Total Observed Volume (TOV)

Definition - What does Total Observed Volume (TOV) mean?

Total Observed Volume (TOV) is the volume of oil including total water and total sediment, measured at the oil temperature and pressure prevailing. This may be either the volume in a tank or the difference between the volumes before and after a transfer. For the purposes of this standard, TOV is the volume taken from the tank capacity table prior to any corrections, such as those for floating roof and the temperature of the tank shell.

Petropedia explains Total Observed Volume (TOV)

Total Observed Volume (TOV) is helpful in calculating the Gross Observed Volume (GOV). GOV has to be calculated for Shore Tanks as well as Marine Tank Vessels and for both the cases, total observed volume is needed.

For Shore Tanks:

TOV is obtained from the shore tank’s capacity table and is entered with the observed innage or ullage.

Gross Observed Volume (GOV) for shore tanks is given by the following formula:

GOV = [(TOV – FW) x CTSh]±FRA

Where, FW is free water for which adjustments need to be done

CTSh is Correction for the Effect of Temperature on the Steel Shell of the Tank

FRA is Floating Roof Adjustment.

For Marine Vessel’s Tank

Gross Observed Volume (GOV) for Marine Vessel tanks is given by the formula below:

GOV = (TOV ± trim or list correction) - FW

Where, FW is free water volume.

Here, TOV is obtained from the vessel’s capacity tables, which are entered with one of the following:

  • The observed ullage or innage, if the trim and/or list corrections are a volumetric adjustment the amount of trim and/or list correction will need to be applied to the TOV quantity to arrive at a trim and/or list corrected TOV.
  • The trim and/or list corrected ullage or innage.
  • The observed ullage or innage and the vessel’s trim. Some capacity tables show varying TOV values for the same gauge under differing conditions of trim.

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