IF you can fill the tank with inert gas or water:
Take a thin piece of copper sheet and punch a hole the size of the screw head (if its exposed, or if its broken off make the hole the size of the bolt/screw itself) and place over the offending item like a bib.
If the screw is broken off flush or below the surface of the hole you can use your mig (or whatever)to fill/build up on top of the screw and the copper 'bib' will help keep things 'contained' to the hole.
Select a nut that just fits over the head/shank and fill that sucker up with a healthy dose of mig/tig or the gas weld of your choice.
Select wrench that fits nut.
Remove offending item.
IF you can't fill the tank with water or inert gas then don't try this on a gas tank
This works great when you've tried (and broken off)easy outs in the frozen bolt/screw. Turn that "OH Fudge" moment into solid success.
No Easy outs? Sacrifice an old tap.
Run an old tap in there till it breaks off and weld it in place, add the nut and away you go.
