Back gas apparatus

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I need to weld fittings on vessels.  It's SS brewing vessels.  1/2"NPT coupling through Sanke kegs.  I'll be welding from the outside, obviously, but I do need the inside to be protected as well.  What I need is (pretty close to) sanitary weld (smooth/easy to clean/no pitting).  I know I need to back gas but I'm not sure what would be the best apparatus for this purpose.  I could use some inspiration...  Filling the whole vessels is out of the question (12-15 gallons each and I might do a bunch).I'm also wondering how to correctly connect this "secondary" gas to my single cylinder and regulator/flowmeter without compromising the need at the TIG torch.  What's the best/right way to do this?Thanks in advance for any help.USINUM - CNC routing workshopPaco's area - blogspot---Lincoln MIGpack180 (GMAW - FCAW)Miller Syncrowave 250
Reply:Originally Posted by PacoI need to weld fittings on vessels.  It's SS brewing vessels.  1/2"NPT coupling through Sanke kegs.  I'll be welding from the outside, obviously, but I do need the inside to be protected as well.  What I need is (pretty close to) sanitary weld (smooth/easy to clean/no pitting).  I know I need to back gas but I'm not sure what would be the best apparatus for this purpose.  I could use some inspiration...  Filling the whole vessels is out of the question (12-15 gallons each and I might do a bunch).I'm also wondering how to correctly connect this "secondary" gas to my single cylinder and regulator/flowmeter without compromising the need at the TIG torch.  What's the best/right way to do this?Thanks in advance for any help.
Reply:This is what I use.  About $300 US if I remember right. Attached Images
Reply:If you can TIG it overhead you don't have to fill the whole thing.  It really wouldn't take long to fill 12-15 gallons anyway.
Reply:My local welding supplier suggest that I would be fine with just a 'Y' on the output.  A double flow meter regulator would be ideal though, he agree.  My concern is that feeding two lines with a single flow meter will "disturb" the correct flow to the torch.Some more opinions?  I wont make a living from welding those fittings on vessels but I may have up to ten vessels in the next year on which I can have from two to six fittings to weld.  Boostinjdm apparatus would cost me ~250$cad.  A 'Y' would cost me ~$50cad.  I didn't count the back gassing hose nor the required fittings.USINUM - CNC routing workshopPaco's area - blogspot---Lincoln MIGpack180 (GMAW - FCAW)Miller Syncrowave 250
Reply:I've made several brew kettles, lauter tuns, etc. out of kegs.  I plasma cut a 10" diamter hole in the top, which fits a standard "Revereware" cooking pot lid.  I've welded on 1/2" SS pipe nipples for a drain valve or whatever.  The way I did it was to machine a step in the end of the pipe nipple so it could be very snugly inserted through a hole in the keg.  So on the inside of the keg, the reduced diameter end section of the nipple set proud of the keg surface by about 1/16", that way you can fusion weld this lip from the inside and get a smooth "sanitary" weld.  On the outside of the keg, the stepped nipple butts up on the keg and helps prevent burn through.  I did not shield the outside, but I kept the heat low, and only got a couple of melt thru spots with minor "sugar", which did not bother me since it was plenty strong and sanitary on the inside.  Of course it would be nice to shield the back side.  Its a little tough to see what you are welding, at arms length, inside a 10" hole but not impossible.
Reply:Paco,A gallon is only .15556 cu. ft.  A 15 gal container has 2.3334 cubic feet of volume.  The cost of 2.5 cu. ft. of Argon, compared to any fitting/aparatus you could fashion, is in the noise level.Plan to do all the fittings on one tank at the same time.  Purge/fill the tank with Argon before you start welding.  Use a y-valve and a ball valve off your flowmeter.  Once you start welding, simply set your flowmeter to about 5 CFH higher than you normally do.  Shut down the gas flow to the tank to just minimal flow.Not perfect.  Dual flowmeter is better  but this is a workable, inexpensive solution.Make sure you provide for a relief at the top of the tank so that pressure doesn't build and blow out your weld.  Argon, being heavier than air, will sit in the tank like if you were filling it with water.PS.  I'd personally use two argon tanks and two flowmeters, but I've got extra argon tanks sitting around.  At most you're talking about a couple dollars worth of argon.  Don't know of any backing shields or other means that could be done for less.Last edited by SundownIII; 04-30-2009 at 07:48 PM.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:Originally Posted by PacoMy local welding supplier suggest that I would be fine with just a 'Y' on the output.  A double flow meter regulator would be ideal though, he agree.  My concern is that feeding two lines with a single flow meter will "disturb" the correct flow to the torch.Some more opinions?  I wont make a living from welding those fittings on vessels but I may have up to ten vessels in the next year on which I can have from two to six fittings to weld.  Boostinjdm apparatus would cost me ~250$cad.  A 'Y' would cost me ~$50cad.  I didn't count the back gassing hose nor the required fittings.
