309LSi

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I am currrently writing a procedure to MIG 304 and 516 GR70. I have decided to use 309 LSi. I am wondering if I can get away without using backing gas. This is going to be an RT'ed joint. Thanks for your responses.
Reply:Any time I weld stainless with out back gas, the other side looks like crap.Thats all I know.What is an RT'ed joint?DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:RT without purge good luck
Reply:Originally Posted by David RAny time I weld stainless with out back gas, the other side looks like crap.Thats all I know.What is an RT'ed joint?David
Reply:i was told by our AI that you dont need to back gas for mig only on tig do you need itChuckASME Pressure Vessel welder
Reply:Years ago, I did some automated weld development for pulsed MIG of 1/4 and 3/8" plate, single pass, open root, horizontal 2G, and was suprised to see the weld penetration of the back side looked OK.  I think that a combination of fast cooling (30 ipm travel), with the open root and a slight drag angle on the torch, provided enough protection to prevent "sugaring".Not sure, but you'll probably need back side shielding, unless the joint is open root and all conditions are just right.  Can you mockup the joint and do some test welds?
Reply:Ever see "sugaring" of the stainless in an x-ray . It wouldn't pass inspection would it?
Reply:Don't know of any code that would allow sugaring.  If RT (radiographic testing, X-ray) is required, it's extreamly unlikely that sugaring would be accepted.
Reply:well all my stainless passed x-ray bend and pull .1G 2G 3G down ,all open root short circuit root with spray fill and covernow tig needs to have backing gas usedChuckASME Pressure Vessel welder
Reply:Thanks for the replies. I will be utilizing backing gas although it is a pain in the a@#.
Reply:Originally Posted by chopper5well all my stainless passed x-ray bend and pull .1G 2G 3G down ,all open root short circuit root with spray fill and covernow tig needs to have backing gas used
Reply:backing gas is not needed with mig, weld will not sugar but with a slight amount of "purge" the bead will look nicer and not as "dirty". where I work we are working on food grade 316 10" sch 10 and not using a "purge" but are using tri-mix for the cover and it seems to be working fine (90+ welds, all x-ray, all good!!)