaded into the tankers for delivery to soda bottlers. Never sees a welding supply house storage tank. I think it's a by-product of the wheat production. Commercial grade for welding, not so clean. But now we are way off topic.
    Just but it from the local gas supplier, all the pub, clubs maccers, bk use it for on site carbonation.

    Also been in many CO2 production plants (mainly liquification), that do go to Coke and Pepsi around the world.

    CO2 comes from all sort of places. A swerage plant is a good source (and good quality), but because of the stigma is not used.

  11. #37
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    Liquid nitrogen vaporized & pumped into a cylinder will start at about 2.4 ppm. The cylinder could cause a slight rise in the moisture but not likely much at all.

    I tested moisture content many times in nitrogen. It always had a dew point below -70C or 2.4ppm. Used a Pittsburgh Cup which was a little like witch craft but always very reliable. Very interesting to test. Standard testing device for many years.

  12. #38
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    Another point to consider, is not just the purging gas, but what you are purging.
    For example copper is a noble metal (fairy non reactive), so in the refrig trade we do use very high grade copper, but in the plumbing industry, the copper purity can be as low 65%, so the impurities within the copper become the issue not the copper itself.

  13. #39
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    Quote Originally Posted by Capz View Post
    Liquid nitrogen vaporized & pumped into a cylinder will start at about 2.4 ppm. The cylinder could cause a slight rise in the moisture but not likely much at all.

    I tested moisture content many times in nitrogen. It always had a dew point below -70C or 2.4ppm. Used a Pittsburgh Cup which was a little like witch craft but always very reliable. Very interesting to test. Standard testing device for many years.
    If liquid nitrogen, I would of thought dew point would always be below -156C (if memory serves me right) critical temp.

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