Reply:I would try to stay away from filling a large chamber with noble gas and subjecting it to ARC. Some guys that work with neon may have some input on this. A bad ground could be a concern. If you stick a tungsten and it disintegrates under power. Things like that with a chamber of noble gas might be bad.If the noble gas was allowed to reach high voltage, caused by an ARC, even though a small amount of amperage is available. Maybe just one amp. You could still achieve very high wattage. There are some high tension lines, that carry less then ten amps. However some are flowing at over 100,000 volts. You could actually use 18 gauge low voltage wire to carry that kind of amperage, except that the wire is not physically capable of carrying that kind of wattage. That is why we call the American wire Gauge, the American wire Guide. So any single power line, at any moment could be delivering 500,000 watts. You do not want to be holding something getting or giving you 500,000 watts of heat or power.        Sincerely,             William McCormickLast edited by William McCormick Jr; 04-30-2009 at 09:40 PM.
Reply:Originally Posted by william mccormick jri would try to stay away from filling a large chamber with noble gas and subjecting it to arc. Some guys that work with neon may have some input on this. A bad ground could be a concern. If you stick a tungsten and it disintegrates under power. Things like that with a chamber of noble gas might be bad.If the noble gas was allowed to reach high voltage, caused by an arc, even though a small amount of amperage is available. Maybe just one amp. You could still achieve very high wattage. There are some high tension lines, that carry less then ten amps. However some are flowing at over 100,000 volts. You could actually use 18 gauge low voltage wire to carry that kind of amperage, except that the wire is not physically capable of carrying that kind of wattage. That is why we call the american wire gauge, the american wire guide. So any single power line, at any moment could be delivering 500,000 watts. You do not want to be holding something getting or giving you 500,000 watts of heat or power.        Sincerely,             william mccormick
Reply:Originally Posted by Boostinjdmwtf???
Reply:Billy Mac,Off the meds again, huh?You keep posting and the guys in the white suits are going to come and get you.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:Maybe I am slow, but it sounds to me that you are saying everybody that has ever backpurged a pipe or a tank is wrongly doing so.  Not trying to pick a fight, but that's the way I understood your post.I will ask....If filling a tank with argon is wrong.  What is the correct way to backpurge a container such as a section of pipe/tube or a tank of some sort?
Reply:I guess we should all be lucky that Billy Mac didn't recommend filling that keg with Hydrogen prior to welding.I really think he's LOST IT this time.  I'm just glad that nobody takes him seriously.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:Originally Posted by SundownIIII guess we should all be lucky that Billy Mac didn't recommend filling that keg with Hydrogen prior to welding.I really think he's LOST IT this time.  I'm just glad that nobody takes him seriously.
Reply:Boostin,You're pretty new on here.Ol Billy Mac is well known.Well known for being a bonafide WACK CASE.Don't get him started on the "tinfoil hats".Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:Hmmmmm.........Is there a Sr ?????
Reply:Originally Posted by SundownIIII guess we should all be lucky that Billy Mac didn't recommend filling that keg with Hydrogen prior to welding.I really think he's LOST IT this time.  I'm just glad that nobody takes him seriously.
