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API Manual of Petroleum Measurement StandardsChapter 12 - Calculation of Petroleum QuantitiesSection 1 - Calculation of Static Petroleum QuantitiesPart 1 - Upright Cylindrical Tanks and Marine VesselsThird Edition, xx/xxxxEI HM1 Part 1Foreword

This two-part publication presents standard calculation procedures for static petroleum liquids. The

two parts consist of the following:

Part 1 - “Upright Cylindrical Tanks and Marine Vessels” - 10/2001

Part 2 - “Calculation Procedure for Tank Cars” – 5/2003

This standard has been developed through the cooperative efforts of many individuals from industry

under the sponsorship of the American Petroleum Institute and the Energy Institute.

Suggested revisions to this publication are invited and should be submitted to the Measurement Coordinator, Exploration and Production Department, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005.

Contents

Section 1 - Calculation of Static Petroleum Quantities

Part 1 - Upright Cylindrical Tanks and Marine Vessels

0 Introduction

1 Scope

2 References

3 Definitions

3.1 General

3.2 Abbreviations

4 Interrelationship between Chapter 12 and Chapter 11.1

5 Hierarchy of Accuracies

6 Rounding and Discrimination

6.1 Data Level

6.2 Rounding of Numbers

6.3 Discrimination

7 Observed Data (Input, Direct, or Primary)

8 Calculated Data (Indirect or Secondary)

9 Calculation of Gross Observed Volume (GOV)

9.1 Shore Tanks

9.1.1 Total Observed Volume (TOV)

9.1.2 Adjustment for the Presence of Free Water (FW) and Tank Bottom Sediments

9.1.3 Correction for the Effect of Temperature on the Steel Shell of the Tank (CTSh)

9.1.4 Floating Roof Adjustments and Corrections (FRA) & (FRC)

9.2 Marine Vessel’s Tanks


9.2.2 Trim Correction

9.2.3 List Correction

9.2.4 Combining Trim and List Corrections

9.2.5 Free Water Volume (FW)

10 Calculation of Gross Standard Volume (GSV) and Total Calculated Volume (TCV) - Shore Tanks and

Marine Vessel’s Tanks

10.1 Gross Standard Volume (GSV)

10.2 Correction for the Effect of Temperature on a Liquid (CTPL) or Volume Correction Factor (VCF)

10.3 Total Calculated Volume (TCV)

11 Calculation of Net Standard Volume (NSV)

11.1 Calculation of the Correction for Sediment and Water (CSW)

11.2 Calculation of the Volume of Sediment and Water (S&W)

12 Calculation of Mass (Weight in Vacuum) and Weight (Weight in Air)

12.1 Introduction

12.2 Calculation Methods

12.2.1 Volume at Standard Temperature to Mass/Weight

12.2.1 Volume at Observed Temperature to Mass/Weight

12.2.3 Calculation of Gross Standard Weight and Net Standard Weight

12.2.4 Calculation of Gross Standard Mass and Net Standard Mass

12.3 Converting Between Mass and Weight

13 Direct Mass Measurement

14 Calculation Sequence

14.1 General

14.2 Volume at Standard Temperature to Mass/Weight Calculation Procedure

14.3 Volume at Observed Temperature to Mass/Weight Calculation Procedure

15 Calculation of Transferred Volumes for Custody Transfer

15.1 General

15.2 Small Lease Tanks

15.2.1 Transferred Volume Calculation Procedure for Lease Tanks

15.3 Volumetric Shrinkage

16 Miscellaneous

16.1 Precautions When Using an Automatic Sampler

16.2 Interrelation of Units

Annex A - Examples of Shore Tank and Marine Vessel Tank Calculations

A1 Custody Transfer Flow Chart – Shore Tank(s) with Automatic Sampler

A2 Custody Transfer Flow Chart - Shore Tank(s) with Individual Tank Samples

A3 Shore Tank Calculation Using Volume At Standard Temperature To Mass/Weight Calculation

Procedure

A4 Marine Vessel Tank Calculation Using Volume at Standard Temperature To Mass/Weight

Calculation Procedure

A5 Shore Tank Calculation of Volume at 15ºC and Weight of p-Xylene using ASTM D1555M

A6 Shore Tank Calculation of Volume at 15ºC, Mass and Weight of MTBE using API MPMS Chapter

11.1/Adjunct to ASTM D1250/Adjunct to IP 200, Table 54C

A7 Shore Tank Calculation of the Weight of Benzene Using Density Correction Coefficients

Annex B - Example of Shell Temperature Correction Factors for Expansion and contraction of

Upright Cylindrical Steel Tanks Due to Temperature

B1 Shell Temperature Correction Factors for Expansion and Contraction of Upright Cylindrical Steel

Tanks Due to Temperature

B2 Application of Shell Temperature Correction

Table B-1 - Correction Factors for Effect of Temperature on the Tank Shell – Reference Temp 60ºF Table B-2 - Correction Factors for Effect of Temperature on the Tank Shell – Reference Temp 15ºC Table B-3 - Linear Thermal Expansion Coefficients of SteelAnnex C - Examples of Floating Roof Adjustment Calculations: Methods 1 and 2

C1 Example when roof calculation is calculated into the tank capacity table

C2 Example when roof adjustment is not calculated in the tank capacity table

Figures

1 -Method to Calculate Vessel’s List Using Amidships Draft Readings

Tables

1 - Significant Digits

2 - Observed Data

3 - Calculated Data

4 - Generalized Crude Oils API Correction to 60ºF

5 - Mass to Weight Density Corrections

6 - Excerpt from API MPMS Chapter 11.1/Adjunct to ASTM D1250/Adjunct to IP 200, Table 5A.

B-1 - Correction Factors for Effect of Temperature on the Tank Shell – Reference Temp 60ºF

B-2 - Correction Factors for Effect of Temperature on the Tank Shell – Reference Temp 15ºC B-3 - Linear Thermal Expansion Coefficients of Steel

API Chapter 12 - Calculation of Petroleum Quantities

Section 1 - Calculation of Static Petroleum Quantities

Part 1 - Upright Cylindrical Tanks and Marine VesselsEI HM1 Part 10 IntroductionThese procedures are intended to encourage a uniform approach to volumetric and mass calculation

of crude oil, petroleum products, and petrochemicals when contained in tanks. This publication will also address calculation sequences, rounding, and significant digits, with the aim that different operators can produce identical results from the same observed data.

1 ScopeThis standard is intended to guide the user through the steps necessary to calculate static liquid

quantities, at atmospheric conditions, in upright, cylindrical tanks and marine tank vessels. The standard defines terms employed in the calculation of static petroleum quantities.

The standard also specifies equations that allow the values of some correction factors to be computed. Fundamental to this process is the understanding that in order for different parties to be able to reconcile volumes, they must start with the same basic information (tank capacity table, levels, temperatures, and

so forth) regardless of whether the information is gathered automatically or manually.

This standard does not address the calculation of clingage, non-liquid material, small quantities (such as onboard quantities, quantities remaining on board, and Wedge Formula, where material is not touching all bulkheads on marine vessels), and vapor space calculations.

2 ReferencesThe following documents are referenced throughout this standard:

API

Manual of Petroleum Measurement Standards (MPMS)

Chapter 1, “Vocabulary” Chapter 2, “Tank Calibration” Chapter 3, “Tank Gauging”

Chapter 7, “Temperature Determination” Chapter 8, “Sampling”

Chapter 9, “Density Determination” Chapter 10, “Sediment and Water” Chapter 11, “Physical Properties Data”

Chapter 15, “Guidelines for the Use of International System of Units (SI) in the Petroleum and Allied

Industries”

Chapter 16, “Measurement of Hydrocarbon Fluids by Weight or Mass” Chapter 17, “Marine Measurement”

Chapter 18, “Custody Transfer”

ASTM1

Adjunct to D1250 Temperature and Pressure Volume Correction Factors for Generalized Crude

Oils, Refined Products, and Lubricating Oils

D1555 Test Method for Calculation of Volume and Weight of Industrial Aromatic

Hydrocarbons and Cyclohexane

D4311 Practice for Determining Asphalt Corrections to a Base Temperature

1 American Society for Testing and Materials, 100 Bar Harbor Drive, West Conshohocken, PA 19428, USA.

IP2

Adjunct to IP 200 Temperature and Pressure Volume Correction Factors for Generalized Crude

Oils, Refined Products, and Lubricating Oils

3 Definitions3.1 GENERAL

The definition of those terms relative to this document can be found in other API or associated documents, as follows:

General Terms - API MPMS Chapter 1

Marine Terms - API MPMS Chapter 17.1 (17.1.3)

Units of Measure and Interrelation – API MPMS Chapter 11.5

International System (SI) Units - API MPMS Chapter 15

3.2 ABBREVIATIONS AND DEFINITIONS

The designation of corrections and correction factors by abbreviations rather than words is recommended to abbreviate the expression, facilitate algebraic manipulation, and reduce confusion. While a combination of upper case, lower case, subscripted, and superscripted notation is used, upper case notation may be used as appropriate. Additional letters may be added to symbolic notations for clarity and specificity.

3.2.1

coefficient of thermal expansion per degree

Cs

The amount by which the density of a material changes, per degree, due to a change in temperature.

3.2.2

correction for sediment and water.

CSW

Corrects a volume, usually at standard temperature, for the effects of suspended sediment and water.

3.2.3

correction for the temperature and pressure of the liquid

CTPL

Corrects a volume at an observed temperature & pressure to an equivalent volume at base temperature and pressure and is equal to CTL x CPL. For the purpose of this standard, base pressure is equivalent to atmospheric pressure and the CPL factor is considered to be 1.00000; therefore, under atmospheric conditions, the CTPL and CTL will be the same value. (CTPL and CTL are referred to as VCF in some

API MPMS standards)

3.2.3.1

correction for the temperature of the liquid

CTL

Compensates for the effect of temperature on a liquid.

3.2.3.2

correction for the pressure of the liquid

CPL

Compensates for the effect of pressure on a liquid.

2 Energy Institute, formerly the Institute of Petroleum, 61 New Cavendish Street, London W1G 7AR, UK.

3.2.4

correction for temperature of the shell

CTSh

The correction factor for the effect of the temperature, both ambient and liquid, on the shell of the tank.

3.2.5

density

Mass per unit volume; i.e. the mass of a substance divided by its volume. When reporting density, the unit used together with temperature shall be explicitly stated; for example, kilograms per cubic meter at 15ºC

or lbs per gallon at 60ºF.

3.2.6.1

floating roof adjustment

FRA

A secondary correction or adjustment for any difference between the reference density and the observed density at tank temperature, when a correction for the roof has been calculated into the tank capacity table using a reference density.

3.2.6.2

floating roof correction

FRC

The correction made to offset the effect of the displacement of the floating roof, when no correction has been built into the tank capacity table.

