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Up Topic Welding Industry / Technical Discussions / Purging SS with Nitrogen vs nitrogen/hydrogen 90/10
- - By Pipeslayer (**) Date 07-03-2008 12:51
what is the major difference if any, I've used nitrogen vs argon and know the difference there? Is it a penetration issue?
Parent - - By js55 (*****) Date 07-03-2008 13:16
Are you asking about purging with hydrogen????
Parent - - By Pipeslayer (**) Date 07-03-2008 14:05
No. About using pure nitrogen as opposed to a 90/10 mix. Is there are quailty issue. There certainly is a cost issuenin the 2.
Parent - - By js55 (*****) Date 07-03-2008 16:15
To my knowledge there is no advantage to purging with a hydrogen mix. Shielding with hydrogen is a different matter. The disadvantage of purging with hydrogen I think is BOOOOOOM!!!!!
90/10 as shielding is called Formier gas and was once common. The hydrogen allows greater speed of welding and penetration and provides cleaner roots as well. It is exclusively, to my knowledge, used with GTAW (at least in the common fusion processes)and as shielding only for roots.
It has fallen into disfavor I think due to H2 cracking concerns but may still be used from time to time with alloys not as susceptible. Not a recommendation on my part. I've never used it but I can see where it would have distinct advantages.
As for nitrogen, its cheap and can be used as a purge, but it is an active gas and the alloy being welded should be considered.
Parent - - By Pipeslayer (**) Date 07-03-2008 17:01
we're welding type 304 SS with 316 filler. I'd like to purge with nitrogen (100%) for a cost savings over the project duration. I don't feel well with Hydrogen.
Parent - - By js55 (*****) Date 07-03-2008 17:09
Do not purge with any kind of hydrogen. Nitrogen is OK in many applications for SS.
May I ask why 316?
Do a search on this forum, we've talked about nitrogen purges on SS before.
Kotecki did a terrific nitrogen purge article in the Welding Journals SS Q and A, if you can find it.
Parent - By Pipeslayer (**) Date 07-03-2008 17:17
Projects specs called for 347 and that is a cheaper wire  than 316. But for overall quality and weldabilty we felt 316 was  the right choice.
Parent - - By GRoberts (***) Date 07-03-2008 19:31
I knew I had read something about this recently- it just took me a while to remember where it came from.  It appears that the author is saying that hydrogen in the purge gas will not require as low an oxygen content on the back side to get an acceptable ID surface as will without hydrogen, or to have smoother root transitions.  Obviusly, the hydrogen content would also need to be kept low to avoid the possiblity of explosion or fire.

http://www.polysoude.com/documents/english/Back_purging_for_welding_of_stainless_steel_pipes.pdf
Parent - By js55 (*****) Date 07-03-2008 19:36
Good find Greg. Got it printed.
Up Topic Welding Industry / Technical Discussions / Purging SS with Nitrogen vs nitrogen/hydrogen 90/10

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