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Thread: Flowing nitrogen while brazing

  1. #21
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    What's curious is using nitro is sounding like new technology. I was shown the method in 1970 when I started in the mechanical end.

    Something that hasn't been known well is brazing with a refrigerant still in the system. Not nitro but residual refrigerant. Most have made repairs like this. Not wanting to use nitro and haul the vac pump. A quickie braze and on your way.
    The heat breaks down the refrigerant into separate molecules. Does this represent a serious contamination? I wouldn't ask an instructor about this as instructors tend to stick to their guns and never recommend anything that might go against the book.
    The system drier might manage this contamination but I'm just throwing it out there. Will refrigerant prevent oxides? Has anyone seen any paper on this?
    Give me a relay with big enough contacts, and I'll run the world!

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  3. #22
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    What's curious is using nitro is far from new technology. I was shown the method in 1970 when I started in the mechanical end.

    Something that hasn't been known well is brazing with a refrigerant still in the system. Not nitro but residual refrigerant. Most have made repairs like this. Not wanting to use nitro and haul the vac pump. A quickie braze and on your way.
    The heat breaks down the refrigerant into separate molecules. Does this represent a serious contamination? I wouldn't ask an instructor about this as instructors tend to stick to their guns and never recommend anything that might go against the book.
    The system drier probably manages this contamination but I'm just throwing it out there. Will refrigerant prevent oxides? Has anyone seen any paper on this?
    Give me a relay with big enough contacts, and I'll run the world!

    You can be anything you want......As long as you don't suck at it.

    If a person wants to create a machine that will be more likely to fail...Make it complicated.

    USAF 98 Bomb Wing 1960-66 SMW Lu49

  4. #23
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    Quote Originally Posted by hvacker View Post
    What's curious is using nitro is sounding like new technology. I was shown the method in 1970 when I started in the mechanical end.

    Something that hasn't been known well is brazing with a refrigerant still in the system. Not nitro but residual refrigerant. Most have made repairs like this. Not wanting to use nitro and haul the vac pump. A quickie braze and on your way.
    The heat breaks down the refrigerant into separate molecules. Does this represent a serious contamination? I wouldn't ask an instructor about this as instructors tend to stick to their guns and never recommend anything that might go against the book.
    The system drier might manage this contamination but I'm just throwing it out there. Will refrigerant prevent oxides? Has anyone seen any paper on this?
    That's a really interesting thought. I generally avoid it because of the nasty smell and burning my nostrils but now I almost want to go try it on some scrap to see what it does.

    Sent from the Okie state usin Tapatalk

  5. #24
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    Hfc’s in open flame form hydrofluoric acid & carbonyl fluoride gases. Both highly toxic.

    Hcfc forms hydrofluoric & hydrochloric acid gases. All highly toxic.

    Read the sds on each....

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  7. #25
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    Quote Originally Posted by ehsx View Post
    Hardly. The best US brazer came in 57th. They typically do brazing on production lines, well trained and had mentors. Plenty of practice. Competition is judged on time & quality. Would like to see how they would have done on larger pipe.
    Pretty sure itsiceman's post was oozing sarcasm.....

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  8. #26
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    Quote Originally Posted by ehsx View Post
    Hardly. The best US brazer came in 57th. They typically do brazing on production lines, well trained and had mentors. Plenty of practice. Competition is judged on time & quality. Would like to see how they would have done on larger pipe.
    Yea sorry. Being sarcastic. There was a different thread of the same topic where I was not team no flow but wasn't dead set in flowing no matter what either.
    I provided a real world example and might have even opened a few eyes who only ever seen the worst case scenario demonstrations.

  9. #27
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    Always do, didn't in the soft solder days, but always do now.

  10. #28
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    Quote Originally Posted by ehsx View Post
    Hfc’s in open flame form hydrofluoric acid & carbonyl fluoride gases. Both highly toxic.

    Hcfc forms hydrofluoric & hydrochloric acid gases. All highly toxic.

    Read the sds on each....

    Well known reaction but it usually won't stop most techs from putting up with the negatives.
    Back when systems were blown off because of a total roast or whatever, exposure was common.

    It depended on the tech what procedure to follow. There isn't one. I've blown off systems that were
    high enough with acids my gauges became copper plated. Before recovery machines there was little choice
    except to blow it off. I would rent a machine rather than expose mine to these contaminates.

    I bought one of the Brute gauge sets some years ago. I thought it would recover faster. When I hooked
    the set to a system I discovered it was a bad burn. The gauges were aluminum with aluminum valve seats.
    The acids ate thru the seats. When I asked the manufacture why aluminum, I was told I shouldn't hook up to
    systems with acid. I asked how one could know that before hooking up?
    Sure I could acid test before BUT when the burn isn't known before hand most will hook up w/o giving thought
    to damaging gauges.
    I milled the manifold, found some brass faucet seats, tapped the holes and screwed the seats in. I don't know
    why Brute didn't consider this problem when they made it.
    Aluminum + acid = bad.
    Give me a relay with big enough contacts, and I'll run the world!

    You can be anything you want......As long as you don't suck at it.

    If a person wants to create a machine that will be more likely to fail...Make it complicated.