3.2.7

free water

FW

The water present in a container that is not suspended in the liquid hydrocarbon. A free water quantity deduction may include bottom sediments.

3.2.8

gross observed volume

###

###

###

###

###

###

###

###

###

###

###

GOV

The total volume of all petroleum liquids and sediment and water, excluding free water, at observed temperature and pressure.

3.2.9

gross standard volume

GSV

The total volume of all petroleum liquids and sediment and water, excluding free water, corrected by the appropriate volume correction factor (CTPL) for the observed temperature and API gravity, relative density, or density to a standard temperature such as 60ºF or 15ºC.

gross standard mass

GSM

The mass of the GSV quantity.

gross standard weight

GSW

The weight of the GSV quantity.

mass

The technical description of mass exists in API MPMS Chapter 11.5; however, within this document it

refers to “weight in vacuum”.

net standard volume

NSV

The total volume of all petroleum liquids, excluding sediment and water and free water, corrected by the appropriate volume correction factor (CTPL) for the observed temperature and API gravity, relative density, or density to a standard temperature such as 60ºF or 15ºC.

net standard mass

NSM

The mass of the NSV quantity.

net standard weight

NSW

The weight of the NSV quantity.

tank shell reference temperature

TShREF

The tank shell temperature used to calculate volumes in the preparation of a tank capacity table;

frequently 60°F, or 15°C, although other temperatures are used.

total calculated volume

TCV

The total volume of all petroleum liquids and sediment and water corrected by the appropriate volume correction factor (CTPL) for the observed temperature and API gravity, relative density, or density to a standard temperature such as 60ºF or 15ºC and all free water measured at observed temperature (gross standard volume plus free water).

total observed volume

TOV

Total measurement volume of all petroleum liquids, sediment and water, free water, and bottom sediments at observed temperature. 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.

temperature of the tank shell

TSh

Observed temperature of the metal (usually steel) shell of the tank.

###

volume correction factor

VCF

This is the same as CTL and under atmospheric conditions is also the same as CTPL, making these three symbols interchangeable; however, only CTPL and CTL are used in equations in this standard.

weight

The technical description of weight exists in API MPMS Chapter 11.5; however, within this document it

refers to “weight in air”.

4 Interrelationship between Chapter 12 and Chapter 11.1Currently, the Manual of Petroleum Measurement Standards is organized into Chapters covering general measurement areas and several of these Standards are interrelated, in particular Chapters 11 and 12. If there is uncertainty amongst users as to which takes precedence the following criteria should be applied.

API MPMS Ch. 11.1 is the primary standard for the determination of the temperature (CTL), pressure (CPL), and combined temperature and pressure (CTPL) correction factors for crude oil, refined products, and lubricating oils, either by presentation of specific implementation procedures or by reference to other publications.

API MPMS Ch. 12 is the primary standard for the calculation of volume quantities. It determines the

discrimination levels (rounding) required for each input variable and correction factor in a specific volume calculation procedure, and the sequence and manner in which to apply the appropriate parameters (RHO b, APIb, RDb, CTL, Fp, CPL, and CTPL).NOTE: The terms RHOb, APIb, RDb, and Fp, are not used in this document.

RHO refers to density, API refers to API Gravity and RD refers to relative density. Subscript “b” refers to

“base” conditions. The “standard” or “base” condition is a defined combination of temperature and pressure at which liquid volumes are expressed for purposes of custody transfer, stock accounting, etc. The terms

standard and base are used interchangeably. Accepted standard temperatures are 60°F, 15°C and 20°C.

Accepted standard pressures are zero gauge pressure (for non-volatile liquids at the standard temperature)

or the liquid’s vapor pressure at the standard temperature (for volatile liquids).

Fp is called the "compressibility coefficient" or "scaled compressibility factor (units of 1/psi)". For additional information on these terms, refer to API MPMS Chapter 11.1.

5 Hierarchy of AccuraciesA hierarchy of accuracies applies in petroleum measurement. At the top are the standards calibrated

by a National Metrology Institute (NMI) such as the National Institute of Standards and Technology (NIST) in the United States. From this level downwards, any uncertainty in a higher level must be reflected in all lower levels as a bias or systematic error. Whether such bias will be positive or negative is unknown as uncertainty carries either possibility.

To expect equal or less uncertainty in a lower level of the hierarchy than exists in a higher level is unrealistic. The only way to decrease the random component of uncertainty in a given measurement system is to increase the number of determinations and then find their mean value. The number of digits in intermediate calculations of a value can be larger in the upper levels of the hierarchy than in the lower levels, but the temptation to move towards imaginary significance (more decimal places) must be tempered or resisted by a wholesome respect for realism.

6 Rounding and Discrimination6.1 DATA LEVEL

In many cases the number of decimal places that are to be used is influenced by the source of the

data itself. For example, if a vessel’s capacity tables are calibrated to the nearest whole barrel, than all subsequent barrel values should be recorded accordingly. However, in those cases where there are no other limiting factors, the operator should be guided as follows by Table 1.

Table 1 - Significant DigitsUnits No. of

Decimals UnitsNo. ofDecimals

LitersGallons

…, xxx.0…, xxx.xx

API Gravity @ 60ºF CTPL xxx.x x.xxxxxa

BarrelsCubic meters

…, xxx.xx…, xxx.xxx

Density lbs/galDensity kg/m3

xx.xxxxxxx.x

Pounds …, xxx.0 Density kg/litre x.xxxxKilograms …, xxx.0 Density correction coefficient x.xxxxxShort tons …, xxx.xxx Relative density x.xxxxMetric tons …, xxx.xxx S & W % xx.xxxLong tons …, xxx.xxx CSW x.xxxxx

Temperature ºFTemperature ºC

xxx.x xxx.xa

TSh ºC / ºF (See Section 9.1.3) xxx.0CTSh x.xxxxx

Note a Not applicable if the implementation guidelines (“Grandfather Clause”) from API MPMS Chapter

11.1-2004 have been invoked. For those invoking the “Grandfather Clause”, the following note, from API MPMS Chapter 11.1-1980, which was applicable to the CTL, is reproduced here for ease of reference. “The standard for determining CTL factors is the computer subroutine implementation procedures of API MPMS Chapter 11.1, Volume X. When fully implemented, this generates a CTL factor of five significant digits. That is, five decimal digits at temperatures above standard temperature (60ºF and 15ºC) and four decimal digits at temperatures below standard temperature. Use of the printed table limits the user to

four decimal digits above and below standard temperature in addition to limiting table entry discrimination to 0.5ºF, 0.25ºC, 0.5 API, and 2.0 kg/m3. In the event of dispute, the computer-generated CTL should take preference.”

6.2 ROUNDING OF NUMBERS

When a number is to be rounded to a specific number of decimals, it shall always be rounded off in

one step to the number of figures that are to be recorded and shall not be rounded in two or more steps of successive rounding. In absolute terms, when the figure to the right of last place to be retained is 5 or greater, the figure in the last place to be retained should be increased by 1. If the figure to the right of the last place to be retained is less than 5, the figure in the last place retained should be unchanged.

6.3 DISCRIMINATION

The rounding and discrimination requirements set forth in this section may be applied to verify

compliance with the calculation procedures of this standard. The data in Table 1 should not be used to construe or imply accuracy requirements or the capabilities (discrimination) of instrumentation used to furnish the measurements.

Where used to verify conformance to calculation procedures, the accounting hardware that displays or prints results from calculations shall have at least 32 bit binary word length or be capable of enough digits to preserve the resolution and display the maximum quantity required for the application – typically, this is

10 digits or better. In certain situations, such as with on-line real time calculations that are required by process measurement instrumentation, the available equipment may not have this capacity. In such cases, rounding and discrimination levels should be as close to the standard as the computing hardware will allow.

7 Observed Data (Input, Direct, or Primary)The input or observed data in Table 2 must be gathered as a first step in the calculation process. This

document does not address how these data are obtained. That information is found in the referenced publications listed in Section 2, and it is assumed, for the purpose of this document, that all such data have been obtained in accordance with these referenced publications. It should be understood that the observed data must be gathered concurrently. In other words, the level gauge, water cut, temperature, and so forth should all be taken at the same time for inclusion on the same measurement ticket or ullage report.

Table 2 - Observed Data

Shore Tanks Marine Vessel’s Tanks

Recorded reference gauge heighta Recorded reference gauge heighta Observed reference gauge heighta Observed reference gauge heighta Innage or ullage or liquid level Innage or ullage of liquid level Innage or ullage of free water level Innage or ullage of free water level

Average liquid temperature ºF or ºC Average liquid temperature ºF or ºC Observed density @ sample temperature Observed density @ sample temperature Percentage of sediment and water Percentage of sediment and water Ambient air temperature Forward draft reading

After draft readingList

a These data points do not have any direct impact on the calculation process. However, they can impact the calculation process indirectly and are usually recorded at this time.

8 Calculated Data (Indirect or Secondary)The data points presented in Table 3 are necessary for the calculation process and are calculated or

extracted using the input data from the previous section.

Table 3 - Calculated Data

Shore Tanks Marine Vessel’s Tanks

Density @ standard temperature Vessel’s trim

Floating roof adjustment or correction Density @ standard temperature Tank shell temperature correction Trim correction and list correction Total observed volume Total observed volume

Free water volume Free water volume

Gross observed volume Gross observed volume

Correction for temperature of liquid Correction for temperature of liquid

Gross standard volume Gross standard volume

Sediment and water (volume or factor) Sediment and water (volume or factor) Net standard volume Net standard volume

Mass or weight (See Section 12) Mass or weight (See Section 12)

9 Calculation of Gross Observed Volume (GOV)The calculation process for shore tanks and marine tank vessels only differs up to the point of

calculating gross observed volume (GOV). From this point on, the calculations are the same.

Refer to Annex A for examples of shore tank and marine vessel tank calculations.

9.1 SHORE TANKS

To calculate the GOV for shore tanks, deduct any free water (FW) from the total observed volume

(TOV) and multiply the result by the tank shell temperature correction (CTSh); then, apply the floating roof adjustment (FRA), where applicable.

GOV = [(TOV - FW) x CTSh] FRA


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

ullage.

9.1.2 Adjustment for the Presence of Free Water (FW) and Tank Bottom SedimentsIt is necessary to determine the amount of FW and bottom sediments, if any, before and after each

product movement into or out of a tank so that the appropriate corrections can be made. This adjustment

(FW) will always be in the form of a volumetric deduction.

9.1.3 Correction for the Effect of Temperature on the Steel Shell of the Tank (CTSh)

Any tank, when subjected to a change in temperature, will change its volume accordingly. Assuming

that they have been calibrated in accordance with API MPMS Chapter 2, upright cylindrical tanks have

capacity tables based on a specific tank shell temperature. If the observed tank shell temperature differs from the capacity table tank shell temperature, the volumes extracted from that table will need to be corrected accordingly.

