Outer Limits 4x4 Board

gday, i have a 1hz 97 80 series with standard exhaust, and it's broken. Where the exhaust bolts to the manifold, it's broken right on the exhaust side of the flange, almost like the weld has completely let go. What i want to know is what may have caused this, the exhaust doesnt look corroded and it's not otherwise damaged in any way.
thanks in advance.

vibration has broken it, the flex joint can cause this if it has gone stiff, or been left out of an aftermarket setup, but u say its std...now might be a good time to look for an alternative like turbo or extracters, but the extracters do thesame at the joints...the 1hz gets a wicked harmonic vibe to it at idle...u may wish to increase revs to 800 or so to minimise it
Andrew