SS tig root help from the pros????

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how is it going everyone? I just got my stainless preasure ticket in the oilfield.i have been welding carbon for years but just dove into the SS. i did my first job yesterday. it was on sched 40 three inch pipe, tig root and 316 stick to fill and cap. i did 9 welds and got them back from xray today and they all passed.  But when i was doing it i was not realy impressed with the root. it was all fused and smooth but it was at best flush if not a little bit concave.  was running knife edge prep and just over an 1/8th gap. 1/8th filler rod. 78-90 amps on a lincoln 305G, 25 purge at the tourch and 25 back purge. the spool was 120 inches total.  ok pros why wont the root go convex. like i said they passed a sour code xray so i guess they were not bad but not perfect. strive for the best.....
Reply:Stainless steel is noticeably  more sluggish than carbon steels (blame the nickel) which means it won't penetrate as much, or wet out quite as nicely. I grew up welding SS so personally I prefer to tig it over carbon steels. personally I would blunt the knife edge with a tiny land, and try keyholing. I would gap the pipe ever so slightly narrower than my rod and let it dig away the land/ keyhole to control my melt-thru.  When I did TIG roots, Flush was what I was shooting for because I could repenetrate if I was a little concave but if I was blowing through it was game over.  Also Personally I don't like doing my root pass with 1/8th I  would use 3/16th I think it's a little more manageable if I keyhole.Do you happen to know what the code is for lack of penetration/underfill at the root?  Sometimes they are more concerned with drop through more than suck back from a usage standpoint.  Finally 25 on the purge seems very high once you purge your whole volume we usually set it at 15 CFH tops. I've seen the back pressure from a high purge cause suckback.Welding EngineerCertified Scrap Producer
Reply:Personally I'd use smaller wire than 1/8". Don't be bashful with the wire , cram it in there. Btw I haven't had a bad hand weld in over 3 years so it works for me. I x-ray butt weld everyday as well to ASME Boiler Code section 1.
Reply:I would also just blunt the tip of your land just a hair and run a tighter gap with a little more amps, this has always helped me get more reinforcement on my roots.  However stainless does not like to wet out as much as CS does so if you run it like this you really need to focus and make sure your breaking down your edges.If I can get a flush bead on SS im happy, just a little suck up at 7 and 4 oclock is pretty normal for me as well.Have we all gone mad?
Reply:Originally Posted by MetarinkaStainless steel is noticeably  more sluggish than carbon steels (blame the nickel) which means it won't penetrate as much, or wet out quite as nicely. I grew up welding SS so personally I prefer to tig it over carbon steels. personally I would blunt the knife edge with a tiny land, and try keyholing. I would gap the pipe ever so slightly narrower than my rod and let it dig away the land/ keyhole to control my melt-thru.  When I did TIG roots, Flush was what I was shooting for because I could repenetrate if I was a little concave but if I was blowing through it was game over.  Also Personally I don't like doing my root pass with 1/8th I  would use 3/16th I think it's a little more manageable if I keyhole.Do you happen to know what the code is for lack of penetration/underfill at the root?  Sometimes they are more concerned with drop through more than suck back from a usage standpoint.  Finally 25 on the purge seems very high once you purge your whole volume we usually set it at 15 CFH tops. I've seen the back pressure from a high purge cause suckback.
Reply:3/16" ss filler is stupid imo. Give it a whirl but please post your results with pics.I run alot of orbital welding equipment and all the filler wire is .035 it just feeds it fast. If I'm welding anything under 3" it's 1/16" filler for me. I'd go 3/32" 3" to ? as long as it isn't thin wall.I think your heat is good.Bigger isn't always better. 9 times out of 10 guys that run big filler on ss at my work usually have crappy welds.
Reply:Heres a couple of ss weld pics on some 2" .440 wall 347. 100% x-ray of course. Btw these welds were welded all the way out with 1/16" filler wire at 78 amps.You can tell in the first pic I can carry a ton of metal even though it's just 1/16" filler. Much more fluid puddle than you will get using larger filler.It works for me. Attached ImagesLast edited by Showdog75; 05-21-2010 at 10:33 PM.