Storage tanks differ from test measures in size and wall thickness. Differences also occur because the tanks cannot readily be sheltered from the elements. Therefore, ambient temperatures as well as product temperatures must be considered when calculating an appropriate correction for the effect of temperature on the shell of the tank. The correction factor for the effect of temperature on the shell of the tank is called CTSh and may be calculated by the following:

Cross-sectional area correction,

CTSh = 1 + 2άΔT + ά2ΔT2

Where: ά = Linear coefficient of expansion of the tank shell material [see note 4]

ΔT = Tank Shell Temperature (TSh) – Tank Shell Reference Temperature (TShREF)

Note 1: Tank Shell Reference Temperature (TShREF) is the tank shell temperature for which the

capacity table volumes were calculated to; typically 60°F, 15°C and 20°C, although other

temperatures are used.

Note 2: The Tank Shell Reference Temperature (TShREF) is usually stated on the capacity table. If this is not the case, contact the company that generated the table. Some capacity tables make reference to an operating product temperature; this should not be confused with the Tank Shell Reference Temperature (TSh REF), which is a tank shell temperature.

Note 3: When calculating ΔT it is important to maintain the arithmetic sign as this value can be positive

or negative and must be applied as such in the CTSh formula.

Note 4: See Table B3 in Annex B for linear expansion coefficients of various metals.

9.1.3.1 For non-insulated metal tanks, the temperature of the shell may be computed as follows (refer to

Annex B):

TSh = [(7 x TL) + Ta ] 8

Where:

TL = liquid temperature.

Ta = ambient temperature.

Note: Ambient air temperature surrounding a storage tank can vary widely. For practical operational

purposes the recommended methods of taking this temperature are: A temperature device carried by the measurement technician into the tank area when

gauging tanks. Take at least one temperature reading in a shaded area. If more than one temperature is taken, average the readings. Shaded external thermometers permanently mounted in the tank farm area.

Local on-site weather stations.

All on site temperature devices, used to record ambient air temperature for the calculation of tank

shell correction factors during custody transfer shall have their accuracy of plus or minus two degrees Fahrenheit verified every three months.

Where the uncertainty of the ambient air temperature is plus or ± 5ºF (± 2.5ºC), the effect on

calculating the tank shell correction factor is 1 in 100,000.

Temperature readings are to be taken 3 feet [1 meter] from any obstructions or the ground.

Additionally, allow sufficient time for temperature readings to stabilize.

9.1.3.2 For insulated metal tanks, the temperature of the shell may be taken as closely approximating the

adjacent liquid temperature, in which case, TSh = TL.

9.1.3.3 The third dimension needed to generate volume - height - is a function of gauging and should be

considered separately. The volumes reflected on tank tables are derived from area multiplied by incremental height. Therefore, K- factors for correction of areas have the same ratio as volume corrections and may be applied directly to tank table volumes. For an example calculation see Annex B.

9.1.3.4 The shell temperature correction factor is to be applied to volumes obtained from capacity tables

that are at standard conditions and are unrelated to the corrections designed to account for volume expansion and contraction of the product itself. Depending upon certain requirements, this shell temperature correction factor may be built into the capacity table for a specific operating temperature.

9.1.3.5 The application of a CTSh does not apply in the following circumstances

To lease tanks and other such small tanks of 5,000 bbls (795 m3)or less

Marine vessels

9.1.4 Floating Roof Adjustments and Corrections (FRC & FRA)

There are two types of floating roofs – internal and external; however, the calculation process to

determine the floating roof adjustment or correction is the same for both types of roofs. The determination of the correction, however, can be addressed in one of two ways:Floating Roof Adjustment (FRA) –This method is used when a correction for the roof has been

calculated into the tank capacity table using a reference density. A secondary correction (or

adjustment) must therefore be calculated for any difference between the reference density and the

observed density at tank temperature. This correction can be positive or negative.

b. Floating Roof Correction (FRC) – In this situation the tank capacity table has not been adjusted for

the roof; therefore a volume, equivalent to the entire weight of the roof, must be calculated and applied as a correction. This correction is always negative and is calculated by dividing the weight of the floating roof by observed density at tank temperature.

Examples of floating roof adjustment and correction calculations can be found in Annex C

Note: No floating roof correction will be accurate if the liquid level falls inside the floating roof’s critical

zone regardless of table style. While the results can be displayed they should not be used for custody transfer.

Note: If a significant amount of water, ice, or snow is present on a floating roof, it should either be

removed or its weight estimated and calculated into the roof correction.

Note: Roof corrections are not applicable for volumes below the critical zone.

9.2 MARINE VESSEL’S TANKS

To calculate the GOV for marine vessel’s tanks, deduct the FW volume from the TOV.

GOV = TOV - FW

In the event of a volumetric trim or list correction as per 9.2.2 Item a, the calculation is as follows:

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

Note: Refer to 9.2.3.


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

a. 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.

b. The trim and/or list corrected ullage or innage.

c. 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.

9.2.2 Trim Correction

The trim correction is applied to compensate for the change in liquid level due to the longitudinal plane

of the vessel not being horizontal.

Subtract the forward draft reading from the after draft reading. If the trim is positive (that is, the after draft reading is larger), the vessel is said to be “trimmed by the stern.” If the trim is negative (that is, the forward draft reading is larger), the vessel is said to be “trimmed by the head.” Note the following:

a. The trim correction is found in the vessel’s calibration tables and is usually a correction to the

observed innage/ullage. However, it can be a volumetric adjustment to the TOV.

b. Trim corrections can be either positive or negative. The trim correction table will state how this correction is to be applied.

c. If trim corrections are not available, it may be possible to calculate this value. Refer to API MPMS

Chapter 2.8A, Section 10.4.

9.2.3 List Correction

List correction is applied to compensate for the change in liquid level due to the vertical plane of the

vessel not being perpendicular to the horizontal. A vessel’s list is usually read from its inclinometer. However, if such an instrument is not available or there is doubt as to its accuracy, then the list can be calculated from the port and starboard amidships draft readings. Refer to Figure 1 for this calculation. Note the following:

a. List corrections are applied in the same manner as are trim corrections.

b. List corrections can be either positive or negative. The list correction table will state how this correction is to be applied.

c. If list corrections are not available, it may be possible to calculate this value. Refer to API MPMS

Chapter 2.8A, Section 10.4.

Insert Figure 1 - Method to Calculate Vessel’s List Using Amidships Draft Readings

(This is the same as is in the current Edition and will not be changed for this edition)

9.2.4 Combining Trim and List Corrections

Caution must be exercised when applying trim and list corrections collectively. In many cases these

corrections are only applicable when the other condition does not exist. For information on the calculation procedure for combined trim and list corrections, refer to API MPMS Chapter 2.8A, Section 10.4.

9.2.5 Free Water Volume (FW)

FW volume is obtained from the vessel tank capacity tables, which are entered with the FW innage or

ullage. As with any liquid in a marine vessel’s tank, FW is subject to the effects of trim and list, and the previously referenced trim and list corrections are applicable to FW, provided that the FW is touching all bulkheads of the tank. If the FW does not touch all tank bulkheads, a wedge condition exists. The

formula for calculating whether or not a wedge condition exists, the application of wedge tables/formulae, and the calculation of the wedge formula can be found in API MPMS Chapter 17.4.

10 Calculation of Gross Standard Volume (GSV) and Total Calculated Volume (TCV) -Shore Tanks and Marine Vessel’s Tanks10.1 GROSS STANDARD VOLUME (GSV)

The GSV is calculated by multiplying the GOV by the correction for the effect of temperature and

pressure on the liquid (or the volume correction factor).

GSV = GOV x CTPL

10.2 CORRECTION FOR THE EFFECT OF TEMPERATURE AND PRESSURE ON A LIQUID (CTPL)

or VOLUME CORRECTION FACTOR (VCF)

If a quantity of oil is subjected to a change in temperature, its volume will increase as the temperature

rises or decrease as the temperature falls. The volume change is proportional to the thermal coefficient of expansion of the liquid, which varies with density (API gravity) and temperature. The correction factor for the effect of the temperature and pressure on a volume of liquid is called CTPL, CTL or VCF. The function of this correction factor is to adjust the volume of liquid at observed temperature to its volume at a standard temperature. The most common standard temperatures are 60ºF, 15ºC, and 20ºC (68ºF).

These correction factors can be obtained from API MPMS Chapter 11.1, the Adjunct to ASTM D1250,

or the Adjunct to IP 200. These computer programs or tables are entered with the observed average temperature and API gravity at 60ºF, a density at 15ºC, a relative density at 60ºF/60ºF, or a coefficient of thermal expansion. To determine which table is applicable, refer to Table 4.

Table 4 - CTPL Factors

Table Product Temp Entry

6A Generalized crude oil ºF API gravity @ 60ºF

6B Generalized products ºF API gravity @ 60ºF

6C Individual & special applications ºF Thermal expansion coefficient

6D Generalized lubricating oils ºF API gravity @ 60ºF

24A Generalized crude oil ºF Relative density @ 60/60ºF

24B Generalized products ºF Relative density @ 60/60ºF

24C Individual & special applications ºF Thermal expansion coefficient

54A Generalized crude oil ºC Density @ 15ºC

54B Generalized products ºC Density @ 15ºC

54C Individual & special applications ºC Thermal expansion coefficient

54D Generalized lubricating oils ºC Density @ 15ºC

60A Generalized crude oil ºC Density @ 20ºC

60B Generalized products ºC Density @ 20ºC

60C Individual & special applications ºC Thermal expansion coefficient

60D Generalized lubricating oils ºC Density @ 20ºC

ASTM D4311 Asphalt to 60ºF, Table 1 ºF API gravity @ 60ºF, Table A or B ASTM D4311 Asphalt to 15ºC, Table 2 ºC Density @ 15ºC, Table A or B

Additionally, ASTM D1555 and D1555M (Metric edition), which tabulates CTL (VCF) for various

aromatic hydrocarbons.

Many products, especially petrochemicals, may have specific volume correction factor tables,

developed by the manufacturer. These are usually in the form of product specific tables of CTL (VCF), showing the factor at observed temperatures, which must be applied to obtain the volume at standard temperature; or, a volume correction factor, per degree difference in observed temperature. While these individual tables can have their own parameters and table entry requirements, their application is the same.

The use of these tables should be by mutual agreement of all parties concerned.

10.3 TOTAL CALCULATED VOLUME (TCV)

Total calculated volume (TCV) is determined by adding the Gross Standard Volume (GSV) to the Free

Water (FW)

TCV = GSV + FW

11 Calculation of Net Standard Volume (NSV)11.1 NET STANDARD VOLUME (NSV)

To calculate NSV, multiply the GSV by the CSW.

