nitrogen purging

[freezy]

When nitrogen purging I seal the hose into the pipe and apply a slight pressure, however I find if its too low the flow rate drops off and if its too high brazing becomes difficult.
Does anyone have any methods or tips they could share.

Someone once told me something to do with balloons, what's this all about - was it a wind up to make me look daft on site????

[Industrial tech]

Hi freezy,

Tape a plastic bag over the other end of the tube and poke one or two small pinholes into it. Set your nitrogen regulator to maintain 3 psig in the pipe and you should be good.

Hope this helps,

Dave

[Brian_UK]

Condoms can also be used if they are easier to come by

[Peter_1]

....Tape a plastic bag over the other end of the tube and poke one or two small pinholes into it. Set your nitrogen regulator to maintain 3 psig in the pipe and you should be good.Dave

You don't need a certain pressure - in fact a pressure isn't allowed - but you need a certain flow.
There excist pressure relief devices - what is the correct name for the bl..y thing you screw on a pressurised bottles - where you can adjust a certain flow instead of a pressure, the same they use when MIG or TIG welding.

[frank]

It's a flowmeter Peter

[Industrial tech]

You don't need a certain pressure - in fact a pressure isn't allowed - but you need a certain flow.

According to the RSES Sam manual you do, and that pressure would be 3 psig

[chillyhamster]

As long as the air is displaced by Ofn then this will provide the desired effect, ie. no oxidisation or scale formation on the inside of the pipe. positive pressure is just a comfort factor to indicate that there is Ofn in the pipe any pressure above atmospheric will suffice.

[jamcool]

stick to 2-3 psig on your pressure regulator leave the flow meter to impress the boss and u will be the cats meow

[Brian_UK]

.....positive pressure is just a comfort factor to indicate that there is Ofn in the pipe any pressure above atmospheric will suffice.

It's funny how we refer to things without always realising what we have said...

Positive pressure is exactly the same as any pressure above atmospheric during the normal ways of the world. Unless we are working within a test chamber of some sort but lets not go there...

[freezy]

Thanks for your replies

Would it not be better to leave the end of the pipe open so the air has an exit route or does this not matter as air contains 78% nitrogen and so it becomes the predominant gas?

[rbartlett]

usually I just stick a screwdriver through the end caps. one to fit the nitrogen hose in and the other to let it out the other end.

first I 'blast' some through then throttle back to a trickle.

bear in mind the pipes will need time to cool below the 'scaling' temperature before removing the nitrogen flow

cheers

richard

[freezy]

usually I just stick a screwdriver through the end caps

wow, you are a strong man, I struggle to get 'em off !!!

[rbartlett]

wow, you are a strong man, I struggle to get 'em off !!!

ah but by sticking a screwdriver through them you don't need to take them off !!

cheers

richard

[Peter_1]

We use heat crimp sleaves for this (with glue) and before heating the sleeves, fit a 1/4 pipe with shraeder valve in it.

[chillyhamster]

Hi Brian, your post is true, but what i ment was, that most people would have a positive pressure ie. one that they could feel rather that a pressure which just displaces the air with 100% Ofn.

[Brian_UK]

Yeah, I know Chilly, I suppose the best test for a slow/low gas flow is the eyeball test but you can't always get the pipe up to your eye; which, i suppose, is where the extra plastic tubing taped into the outlet pipe comes in useful.

[sean1]

the way i was tought in college was to leave the end open and never to obstruct the end and set the regulator to 2-3 psi

[chilly]

Hi Guys,

Heres my 2 pence worth.

I first of all connect the guage to one pipe, and disconned the other, Tape it up and make a very small hole at the top of the taped off end. Theory - nitogen is higher than oxigen.

I then apply about 3 psi and leave it to blow through for a while, This is the rule of thumb bit, the longer and bigger the pipe, the longer i will leave it, between 1 and 10 minutes. If Im feeling pushed for time i will give it a good blast (50psi) of nitrogen before i tape the end and then poke my small hole at the top. I usualy use abit of brazing rod to poke my hole. After ive purged it to a point where i feel all oxigen hass been replaced by nitrogen throughout the entire pipe, I will drop the pressure right down, and i mean Right down I wet the back of my hand and I want to feel a slight but definate draft of nitrogen leving the pipe, I do not expect to see a reading on my guage, If I do it will be 1 psi or less. Then I widen the hole to about 3mm wide but ensure it stays at the top of the pipe end, This is to stop air / oxigen re entering the pipe.

Then i braze my pipe content in the knowlage it is imposable for the copper to oxadize, as there is absolutly no oxigen to react inside the pipe.

It is very common when people have just connected a nito line, opened the guage to a couple of psi and started brazing imediatly or within afew seconds, for oxidization to occure. The object is to totaly remove oxegen, dropping the oxegen level so there is more nitrogen mix is simply not the objective and will aloow oxidization.

[Brian]

As long as Nitrogen is present in the tube, oxidisation will not occur. Just pressurise the tube above atmospheric and then allow a very slight flow of nitrogen, the rest will take care of itself. Don't take the pressure too high and make sure there are no other external leaks before the brazed joint, which could cause the venturi effect i.e. make sure your brazes' are good upto that point (brazing isnt that hard!)

[chilly]

As long as Nitrogen is present in the tube, oxidisation will not occur. Just pressurise the tube above atmospheric and then allow a very slight flow of nitrogen, the rest will take care of itself. Don't take the pressure too high and make sure there are no other external leaks before the brazed joint, which could cause the venturi effect i.e. make sure your brazes' are good upto that point (brazing isnt that hard!)

Have to disagree, Just because nitrogen is present doesnt mean you wont get oxidisation, Infact this is the kind of thinking that is causing people to go to the trouble of setting up their nitrogen only to deem it totaly inefective because they havent used it properly, If you dont use nitrogen and braze with natural air in the pipe i trust you have no problem beleveing oxidisation will take place, But then there is Nitrogen in the air naturaly.

The point is before you braze you need to remove ALL oxegen from the air in the pipework. Only then will you not get oxidisation. Nitrogen is not a gas that when introduced in any amount will magicaly stop oxidisation,

I think its important to highlight, Nitrogen does absolutly nothing, it is just a cheap off the shelf gas that we can use to replace the oxegen around the pipe. Ie we cannot remove the oxegen without replaceing it withsomething , nitrogen is a handy gas we can replace it with, and as it naturalu occurs in the atmosphear anyway we can release as much as we want of it safley.

To inhibit oxi(egen)dation we need to remove the oxigen compleatly. To do diferently just reduces the oxidisation, it doesnt stop it.

[Brian]

That is exactly what I have just said Chilly. PRESSURISE the pipe first then allow a FLOW of nitrogen. This gives the effect of PURGING the line. Then continue to allow nitrogen to flow. This will remove all the OXYGEN in the line. Simple as that!

[chilly]

Peace

I've no doubt you mean it correctly, but the way you worded it could have been interprated totaly diferent.