If it makes a difference OP, you're fortunate to have a flange with a nut and bolt setup rather than a bolt threading into the flange itself. That means you can just whale on it and break the bolt to remove it, just replace the bolt. If it were one of those setups like where there's a spring bolt that threads into the actual flange, that's a risky proposition if you break the bolt because the remaining portion is still threaded in. If it were me I'd just torch these free, if not break the bolts in this situation and replace them in a heartbeat.
Originally Posted by dishdude
Has anyone ever seen a rusted out cat? I thought they got hot enough to burn off any moisture that would cause rust through.
I have, the Altima I junked had an exhaust system that was rotten. The catalytic converter looked exactly like this one down to the color and texture of the rust LOL. The heat shield that was originally spotwelded on had long ago rusted off and disappeared leaving the shell to be battered by the elements and eventually rust through, leaving holes in the shell. I found the holes because there were soot marks indicating where the exhaust was leaking.
In my case I caught it before it broke off completely like the OP's did. On mine they had a bracket with two hangers attached to it that sits between the flange of the exhaust and cat, that bracket had completely rusted away so there was already stress on my exhaust.