NSV = GSV x CSW

This, can be expanded to:

NSV = GSV x [(100 – S&W %) 100]

11.2 CALCULATION OF THE CORRECTION FOR SEDIMENT AND WATER (CSW)

To calculate the CSW value, the percentage of S&W must be known. Deduct the S&W percentage

value from 100, thus determining the NSV as a percentage of the GSV, divide this by 100, and multiply the GSV by it.

CSW = (100 - S&W %) 100

On multiple tank shipments, NSV can be calculated on a tank-by-tank basis if the individual S&W

values are known. However, it can be calculated on a grade or parcel basis if the S&W was analyzed on an appropriate representative sample.NOTE: Crude oil and some liquid petroleum products contain sediment and water suspended or entrained throughout

1.11.00.9

###

that fluid. The quantity of sediment and water is determined by laboratory analysis of a representative sample and is expressed as a percentage, usually volume percent. For information on how sediment and water analysis is performed, refer to API MPMS Chapter 10 or its ASTM equivalents.

11.3 CALCULATION OF THE VOLUME OF SEDIMENT AND WATER (S&Wvol)

It is frequently necessary to calculate the actual volumetric value of S&W. This can be achieved by

subtracting the net standard volume (NSV) from the Gross Standard Volume (GSV).

S&WVOL = GSV - NSV

12 Calculation of Mass (Weight in Vacuum) and Weight (Weight in Air)12.1 INTRODUCTION

While the terms mass and weight have there own definitions within the scientific community, when

referred to in this document, mass will refer to weight in vacuum (vacuo) and weight will refer to weight in air. If the same material is measured in a vacuum and then in air, the measured quantity in air will be lighter than that of the measured quantity in vacuum by an amount equal to the volume of air displaced by the material being measured. In other words the weight measured in air is affected by the “buoyancy” of the air surrounding the object.

The routines, however, for calculating mass and weight are the same, they just use different factors.

12.2 CALCULATION METHODS

There are two common methods utilized to calculate mass and/or weight, both of which are capable of

calculating either of them.

12.2.1 Volume at Standard Temperature to Mass/Weight Method

This method corrects the volume at the observed temperature to the volume at the standard

temperature by applying a CTPL or CTL (VCF) after which the weight/mass is obtained by multiplying the standard volume with the density at the same standard temperature. If mass is required use the density in vacuum. If weight is required use the density in air

12.2.2 Volume at Observed Temperature to Mass/Weight

This method adjusts the density at standard temperature to its density at observed temperature by use of

a thermal expansion coefficient per degree, then, multiplying it by the volume at observed temperature to obtain mass or weight. If mass is required use the density in vacuum. If weight is required use the density in air

12.2.3 Calculation of Gross Standard Weight and Net Standard Weight

Gross Standard Weight (GSW) and Net Standard Weight (NSW) are calculated by multiplying the GSV or

NSV by the appropriate density in air. NSW = NSV x Density in air

GSW = GSV x Density in air

12.2.4 Calculation of Gross Standard Mass and Net Standard Mass

Gross Standard Mass (GSM) and Net Standard Mass NSM are calculated by multiplying the GSV or NSV

by the appropriate density in vacuum. NSM = NSV x Density in vacuum

GSM = GSV x Density in vacuum

12.3 CONVERTING BETWEEN MASS AND WEIGHT

As the difference is equal to the weight of the volume of air displaced by the object being weighed, high

density materials will displace less air than low density materials; therefore, the difference between weight in air and weight in vacuum varies with density and will have the greatest impact on low density materials. While this difference is not large, it is measurable and typically impacts the third and fourth decimal place of the density, by an amount shown in the table below.Table 5 – Mass to Weight Density Corrections

Density Range(kg/m3)

Density Correction(kg/m3)

Less than 996.6996.6 – 1,663.5Greater than 1,6635

The majority of petroleum based materials are in the density range of 600.0 to 996.6 kg/m3, therefore, the most common correction is 1.1; however, densities above 996.6 kg/m3 are not uncommon, especially in the chemical industry. When adjusting a density in vacuum to its corresponding density in air, the correction is subtracted. When adjusting a density in air to its corresponding density in vacuum, the

correction is added.While the use of Table 5 to adjust densities for mass to weight calculations and vice versa is

convenient and quick, especially for field applications, API MPMS Chapter 11.5.3 specifies a formula for making this conversion, which is reproduced below.

The following equation expresses the relationship between Density in Vacuum in kg/m3 at 15 C and

Density in Air at 15 C in kg/m3

15 in kg/m3

= 1.000149926 D15

Where: D 15

= Density in Air

D15 = Density in Vacuum

In the event of a dispute or when greater discrimination is required than is provided for by Table 5, the

formula specified in API MPMS Chapter 11.5.3 shall be used.

13 Direct Mass MeasurementSome measurement methods, for example hydrostatic tank gauges, determine mass by measuring

liquid head rather than liquid level. The calculation algorithms used by these methods may include corrections for the effect of temperature and pressure on the liquid (10.2), for the effect of liquid density on the floating roof (9.1.4), or the effect of temperature on the shell of the tank (9.1.3). In such cases,

these corrections should not be duplicated. For calculation procedures, refer to API MPMS Chapter 16.2.

14 Calculation Sequence14.1 GENERAL

It is outside the scope of this document to instruct the user in the procedures and techniques

necessary to obtain all the observed information that will be needed in order to calculate a net volume. It is the user’s responsibility to obtain that information from the standards referenced earlier. While there are some precautionary notes in the text of this document, it is assumed that the user will come to this standard with all the observed information necessary to begin to calculate net volumes. The information needed is liquid level, FW level, product temperature, ambient temperature, density, and S&W percentage. It will also be necessary to have the capacity table and applicable correction factor tables or

subroutines. Any deduction that is inappropriate for a particular application will be a zero deduction, and

any correction that is inappropriate will be held at 1.00000. The calculation routine will be the same.

14.2 VOLUME AT STANDARD TEMPERATURE TO MASS/WEIGHT CALCULATION PROCEDURE

The calculation sequence follows that of the preceding sections. The flow is as follows (see Figures A-

1 and A-2):

TOV GOV GSV NSV NSW

or

TOV GOV GSV NSV NSM

a. With the liquid level or gauge, enter the capacity table and record the TOV, as recorded in the table.

b. Subtract any gauged FW volumes. The FW volume is obtained by entering the capacity table with the gauged FW level.

c. Apply the CTSh to arrive at the GOV.

d. Correct this quantity for any applicable FRA or FRC.

e. Correct the GOV to standard temperature. This is done by multiplying the GOV by the CTPL to arrive at the GSV.

f. Adjust for any measured amount of S&W. This is done by multiplying GSV by the CSW. g. If net standard weight [NSW] is required, multiply the result from Item f. the density in air

h. If net standard mass [NSM] is required, multiply the result from Item f. the density in vacuum

The mathematical formulae for the various required values can be expressed as follows:

GSV = {[(TOV - FW) x CTSh] FRA} x CTPL

GSW = {[(TOV - FW) x CTSh] FRA} x CTPL x Density (in air or vacuum as required)

NSV = {[(TOV - FW) x CTSh] FRA} x CTPL x CSW

NSW = {[(TOV - FW) x CTSh] FRA} x CTPL x CSW x Density (in air or vacuum as required)

Chain calculations must be performed. Only the final result in the calculation is to be rounded. If it is

necessary to report any intermediate values, the figure should be rounded as required in Section 5; however, the rounded figure is not to be inserted into the calculation sequence. See Annex A for examples of shore tank and marine vessel tank calculations.

14.3 VOLUME AT OBSERVED TEMPERATURE TO MASS/WEIGHT CALCULATION PROCEDURE

The calculation sequence follows that of the preceding sections.

TOV GOV Mass or Weight

a. With the liquid level or gauge, enter the capacity table and record the TOV, as recorded in the table.


c. Apply the CTSh to arrive at the GOV.

d. Correct this quantity for any applicable FRA or FRC.

e. Correct the GOV to mass or weight. This is done by multiplying the GOV by the density in air at observed temperature to arrive at the weight or density in vacuum at observed temperature to arrive at the mass.NOTE: This method is not normally used on crude oils or other materials where net standard volume [NSV] or netstandard weight [NSW] is required. Should this be required, the density at standard temperature should be applied to the mass or weight, as appropriate, to arrive at gross standard volume [GSV].

The mathematical formulae for the various required values can be expressed as follows:

GOV = {[(TOV - FW) x CTSh] FRA}

Mass or Weight = {[(TOV - FW) x CTSh] FRA} x Density at Observed Temperature (in air or vacuum as

required)

Density at standard temperature is converted to density at observed temperature as follows:

( Cs)

t s t

Where:

ρt = density at measured temperature

ρs = density at standard temperature

= difference in temperature (standard - measured)t

Cs = coefficient of thermal expansion per degree

Chain calculations must be performed. Only the final result in the calculation is to be rounded. If it is


15 Calculation of Transferred Volumes for Custody Transfer15.1 GENERAL

The calculation routines specified in this document are specific to the quantity of material in a tank whose

contents are not in motion. The calculation of transferred volumes for custody transfer typically involves performing the same calculation before and after a transfer and determining the difference. If multiple tanks are involved this process is repeated for each tank and the sum of the quantity transferred from each tank is the total quantity transferred. However, when multiple tanks are involved, there are numerous variations on how the total transferred quantity can be calculated. In many cases the GSV is

calculated from each tank’s opening and closing measurements, and then additional calculations to NSV

and mass or weight are made collectively to this quantity. Alternatively, the individual opening and closing readings can be calculated to NSV, mass or weight and totalized accordingly. The differences resulting from these variations are usually very small and it is not the intent of this standard to specify a single method for this. Examples A1 and A2 in Annex A outline two of the more commonly used methods; however, these should not be construed as the only acceptable methods. The method used for custody transfer should be that as agreed to by the commercial parties to the transaction.

15.2 SMALL LEASE TANKS

Lease tanks differ from storage tanks not only in size but in gauging procedure. Therefore, it is

necessary to establish unique calculation procedures for lease tanks. This procedure is applicable to lease tanks of 5,000 barrels (795 m3) or less and assumes that the clearance sample has verified merchantable oil at least 4 inches below the tank outlet. The CTSh is not significant to these situations

and should not be applied.

15.2.1 Transferred Volume Calculation Procedure for Lease Tanks

The following are the procedures for calculating transferred volumes for lease tanks:

a. With the liquid level or gauge, enter the capacity table and record the TOV for the opening gauge.

b. Correct for the temperature of the oil. This is done by multiplying the answer from Item a. by the

CTPL, arriving at the GSV, and rounding appropriately.

c. With the liquid level or gauge, enter the capacity table and record the TOV for the closing gauge.

d. Correct for the temperature of the product. This is done by multiplying the answer from Item c. by the

CTPL, arriving at the GSV, and rounding appropriately. e. Subtract the closing GSV from the opening GSV.

f. The last correction shall be to adjust for any measured amount of S&W. This is done by multiplying

the ∆GSV obtained from Item e. by the CSW and rounding appropriately.

