as Denny points out, pipe is 'named' by it's ID, is generally thicker walled than any tubing [specified by its "Schedule" class], and is meant to hold internal pressure .... exhaust uses
tubing of various wall thickness, thinner than Schedule 40 pipe, some a lot thinner, if you used the thinnest you might find having your own bender useful for frequent replacements
OTOH exhaust tubing is thinner wall than conduit, which is made by a different process of cheaper material
Bill
