Not the entire barrel, just the parts of the silencer that is built onto the barrel. Basically looking at the gun you would have (From outside to inside): Sound Suppressor shell, Sound Suppressor innards, Gun Barrel. The middle part is what would need to be replaced on an integral sound suppressor.
For normal sound suppressors, they're so cheap that replacing the innards isn't really cost effective. Better to toss the whole thing and just use a fresh one. For internal ones though, tossing the whole gun would get expensive, hence breaking down and replacing the parts inside that dampen sound.