15.3 VOLUMETRIC SHRINKAGE

Volumetric shrinkage occurs when light hydrocarbons are mixed with much heavier hydrocarbons. The

tables and calculation routines are specified in API MPMS Chapter 12.3. It is not normal practice to

include these quantities in custody transfer calculations as the volumes lost are not available again, except through refining. Any adjustments made as a result of volumetric shrinkage are strictly upon agreement of the commercial parties involved.

Note: Mass or weight is not affected by volumetric shrinkage.

16 Miscellaneous16.1 PRECAUTIONS WHEN USING AN AUTOMATIC SAMPLER

When automatic sampling systems are employed for product transfer, tanks with varying densities

(crude oil systems, for example) will need to accumulate base data differently than for transfers that do not include the use of an automatic sampler. While the volume calculation procedures for movements into a tank involving an automatic sampling system will be the same, the method of collecting the base information will be different. (Movements out of a tank are less affected as there is less blending of densities taking place). However, it may be necessary to report the density, as determined from the automatic sampling system, somewhere on the measurement ticket or report. Regardless, it will still be necessary to sample the tank before and after a receipt because of the following:

a. At the beginning of the transfer, there is nothing in the sampler and therefore nothing on which to base

opening measurements.

b. After the transfer, the incoming product has been blended with whatever was in the tank. In order for the CTPL and FRA to be correct, they will have to be based on the density of the product as found in the tank.

c. The tank’s FW level must be left the same on the closing report as on the opening report. All deducted water volumes should come from the sampler and be accounted for in the form of correction for S&W (CSW).

d. S&W are usually only deducted on crude oil cargoes. Petroleum products are not usually corrected for S&W unless required as a commercial condition or other specific requirement; therefore net standard volume = gross standard volume.

16.2 INTERRELATION OF UNITS

It is frequently necessary to convert from one type of unit to another using a conversion factor. These

conversion factors are found in API MPMS Chapter 11.5 of which there are three subchapters: Chapter 11.5.1 - Conversions of API Gravity at 60 F

Chapter 11.5.2 - Conversions for Relative Density (60/60 F)

Chapter 11.5.3 - Conversions for Density in vacuum at 15 C

These three standards replace the Density/Weight/Volume Intraconversion tables formerly located in

API MPMS Chapter 11.1, Volumes XI/XII. There are separate conversion factors for mass and weight,

depending upon which one is required.

Due to the complexity of these interrelations there is frequently more than one way of performing these

conversions and this standard does not attempt to define any specific routines for converting from one unit to another; however, the user should be guided by the following:

Conversion units that are “exact by definition” are to be considered primary and shall be used whenever possible

Conversion processes shall not produce a result that contradicts an “exact by definition” value

The use of multiple conversion factors should be avoided if possible. If this cannot be avoided the process that uses the least number of conversion factors shall be used.

ANNEX A –EXAMPLES OF SHORE TANK AND MARINE VESSEL TANK CALCULATIONS (NORMATIVE)

Example A-1 Custody Transfer Flow Chart – Shore Tanks with Automatic SamplerOPENING GAUGE CLOSING GAUGE

TOTAL

OBSERVED VOLUME

Minus Free

Water

Multiply by CTSh

Plus or Minus Floating Roof Adjustment or Correction

TOV

DEL/REC

TOTAL

OBSERVED VOLUME

Minus Free

Water

Multiply by CTSh

Plus or Minus Floating Roof Adjustment or Correction

Notes:

1. For multiple tank movements add each tank’s delivered or received GSV and proceed as shown.

2. Facilities that apply the

vessel’s free water to the transferred quantity shall apply this immediately prior to the CSW correction

3. Tank free water (FW) on opening and closing must remain constant.GROSS

OBSERVED VOLUME

GOV

DEL/REC

GROSS

OBSERVED VOLUME

Multiply by CTPL

(VCF)

Multiply by CTPL

(VCF)

GROSS

STANDARD VOLUME

GROSS

STANDARD VOLUME

TOTAL GSV

DELIVERY or RECEPT

Multiply by Density in Air

Multiply by Density in Vacuum

GROSS STANDARD WEIGHT

GROSS STANDARD MASS

Multiply by Correction for

Sediment & Water (CSW)

TOTAL NSV

DELIVERY or RECEPT

Multiply by Density in Air

Multiply by Density in Vacuum

NET STANDARD WEIGHT

NET STANDARD MASS

Example A-2 Custody Transfer Flow Chart – Share Tank(s) with Individual Tank SamplesSingle Tank Calculation

OPENING GAUGE CLOSING GAUGE

Note: For multiple tank

movements add each

tank’s delivered orTOTAL

OBSERVED VOLUME

Minus Free

Water

TOV

DEL/REC

TOTAL

OBSERVED VOLUME

Minus Free

Water

received quantity as

appropriateMultiply by CTSh

Multiply by CTSh

Plus or Minus Floating

Roof Adjustment or

Correction

Plus or Minus Floating

Roof Adjustment or

Correction

GROSS

OBSERVED VOLUME

GOV

DEL/REC

GROSS

OBSERVED VOLUME

Multiply by CTPL

(VCF)

Multiply by CTPL

(VCF)

GROSS

STANDARD VOLUME

GSV

DEL/REC

GROSS

STANDARD VOLUME





NET

STANDARD VOLUME

NSV

DEL/REC

NET

STANDARD VOLUME

Density

in Air

Density in

Vacuum

Density

in Air

Density in

Vacuum

435,218.32 435,218.32

1.00032 435,203.17

0.98676429,478.47

0.9988

428,963.09

NET

STANDARD WEIGHT

NSW

DEL/REC

NET

STANDARD WEIGHT

NET

STANDARD MASS

NSM

DEL/REC

NET

STANDARD MASS

Example A-3

Shore Tank Calculation

Using

Volume at Standard Temperature to Mass or Weight Calculation Procedure

Analytical and Observed Data

Liquid level gauge 46’ 06 1/4”

Free water gauge 00’ 10 3/4”

API gravity @ 60ºF 33.7 (rounded from 33.69) Liquid temperature ºF 88.3

Ambient temperature ºF 71.5

Temperature of tank shell ºF (TSh) 86.0 (rounded from 86.2) Sediment and water percent 0.12%

CalculationCalculated or Derived Data Symbol Reported Unit Barrels or

Long TonsRunning Calculation (Not Reported)

Total observed volume1 TOV1

Free waterGross observed volume2

FW GOV2 -154.37435,063.95

-154.37435,063.95

Correction for temperature of shell CTSh 435,203.1704643

Floating roof adjustmentGross observed volume

FRA +37.89435,241.06

+37.89435,241.0604643

Correction for temperature ofLiquid (Table 6A)

Gross standard volumeCTPLGSV

429,478.4688233

Correction for sediment and water4 CSW

Net standard volume NSV 428,963.094663

Density in air (Long tons per bbl) 0.13373 (API MPMS Chapter 11.5.1)

Net standard weight (long tons) NSW 57,365.235 57,365.23464883

Alternate Calculation from Net Standard Volume if Net Standard Mass is required:

Density in vacuum (Long tons per bbl) 0.13390 (API MPMS Chapter 11.5.1)

Net standard mass (long tons) NSM 57,438.158 57,438.15837493

NOTES:

1 Quantity from the tank capacity table using the liquid level gauge to enter the table. For this example, it is assumed that any correction to the gauge, due to expansion or contraction of the tape itself, has already been made. This issue is not addressed in this standard. The user should refer to the tape manufacturer’s instructions for specific details.

2 Gross observed volume, uncorrected for the temperature of the tank shell and floating roof adjustment.

3 As displayed on a 12-digit calculator. Actual discrimination is determined by the calculating capacity of the calculation hardware.

4 Refer to 11.3 to calculate the volumetric value for sediment and water.

Example A-4

Marine Vessel Tank Calculation

Using

Volume at Standard Temperature to Mass or Weight Calculation Procedure

35,118.65

34,982.93 34,982.9342.8034,940.13 34,940.13

34,471.48

3

34,412.88

1289561 1289561

1.00016 1284329

0.98676 1263586


Liquid level gauge (ullage) 4’ 06 1/4”

Free water gauge (ullage) 55’10 3/4”

API gravity @ 60ºF 27.1 (rounded from 27.14) Liquid temperature ºF 91.1

Sediment and water percent 0.17% Forward draft 36’ 06” After draft 38’ 00” Trim (by the stern) 1’ 06” List (vessel upright) No list

Calculation

Calculated or Derived Data Symbol Reported Unit Barrels or RunningLong Tons Calculation

(Not Reported)

Total observed volume1

Trim correction (volumetric)2

TOV1

Trim2

35,118.65-135.72

Total observed volume TOVFree water (by wedge) FWGross observed volume GOVCorrection for temperature of liquid CTPL 0.986 59 (Table 6A)Gross standard volume GSV 34,471.48419773

Correction for sediment and water4 CSW 0.998

Net standard volume NSV 34,412.88267453

Density in air (Long tons per bbl) 0.13930 (API MPMS Chapter 11.5.1)

Net standard weight (long tons) NSW 4,793.715 4,793.71455655 3

Alternate Calculation from Net Standard Volume if Net Standard Mass is required:

Density in vacuum (Long tons per bbl) 0.13947 (API MPMS Chapter 11.5.1)

Net standard mass (long tons) NSM 4,799.565 4,799.564746613

NOTES:

1 Quantity from the vessel’s tank capacity table using the liquid level ullage gauge to enter the table.

2 Not all trim (or list) corrections are volumetric. Many are linear adjustments that are made to the observed ullage. In this case, the adjustment would be made before entering the vessel’s capacity table and a volumetric adjustment would not be necessary. If a volumetric list correction was applicable, it would be applied at this point in the calculation.


4 The volumetric value for sediment and water is determined by subtracting the net standard volume from the gross standard volume.

Example A-5

Shore Tank Calculation of Volume at 15ºC and Weight of p-Xylene using ASTM D1555M


Liquid level gauge 4606 mm

Free water gauge 10 mm Density at 15ºC kg/l (air) 0.8643 kg/l Liquid temperature ºC 22.3ºC Ambient temperature ºC 18.0ºC

Temperature of tank shell ºC (TSh) 22.0ºC (rounded from 21.8 ºC)

CalculationCalculated or Derived Data Symbol Reported Unit Litres / kg Running Calculation

(Not Reported)


Free waterGross observed volume2

FW GOV2 -54371284124

-54371284124

Correction for temperature of shell CTSh 1284329.459843


FRA -37891280540

- 37891280540.459843

Correction for temperature of [VCF]Liquid (Table ASTM D1555)Gross standard volume at 15ºC

CTPLGSV

1263586.104153

0.86431092117

1289561 1289561

1.00013 1289729

1277710

0.7440950616

Density in air at 15ºC kg/lWeight

1092117.469813

NOTES:

1 Quantity from the tank capacity table using the liquid level gauge to enter the table. For this example, it is assumed

that any correction to the gauge, due to expansion or contraction of the tape itself, has already been made. This issue is not addressed in this standard. The user should refer to the tape manufacturer’s instructions for specific details.

