My mufler pipe disconnected from the flange. I came across two posts here that explained how they fixed it useing a sleeve. I wished they had photos, but they did not. I decided to post mine for others... Hope it helps someone.
A couple of point to think about:
1.The grinder disc could not cut all the way through the pipe under the car. I could not position the cutter so I could get all the way around like I did on the muffler part when it was off the vehicle. I had to twist the piece hard and move it back and forth a few times to fatigue it off. Perhaps a larger size grinder would do a job better.
2. Once both sided are cut there is some lenght lost to the cut off. When I put the pipes together the pipe would hang somewhat different. When I went for the first ride it stared vibrating against the heat cover and make a crazy loud sound. On higher RPMS the short tail of the exhaust pipe at the very end would vibrate agains the bumper cutout part as well. I had to re-adjust the pipe a bit. Bend the shield around a bit trying to move it away from the pipe. Finally got it place. Will see if it stays put.
Good luck with your repair.
Alternatively you can go to a muffler shop and they will do the same for you, except they will likely weld the sleeve.