Tools & Fabrication - Tig welding a thick mondo flange on schdle 5 piping

I went out to Tulsa welding school back in 92 ,so I have been in this trade for awhile,I'm proficent in tig coppernickel,ss 316,347,304,inconel & monel but have not welded much aluminum with the heliarc rig,so I have a c5 fi paxton novi 2k & I'm putting on the mondo bov,the piping going to the system is the ecs kit,to me it looks as thin as schdle 5 stainless,so I grab this rig & its got a foot pedal ,no big deal so I hook up the remote & get a peice to set the machine on,well the shop has no thin wall aluminum ,so I turn the machine down to around 50 amps On a miller & I set the aluminum billet flange on the piping & focus my heat on the flange,it won't even come close to melting the flange ,so bump it up 10 more & I ended up scorching the thin piping, so I'm now thinking ,I've gotta fill the hole & tack off the flange in sections, get the heat hot enough to melt the flange & roll the wire down to the piping as I. Wipe to that. Side,I am using the only thing the guy had in the shop & that's 1/16 tungsten&1/8 filler wire ,I may have to run to the welding supply store & get some 3/32 wire,but I know ,I could use the 1/16th wire as well but,the issueis the billet aluminum flange going on schdle 5 piping,how would u do it,any suggestions?I'm all ears,btw most of pipe welding has been open butt double bevel groove on a 37&1/2 deg angle,& if the pipe needed mitered the fitter got a donkey dik & fixed the transition

You need at least 1/8th tungsten, and 3/32 wire. Also, I've found that pre-heating thick pieces is a good idea. Then concentrate most of your heat on the flange, and just wash up on the pipe. Gotta be patient with thick aluminum stuff, don't just mash the pedal.

Yes, the 1/8th tungsten holds heat much better than the 3/32 or the 1/16th tungsten & on top of that, he had the red thorolated tungsten for the aluminum ,shouldhave been,or should be green for aluminum,I have welded alumnum with the red it just balls up pretty much as soon as you strike an arc with it, I also prefer the thumb control as well,but beggrs can't be choosers, problem is today is the day I am wanting to get the welding done & being its the 1st nothibg is open,this project is being done in sarasota,fl & I drove 8hrs to have someone tune my car in sd,no one in Mobile ,al has hp tuners that can tune a c5,c6 or an f body,only bubba /james parker. Rwtd,he only does Maf tunes

3/32 Will do anything you need to do.
Tip #1 use 2% thoriated, the thoriad carries the amps much better than pure tungston.
Tip #2 use 50/50 argon helium mix gas. The gas changes the game. With 50/50 you can weld things that you wouldn't dream of with pure argon.

Good advice in here. I didn't know we had some experienced welders hanging around. I wont bother typing my advice out bc it would mirror whats already been said.