Were worn boilers the reason for scrapping?

Were worn-out boilers and machinery the main reason these ships were scrapped?

Not consistently. Some scrapped ships had received newer boilers, while reserve status appears more important to the disposal pattern.

Machinery condition does not sufficiently explain the disposal pattern. Some ships had been given new boilers not long before being scrapped, while vessels in active service were less likely to be withdrawn. The surviving pattern does not track a consistent engineering threshold. Reserve status appears to have made a ship easier to cut from the visible fleet.