Anvils no longer seem to have random damage. It goes straight from slightly damaged to damaged and then very damaged and then poof! Gone. So far I've gone through 3 anvils in a very short space of time. This is a new 1.13 world. In my old 1.12 world I've still got my original anvil, that I've had for ages. In 1.13 the damage randomiser is definitely off.