Shore quantity

Sounding - the height of the oil level
Ullaging - the height of the space above the oil level

Bulk Oil and liquid (except petroleum & solvent) are measured by simple formula

Volume in M3 or Kilo-Liters (KL) @ obsd temp x density @ the same temp = metric tons

a) Volume in vertical uniform storage tank

The calibration consists of 2 parts

- the bottom cone of the tank - irregular and measure by direct pouring of water or other liquid of known density - terms as dead-stock

- the uniform vertical cylindrical section using the formula Volume (V)

V = 4/3 (pi)x H x R3 where R is the radius & H is the height of oil

Volume of oil at any point = dead-stock + volume @ H height

Sound logical - what seemed to be the problem then?

1. the measurement of dead-stock - if there is an inherent error as it is done by physical poring of known volume of liquid (laborious and subject to human error). It is why never encourage emptying of the tank

Latest quickie method using optical method cast more doubts to the accuracy of the method

2. The formula assuming a perfect cylindrical shell of a perfect circle, in actual case it is not and complicated by the thickness of the steel

3. Some standard like Chinese take the expansion of steel into consideration. Personally i think it is pure academic

The most important factor is still commercial

The official custodian of the oil is normally the storage terminal. Oil is delivered to the terminal by truck or tankers and the weight is registered by the weighbridge weighing. - this is called book figure

During export, the weight is ascertaining by ullaging in the presence of surveyor or independent party - obviously installation do not wish to see the ullaging less than the book-figure, even by 1mt out of 2000mt - some fuzzy exporter will complaint.

The installation didn't cheat actually - as the calibration is often done by independent calibrator - they are being called back for recalibration.

Due to competition - the recalibration is at calibrator due to their "mistakes". A smart calibrator is calibrate the physical slightly above the tolerance, say 0.1% - hardly noticeable by any standard. However for a medium refinery @ 1000mt capacity, the gain is 1mt per day or 300-400mt for yr and @ usd500per mt = usd150,000. This is the "operation yield" as compare to production yield (Imagine if they do cheat actually, a medium size terminal that i know reportedly gain 2000mt per year in book figure...... not me company of course)

Interesting question, if the shipper one day turn importer?? will they suffer "operation loss" - possible but avoidable.

How? covered the dead-stock with some oils before receiving the oil - this is the place the smart calibrator likely to give the bonus to the installation