I have a small project coming up, it will require eight welds eight inches long on 16gauge stainless. I am not likely to do much more stainless work any time soon, is it absolutely necessary to use helium/argon mix on stainless or would I be able to "make do" with pure argon on this project? I hate to rent or buy another tank of gas that will be seldom if ever used.
Ar/He/H2 can be used to get a better color match on 300 series stainless.
The hydrogen "helps decrease the residual oxide on the weld deposit, minimizing or eliminating the need for postweld cleaning. As the thickness of the base metal increases, the hydrogen or helium content of the argon blend should increase to achieve the desired weld appearance and shape."
From a cool article "Selecting a sheilding gas for joining stainless steel" here: