Proper welding process for 3/8" thick stainless tube butt weld

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I am a long time lurker and a semi-novice welder.TIG and stainless are newer to me and I am only doing small light fabrication with that process right now.My question is about a situation at work (I will not be doing the welding) We have a large stainless vessel 9' 10" diameter, 13.5" high. It holds a LOT of liquid. In order to stand it up in the building they had to cut 2 of the legs off to erect and will be welding them back on once it is up-right.The legs are Stainless tubing at what I would guess is 3/8" thick and somewhere around 8-10" diameter I would guess.From the looks of their prep work it looks like they will be butt welding them back together. They are cut sort of straight with a porta band and look like they were marked so they could put them back on at the exact same orientation so the uneveness will line back up. The knocked the corners off the cut at a rough 45, but only about an 1/8" worth. They have an Econotig sitting there ready to go.I am no pipe welder but it seems to me it would be important to get full penetration on these welds and given what I see done for prep this won't be the case. I could be wrong, thats why I am asking you guys. What would the pros do? These guys are kind of a jack of all trades rigging co. and they fab some stuff as needed so maybe I shouldn't be second guessing them but it is a very expensive tank and a lot of weight in fluid will be in it.Thanks for any feedback you may have
Reply:Since there shouldn't be any significant side load, I'm guessing it will be ok with out full penetration under compression.  Are the legs going to be gusseted?Miller Dynasty 200DXMiller 252 Miller 250xMiller Syncrowave 250Miller AEAD200 LegendMiller 375 Xtreme plasmaLincoln WeldPak 100Victor O/A
Reply:Originally Posted by AKmudSince there shouldn't be any significant side load, I'm guessing it will be ok with out full penetration under compression.  Are the legs going to be gusseted?
Reply:Originally Posted by fastbubNo gussets
Reply:50 1/2" long to where they weld to the tank. The legs are welded to some plate that is thicker than the walls of the tank  to spread out the load. The legs themselves where cut roughly in half and will be butt welded back together. Looking at the drawings, the legs are actually Schedule 40 6" stainless so .28" thickLast edited by fastbub; 11-11-2013 at 07:00 PM.
Reply:I would say Full Pen with a purge on back side ,, think about it, the original design called for a single piece. If they are going with a partial pen the I would recommend some kind of reinforcement such as gussets
Reply:I would want full penetration, bevel with appropriate land.It could be accomplished by rolling a backing ring to be tacked to one of the open ends, just for ease of welding.
Reply:You're gonna have to bevel the edges to get a sound full pen weld.  IIRC, the Econotig is a very underpowered low duty cycle machine.  You could likely solar flux the inside of the leg tubing, then weld it without back purge as there would be no problem inside the legs if the flux cracked off some day.  I'd want to have at least 250 amps on the dial and a pedal to weld .280 stainless.  I think your machine puts out 160 amps.TA Arcmaster 300CM3XMT 304S22P12 suitcase feederX-Treme 12VSOptima pulserTA161SMaxstar 150STLHypertherm PM45OP setupStihl 020AVP, 039, 066 Magnum
Reply:A process vessel that holds liquid is subjected to dynamic loads, eg. fatigue. You don't want partial pen welds on those legs.As Argon is heavier than air, you'll need to insert it from above the weld into those legs, or choose another suitable method or gaz.
Reply:Originally Posted by Drf255You're gonna have to bevel the edges to get a sound full pen weld.  IIRC, the Econotig is a very underpowered low duty cycle machine.  You could likely solar flux the inside of the leg tubing, then weld it without back purge as there would be no problem inside the legs if the flux cracked off some day.  I'd want to have at least 250 amps on the dial and a pedal to weld .280 stainless.  I think your machine puts out 160 amps.
Reply:Originally Posted by kingneroA process vessel that holds liquid is subjected to dynamic loads, eg. fatigue. You don't want partial pen welds on those legs.As Argon is heavier than air, you'll need to insert it from above the weld into those legs, or choose another suitable method or gaz.
Reply:Originally Posted by Showdog75250 amps tigging stainless? What are you smoking? This is my daily bread and butter and I can tell you I've never seen ANY stainless tig welded anywhere near 250 amps.
Reply:Originally Posted by rgfab242I think he was meaning he would want a 250A for the duty cycle more than the top end. A 250A machine would be able to run the necessary amperage all day long. That Econotig is only gonna run a minute or two before it needs 8 or 9 minutes of cool down time.
Reply:That calculator is SO far off when it comes to code tig welding it isn't even funny. I weld pressure parts to asme code and even the orbital welders I run don't come close to 250 amps on very heavy wall stainless. Not even on carbon. I very rarely see 100 amps on stainless hand welding period.
Reply:??? 5 inches per minute at 300 amps???I am having trouble wrapping my head around that....little help?
Reply:Originally Posted by geezerbill??? 5 inches per minute at 300 amps???I am having trouble wrapping my head around that....little help?
Reply:I've given this some more thought today. My responses were directed to out of position welds like this repair will have to be made in. The Miller chart I'm pretty sure is based on flat welds. There's a big difference in what kind of heat a easy flat weld can handle verses out of position welds. I still think the Miller chart is out of line for the majority of welders even if welding flat. With that said I rarely see north of mid 80's amperage wise tigging stainless tubing. I weld my share of 2" .440 wall 347 100% x-ray stainless. Just my 2 cents.
Reply:this may be a double post, the first went off to never, never land.it appears to me that the numbers given were extrapolated from the lowest grouping.  i don't know that position was factored in but it may well have been.250/300 amps?   .187 dia tig rod,  never used it.you obviously weld quite a bit of stainless but for myself i don't find i have to radically change the amperage for an out of position weld.  there may be some variation but not a lot.  more a function of material thickness than anything else.  isn't that true.?Last edited by ncountyline; 11-14-2013 at 08:11 PM.
Reply:I'm talking 5g and 6g butt welds on tube. Ain't happening at 200+ amps.