[Benpower]

Hi all,

I have to purge weld a 1000 ltr tank 304 St steel.
Can I use nitrogen without any problems for purging.
I assume fill volume from top as nitrogen is lighter than oxygen?
Do any other rules apply when purging with nitrogen?

Cheers Ben

[Otto Nobedder]

Nitrogen is fine for purging. When TIG welding, the puddle behaves just slightly differently, in a way I can't really explain, but it's not a problem. The density difference between nitrogen and atmosphere/oxygen is so slight that where you introduce it is immaterial; Flowing at any rate that will provide enough volume exchanges in your lifetime will cause mixing. One option is to introduce it very cold at the bottom, or very hot at the top.

Haven't you asked this question already?

Steve S

[Benpower]

Thanks Steve,

I have asked questions about purging but not with nitrogen. Can mixing be avoided with argon if one introduces it at a very low rate, in turn saving on gas?

[Otto Nobedder]

Argon will have to be introduced painfully slow (time consuming) and still require at least two volumes of exchange to get close to the ideal "0%" oxygen. Nitrogen is one-tenth the cost in high volume, so you could do five volume exchanges of N2 for the same cost as two of argon. (Roughly.)

Using N2 from a dewar gives you the option of feeding it quite cold. This makes the N2 more dense and settle easily, and you could gauge the completion of purge by measuring outgas temperature high in the vessel.

I hope I'm making sense... I'm a bit in my cups this evening and don't want to mislead you because of my alcohol content...

Steve S

[Benpower]

Hey Steve,

Thanks, hope you are having a good night!
When you say painfully slow, how many L/min would you recommend?

Cheers