Newb question:want to weld flange to cat pipe, but cat doesn't slip into ID of flange

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On most car exhausts i notice the pipe slips inside the ID of the flange and a fillet weld is done on the outside of the pipe (#2 in the diagram below).I have an exhaust flange with 2.5" ID, but my cat also has 2.5" ID (and 2.625" OD).I don't have any spare 2.5" tubing lying around to slip into the flange and cat right now, if I just sit the cat on top of the flange and do a fillet weld (#2 as shown below, excuse the crude photoshop) will that be strong enough?
Reply:You could butt weld it and be fine or go to the muffler shop and get a short piec of 2.5" and insert it.  Its only an exhuast pipe not a steam line.Dan D.Manipulator Of Metal
Reply:Another option would be to take the flange to a fab shop with a lathe and have them open up the hole to 2.625 so the cat pipe slips into the flange. Most shops would probably do that pretty inexpensively. Might be worth a couple phone calls just to save yourself the headache. If you do butt weld the pipe to the flange, make sure you put more heat into the flange (steeper angle towards the flange, shallower towards the pipe) to get better penetration without burning through the pipe. I've failed many cars on inspection due to bad/cracked welds leaking exhaust."You cannot inspect quality into a product, it must be manufactured into the product."Millermatic 210Miller Thunderbolt AC/DC Blue-Point (Smith) O/A
Reply:I have welded plenty of exhausts the way you describe in picture 2.You don't always have that nice slip together guide to mock things up before you weld.Leave a little, less than a 1/16 of an inch gap between the pipe and what you are welding it to, that will help you achieve full fusion between the pipe and what you weld it to.old Miller spectrum 625 Lincoln SP-135 T, CO2+0.025 wireMiller model 250 and WP-18V torchCraftsman 100amp AC/DC and WP-17V torchCentury 115-004 HF arc stabilizerHome made 4 transformer spot welderHome made alternator welder
Reply:Thanks for the tips everyone!  It's my first time welding something besides scrap so it came out kinda ugly, but I think it'll hold.  Definitely needed to point the electrode towards the flange or else I wouldn't be able to keep the puddle going.  I ended up using a 1/32" gap before welding but it seemed to shut substantially after tacking.  Maybe next time I'll try a 1/16" gap.
Reply:Originally Posted by ingrate...  Definitely needed to point the electrode towards the flange...
Reply:I TIG all my exhaust welding projects.www.tjsperformance.comDynasty 300 DXHTP 240HTP Microcut 380Hyperthem 85JD2 Hyd Bender and HF Hyd Ring Roller all in one =(Frankenbender)Bpt. Mill/DRO4' x 8' CNC Plasma TableInstagram: tjsperformanceYT: TJS Welding and Fabrication
Reply:Originally Posted by Mikel_24Did you actually stick welded this thing? If so, congratulations. The welder of choice for exhaust work is usually a MIG. Even the 110v migs suffice for this applications since so little heat is needed. Acomplishing the same thing with stick welding is much harder!Mikel