i think you're right on point there BDI. the pipe is almost the same as a petrolium holding vessel considering the stuff that runs through there all the time. the inert gas will work to fill the chamber safely lowering the explosion danger when you heat the pipe from the outside. however, if you only have small dings is it really worth it to risk life and limb to remove small dents? a couple hundred $ for a new pipe seems like a good buy compared to what could happen when pressurizing with air or some of the other things i've seen mentioned in this thread. by the way, if you use the method described by BDI, fill the pipe with inert gas then heat your dinged area if it doesn't pop out then while still hot, place a piece of ice in the center of the ding. the rapid cooling of the small area will shrink it thus popping the ding out while the rest of the pipe around the ding will remain in an expanded state till cooled off. i've done this with hail dents on an old truck i used to have, done on a 100 degree plus day and ice on the hail dent. worked great. MADDOGGY