Reply:Well Billy,I'm not even going to address most of your rediculous comments, however one did stand out.You want to let Miller know that their inverter tig machines CANNOT weld in AC mode without HF.  The Dynasty series, in particular, use HF for starting the arc only.  They do not operate in HF Continuous.Please go take your meds.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:Originally Posted by William McCormick JrI would try to stay away from filling a large chamber with noble gas and subjecting it to ARC. Some guys that work with neon may have some input on this. A bad ground could be a concern. If you stick a tungsten and it disintegrates under power. Things like that with a chamber of noble gas might be bad.If the noble gas was allowed to reach high voltage, caused by an ARC, even though a small amount of amperage is available. Maybe just one amp. You could still achieve very high wattage. There are some high tension lines, that carry less then ten amps. However some are flowing at over 100,000 volts. You could actually use 18 gauge low voltage wire to carry that kind of amperage, except that the wire is not physically capable of carrying that kind of wattage. That is why we call the American wire Gauge, the American wire Guide. So any single power line, at any moment could be delivering 500,000 watts. You do not want to be holding something getting or giving you 500,000 watts of heat or power.        Sincerely,             William McCormick
Reply:Originally Posted by William McCormick JrI would try to stay away from filling a large chamber with noble gas and subjecting it to ARC. Some guys that work with neon may have some input on this. A bad ground could be a concern. If you stick a tungsten and it disintegrates under power. Things like that with a chamber of noble gas might be bad.If the noble gas was allowed to reach high voltage, caused by an ARC, even though a small amount of amperage is available. Maybe just one amp. You could still achieve very high wattage. There are some high tension lines, that carry less then ten amps. However some are flowing at over 100,000 volts. You could actually use 18 gauge low voltage wire to carry that kind of amperage, except that the wire is not physically capable of carrying that kind of wattage. That is why we call the American wire Gauge, the American wire Guide. So any single power line, at any moment could be delivering 500,000 watts. You do not want to be holding something getting or giving you 500,000 watts of heat or power.        Sincerely,             William McCormick
Reply:Originally Posted by schofner413I work at an aerospace company that specializes in making IGV's which are the very front of the b-52 engine behind the nose cone that directs the air flow into the engine. These parts are make entirely out of AMS 4911 titanium. As you know, titanium reacts with the oxygen (among other things) in the air when heated above 800oF, and basically turns into a rainbow without a pot of gold at the end.  Well, I've been welding these parts for about 2 years now and they are welded inside a tank that is about 6' in diameter and 1' wide. We let these tanks purge with ARGON for at least a half an hour before we can start welding. We have manufactured at least 1000 of these parts since I've worked there, and not once have I ever heard of this problem with noble gases. The part that you are welding on in a chamber is (or should be) grounded. The reason that lightening travels through the air from the big grey clouds is because it is looking for a ground. Now, knowing that electricity looks for the path of least resistance, one (Ben Franklin) would think that the air, or actually the moisture in the air is that path and not the noble gas in the air. I myself have become the path of least resistance a couple times while welding, and the worst that has happened was I let my foot off the pedal instantly(subconscious reaction?) and felt very alert, better than a cup of coffee to wake you up!!     The point Im getting at is that ARGON is a shielding gas that has been used in welding for a long time, because it works. Personally I think that having an oxygen cylinder in a fab shop is much more dangerous than using ARGON in a tank..........just my $.02
Reply:Originally Posted by SundownIIIWell Billy,I'm not even going to address most of your rediculous comments, however one did stand out.You want to let Miller know that their inverter tig machines CANNOT weld in AC mode without HF.  The Dynasty series, in particular, use HF for starting the arc only.  They do not operate in HF Continuous.Please go take your meds.
Reply:Billy Mac,I really appreciate your explaining your personal situation (getting shocked, etc) to us in great detail.  It makes it much easier to understand where you're coming from.YOU FRIED YOUR BRAIN.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:Think I might change my name, I may get confused with this guy, whom is already deeply confused !!!!BillyOriginally Posted by BillyThink I might change my name, I may get confused with this guy, whom is already deeply confused !!!!Billy
Reply:This is how we do it, Disclaimer; "I am just an a$$hole welder, don't take it personally ."
