I need to weld a flange to exhaust tubing for a wastegate on a turbo set up. my concern is the flange is pretty thick compared to the tubing. i still mneed to get my tubing but the flange is 3/8 thick mild steel, the tubing will be most likely 16 or 18ga galvanized. there is a relief cut in the flange to insert the tube, do I need to try and weld this on the inside and out, then grind the inside smooth. its final location will be just off the exhaust manifold, only thing separating the two will be the wastegate, so it's going to get a lot of heat in its life.

my welder is a Hobart 140, 110v with an Argon mix.

am I going to be over my head with this and need to take it to someone? I'm a newbie on the welding scene but I'm mechanically handy guy, so I learn pretty quick. I hope I put enough info in here to get some help on this, if not tell me what you need to know.