Be careful sanding or otherwise removing material from any kind of pressurized vessel.
These things can explode!
In fact, I wonder just what the pressure is inside a full Propane
tank, and what their life is.
I have dealt with 3000psi tanks the size of a grapefruit for opening aircraft doors in an emergency, and after 100 cycles, they have to be tested. Interestingly, they blow up like balloons, but only a few thousanths of an inch. When they go beyond a certain point, it is a sign that the steel is fatiguing and they have to be replaced.
A charter member of the Buffalo Plaid Brigade!
Whether you think you can or think you can't, you're right.