Stainless Exhaust Without Argon Purge, V-Band vs Marman flanges

You can weld Stainless without argon purging. You just need to cut a backing band and properly tack it into place.
There are many different kinds of V-Band flanges. Standard V-band flanges are great because one size fits all. The standard machined steel ones that fit over the tube need to have the tube stick out on one side and recessed on the other, so the assembly holds itself together during assembly and doesn't leak so easily. Care must be taken during the welding process to minimize gap and accompanying weld distortion. Any inconsistent gap is going to cause distortion, since more weld metal = more heat distortion. Whatever gap you do have during fitment, keep it even by distributing your tack welds. Flanges with grooves in them are easier to weld, but there's no guarantee. The benefit of grooved V-band flanges is shallow assembly.
Marman V-band flanges are a stamped steel creation. Since they're made of steel tubing, it's easier to get a perfect fitment and equally perfect weld. Easily the best choice for most exhaust systems. As long as the flange doesn't glow red hot, you're in good shape.
304 Stainless steel is most corrosion resistant below 700F, 375C. As long as it's blue, you're home-free, life is good, and the steel isn't even trying. Once it turns grey, you're past 450C, 800F. That's fine, but it lets you know that you're making it earn its life.
--Sure, you can run 304 stainless steel to 1500F, 800C, Bright orange red hot. Avoid bombarding it with salt water during these times. It's not the end of the world, but you're in the realm of aging, instead of time-proof.
Marman and conventional V-bands are both great pieces if implemented correctly.

[@DORIGTT]

I love your welding method for 'eliminating' the need to back purge. It solves a problem I'm having with a seam splitting. Thanks a mint!

[@deankay4434]

I am going to watch again, listen closely but it sounds like the name should be "The Good, The Bad and The Ugly". Now, nothing against the video at all, but at the very end, those who don't have everything we need for "V-Bands" proper or perfect good looking welds, should not even try! I like your insert collar to prevent "Sugering" but after 40+ years of fixing cars, ASE Master Tech since 78, my MIG was new in 84 and built like a tank. It doesn't have cable TV, Wi-Fi or 8 other functions, I just plain welds. Adjust heat & wire speed and go all day. I have no plans to buy any TIG or more gas tanks. If aligned correctly and proper hangers out the back, my "Resto-Mod" 67 C10 with OD auto I bench build two years ago & well tested 5.3L truck engine W/Low miles will serve me fine. I am simply researching the 50+ things and paint chemistry has change much less catalytic converters that require 300 series stainless steel in front and 400 series behind. I am not building a trailer queen and 9 tubs of mirrors & cleaning products traveling to shows as I build a trophy case! Just driving to visit, buy food and take a drive when it is nice. You ride a motorcycle to clear your head as it forces you to focus on the task at hand which is defensive driving as no one can put down a damn call when going thru a stop sign or light that is RED. So, I appreciate the tips and some info you did share. But argon tank is not coming home with me. Thanks. DK.

[@Dr_Xyzt]

Right on! Sugaring is an intermittent problem. If you have a stainless weld that's sugared and flatten the tube with a hammer, it'll crack. So, the vibration from the exhaust may cause it to split when you least expect it. I have lightly sugared some test pieces and they took a lot of abuse, so there's a certain amount of sugaring that's okay, at least on car parts.