2 Gross observed volume, uncorrected for the temperature of the tank shell and floating roof adjustment.


Example A-6

Shore Tank Calculation of Volume at 15ºC, Mass and Weight of MTBE using

API MPMS Chapter 11.1/Adjunct to ASTM D1250/Adjunct to IP 200, Table 54C


Liquid level gauge 5810 mm

Free water gauge None Found

Coefficient of thermal expansion 0.0014202 alpha per ºC Density in air at 15ºC kg/l 0.7429

Liquid temperature ºC 22.5ºC Ambient temperature ºC 12.0ºC

Temperature of tank shell ºC (TSh) 21.0ºC (rounded from 21.1 ºC)


(Not Reported)




FRA -37891285940

- 37891285939.64293 3

Correction for temperature of [VCF]Liquid CTPL 0.99360 (API MPMS Chapter 11.1, Table 54C)2

Gross standard volume at 15ºC GSV 1277710 1277709.629213

Density at 15ºC kg/l (air) 0.7429

Weight (in air) 949210 949210.48354 3

For Conversion to Mass (weight in vacuum)

Density at 15ºC kg/l (air) 0.7429

Density adjustment + 0.0011 (From Table 5 in Section 12.3) Density at 15ºC kg/l (vacuum) 0.7440

Gross standard volume at 15ºC GSV 1277709.629213

Density at 15ºC kg/l (vacuum)Mass (weight in vacuum) 950615.9641323

Notes:

1 Quantity from the tank capacity table using the liquid level gauge to enter the table. For this example, it is assumed that any correction to the gauge, due to expansion or contraction of the tape itself, has already been made. This issue is not addressed in this standard. The user should refer to the tape manufacturer’s instructions for specific details.

2 MTBE has a special application table, which is a function of the API MPMS Chapter 11.1/Adjunct to ASTM D1250/Adjunct to IP 200 “C” Tables; however, this example is applicable to any CTPL/VCF that derives form these “C” tables.


ExampleA-7Shore Tank Calculation of the Weight of Benzene

Using

Coefficient of Thermal Expansion per Degree (Cs).

The Density at standard temperature is converted to Density at Measured temperature, which is then

applied to the measured volume to give mass or weight, as appropriate.


1289561 1289561

1.00013 1289729

0.8756 1125969

0.88311275018 1275018.4026

Liquid level gauge 5810 mm Free water gauge None Found Density at 15ºC (air) kg/l 0.8831 kg/l (air) Thermal Density Coefficient / ºC 0.00100 kg/l per ºC Liquid temperature ºC 22.5ºC

Ambient temperature ºC 12.0ºC

Temperature of tank shell ºC (TSh) 21.0ºC (rounded from 20.8ºC)


(Not Reported)




FRA -37891285940

- 37891285939.64293 2

Density at Obs. Temp. 22.5ºC kg/l (air)Weight (in air)

1125968.75134 2

Density at 15ºC, kg/l (air)Liters at 15ºC

t

Where:

( Cs)

s t

Note:

1 Quantity from the tank capacity table using the liquid level gauge to

ρt = density at measured temperature

ρs = density at standard temperature

= difference in temperature (standard - measured)

t

Cs = coefficient of thermal expansion per degree

Density at 15ºC 0.8831 kg/l (air) Expansion coefficient 0.00100 kg/l per ºC

ρt = 0.8831 + ([15.0 – 22.5] * 0.00100)

= 0.8831 + (-7.5 * 0.00100)

= 0.8831 – 0.00750

= 0.8756

enter the table. For this example, it

is assumed that any correction to the gauge, due to expansion or contraction of the tape itself, has already been made. This issue is

not addressed in this standard. The user should refer to the tape

manufacturer’s instructions for

specific details.

2 As displayed on a 12-digit calculator. Actual discrimination is

determined by the calculating

capacity of the calculation hardware.

ANNEX BEXAMPLE OF SHELL TEMPERATURE CORRECTION FACTORS FOR EXPANSION AND CONTRACTION OF UPRIGHT CYLINDRICAL STEEL TANKS DUE TO TEMPERATURE (NORMATIVE)

For mild steel tanks with a linear coefficient of expansion of 0.0000062/°F, use Table B1. For temperatures

outside the range of this table or for other coefficients expansion, use the formula in 9.1.3.

This table is applicable to tanks whose capacity tables were calculated at a reference tank shell

temperature of 60°F. For tanks with capacity tables calculated at a reference tank shell temperature other than 60°F, the table can still be used. However, it is necessary to subtract the reference temperature from the shell temperature and then add 60 to arrive at the temperature used to enter the table. It is important to pay attention to the algebraic signs (positive or negative) when performing this calculation.

B.1 Shell Temperature Correction Factors for Expansion and Contraction of Upright Cylindrical

Steel Tanks Due to Temperature

B.1.1 Tanks undergo expansion or contraction due to variations in ambient and product temperatures.

Such expansion or contraction in tank volume may be computed once the tank shell temperature is determined.

B.1.2 For tanks that are insulated, the tank shell temperature (TSh) is assumed to be the same as the

temperature of the product (TL) stored within the tank (that is, TSh = TL). For tanks that are not insulated, the shell temperature is a weighted average of the ambient and the product temperature based the following equation:

TSh = [(7 x TL) + TA] / 8

Where TL = liquid product temperature

TA = ambient air temperature

B.1.3 Once the shell temperature is determined, the shell temperature correction factor (CTSh) is

computed using the following equation:


Where: ά = Linear coefficient of expansion of the tank shell material


B.2 Application of Shell Temperature Correction

Case 1: Capacity table at tank shell reference temperature (TShREF) of 60°F, of mild steel, non-

insulated construction with a linear coefficient of expansion of 0.000062/°F.

- Volume at a given level (tank shell reference temperature [TShREF] 60°F) = 100,000 bbls.

- Ambient Temperature = 70°F.

- Product Temperature = 155°F.

- Compute capacity table volume reflecting above conditions.

Solution:

a. Calculate shell temperature (TSh) at 155°F product temperature:

TSh = [(7 x TL) + TA] / 8

TSh = [(7 x 155) + 70] / 8

TSh = 144°F (rounded to nearest 1°F)

b. Compute ΔT


ΔT = 144 - 60

ΔT = 84

c. Compute the shell temperature correction factor (CTSh) for 144°F


ΔT = Tank Shell Temperature (TSh) - Tank Shell Reference Temperature (TShREF) CTSh = 1 + (2 x 0.0000062 x ΔT) + (0.0000062 x 0.0000062 x ΔT x ΔT)

CTSh = 1 + (0.0000124 x 84) + (0.00000000003844 x 7056)

CTSh = 1 + 0.0010416 + .00000027123264

CTSh = 1.00104 (rounded to five decimal places)

d. Compute the correct volume:

V = Volume at TSh 60°F x CTSh FOR 144°F

V = 100,000 bbls x 1.00104

V = 100,104 bbls.

Case 2: Capacity table already corrected for a tank shell temperature of 185°F, on a mild steel non-

insulated tank [see note below].

- Volume at a given level (tank shell reference temperature [TShREF] 185°F) = 100,000 bbls.

##################

- Ambient Temperature = 70°F.

- Product Temperature = 155°F.

- Compute capacity table volume reflecting above conditions.

Solution:

a. Calculate shell temperature (TSh) at 155°F product temperature:

TSh = [(7 x TL) + TA] / 8

TSh = [(7 x 155) + 70] x 70

TSh = 144°F (rounded to nearest 1°F)

b. Compute ΔT

ΔT = Tank Shell Temperature (TSh) - Tank Shell Reference Temperature (TREF)

ΔT = 144 - 185

ΔT = -41

c. Compute the shell temperature correction factor (CTSh) for 144°F


ΔT = Tank Shell Temperature (TSh) - Tank Shell Reference Temperature (TREF) CTSh = 1 + (2 x 0.0000062 x ΔT) + (0.0000062 x 0.0000062 x ΔT x ΔT)

CTSh = 1 + (0.0000124 x -41) + (0.00000000003844 x 1681) CTSh = 1 - 0.0005084 + .00000006461764

CTSh = 0.99949 (rounded to five decimal places)

d. Compute the correct volume:

V = Volume at TSh 185°F x CTSh FOR 144°F V = 100,000 bbls x 0.99949

V = 99,949 bbls.

Note: For tanks that specify a product operating temperature, it will be necessary to obtain the actual

Tank Shell Reference Temperature (TShREF) that was used to compute the capacity table volumes. If the tank is insulated, it can be assumed that the Tank Shell Reference Temperature (TShREF) is the same as the product operating temperature. If the tank is not insulated, the user should contact the company that generated the capacity table to determine what tank shell reference temperature (TSh REF) was used.

Table B3 - Linear Thermal Expansion Coefficients of SteelType of Steel Coefficient per °F Coefficient per °CMild Carbon 0.00000620 0.0000112304 Stainless 0.00000960 0.0000173316 Stainless 0.00000883 0.000015917-4PH Stainless 0.00000600 0.0000108Table B-1 - Correction Factors for effect of Temperature on the Tank ShellFor mild steel tanks with a linear coefficient of expansion of 0.0000062/°F, whose capacity tables werecalculated ala tank shell reference temperature (TShREF) of 60°F. For temperatures outside the range of this table use the formula in API MPMS Chapter 12, Section 1, Part 1, Subpart 9.1.3.Shdl Shdl Shdl Shdl Shdl Shdl Sh<ll Shdl Shdl Shdl Shdl Shdl Shdl Sh<ll

Temp Correction Temp Correction Temp Correction Temp Correction Temp Correction Temp Correction Temp

COF) Factor COF) Factor COF) Factor COF) Factor COF) Factor COF) Factor COF)

