Using Nitrogen as a Shield Gas

[MotoFab]

Has anyone used Nitrogen as a shield gas for either GMAW or GTAW? I understand that Nitrogen is more or less used for 'back shielding' (term?).

But the commonly reported issue seems to be embrittlement this and embrittlement that.

"Hydrogen embrittlement. No Nitrogen embrittlement. No only a shield gas for the back side."

I sort of get the impression that the people speaking had not done any experimentation with a process of Nitrogen as the primary shield. Or tested the weld results. Sort of like the disparate POVs about polarity and gas with DC GTAW and Aluminum.

I cannot judge for myself because my supply is a small 80A Inverter SMAW. But I have played around so as to run itsy bitsy lap welds on 22ga steel using 1/16 6013. 20% of the time I burn through, but I just wanted to see if it could be done. (And maybe that is no big deal, I have no way of actually knowing.)

So please, how much violating of 'it can never work' or 'you're not supposed to' experience and testing have you done with Nitrogen?

Thanks fellas.

- Jim

[slamdvw]

I tried N2 on MIG... had better results running no gas at all. MM135, .023 wire on 1/8mild steel tubing,...

Have yet to try it on GTAW though... give me something to do tomorrow.

[gnm109]

I've never heard of it used as a shielding gas nor have I done it myself. My only question would be....why? It can't be any less expensive than Argon or argon C02.

The only use I've ever encountered for nitrogen gas was when I worked in the aeospace industry. They used it on pneumatic valves to open and close them. It's apparently very dry and resists moisture in pneumatic systems.

[chopper5]

i've only used it for a backing gas

[MotoFab]

Thanks for the answers so far guys.

I was wondering about the use of nitrogen as a shield gas because nitrogen can be and is often made on site from compressed air with a 'gas selective membrane' system. The essentially 'one time + maintenance' investment makes it very inexpensive for many industrial uses, as an oxygen purge gas, or chemical component.

Many other gasses can be 'sieved' in the same way, argon, CO2 etc. I am reading over some patents about the process.

Nitrogen is often used and generated on site as the shield gas for the now standard lead-free soldering process. Often bottled nitrogen was made the same way.

So I am asking about it as a primary shield gas. Since it is 'really great' for back purging, I was thinking that it might not be 'fully and oppositely unusable' as the primary shield.

Anyone else experimented with it as a primary shield?

- Jim

[Tailshaft56]

I'm sure it's been tried. Some one is always trying to find a better method. The gasses that are commonly used today are used because they have been found to give the best results or they are more economical to use. At one time gtaw was done exclusively with helium. This was a patented process of ( I think ) Union carbide hence the trade name Heliarc. Argon has largely replaced helium with modern gtaw process primarily do to the lower cost of the gas. There advantages and disadvantages to either gas.

I have seen nitrogen used as a purge gas as it will very readily absorb moisture. I believe the bottles you used to see tied to phone poles were nitrogen used to dry the old lead shielded phone lines.

[Steel66]

The reason why nitrogen is not used as a shielding gas for welding is because it is not an inert gas. Nitrogen can conduct electricity. It's a very poor conductor, but nevertheless, it can. Argon is much more expensive, but it is inert and very dense which makes it a perfect shielding gas. The additional components for shielding gases (O2, CO2, He, even Hydrogen) are all for specific welding applications and will either create a more fluid puddle or something like that.

[MAC702]

Originally Posted by MotoFab

I was wondering about the use of nitrogen as a shield gas because nitrogen can be and is often made on site from compressed air with a 'gas selective membrane' system. The essentially 'one time + maintenance' investment makes it very inexpensive for many industrial uses, as an oxygen purge gas, or chemical component.

Many other gasses can be 'sieved' in the same way, argon, CO2 etc. I am reading over some patents about the process.

Nitrogen is often used and generated on site as the shield gas for the now standard lead-free soldering process. Often bottled nitrogen was made the same way.

Dang, Jim, you've had me in the research books all morning out of curiosity, as well!

Now, I've seen these nitrogen generators for sale, and it got me thinking. If you get pure nitrogen out of the other end, that means the thing is venting oxygen-rich air at the same time, right?

