View Full Version : brazing under nitrogen

24-03-2007, 10:38 PM
I have a question about brazing under nitrogen gas. I usually use nitrogen for VRV refrigeration pipe work with flow between 3 and 5 liter/min.
What's your opinion about it, is there a relation or a formula between the pipe diamater and the flow of the nitrogen gas ?
Thank for a prompt reply

The MG Pony
25-03-2007, 01:18 AM
it isn't about the flow per say it is about air displacement, little flow as plausible is my preferred method. Give it one good burst to drive all the air out then crank it down to just enough to keep air from getting back in.

25-03-2007, 05:54 PM
When we wrote our brazing procedures we could not find specific information relating pipe size to flow rate. Generally the literature just says to get rid of the oxygen. We tell our service people the following in our brazing procedures.
The procedure must be as follows:
ˇConnect a nitrogen cylinder to one end of the pipework to be jointed using a regulator set to a low pressure, the far end of the pipework to be open to atmosphere;
ˇTurn on the gas and regulate the flow to a flow rate can easily be felt on the back of a moistened hand about 0.03 to 0.06 CFM (about 1 to 2 liters per minute).
ˇThe nitrogen should be allowed to flow without building up a pressure in the pipeline. On larger diameter lines a plastic cap with a small hole punched in it can be fitted over the far end of the line to reduce the volume of gas required.
ˇContinue the flow until the joints have cooled.

The important things to remember are to create an atmosphere inside the tube that will not allow oxides to form, the nitrogen must start before you start brazing and continue until after the joint has cooled and do not allow the pressure to build up.
It can be difficult to set a flow rate so we allow them to adjust the flow rate until they can feel the nitrogen flow.

23-10-2010, 10:15 PM
when brazeing compressor inlet and outlet .can able to run nitrogen

23-10-2010, 11:00 PM
when brazeing compressor inlet and outlet .can able to run nitrogen
Is this statemant or question?
What ".can" mean?

24-10-2010, 08:30 AM
I must agree with MG Pony,displace the air/oxygen first with a brief burst and just have the nitro slowly slowly purging while you weld.