0.99926 45 0.99981 90 1.00037 135 1.00093 180 1.00149 225 1.00205 270

1 0.99927 46 0.99983 91 1.00038 136 1.00094 181 1.00150 226 1.00206 27

2 0.99928 47 0.99984 92 1.00040 137 1.00096 182 1.00151 227 1.00207 272

3 0.99929 48 0.99985 93 1.00041 138 1.00097 183 1.00153 228 1.00208 27

4 0.99931 49 0.99986 94 1.00042 139 1.00098 184 1.00154 229 1.00210 274

5 0.99932 50 0.99988 95 1.00043 140 1.00099 185 1.00155 230 1.00211 275

6 0.99933 51 0.99989 96 1.00045 141 1.00100 186 1.00156 231 1.00212 276

7 0.99934 52 0.99990 97 1.00046 142 1.00102 187 1.00158 232 1.00213 277

8 0.99936 53 0.99991 98 1.00047 143 1.00103 188 1.00159 233 1.00215 278

CorrectionFactor

#########

2881289###

#########

294295296297###############

38 0.99973 83 1.00029 128 1.00084 173 1.00140 218 1.00196 263 1.00252 308 1.0030839 0.99974 84 1.00030 129 1.00086 174 1.00141 219 1.00197 264 1.00253 309 1.0030940 0.99975 85 1.00031 130 1.00087 175 1.00143 220 1.00198 265 1.00254 310 1.0031041 0.99976 86 1.00032 131 1.00088 176 1.00144 221 1.00200 266 1.00256 31 1.0031142 0.99978 87 1.00033 132 1.00089 177 1.00145 222 1.00201 267 1.00257 31 1.0031343 0.99979 88 1.00035 133 1.00091 178 1.00146 223 1.00202 268 1.00258 31 1.0031444 0.99980 89 1.00036 134 1.00092 179 1.00148 224 1.00203 269 1.00259 314 1.00315

2144 0.99868 0.99969 46 1.00069 91 0.00170 136 18 0.003 22643 0.99871 2 0.99971 47 1.00071 92 1.00172 137 1.00272 182 1.00373 2242 0.99873 3 0.99973 48 1.00074 93 1.00174 138 1.00275 183 1.00375 22841 0.99875 4 0.99975 49 1.00076 94 1.00176 139 1.00277 184 1.00378 22940 0.99877 5 0.99978 50 1.00078 95 1.00179 140 1.00279 185 1.00380 230 1.0048039 0.99880 6 0.99980 51 1.00080 96 1.00181 141 1.00281 186 1.00382 231 1.0048338 0.99882 7 0.99982 52 1.00083 97 1.00183 142 1.00284 187 1.00384 232 1.0048537 0.99884 8 0.99984 53 1.00085 98 1.00185 143 1.00286 188 1.00387 233 1.0048736 0.99886 9 0.99987 54 1.00087 99 1.00188 144 1.00288 189 1.00389 234 1.0048935 0.99888 10 0.99989 55 1.00089 100 1.00190 145 1.00290 190 1.00391 235 1.0049234 0.99891 11 0.99991 56 1.00092 101 1.00192 146 1.00293 191 1.00393 236 1.0049433 0.99893 12 0.99993 57 1.00094 102 1.00194 147 1.00295 192 1.00395 23 1.0049632 0.99895 13 0.99996 58 1.00096 103 1.00197 148 1.00297 193 1.00398 238 1.0049831 0.99897 14 0.99998 59 1.00098 104 1.00199 149 1.00299 194 1.00400 239 1.0050130 0.99900 15 1.00000 60 1.00100 105 1.00201 150 1.00302 195 1.00402 240 1.0050329 0.99902 16 1.00002 61 1.00103 106 1.00203 151 1.00304 196 1.00404 241 1.0050528 0.99904 17 1.00004 62 1.00105 107 1.00205 152 1.00306 197 1.00407 242 1.0050727 0.99906 18 1.00007 63 1.00107 108 1.00208 153 1.00308 198 1.00409 243 1.00510

'999819 0.99949 641.00005 109 1.00061 154 1.00117 199 1.00172 244 1.00228

20 0.99950 65 1.00006 110 1.00062 155 1.00118 200 1.00174 245 1.00230 29021 0.99952 66 1.00007 111 1.00063 156 1.00119 201 1.00175 246 1.00231 2922 0.99953 67 1.00009 112 1.00064 157 1.00120 202 1.00176 247 1.00232 292

23 0.99954 68 1.00010 113 1.00066 158 1.00122 203 1.00177 248 1.0023324 0.99955 69 1.00011 114 1.00067 159 1.00123 204 1.00179 249 1.0023425 0.99957 70 1.00012 115 1.00068 160 1.00124 205 1.00180 250 1.0023626 0.99958 71 1.00014 116 1.00069 161 1.00125 206 1.00181 251 1.0023727 0.99959 72 1.00015 117 1.00071 162 1.00127 207 1.00182 252 1.0023829'

50 l6 l.0007 53 .00 .O '"

NOTE IFTANK IS INSULATEDUse Product Temperature as Tank Shell Temperature in This SituationTable B-2- Correction Factors for effect of Temperature on the Tank ShellFor mild steel tanks with a linear coefficient of expansion of 0.00001116fCC, whose capacity tables werecalculated ala tank shell reference temperature (TShREF) of 15°C. For temperatures outside the range of this table use the formula in API MPMS Chapter 12, Section 1, Part 1, Subpart 9.1.3.Shdl Shdl Sh<ll Shdl Shdl Shdl Shdl Shdl Shdl Shdl Shdl Sh<ll Shdl ShdlTemp Correction Temp Correction Temp Correction Temp Correction Temp Correction Temp Correction Temp

COC Factor C0C Factor oc Factor Factor Factor Factor C0C

CorrectionFactor

l.00270 1.004 721.004 741.004 761.004 78

26 0.99909 19 1.00009 64 1.00109 109 1.00210 154 1.00310 199 1.00411 244 1.0051225 0.99911 20 1.00011 65 1.00112 110 1.00212 155 1.00313 200 1.00413 245 1.0051424 0.99913 21 1.00013 66 1.00114 111 1.00214 156 1.00315 201 1.00416 246 1.0051623 0.99915 22 1.00016 67 1.00116 112 1.00217 157 1.00317 202 1.00418 24 1.0051822 0.99917 23 1.00018 68 1.00118 113 1.00219 158 1.00319 203 1.00420 248 1.0052121 0.99920 24 1.00020 69 1.00121 114 1.00221 159 1.00322 204 1.00422 249 1.0052320 0.99922 25 1.00022 70 1.00123 115 1.00223 160 1.00324 205 1.00425 250 1.0052519 0.99924 26 1.00025 71 1.00125 116 1.00226 161 1.00326 206 1.00427 251 1.0052718 0.99926 27 1.00027 72 1.00127 117 1.00228 162 1.00328 207 1.00429 252 1.0053017 0.99929 28 1.00029 73 1.00129 118 1.00230 163 1.00331 208 1.00431 253 1.0053216 0.99931 29 1.00031 74 1.00132 119 1.00232 164 1.00333 209 1.00433 254 1.0053415 0.99933 30 1.00033 75 1.00134 120 1.00234 165 1.00335 210 1.00436 255 1.0053614 0.99935 31 1.00036 76 1.00136 121 1.00237 166 1.00337 211 1.00438 256 1.0053913 0.99938 32 1.00038 77 1.00138 122 1.00239 167 1.00340 212 1.00440 257 1.0054112 0.99940 33 1.00040 78 1.00141 123 1.00241 168 1.00342 213 1.00442 258 1.0054311 0.99942 34 1.00042 79 1.00143 124 1.00243 169 1.00344 214 1.00445 259 1.0054510 0.99944 35 1.00045 80 1.00145 125 1.00246 170 1.00346 215 1.00447 260 1.00548

9 0.99946 36 1.00047 81 1.00147 126 1.00248 171 1.00348 216 1.00449 261 1.005508 0.99949 37 1.00049 82 1.00150 127 1.00250 172 1.00351 217 1.00451 262 1.005527 0.99951 38 1.00051 83 1.00152 128 1.00252 173 1.00353 218 1.00454 263 1.005546 0.99953 39 1.00054 84 1.00154 129 1.00255 174 1.00355 219 1.00456 264 1.00557

NOTE IFTANK IS INSULATEDUse Product Temperature as Tank Shell Temperature in This Situation

ANNEX CEXAMPLES OF BOTH TYPES OF FLOATING ROOF ADJUSTMENTS (NORMATIVE)

C1: Example when roof calculation is calculated into the tank capacity table:

Calculation of the secondary correction for the difference between the reference density

and the observed density when the primary roof correction is built into the capacity table using reference density.

Input Data:

Product: Crude Oil

API gravity @ 60ºF: 40.3

Temperature of liquid: 84.0ºF

Excerpt from a tank capacity table:

“A total of 4,088.2662 barrels was deducted from this table between 4 feet 00 inches and 5 feet 00 inches for floating roof displacement based on a weight of 1,215,000 pounds and a gravity of 35.0 API. Gauged quantities above 5 feet 00 inches reflect this deduction but shall be adjusted for varying API gravities at tank temperature according to the following.”

Referenced observed API gravity 35.0: no adjustment

For each 1.0 API below 35.0 API: add 24.59 barrels

For each 1.0 API above 35.0 API: subtract 24.59 barrels

Step 1: Calculate the observed API gravity for an API gravity at 60ºF of 40.3 and an

observed temperature of the liquid of 84.0ºF. This is done by working backwards using API MPMS Chapter 11.1/Adjunct to ASTM D1250/Adjunct to IP 200, Table 5A (or 5B if the tank content is a petroleum product) as shown in Table 4.

Note: Table 6 is an excerpt from using API MPMS Chapter 11.1-1980/Adjunct to

ASTM D1250-80/Adjunct to IP 200/80, Table 5A.

Note: When the API gravity @ 60 F does not fall on an exact gravity, the user must interpolate

between gravities to arrive at the correct observed gravity. For example, the API @ 60 F to be corrected to observed, is 40.3. Looking up the gravity on Table 4 indicates the gravity falls between

40.0 and 40.4 or 3/4 of the difference between the observed gravities at the top of the table. The

API of 40.3 falls between the observed gravities of 42.0 and 42.5, which have a difference of 0.5 gravity. To determine what 40.3 equates to as an observed gravity, calculate what 3/4 of 0.5 gravity. The calculation equates to 0.4 (rounded). Add this to the 42.0 and the observed gravity that equates to 40.3 @ 60 is 42.4 API.