Does it get ALL the nitrogen, or are there still significant amounts in the vented air? If it gets all of it, then it seems like the vented part would be 99.75% (or so) oxygen. The fact that this isn't an advertised feature has me thinking it must not get all the nitrogen, just enough to accumulate it.

[76GMC1500]

Nitrogen gas oxidizes at high temperature. I don't think the EPA would approve of you using nitrogen because you will be giving off a lot of NOx as well. Doesn't diffusing nitrogen into the surface of a metal make it hard as well like nitriding a crankshaft?

[pulser]

See attached discussion by Ed Craig on nitrogen purge.

http://www.weldreality.com/stainlesswelddata.htm

[MotoFab]

Originally Posted by MAC702

Dang, Jim, you've had me in the research books all morning out of curiosity, as well!

Now, I've seen these nitrogen generators for sale, and it got me thinking. If you get pure nitrogen out of the other end, that means the thing is venting oxygen-rich air at the same time, right?

Does it get ALL the nitrogen, or are there still significant amounts in the vented air? If it gets all of it, then it seems like the vented part would be 99.75% (or so) oxygen. The fact that this isn't an advertised feature has me thinking it must not get all the nitrogen, just enough to accumulate it.

I was thinking that too MAC, about the O2 'dregs', and had my ideas as well.

But the membrane is not strictly a sieve. Instead it is sort of a media that the different gas elements in the atmosphere travel through at different rates. The 'mixed' atmosphere gets pushed into the length of media and get 'stratified' if you will. Like a pousse-café, but using the friction of the length of filter media instead of gravity.

Gas spectrum analyzers 'stratify' the input elements by letting them travel through many miles of tiny capillary tubing, and the elements have different friction with the wall of the tubing, and travel at different speeds. So the element start out of the gate, but arrive win, place, and show at the finish.

The 'friction' of the packed media in the cylinder, and the 'long distance' of the great surface area (think carbon filter), produces a similar effect to a horse race.

Depending on the application, two media cylinders are used to get a constant supply of gas. One is being filled, and the other is being 'backflushed'.

To get scientific levels of purity, the output gas is passed through the process any number of additional times. If I recall, the first pass is 98% pure or so. The next pass then removes 98% of the remaining 2%, and so on.

Anyway, these 'molecular sieves' and associated hardware have been developed for all sorts of gasses, I was just asking about Nitrogen because it was the first 'gas filter' I came across that was at all related to welding. But there are molecular sieve gas generators for Argon, CO2 and many others.

Nitrogen molecular sieves have a ready market in industry, and the cost of the generators has come down over many years. It seems that since nitrogen is a good backshield gas, that essentially free nitrogen would have made it into the welding supply chain.

- Jim

[MotoFab]

Originally Posted by 76GMC1500

Nitrogen gas oxidizes at high temperature. I don't think the EPA would approve of you using nitrogen because you will be giving off a lot of NOx as well. Doesn't diffusing nitrogen into the surface of a metal make it hard as well like nitriding a crankshaft?

I understand. That makes sense. Do the plasma cutters that use shop air have that NOx problem as well? I mean, as they use a nitrogen/oxygen supply.

- Jim

[MAC702]

I remember reading that Ed Craig info. That was a good review. The diatomic nitrogen molecule breaks down in the arc. At that point, monatomic nitrogen is now soluable in the weld. At least with stainless, anyway. So backpurging is okay, because it doesn't really see the arc, just protects the hot metal.

So I wonder if there are the same issues here with the plasma cutter?

Now, the real question: Did Ed Craig write it, or steal it from someone else with no credit? Read the bit about when to use 308, 309, and 316 fillers on that same page. It is directly plagiarized from Lincoln Electric's website.

[MotoFab]

Originally Posted by pulser

See attached discussion by Ed Craig on nitrogen purge.

http://www.weldreality.com/stainlesswelddata.htm

Thanks for the link, and for the comments too, everyone.

I think we are looking at the same thing MAC. I do not know of Ed Craig, I was just looking at the text.

I see from pulser's link that certain gases "can" and "may" and "might" cause some issues. And I am not pointing to any lack of credibility, only lack of certainty. I think these are the times that best fit the purpose of 'process development'.

