The tips & tricks guy seemed to rabbit on a bit, some of it was American based but other wise it was mostly good advice.
"when you seal up the joint, often times pressure builds up and blows a hole and disrupts the gas shielding and causes porosity. You can either drill a small vent hole in a place that will allow or stop right before you seal it up and let cool for a minute before coming back and hitting it quick to close it up...or 309 stainless rod will let you overcome the porosity..if the application will allow for this."
This "blow out" is common on any sealed tube, no matter what the material & is worst when the tube is sealed & you try to weld a gussets in the middle of the sealed tube. People often ask me why my frames have a small 3mm hole drilled in every tube in my frames, this is why. I would dispute that the stainless would cure this though.
When the pressure from the heat builds up it wants to break through the weakest point, being the molten weldpool. Usually when it blows through it deposits a great lump on the tungsten electrode forcing you to stop to clean it.
I have had this "blow through" on many stainless jobs so I can't see how stainless filler would cure it.
The lower grade stainless makes sense as they have less nickel in them, but few firms stock the lesser grades as they can't afford to mix the lower grade filler into 316 jobs, but 316 filler is fine with most grades of stainless.
As well as Argon-arc, TIG & GTAW being the same thing, Heliarc is also the same. It's the American name. You can use either argon or helium as the shrouding gas, both are inert gases & shield the weld from the atmosphere.
I believe Helium burns a bit hotter & is suitable for some special applications.
I hear Argon is common out of Bass Strait whereas the USA Helium comes out of some fields in Canada so it's mostly the economics of gas prices why our countries use different gases
