Incrustation is defined, for the purpose of this recommended practice, as any material that adheres to the internal vertical sidewall surfaces of a tank when the tank is otherwise empty.
API RP 2556-1993 history
1993API RP 2556-1993 Correcting Gauge Tables for Incrustation (Second Edition)
1968API RP 2556-1968 Recommended Practice for Correcting Gage Tables for Incrustation (FIRST EDITION)