How to take up this space?

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Here is a diagram of something I am trying to do.  This a turbo flange it is stainless steel.  I have a 2.5" pipe that i squashed a little bit in a vice so that is fits the rectangle as best as possible.  There remains, however, a little space at each corner for air to escape.  The diagram exaggerates the space by ALOT but you get the idea.  The true space is maybe more like 2 - 3mm of gap vs the 4mm I say in diagram.  Its too difficult to hold the pipe and shoot a pic so I tried it this way.  What is the best way to fill in that area?  It is MUCH too small to cut a piece of metal to fit in each corner - though the diagram makes it seem like its big enough to do that, it is not!  We will be using a Snap On Flex TIG with pure argon.  Both the flange and the mating pipe are stainless steel which will be welded with 309 filler rod.  Do I bother fluxing anything someone recommended that.  Also, will acetone clean the material well or is that not recommended for this material?  Any general advice?  Oh, the pipe is 16 - 18 gauge stainless and the flange is 1/2" thick stainless.  I only get one shot at this so what amperage and gas flow is recommended and what cup size?  Thanks in advance guys.
Reply:Instead of fitting a piece into each corner, can you cut one piece that overlaps the flange, but has the proper hole for the pipe?  Sort of a second flange on top of the big flange.If doing another, can you just cut the oval in the big flange to start with?
Reply:Originally Posted by Jon KHere is a diagram of something I am trying to do.  This a turbo flange it is stainless steel.  I have a 2.5" pipe that i squashed a little bit in a vice so that is fits the rectangle as best as possible.  There remains, however, a little space at each corner for air to escape.  The diagram exaggerates the space by ALOT but you get the idea.  The true space is maybe more like 2 - 3mm of gap vs the 4mm I say in diagram.  Its too difficult to hold the pipe and shoot a pic so I tried it this way.  What is the best way to fill in that area?  It is MUCH too small to cut a piece of metal to fit in each corner - though the diagram makes it seem like its big enough to do that, it is not!  We will be using a Snap On Flex TIG with pure argon.  Both the flange and the mating pipe are stainless steel which will be welded with 309 filler rod.  Do I bother fluxing anything someone recommended that.  Also, will acetone clean the material well or is that not recommended for this material?  Any general advice?  Oh, the pipe is 16 - 18 gauge stainless and the flange is 1/2" thick stainless.  I only get one shot at this so what amperage and gas flow is recommended and what cup size?  Thanks in advance guys.
Reply:Originally Posted by RojodiabloWell, if the flange is 1/2" and the tube is only 16-18ga, I would suggest 60-100A for the welding, but I would preheat the flange around the weld area a bit before welding. Theory.... only enough heat to fuse the thin material well to the thick material. As for the gap, just spot weld, backfill. Using enough heat to truly melt the 1/2 by itself will cause warpage galore in the thinner material, and the weld may look good, but not be stuck on very well. Preheating to ??800-1200f will ensure a fast flowing, pure fusion weld that you can trust, and you can post heat a bit to let the piece cool pretty close to where youwant it. I am not saying it will be perfectly true when you get done. But I bet it will be very good, and suit your needs.
Reply:I would rather use a mapp gas torch or oxy/ acetaline. But it can be done with butane. It will just take a few to heat it up.
Reply:I have no experience with that what so ever i want to stick to the tig
Reply:What is the circumference of the pipe versus the perimeter of the rectangular opening? Can the pipe (or tube) be hammer formed to fit into the opening a little better without it being too thin? If it wouldn't end up being too thin to weld, I would spend time with some hammer forms and body hammers making a nice transition from round to rectangular in the pipe before welding.Patrick
Reply:Originally Posted by Jon KI have no experience with that what so ever i want to stick to the tig
Reply:They have transition pieces for going into a T3 or T4 flange. They make it look nice but in all honesty it's not needed. The air will flow around those edges irregardless of the corners being there. As someone else said, you can either fill it, or you can cut other material to fit and fill. I've done quite a few of these, so let us know if you need more help.John -  fabricator extraordinaire, car nut!-  bleeding Miller blue! http://www.weldfabzone.com
Reply:MicroZone, I am more interested in "filling" the area... what do you recommend
Reply:I normally take similar material and make a copy of the areas needed to fill. Place them in the fill area, tack a few times, and finish.John -  fabricator extraordinaire, car nut!-  bleeding Miller blue! http://www.weldfabzone.com
Reply:The area is just a sliver though, I can't cut material that small.
Reply:If it's just a sliver, tack to fill....as previously stated. If you get over-zealous with the tacking, pick up your friendly grinder. John -  fabricator extraordinaire, car nut!-  bleeding Miller blue! http://www.weldfabzone.com
Reply:If you're concerned about distortion, and the gaps are as small as you say, with stainless, start running stringers on the flange, and lay stringer on stringer until you bridge the gap.  That keeps the heat out of the tube and reduces distortion.  And again, stringers, don't weave.I read something above about using flux.  Never use flux GTAW welding stainless.  Clean the parts using acetone and a stainless wire brush.  Use pure argon.I r 2 a perfessional
Reply:Originally Posted by kbnitIf you're concerned about distortion, and the gaps are as small as you say, with stainless, start running stringers on the flange, and lay stringer on stringer until you bridge the gap.  That keeps the heat out of the tube and reduces distortion.  And again, stringers, don't weave.I read something above about using flux.  Never use flux GTAW welding stainless.  Clean the parts using acetone and a stainless wire brush.  Use pure argon.
Reply:Originally Posted by Jon KThanks - when you say stringers you mean just set the arc and flow filler in the gap without oscillating the torch like  ()))))))))) ?  Excuse my ignorance.
Reply:I am having a ton of trouble even getting the arc to go... argh.  See my other thread titled "Disappointing Stainless Tig results"
Reply:Originally Posted by Jon KI am having a ton of trouble even getting the arc to go... argh.  See my other thread titled "Disappointing Stainless Tig results"