Expanding drum for sanding inside of a pipe/tube?

Like a cylinder hone?

It's called "brake shoes".

The "drum" _IS_ the pipe/tube. It fits around the shoes.

inside - shoes outside - drum

For smallish tubing, miscegenation between a cylinder hone and a flap wheel:

Cut a piece of m/s rod of suitable diameter to a suitable length. Tear off a strip of emery cloth of suitable grit and suitable width (from a sheet) or a suitable length (from a roll). Tape one end of the strip to one end of the rod with duct or Gorilla tape. Wrap the strip around the rod, abrasive surface outward. (Yes, you have to wrap in the right direction or use a reversible drill when you don't.) Put the rod in your electric drill, insert the wrap into the tube and spin it. If the flap becomes worn, tear off a bit and continue.

Variations on this, along with determination of "suitable", may do what you want.

Or slit the rod lengthwise and put one edge of the abrasive in the slit. this is probably a little more secure than tape, but a hell of a lot more work. - leave it to someone from the right side of the country to find the easier way!

Rifle cleaning rods with swabs and abrasive grit, or with a bit of sandpaper instead of a swab.

Gee I wish I'd thought of suggesting that.

Oh wait, I did.