I tried this on a few pipes before that were BADLY damaged. Picco 2651 .. dent on the inside portion of the stinger from drive pulley ... came out fine.
Tried it for some Novarossi pipes I have and one was a success and the other blew up too big.
You have to master it .. I personally cap off all the niples and leave the exhaust port open ... fill to the top let it sit and expand.
You do have to do it a few times.
If your stinger is dented in .. run the car 1 tank so the pipe gets HOT and pull the stinger out VERY VERY CAREFULLY!
Good luck.