This dumb ass idea was born from watching a guy on YouTube getting dents out of a 2 stroke exhaust. He pressurized to 150psi, heated up the dents and they popped right out.
Those two smoke guys are magic. Somehow they can also remove dents from pipes by filling with water and freezing them. Maybe they just say that to get dupes like me to try it?
I never could figure out how to seal an exhaust pipe well enough to hold 150psi. I can't even find clamps that hold my mufflers on tightly, with or without beer can shims.