Reply:Originally Posted by William McCormick JrI do not agree that the oxygen and acetylene tank is more dangerous then the argon or helium tank. Only because I have never had an accident with the oxygen and acetylene, while doing work with them. Because I know what oxygen and acetylene can do. When I was hurt, it was with helium. DC beam welding in straight polarity. If I had known that could happen it would not have happened. I have been hurt fooling around making large bags of oxygen and acetylene. I had one blow up in my hands, a large heavy duty lawn and leaf bag. Ha-ha. I had slight whistle in my ears, a little burning in my chest. But laughed actually. You never had a problem because you never let your ground go. Listen to some of these guys talking about slapping a ground clamp on a tank that might be sitting on cement or worse asphalt.  I let sparks dance on me, I get hit with my laser power supply, and I do not even flinch. One time it was hitting me for a couple seconds before I even realized it. Helium is high voltage stuff if you let it get away from ground. Argon is too, but helium is even more dielectric. I like that you share your experience, but I have checked this out, and it is real. It is not recommended that you fill large areas with helium or argon and use electrical equipment within. Do you vacuum out the chamber before put in the argon? If you leave the vacuum on for a while, you might notice a lot less moisture in the chamber.        Sincerely,             William McCormick
Reply:Think that this would work?  I would use a thin foil gasket to make a better seal. Attached ImagesUSINUM - CNC routing workshopPaco's area - blogspot---Lincoln MIGpack180 (GMAW - FCAW)Miller Syncrowave 250
Reply:Would you really nead the thin foil gasket? The gas needs a way out. If you seal it up tight the pressure is going to push your weld puddle out. Just think of your welding torch, it doesn't seal against the part you're welding. So long as you have the shielding gas flowing over the weld zone pushing the atmosphere away you should be good. I think your purge device would probably work just like it is.
Reply:Originally Posted by William McCormick JrBasically what point do you not agree with?I can say things about people, nasty things, with no scientific knowledge or even the slightest bit of understanding. I could probably keep the guys on the board laughing for hours. But what does that have to do with noble gas in large volumes?Basically what point do you not agree with?       Sincerely,             William McCormick
Reply:Originally Posted by MetarinkaYou can't get such a high voltage step up from an argon filled container for so many reasons.the ionization potential of inert gases IS high and yes that IS why it's harder to keep an arc going in helium. That's also why they invented square waves as the amperage will theoretically never drop to 0, but jump immediately to the rated current.You can weld square waves without HF but it's harder to maintain an arc.anyways there's no real shock hazard outside of what is already common from welding when using an inert purged chamber. Because of skin affect.  The electric arc will always take the path of least resistance which will be the surface of the metal shell. Not the volumes of dielectric gas. In order to create the needed resistance you would have to create an insulated area where nothing had greater potential than the argon path.even if that was all said and done. you would never be able to step a welder up to 50,000v or some other absurdly high voltage.  high freq start units are already high voltage (albeit very low current) and they don't kill anyone.  even at 100% efficiency if you managed to step up a normal weld current lets say 50 amps and 20 v to 50,000v you would be down to 0.02A (V x A= watts)  and at 0.02A with no resistance that's not enough juice to kill you, but it would give you a nasty jolt.  Any Tig welder who has lived long enough has got some shocks from high frequency starts. But they aren't lethal.also mind you no step up transformer is that efficient, and due to many other principals and resistance of any loop you would loose a good deal of energy just trying to hit 50,000v so it would be less than 0.02A.
Reply:Originally Posted by Boostinjdmwtf???
Reply:can you get inside of the vessel? If you can, then make a cup out of metal that will completely surround the back side of the weld by an inch or so.
Reply:Originally Posted by Marcel BauerLovin' it!!!Very entertaining thread...
Reply:Originally Posted by MetarinkaYou can't get such a high voltage step up from an argon filled container for so many reasons.the ionization potential of inert gases IS high and yes that IS why it's harder to keep an arc going in helium. That's also why they invented square waves as the amperage will theoretically never drop to 0, but jump immediately to the rated current.You can weld square waves without HF but it's harder to maintain an arc.anyways there's no real shock hazard outside of what is already common from welding when using an inert purged chamber. Because of skin affect.  The electric arc will always take the path of least resistance which will be the surface of the metal shell. Not the volumes of dielectric gas. In order to create the needed resistance you would have to create an insulated area where nothing had greater potential than the argon path.even if that was all said and done. you would never be able to step a welder up to 50,000v or some other absurdly high voltage.  high freq start units are already high voltage (albeit very low current) and they don't kill anyone.  even at 100% efficiency if you managed to step up a normal weld current lets say 50 amps and 20 v to 50,000v you would be down to 0.02A (V x A= watts)  and at 0.02A with no resistance that's not enough juice to kill you, but it would give you a nasty jolt.  Any Tig welder who has lived long enough has got some shocks from high frequency starts. But they aren't lethal.also mind you no step up transformer is that efficient, and due to many other principals and resistance of any loop you would loose a good deal of energy just trying to hit 50,000v so it would be less than 0.02A.
