Actually, rushing the heat IS the main issue in my experience. You get uneven expansion that locks in stress before the bolts even come tight. That port-a-power method is a solid fix, but man, you gotta control that temp climb next time.
Half an inch out on a 24-inch line... that's a big pull. You said it warped from rushing the heat, but that's usually more about the cooling rate, not the heating. If you heat it too fast and then cool it quick, that's when it really wants to walk off. Seen it on a 16-inch condensate line last year. We ended up using a couple of big port-a-power rams and a lot of careful heat to walk it back into plane.