    USAF 98 Bomb Wing 1960-66 SMW Lu49

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  12. #29
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    Nitro is a must and anybody doubting it go do some testing and look inside to see everything you are putting into the system.
    When I was deciding on what to do for a bunch of mini splits at my rental properties I did a simple test.. a couple of copper pieces brazed and the same sizes silver soldered. Than I did a simple vise test by squeezing the pipes until they pulled away from the braze or silver solder. No doubt the braze was stronger but the insides of the pipes were black and black pieces loose. The silver solder stayed together until I just about flattened the joint.
    To braze without nitro I would fire the tech on the spot .
    No nitro equipment I would trust silver solder ..
    Last edited by BVdog; 07-21-2021 at 12:00 AM. Reason: spelling

  13. #30
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    Quote Originally Posted by ehsx View Post
    Recommended. But if oxygen flow to the inside is blocked and the pipe is not overheated brazing will not cause carbonizing inside of the pipe and no discoloration.
    Larger pipes this becomes more difficult. When using nitrogen open pipes should be blocked or blanked so that nitrogen flow is restricted to a minimum. Pipe should not have any pressure.
    Good info along with those pictures. So no nitrogen was used on those joints? Just a big, fat, quiet, properly dialed in flame just getting the pipes hot enough to flow the braze? Or at least I'm guessing is how they achieved that along with years of practice.

  14. #31
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    The pipe ends were blocked, standing on end, so no thermal air flow. No nitrogen, no excess heat, correct tip selection & settings, proper preheat….

  15. #32
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    Most of the guys I have worked with don’t purge nitrogen. I do most of the time, but it has caused leaks. My company won’t pay for a purging regulator, so I have to use a regular regulator. It’s very hard to keep it at a constant low flow. I did some testing years ago by purging nitrogen through an open 1/2” OD pipe and brazed in some couplings. I found that it took a pretty good flow to prevent oxidation inside the pipe. Maybe it was due to the pipe being open on the outlet.

  16. #33
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    Quote Originally Posted by hands View Post
    Most of the guys I have worked with don’t purge nitrogen. I do most of the time, but it has caused leaks. My company won’t pay for a purging regulator, so I have to use a regular regulator. It’s very hard to keep it at a constant low flow. I did some testing years ago by purging nitrogen through an open 1/2” OD pipe and brazed in some couplings. I found that it took a pretty good flow to prevent oxidation inside the pipe. Maybe it was due to the pipe being open on the outlet.
    That could have been it. If the opening is too big then it spills out while letting air mix in. You should plug the end and make a small hole in the end of the plug so that you can create enough velocity out of that hole to stop air from mixing. I have found this to usually only become problematic if brazing near the end of the pipe.

    You want to make sure you are blowing out the system before starting your purge otherwise you are just slowly feeding the braze with a slug of air that is between the outlet and the nitrogen.

    There are a number of other factors that can cause carbon, for example when oil is burnt it can cause carbon, other additives if they remain may also create filth inside the pipe. The nitrogen will push out the air that entered while the repair was being preformed so it will still lessen the severity of the debris formed inside the pipe so it is still a good idea to use it, in fact it’s even more important to use it knowing that there already will be stuff inside the system that will partially plug a small strainer. If the nitrogen is not used then that may be the difference of negligible quantity’s and a call back visit to clean the strainer.
    Quickly, I must hurry, for there go my people and I am their leader!

  17. #34
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    I suppose that you mean a flow of nitrogen at 5 psi when we braze pipe lines in the system to eliminate oxidation

  18. #35
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    Quote Originally Posted by bornjanuary25 View Post
    I suppose that you mean a flow of nitrogen at 5 psi when we braze pipe lines in the system to eliminate oxidation
    Negative. Limit nitrogen flow to the minimum to prevent air entry. The line should not be under a measurable gauge pressure, restrict pipe ends so there is only a slight flow. If not capped on large horizontal pipes nitrogen will flow in the bottom of the pipe at low flow rates. Gauges are available that read flow instead of pressure for low flow rates.

    Filler will not flow properly if the joint is under pressure.

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  20. #36
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    Quote Originally Posted by bornjanuary25 View Post
    I suppose that you mean a flow of nitrogen at 5 psi when we braze pipe lines in the system to eliminate oxidation
    Yup, 5psi is WAY too high, unless you are just purging, then dropping pressure off before brazing.

    With any notable pressure, you run the risk of blowing out joints.

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  22. #37
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    Quote Originally Posted by 71CHOPS View Post
    Yup, 5psi is WAY too high, unless you are just purging, then dropping pressure off before brazing.

    With any notable pressure, you run the risk of blowing out joints.
    As you know 5 psig form nitrogen cylinder is too low pressure and the flow corresponding this pressure is too low also specifically when you release this flow

  23. #38
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    Quote Originally Posted by bornjanuary25 View Post
    As you know 5 psig form nitrogen cylinder is too low pressure and the flow corresponding this pressure is too low also specifically when you release this flow
    What?

  24. #39
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    Quote Originally Posted by pecmsg View Post
    What?
    What 2x?

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    “If You Can Dodge A Wrench You Can Dodge A Ball”

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