Argon Purge
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Thread: Argon Purge

  1. #1
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    Argon Purge

    I had to put some Tri-Clover fittings on a S.S. tank yesterday that is being used to make hard liquor. It’s a stand up tank that measures 2’ in diameter and 5 ˝’ tall. Because it has to deal with a consumable product it has to have smooth welds on the inside, but it’s not possible to weld the inside. The only way to achieve this is by back purging the inside with argon, crank the heat up a little and allow the metal melt on the inside for a full-penn weld. So I threw a hose inside connected to a bottle at about 15cfm for about 5 minutes and then I welded the bottom fitting. I had it capped off so none of the argon could escape. I looked inside the fitting to see that it did work okay. So I started the purge again for the top fitting and waited. After about 20 minutes I still wasn’t sure if it was fully purged and didn’t know how to test it until I came up with an idea. I used a lit lighter and placed it down inside the tank to see if there was any oxygen left and it still burned. So I checked it 10 minutes later and the lighter went out as soon as I got it close to the top of the tank. So I was good to go on my welding.
    Just thought I would share my new trick on purging big tanks with you all.

    -Mike
    Common sense in an uncommon degree is what the world calls wisdom.

  2. #2
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    Re: Argon Purge

    Did you arrange payment in liters?

    It is difficult to know when the vessel has been purged enough. An oxygen meter is the best way, but very expensive. A canary wouldn't work, it probably croaks at about 15% O2, still too high for welding. I have seen a crude tungsten filament device powered by a battery, if the O2 is low enough, the filament will glow red and not burn up.

    I wonder what Oxygen level is needed to support a butane lighter flame? I suspect O2 could still be fairly high, several percent, but not support a flame. SS welding in critical applications requies O2 in the less than 100 ppm level, can't see that hard liquor would be that critical though.

    Quote Brainfarth: "So I threw a hose inside connected to a bottle at about 15cfm for about 5 minutes and then I welded the bottom fitting. I had it capped off so none of the argon could escape."

    Usually, the purged vessel is vented through a hole somewhat smaller than the inlet, so that the system is slightly pressurized and the air can escape out of the vessel. Since argon is heavier than air the vent may work best at the top of the vessel. On large vessels, a slow, gentle flow of purge gas may reduce mixing due to turbulence and allow the somewhat stratified air to be expelled using less argon purge.

    Is it possible to show a pic of the weld penetration? The discoloration of the weld penetration and HAZ will indicate how well the vessel was purged.

    This link shows weld color vs O2 content of the purge.
    http://www.intercononline.com/welding/ypurge.htm

    This a spreadsheet to calculate purge time as a function of pipe size. http://www.sperkoengineering.com/htm...ime%207-00.XLS
    Last edited by pulser; 09-13-2007 at 01:20 PM.

  3. #3
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    Re: Argon Purge

    Did a quick search and came up with the following:

    "Qu.4 What oxygen level is required to keep the candle burning?
    The candle was extinguished after 30 seconds when the air was made up with 18.8% oxygen. This shows that the candle flame requires an oxygen level of greater than 18.8% oxygen to remain alight."

    From this site: http://www.picotech.com/experiments/...n/results.html

  4. #4
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    Re: Argon Purge

    It's not the same thing, pulser. When you are purging a tank, you try to do so slowly and gently, so as not to mix the argon with the air inside the tank. The idea is to slowly fill the tank with argon, pushing out the air that was inside before.
    Miller Econotig
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    Yes ma'am, that IS a screwdriver in my pocket!

  5. #5
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    Re: Argon Purge

    Joe,
    what's not the same thing?

    And didn't you just say the same thing I said, purge slow & push out the air?
    Last edited by pulser; 09-13-2007 at 02:33 PM.

  6. #6
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    Re: Argon Purge

    I have been told that in this area , (World Famous Napa Valley ) nitrogen is also used for purging S.S. tanks(during welding ) for wine (they say it's "Good Enough". and nitrogen is a whole lot cheaper gas .
    [SIZE="5
    "Yardbird"

  7. #7
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    Re: Argon Purge

    Quote Originally Posted by pulser
    Joe,
    what's not the same thing?

