Re: easy/safe to weld exhaust pipe with propane torch?
doing anything with propane is not welding...it would be soldering at best.
Propane just doesn't get hot enough to melt anything more than silver solder. it will not melt brazing rod.
map gas might, but i'm afraid that you may end up with a cold joint which will eventually fail (but i could be wrong because i've never used map gas)
if you want to "weld" you need to get a wire feed welder to do the job right, and use steel pipe.