Technical Broken Exhaust Flange Studs

Wire wheel>weld nut on>cool with oil heat again> hit it with an impact while hot.

 

If you can grab any portion of the stud, heat the manifold:

 

I just went through this recently
tried the old standby for me,
got the flange dull red
and promptly twisted the stud off
it was soft as butter
presumably from a long rough life.

I was lucky enough to drill dead center clean
worked a bit of the bolt thread out with a pick,
just enough to get a tap started
used plenty of cutting oil and followed the old threads