What a PITA! I hate working on Audis. F'ing Germans don't think anyone will have to take anything apart in the car. Same idiot must have designed their exhaust bolt locations as the Subaru Mad Dad headers. Cat to downpipe has a 3 bolt flange and of course one is right behind where the pipe bend towards it instead of either side of it.
And I have no idea how I will get to the bottom turbo flange 17mm nut once the flange is attached to the cat again and in the car. Yes, the intelligent Germans decide to put the only cat in the engine compartment, not under the car.
Oh well, enough whining.
Pipe is not ultra thin. At least a couple millimeters thick. Flange is a big heavy thing. It was welded and then ground smooth from the inside. Very little weld penetration, or so even that it fatigued almost perfectly all the way around.
A nice weld on the outside would have easily taken the tension put on it.
I'll bring it to the meet if you are going to be there to look at and decide if you want to take a shot at it.