General Incrustation is defined@ for the purpose of this recommended practice@ as any material which adheres to the internal vertical sidewall surfaces of a tank@ when the tank is otherwise empty. Incrustation has the same effect on tank capacity as deadwood (anything which displaces liquid inside the tank) and should be treated as such so long as it remains in the tank. The problem of deducting the volume of liquid displaced by incrustation is complicated by two of its basic and typical characteristics-first@ incrustation is difficult to measure; second@ its thickness is usually variable. Some oils present no incrustation problem; however@ many do@ usually on a fieldwide basis. The error in measurement from any one tank may be slight; but the accumulated error from an entire field@ or from any one tank over a period of time@ could be substantial. The error always has the effect of indicating too large a tank capacity; therefore@ a receiving carrier cannot be expected to continually absorb the effect of these errors. The method selected to correct the error should depend upon the desired approach to accuracy of measurement. Table 1 shows the percent of error of measurement caused by varying thicknesses of uniform incrustation in tanks of various sizes. This table may be used as a guide by the tank owner and the carrier when negotiating an allowance for incrustation. After it has been established that incrustation is causing a substantial loss to a carrier@ or to any other receiver using affected tank gages as the basis for custody transfer measurement@ it is the responsibility of the tank owner to provide a vessel which will permit accurate measurement or to agree to a reasonable adjustment.
API RP 2556-1968 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)