    And didn't you just say the same thing I said, purge slow & push out the air?
    Wierd, somehow I did not see your first post in this thread, only the second. I am at a loss as to how that happened.
    Miller Econotig
    Cutmaster 38

    Yes ma'am, that IS a screwdriver in my pocket!

  8. #8
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    Re: Argon Purge

    Everyone knows..or should know by now that argon is heavier than "atmosphere"..

    If you can get the hose to the bottom then the atmosphere will rise out the top because its the only way out..
    Even if you can't it should work out just fine anyway..

    ...zap!


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  9. #9
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    Re: Argon Purge

    Quote Originally Posted by Roy Hodges
    I have been told that in this area , (World Famous Napa Valley ) nitrogen is also used for purging S.S. tanks(during welding ) for wine (they say it's "Good Enough". and nitrogen is a whole lot cheaper gas .
    Good point Roy, you're right.
    As long as nitrogen is not exposed to the arc, which it is not on a closed root joint for the tank or pipe, it will remain a diatomic molecule (N2, two atoms) and will not react adversely with the stainless steel. If used in the shielding gas on the arc side of things, N2 will break down into atomic N, and react with the SS.

    Here is some previous discussion on Nitrogen.
    http://www.weldingweb.com/showthread...nitrogen+purge

  10. #10
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    Re: Argon Purge

    zap,

    Mostly true but not totally accurate that "argon is heavier than 'atmosphere' ".

    CO2 is heavier than argon. There is a lot of CO2 in the atmosphere.

    weight of argon = 40
    weight of O2 = 32
    weight of N2 = 28
    weight of water vapor = 18
    weight of CO2 = 44

    Ignoring all trace percentages of atmospheric noble/inert gases or other atmospheric items like hydrocarbon vapors or other solvent vapors, etc.

    Really heavier than atmosphere (again ignoring the trace percentages) would be krypton (weight=84), xenon (weight=131), or radon (weight=222). Purge with them. $$$$$$$

    For general practical purging, argon works. Nice slow argon fill in the bottom of the tank/pipe/vessel and allow the original atmosphere to be gently displaced and pushed out the top somewhere.

    Critical work may use a vacuum purge first and then inert backfill or be done in the vacuum chamber itself.
    Last edited by MoonRise; 09-13-2007 at 06:22 PM.

  11. #11
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    Re: Argon Purge

    Thats what I like about this place

    Getting to the very bottom of the equasion..

    Between you and pulser we have a top notch "break it down" team..


    ...zap!


    I am not completely insane..
    Some parts are missing

    Professional Driver on a closed course....
    Do not attempt.

  12. #12
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    Re: Argon Purge

    I should rephrase that… I capped the tank off with a 4x4 magazine held down with a roll of duct tape.
    Unfortunately I don’t have any photos because the tank is in Portland brewing Ouzo right now. I never knew that is was illegal to make that stuff in the states till recently.
    I didn’t have any purge time calculations available to me at the time, so I had to do a bit of guesstimation. I had to do some more purging today with a 3” S.S. tube. The inside came out with flying colors. All straw colored.
    I never knew that CO2 was heavier than argon. Good reads.


    -Mike
    Common sense in an uncommon degree is what the world calls wisdom.

  13. #13
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    Re: Argon Purge

    If the argon mixes with the atmospheric air, it will not seperate, so slow is key. The rule I was always taught was run about 5 volumes of purge gas, nice and slow. This helps insure that the little bit of mixing that is inevitable is taken care of.

    So, for for the tank you started on, which is about 20CF, that would be about an hour per volume at 20CFH. Of course, for the bottom, the mixing could be minimized and the bottom isolated by putting a fine screen (like fine mesh SS window screen) around the volume being purged, and purge inside the screen. Amazingly, in the absence of a breeze, this pretty well isolates the volume being purged from air being drawn back in by turbulence from the outlet of the purge line.

  14. #14
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    Re: Argon Purge

    Anyone here ever use flux coated TIG wire? Does a fine job but takes a bit of getting used to. But I believe it has no code spec and is therefore unusable in code app's. Saves a ton of argon and time as well in non code situations. But hey, what the customer don't know won't hurt em either.