I was just wondering if anyone has gone beyond both teachings and initial point of view. And actually tried to take the use of nitrogen as a primary shield gas anywhere.

I am not saying you should now start trying this out from my suggestion, and on your dime, but maybe some have already gone to some lengths out of necessity or intentional practice.

There is certainly no denying the 'textbook' examples. I am just not clear that nitrogen is 'really great' in one place, and 'could not be worse' only .060" away. But such is the blessing and curse if innocence.

Certainly appearance can be an issue. And ultimate weld strength can be an issue.

I know we animals love our bad news, estimable or not. I think the obedient acceptance of bad news is related to survival. But that is the blessing and curse of human consciousness to both be aware of and have to deal with that older and better-developed part of us. You know, so new things can be tried and perfected beyond the point of textbooks. Lots of things have inertia, and point of view is quite formidable in that regard.

From the looks of it, welding will probably become a permanent hobby of mine. And as I find out more and more about the industry, it looks more and more like every other industry. And I did not see the need to 'feed the beast' as it were. You for sure understand the idea of 'biting the hand that feeds'. It looks to me that industry in general 'bites the hand it's feeding'. Ouch, no thanks.

- Jim

[B2N3 Welder]

We use N3 for shielding and back purge for 2205 duplex with 2209 filler and supposedly its to replace the nitrogen in the material while your burning it while welding and its the only way ive seen so far to get it too pass tests at -40.

[Diverbill45]

I've only used Nitrogen as a shielding gas once and it was a 90-10 mixture with hydrogen.

This mixture was used because the customer didn't want any blueing of the stainless steel on the inside of the pipe because deironized water was going to be used in the pipe. This worked quite well and the inside of the pipe around the weld bead turned out looking like chrome, with no blueing in the heat effected area.

[chicksdigwagons]

I think for the most part its not used as a primary sheild because of poor arc stability. Something to do with ionization capacity. Its all a little fuzzy for me right now, but thats the jist of it. Nitrogen does have its applications, but for most general welding an Argon based mix is the best so why bother with anything else?

[MotoFab]

Thanks for your answers guys.

I was wondering about the use of nitrogen as a shield gas because nitrogen is often made on site from compressed air with a 'gas selective membrane' system. The essentially 'one-time plus maintenance' investment makes it very inexpensive for many industrial uses, as an oxygen purge gas, or chemical component.

Read 'very inexpensive' as nearly free after the equipment investment.

Gas selective systems for Nitrogen are well developed and available. That is why I asked about it as a shield gas.

Gas selective systems, for Argon and CO2 say, are less well developed.

But equipment to generate Argon and other gasses from air will become more developed.

And the cost of bottled gas may come down as a result.

Plasma welding looks like one of the next big things that is inching its way down the price and supply line to your shop. I mean, it is not really an advanced process. It is essentially a straightforward reconfiguration of a plasma cutting torch. But it'll likely be priced to the moon with the addition of a $10 LCD panel and other fancy stuff to the major internals of a plasma cutter.

I am not getting down on the welding power supply industry, most every industry does it. Do you think the LCD screen on a washing machine is the reason for the price doubling?

Plasma arc welding (what is the acronym?) is a big gas user from what I have seen. Long-term 'free' gas looks fairly inviting.

- Jim

[pulser]

Link below is article concerning use of Argon with 1% Nitrogen shielding gas mix for the purpose of reducing ferrite formation in pulsed TIG welds of 304L stainless steel. With regard to welding problems with the mix, the author says that 1% Nitrogen tends to produce undercut as weld speed is increased, and says that 2% produces slag inclusions.

This topic brings to mind that in critical applications such as nuclear power piping, where control of ferrite in 300 series stainless steel welds is important, the welder should be aware that changes in the weld shielding may affect nitrogen pickup from the atmosphere and in turn affect the weld metallurgy.

As pointed out by the author, in general terms, a 300 series SS weld may be more prone to solidification cracking (hot cracking) if ferrite is less than about 3%. Ferrite helps prevent hot cracking related to sulfur content by holding sulfur in solution so that it is not in the form of a weak film around the austenite grain boundaries. Additionally, ferrite above 12% may be detrimental to corrosion Resistance of the SS.

http://aws.org/conferences/abstracts...apers/PE3A.pdf