API RP 2556:1993(R2013) pdf download.Correction Gauge Tables For Incrustation
1.1 Scope
Incrustation is defined, for the purpose of this recom- mended practice, as any material that adheres to the internal vertical sidewall surfaces of a tank when the tank is other- wise empty. Incrustation has the same effect on tank capacity as dead- wood (anything that displaces liquid inside a tank) and should be treated as such as long as it remains in the tank. The problem of deducting the volume of liquid displaced by incrustation is complicated by two of incrustation’s basic and typical characteristics: First, incrustation is difficult to mea- sure, and second, its thickness is usually variable. Some oils present no incrustation problem, but many others do, usually on a field-wide basis. The error in mea- surement from any one tank may be slight, but the accumu- lated 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 accu- racy of measurement. The tables given in this recommended practice (see Section 4) show the percent of error of measurement caused by vary- ing thicknesses of uniform incrustation in tanks of various sizes. These tables may be used as a guide by the tank owner and the carrier to negotiate an allowance for incrustation. If it is established that incrustation is causing a substantial loss to a carrier or to any other receiver using affected tank gauges as the basis for custody transfer measurement, it is the responsi- bility of the tank owner to provide a tank that will permit an accurate measurement or to agree to a reasonable adjustment.
3.3 Heat
If the incrustation is caused by a product that contains wax or gum, the most practical and accurate solution is to ensure that the liquid and the shell temperatures remain at a level above the pour point of such product throughout the delivery cycle. Insulating the tank or the application of heat may be accomplished by any safe and practical means, such as steam coils or heating systems, but direct fire is specifically not recommended.
API RP 2556:1993(R2013) pdf download
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