Removing a Stuck Bead From a Mandrel
Here's what I have found works particularly well for removing long, thin glass beads from a mandrel (a tip from my book 'Reflections, the Diary of a Glass Beadmaker'). Tubes can be more difficult to remove from your mandrel than other types of beads due to the larger amount of glass that is in contact with the mandrel.
Soak the beads in water for a little while. Grab mandrel right below the bead with vice grips (at the long end of the mandrel). Make sure the vicce grips are tight on the mandrel and perpendicular to it. Grab the bead firmly with a paper towel or flexible jar opener. Turn the whole apparatus so that the bead is at the bottom. Grip the bead firmly and (here's the trick!) wiggle the vice grips (not the bead) back and forth and turn them until the bead loosens. Once the bead has loosened, twist and pull it to remove completely.
I have heard that soaking in vinegar may help, and also that putting a bead in the freezer might help because the metal mandrel contracts a little bit. For me, the vice grips method works best.