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f

r

rude lcul tions

Definitions

1.1 Free water.

The measured volume of water in a tank not in suspension with the liquid in

the tank at observed temperature.

Expressed in

cubic meter

or/and

barrels

1.2 Total Observed Volume (TOV).

J' (

The t9tal measured volume of all petroleum Iiquids,BS&W,and free water at

observed temperature. .

Expressed in

cubic meter

orland

barrels

1.3 Gross Observed Volume (GOV).

The total volume of all petroleum liquids and BS&W,but excluding free water,at

observed temperature.

Expressed in

cubic meter

or/and

barrels

GOV = TOV - Free Water

1.4 Net Observed Volume (NOV).

The total volume of all petroleum products but excluding free water and BS&W

at observed temperature.

Expressed in

cubic meter

and/or

barrels

NOV = TOV - Free Water - BS&W

NOV = GOV - BS&W

5 Gross

Standard Volume (GSV).

t (

.

The total volume of all petroleum products and BS&W,but excluding free water

corrected by the appropriate volumecorrectionfactor (VCF) for observed

temperature and density to a standard temperature.

Expressed in

cubic meter

or

barrels

GSV = GOV x VCF

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appropriate volumecorrectionfactor for observed temperature and density to a

standard temperature and all free water at observed temperature.

Expressed in u i meter and/or b rrels .

TeV = GSV + Free Water

1.8 Bottom S~diments and Water (BS W).

Quantity of sediments and water into the total amount of petroleum products.

Expressed as a percentage as determined by tests.

1.9 Observed TemQerature.

Temperature of cargo measured at various places in the tank. Mean tempera-

ture is determined.

1.10 Standard Temperature.

Tem perature of 15e in the metric system,or 60F in the American system.

All volumes must be converted to this temperature before comparing.

2 Relationship: density specific density API Gravitv

Gravity is a mass-per-unit-volume relationship.

With petroleum products the relationship is expressed as specific gravity.

The following definition applies:

mass of equal volume water at to

kg

kg

mass of given volume oil at to

Specific gravity =

Temperature normally equal to 60F or 15e.

Specific gravity is sometimes called rel tive density

oil density at GOF kg/l

Relative density GO/GOF=

water density at GOF kg/l

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3. Mass and weiqht relationship.

3.1 Mass.r

The mass of a substance is the quantity it contains. It is independant of external

conditions.ln oil measurement, it is often referred to as weight-in-vacuo.

The metric unit is the kg where 1000kg equals 1 metric tonne.

Followingrelationship applies:

mass of oil

=

volume of oil at tOCx oil densi~yattOC

3.2 Weight.

Theweightof a substance (calledweight-in-air)is the mass which a substance

appears to have whenweighted in air.

Thewe.ightis calculated usingthe followingequation:

weight of oil =

volume of oil x weight correction factor

-

~,

3.3 Weiqht Correction Factor

(WCF).

The weight correction factor must be obtained from the appropriate table in the

Petroleum Measurement Tables.

In the American system the WCF can be obtained from table II Long tons per barrel

at 60F against API gravity at 60F .

In the metric system the WCF can be obtained from table 56 Kilograms per liter at

15C and liters at 15C per metric ton against density at 15C .

The WCF can be easily obtained by subtracting 0.0011 kg 1from the density at

15C.

Unfortunately it is much easier to subtract than to consult Table 56.This has led to

the problem that it is no longer obvious which density is used: the density or the

WCF.

4.Unit Conversion.

~

Units can be easily interchanged by using the approprtate table from petroleum measure-

ments Table Vol XI Entry with API or Vol XII Entry with Relative Density .

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Waterdip

Ullage

UllaQe Tables

TOV-H20

GOV (Gross

m3 observed volume)

.1

GOV * VCF

GSV (Gross

m3 standardvolume)

GSV*density

@ 15C

Temperatures

Tt T~~Tb Tm

I

Oil mass

invacuo

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- TOV: 100000m3 at 30C Density: 0.8520 at 15C

VCF from Tab e 54A: 0.9873

t WCF from Table 56 : 0.8509

-

GSV 100000 x 0.9873:;; 98730 m3

- Weight in vacuo = 98730 x 0.8520 = 84117.96 MT (= oil mass)

- Weight in air = 98730 x

0.8509 = 84009.36 MT

General remark concefT\jng metric calculations:

In the metric system both weight in air and weight in vacuo can be easily calculated.

But this can lead to confusion if calculation form is not clearly labelled.

Table 53A:

Table 54A:

Table 56:

Generalized crude oils.Correction of observed density to density 15C,

Generalized crude oil.Correctionof volumeto 15C(againstdensity

at

15C).

Kilogram per liter at 15C and liters at 15C per MT against density at 15C,

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t

5 American system

Schematic layout of calculations:

API WCFin

air I

UlJage Waterdip

Temperatures

Ullaqe Tables

Tt + Tm + Tb= Tm

3

TOV *6.28981

m3

Bbls

Free H2O

m3 MT

LT

*6.28981

Bbls

6A

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Notes:

Temperature: see Calculating Representative Cargotemperatures .

- Oil weight is calculated weight in air) : oil mass can only be calculated by

converting API to density and to preform the metric system calculation.

- For calculations in LT table II must be consulted for calculations in metric ton

table 13.

- If in LT the free water must also be converted to L1. LT = MT x 1.016047)

- The calculations for LT are the most accurate.

Exam~

- TOV= 100000m3

.- TOV= 628981 Bblsat 86F API 34,49

- VCF from Table 6A : 0.9877

- WCF from Table 11 : 0.13309

- WCF from Table 13: 0.13520

- GSV= 628981 x 0..9877= 621244.54 Bbls

- Weight in air= 621244.54 x 0.13309 = 82681.4 LT

= 621244.54 x 0.13520 = 83992.3 MT

If formula for LT / MT -conversion is being used, a tonnage of 84008.2 MT is found a

difference of about 16 MT)

Used as auide:

.

-

Essomarine conversion tables and charts.

- BPpublicationof Lionel Downer.

- ShellpublicationJanuari 1980 CargoCalculations.