Reply:Originally Posted by PacoThink that this would work?  I would use a thin foil gasket to make a better seal.
Reply:What kind of flow do you guys use for "continuous" back purging?I'm having a bit of hard time getting it correctly purged.  Maybe it has to do with the fact this Argon is heavier than air and I'm trying to purge upward from down (welding flat and purge apparatus is under to the other side)...  or there's too many leaks (that's why I was considering using an aluminum gasket)...  or not enough purge gas coming (I've tried 5 to 10 CFH)...  or all of three...?!I should expect shiny or slightly colored SS on the purged side, correct?USINUM - CNC routing workshopPaco's area - blogspot---Lincoln MIGpack180 (GMAW - FCAW)Miller Syncrowave 250
Reply:Originally Posted by PacoWhat kind of flow do you guys use for "continuous" back purging?I'm having a bit of hard time getting it correctly purged.  Maybe it has to do with the fact this Argon is heavier than air and I'm trying to purge upward from down (welding flat and purge apparatus is under to the other side)...  or there's too many leaks (that's why I was considering using an aluminum gasket)...  or not enough purge gas coming (I've tried 5 to 10 CFH)...  or all of three...?!I should expect shiny or slightly colored SS on the purged side, correct?
Reply:i just did your project a couple weeks ago. here is what i did. first we used full 1/2 npt fittings so we could thread in a screen from the inside and a valve to the outside. I placed the fitting centered in the wall of the keg so the weld would be in the spot where their weren't any threads. for a purge i cut a soda can in half and taped it to the inside of the keg. I don't have a back purge setup for the dynasty yet so i just put the torch over the NPT fitting and hit the pedal and let the gas flow into the backside that way. I also did this after welding every quarter of the fitting to keep the gas turning over. the end result was a little light blue color in spots on the back side but zero sugar. keep in mind that all of you fittings are pre/during boil so you don't have to have that super smooth sanitary weld on the inside. if it were your fermentor that would be another story.I am getting ready to build a gravity system to mount these kegs and plan on posting up some pics when it is all done.
Reply:This is what I get.  Most of it disappear with some hand brushing with SS brush and pickling take care of the rest.  I was expecting the back purged area to look like the front area...  It's not burned like when there's no back purge but it's definitely oxidized on surface.USINUM - CNC routing workshopPaco's area - blogspot---Lincoln MIGpack180 (GMAW - FCAW)Miller Syncrowave 250
Reply:Just asking a question here, dont take offense. OK?  What would happen if you filled the container to be welded with water first and then hung the hose in there to back purge the weld zone. Too much moisture? Just a thought.  Harold
Reply:Originally Posted by WelderskelterJust asking a question here, dont take offense. OK?  What would happen if you filled the container to be welded with water first and then hung the hose in there to back purge the weld zone. Too much moisture? Just a thought.  Harold
Reply:Hope somebody else gives a better reason to not fill the tank with water and purge with gas. If not I think I would not even hesitate. I dont think either one of these reasons would have been thought of.
Reply:Should I expect a different aspect or color from the back purged weld?Link to pictures.Thanks for feedback.USINUM - CNC routing workshopPaco's area - blogspot---Lincoln MIGpack180 (GMAW - FCAW)Miller Syncrowave 250
Reply:Originally Posted by PacoShould I expect a different aspect or color from the back purged weld?Link to pictures.Thanks for feedback.
Reply:Originally Posted by 4sfedPaco,You're not getting a good purge on those welds.  Either wait longer for the tank to purge, or make a small container to cover just the area you want to protect.Jim
Reply:Originally Posted by PacoThat's exactly what I'm doing   I wait at least a minute before starting to weld for the can to fill with argon.  Also, I fitted an aluminum gasket to seal most of the leak even though I want some bleeding to occur.  I know the argon is there as a match will suddenly extinguish when pass over the hole.  I'm purging constantly during the weld at ~3-5 CFH.Below is the exact setup I have.
Reply:Are you sure the can isn't trapping air?  Like an air pocket under an overturned bowl in the kitchen sink.  I'd ditch the can, put a piece of tape over your fitting an purge the whole keg.  Just don't stick your head in there....My name's not Jim....
Reply:Kinda new here, but have you guys tried this stuff? I just tried it, and seems to work pretty good.http://www.solarflux.com/Pages/Productinfo.htmlHobart BetaMig 250Miller Dynasty 200DX