    ELVIS

  15. #15
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    Re: Argon Purge

    I'm not sure there is such a thing as "flux cored TIG wire". I've been certified in ASME 316 flux cored wire. And I'm pretty sure that they don't have a filler rod with cored flux for TIG welding applications that meet any kind of code. With an argon background, any additional coverage would be pointless. And to mention that in those applications with flux, they add various strengths to the metal. Sounds more like you are using flux core wire as a filler to save money. And I'm not sure how you can TIG without argon.. to save money. I've gone as far as to use 316-16 welding rod as filler(banging the flux off) because I forgot my filler rod. I'm sure that in an extreme application that it would fail, but since it was not, I took the chance. ! Be aware of what you are doing and the repercussions of what hazards it may cause.

    As for a breeze, I was not worried about air mixing with the gas after a few minutes since the fittings were at the bottom of the tank, especially at 15cfm enclosed. The corners rolled over nicely, but not in a 1 ppm atmosphere. They were almost in blue'ish range . But as for the second set at the top, they were almost clear (that's where I get my average of straw. ). Mostly because of my lack of confidence of purging such a large tank. I'm sure I could have saved a few bucks in gas if I had known the amount of time it took for a clean purge.

    -Mike
    Last edited by Brainfarth; 09-15-2007 at 03:53 AM.
    Common sense in an uncommon degree is what the world calls wisdom.

  16. #16
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    Re: Argon Purge

    There is both flux-cored and flux-coated wre intended for TIG.

    For a decent discussion: http://www.aws.org/cgi-bin/mwf/topic_show.pl?tid=8934

  17. #17
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    Re: Argon Purge

    Ahh... I thought he was using corred wire from a MIG application.
    Scratch part of that last message.
    Common sense in an uncommon degree is what the world calls wisdom.

  18. #18
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    Re: Argon Purge

    Enlpck...good link there. It is as explained in that thread. Takes some getting used to, has no code procedure, but works awesome when you spend some time practicing with it. I find the hardest part of using it is how hard it is to see the weld puddle because it is always covered with flux. Also, you must of course use argon as usual through the torch else you fry your tungsten. I will take afew minutes this week and perform a weld using it, then post pics to show those who may be interested in trying it how well it can work. Huge time saver but is not listed as a code procedure. Hope I didn't take this thread off track.

    ELVIS
    Last edited by ElvisW; 09-16-2007 at 11:03 PM.

  19. #19
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    Re: Argon Purge

    I'd like to mention one drawback regarding flux coated tig wire. Say you are welding an open root head seam on a vessel, and there is no way to get at the root from the inside after welding. Using flux coated wire will obviously leave behind slag both inside and out. Some of it will pop off as the weld cools and shrinks (don't get too close, it has a way of finding my lips and that HURTS), but many times some will remain and I believe one reason this wire is not listed is because of this. A customer doesn't want slag laying around inside a pipe or vessel. I have found a way around this though and it works in most cases. After the weld is completed, take an air chisel and bang the heck out of the entire weld, this will loosen the remaining flux that may be hanging around inside there. Then either rinse it or blow the debris out. Perhaps this will be helpful info.
    BTW, the wire we use is manufactured by ESAB. I'm sure there are others.

    http://products.esabna.com/EN/home/f...tainless_steel

    ELVIS
    Last edited by ElvisW; 09-16-2007 at 11:18 PM.

  20. #20
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    Re: Argon Purge

    While in this thread, i'd like to ask a pertinent question of my own. Has anyone access to a purge chart of sorts? I'd be interested in having a general idea of purge times relating to vessel/pipe size and flow rate. We all hate guessing and wasting unnecessary gas. And welding a bit to see of course means ruining what purge you already had. Please, no PLEASE help me find one! And Brainfarth too.

    ELVIS
    Last edited by ElvisW; 09-16-2007 at 11:45 PM.

  21. #21
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    Re: Argon Purge

    Elvis, check post #2,at the bottom.

  22. #22
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    Re: Argon Purge

    DUH.....thanks TEK. Missed that.

    ELVIS

    So as not to confuse anyone, I'm not always allowed to use said flux wire and have to purge at times like the rest of you!
    Last edited by ElvisW; 09-17-2007 at 01:05 AM.

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