you are not clear on the size, grade, filler, gas, machine used or what have you of your process, if you want good answers you need to provide details of material grade, thickness, joint configuration, filler grade, machine used, process used (including gas mixture).......what I gather your welding is .30 approx SS material. ASSUMING GTAW
So given the info/GUess I got I will say this: .040 tungsten (thoriated is fine, #6 cup, 15 cfh for fillet/20cfh for butt (#15 gas lens would be way better), 100%argon......use a thick tight fitting (1/8") copper plate for backup on either joint or use a steel/copper fixture with a prodigious gas backup. For this I would be using a .25-.20 filler for first choice, .030 filler second choice.
Your tungsten is LARGE for the job unless you are really sharpening it to a needle, bout a 3/8 length of grinding. A negative torch angle is not a bad idea, in other words push your gas back over the hot puddle....thats where the grey is coming from...inadequate gas coverage because the puddle is long to cool...SS is notorious for this...a pretty good size lens cup will solve this issue. Make sure your stickout allows for your tungsten to end up shiney and maybe blued......if your tungsten is turning dark at all you have way too much stickout.
Give the above info and you will get specific parameters to make it go well.