Step 2: Calculate the difference between the observed API gravity and the referenced

observed API gravity as follows:

Referenced observed API gravity 35.0: no adjustment

For each 1.0 API below 35.0 API: add 24.59 barrels

For each 1.0 API above 35.0 API: subtract 24.59 barrels

Referenced observed API gravity: 35.0

Observed API gravity @ 84ºF: 42.4

difference: 7.4

For each 1.0 API above 35.0 API, subtract 24.95 barrels. (7.4) x (-24.59) = -181.97 barrels

42.4

75.0 38.8 39.2 39.7 40.2 40.7 41.2 41.7 42.2 42.7 43.2 43.6 75.0

75.5 38.7 39.2 39.7 40.2 40.7 41.2 41.6 42.1 42.6 43.1 43.6 75.576.0 38.7 39.2 39.7 40.1 40.6 41.1 41.6 42.1 42.6 43.1 43.6 76.076.5 38.6 39.1 39.6 40.1 40.6 41.1 41.6 42.0 42.5 43.0 43.5 76.577.0 38.6 39.1 39.6 40.1 40.5 41.0 41.5 42.0 42.6 43.0 43.5 77.0

77.5 38.6 39.0 39.5 40.0 40.5 41.0 41.5 42.0 42.4 42.9 43.4 77.5

78.0 38.5 39.0 39.5 40.0 40.5 40.9 41.4 41.9 42.4 42.9 43.4 78.078.5 38.5 39.0 39.4 39.9 40.4 40.9 41.4 41.9 42.4 42.8 43.3 78.579.0 38.4 38.9 39.4 39.9 40.4 40.9 41.3 41.8 42.3 42.8 43.3 79.079.5 38.4 38.9 39.4 39.8 40.3 40.8 41.3 41.8 42.3 42.8 43.2 79.5

80.0 38.3 38.8 39.3 39.8 40.3 40.8 41.3 41.7 42.2 42.7 43.2 80.0

80.5 38.3 38.8 39.3 39.8 40.2 40.7 41.2 41.7 42.2 42.7 43.2 80.581.0 38.3 38.8 39.2 39.7 40.2 40.7 41.2 41.7 42.1 42.6 43.1 81.081.5 38.2 38.7 39.2 39.7 40.2 40.7 41.1 41.6 42.1 42.6 43.1 81.582.0 38.2 38.7 39.2 39.6 40.1 40.6 41.1 41.6 42.1 42.5 43.0 82.0

82.5 38.1 38.6 39.1 39.6 40.1 40.6 41.0 41.5 42.0 42.5 43.0 82.5

83.0 38.1 38.6 39.1 39.6 40.0 40.5 41.0 41.5 42.0 42.5 42.9 83.083.5 38.1 38.5 39.0 39.5 40.0 40.5 41.0 41.4 41.9 42.4 42.9 83.584.0 38.0 38.5 39.0 39.5 40.0 40.4 40.9 41.4 41.9 42.4 42.8 84.084.5 38.0 38.5 39.0 39.4 39.9 40.4 40.9 41.4 41.8 42.3 42.8 84.5

85.0 37.9 38.4 38.9 39.4 39.9 40.4 40.8 41.3 41.8 42.3 42.8 85.0

85.5 37.9 38.4 38.9 39.4 39.8 40.3 40.8 41.3 41.8 42.2 42.7 85.586.0 37.9 38.3 38.8 39.3 39.8 40.3 40.7 41.2 41.7 42.2 42.7 86.086.5 37.8 38.3 38.8 39.3 39.7 40.2 40.7 41.2 41.7 42.2 42.6 86.587.0 37.8 38.3 38.7 39.2 39.7 40.2 40.7 41.1 41.6 42.1 42.6 87.0

87.5 37.7 38.2 38.7 39.2 39.7 40.1 40.6 41.1 41.6 42.1 42.5 87.5

88.0 37.7 38.2 38.7 39.1 39.6 40.1 40.6 41.1 41.5 42.0 42.5 88.088.5 37.7 38.1 38.6 39.1 39.6 40.1 40.5 41.0 41.5 42.0 42.5 88.589.0 37.6 38.1 38.6 39.1 39.5 40.0 40.5 41.0 41.5 41.9 42.4 89.089.5 37.6 38.1 38.5 39.0 39.5 40.0 40.5 40.9 41.4 41.9 42.4 89.5

90.0 37.5 38.0 38.5 39.0 39.5 39.9 40.4 40.9 41.4 41.8 42.3 90.0

Floating roof adjustment = -181.97 barrelsTable 6

Generalized Crude Oils API Correction to 60ºF

API Gravity at Observed Temperature

Temp. ºF 40.0 40.5 41.0 41.5 42.0 42.5 43.0 43.5 44.0 44.5 45.0 Temp ºF

Corresponding API Gravity at 60ºF

*Denotes Extrapolated Value API Gravity = 40.0 to 45.0

C2: Example when roof adjustment is not calculated in the tank capacity table

The roof deduction is calculated by dividing the weight of the floating roof by the weight per unit volume at

standard temperature multiplied by the CTPL to bring this to observed conditions.

Roof correction = Weight of roof

Density in air x CTPL

Note: The density units must be consistent to both the CTPL and the units of the roof weight, in addition

to being a density in air. For example, if the density is lbs/gal @ 60ºF, then the roof weight must be in pounds and the CTPL applicable to a standard temperature of 60ºF. Additionally, this particular example will yield a roof correction in gallons. If the table units are in barrels, it will be necessary to divide the result by 42.

Calculate a floating roof adjustment when no corrections have been made to the tank

capacity table for the roof. (See note.)

Gross observed volume corrected for CTSh = 242,362.15 barrels

Product: Crude Oil

API gravity @ 60ºF: 40.3

Temperature of liquid: 84.0ºF CTPL (Table 6A): 0.9879

Weight of floating roof: 1,215,000 pounds

Weight per unit volume of liquid: 6.858 pounds/gallons (See note.)

FRC = weight of roof

density in air x CTPL

FRC = 1,215,000

6.858 x 0.9879

FRC = 179,335.26 gallons = -4,269.89 barrels

Gross observed volume corrected for FRC = 238,092.26 barrelsNOTE: The FRC correction is always negative and must be subtracted from the tank volume.


Table B-1 - Correction Factors for Effect of Temperature on the Tank Shell – Reference Temp 60ºF Table B-2 - Correction Factors for Effect of Temperature on the Tank Shell – Reference Temp 15ºC Table B-3 - Linear Thermal Expansion Coefficients of Steel

B-2 - Correction Factors for Effect of Temperature on the Tank Shell – Reference Temp 15ºC B-3 - Linear Thermal Expansion Coefficients of Steel


quantities, at atmospheric conditions, in upright, cylindrical tanks and marine tank vessels. The standard defines terms employed in the calculation of static petroleum quantities.



The definition of those terms relative to this document can be found in other API or associated documents, as follows:



Mass per unit volume; i.e. the mass of a substance divided by its volume. When reporting density, the unit used together with temperature shall be explicitly stated; for example, kilograms per cubic meter at 15ºC


The correction made to offset the effect of the displacement of the floating roof, when no correction has been built into the tank capacity table.

The water present in a container that is not suspended in the liquid hydrocarbon. A free water quantity deduction may include bottom sediments.

The total volume of all petroleum liquids and sediment and water, excluding free water, at observed temperature and pressure.





This is the same as CTL and under atmospheric conditions is also the same as CTPL, making these three symbols interchangeable; however, only CTPL and CTL are used in equations in this standard.

is organized into Chapters covering general measurement areas and several of these Standards are interrelated, in particular Chapters 11 and 12. If there is uncertainty amongst users as to which takes precedence the following criteria should be applied.

is the primary standard for the determination of the temperature (CTL), pressure (CPL), and combined temperature and pressure (CTPL) correction factors for crude oil, refined products, and lubricating oils, either by presentation of specific implementation procedures or by reference to other publications.

discrimination levels (rounding) required for each input variable and correction factor in a specific volume calculation procedure, and the sequence and manner in which to apply the appropriate parameters (RHO b, APIb, RDb, CTL, Fp, CPL, and CTPL).

base” conditions. The “standard” or “base” condition is a defined combination of temperature and pressure at which liquid volumes are expressed for purposes of custody transfer, stock accounting, etc. The terms

is called the "compressibility coefficient" or "scaled compressibility factor (units of 1/psi)". For additional information on these terms, refer to API MPMS Chapter 11.1.




11.1-2004 have been invoked. For those invoking the “Grandfather Clause”, the following note, from API MPMS Chapter 11.1-1980, which was applicable to the CTL, is reproduced here for ease of reference. “The standard for determining CTL factors is the computer subroutine implementation procedures of API MPMS Chapter 11.1, Volume X. When fully implemented, this generates a CTL factor of five significant digits. That is, five decimal digits at temperatures above standard temperature (60ºF and 15ºC) and four decimal digits at temperatures below standard temperature. Use of the printed table limits the user to

four decimal digits above and below standard temperature in addition to limiting table entry discrimination to 0.5ºF, 0.25ºC, 0.5 API, and 2.0 kg/m3. In the event of dispute, the computer-generated CTL should take preference.”






Observed reference gauge heighta Observed reference gauge heighta Innage or ullage or liquid level Innage or ullage of liquid level Innage or ullage of free water level Innage or ullage of free water level


These data points do not have any direct impact on the calculation process. However, they can impact the calculation process indirectly and are usually recorded at this time.


Sediment and water (volume or factor) Sediment and water (volume or factor) Net standard volume Net standard volume

; then, apply the floating roof adjustment (FRA), where applicable.



) is usually stated on the capacity table. If this is not the case, contact the company that generated the table. Some capacity tables make reference to an operating product temperature; this should not be confused with the Tank Shell Reference Temperature (TSh REF), which is a tank shell temperature.

gauging tanks. Take at least one temperature reading in a shaded area. If more than one temperature is taken, average the readings.

shell correction factors during custody transfer shall have their accuracy of plus or minus two degrees Fahrenheit verified every three months.



determine the floating roof adjustment or correction is the same for both types of roofs. The determination of the correction, however, can be addressed in one of two ways:


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.

c. 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.


b. Trim corrections can be either positive or negative. The trim correction table will state how this correction is to be applied.


b. List corrections can be either positive or negative. The list correction table will state how this correction is to be applied.

corrections are only applicable when the other condition does not exist. For information on the calculation procedure for combined trim and list corrections, refer to API MPMS Chapter 2.8A, Section 10.4.


formula for calculating whether or not a wedge condition exists, the application of wedge tables/formulae, and the calculation of the wedge formula can be found in API MPMS Chapter 17.4.



ASTM D4311 Asphalt to 60ºF, Table 1 ºF API gravity @ 60ºF, Table A or B ASTM D4311 Asphalt to 15ºC, Table 2 ºC Density @ 15ºC, Table A or B


value from 100, thus determining the NSV as a percentage of the GSV, divide this by 100, and multiply the GSV by it.

values are known. However, it can be calculated on a grade or parcel basis if the S&W was analyzed on an appropriate representative sample.




a thermal expansion coefficient per degree, then, multiplying it by the volume at observed temperature to obtain mass or weight. If mass is required use the density in vacuum. If weight is required use the density in air

density materials will displace less air than low density materials; therefore, the difference between weight in air and weight in vacuum varies with density and will have the greatest impact on low density materials. While this difference is not large, it is measurable and typically impacts the third and fourth decimal place of the density, by an amount shown in the table below.

, therefore, the most common correction is 1.1; however, densities above 996.6 kg/m3 are not uncommon, especially in the chemical industry. When adjusting a density in vacuum to its corresponding density in air, the correction is subtracted. When adjusting a density in air to its corresponding density in vacuum, the

Chapter 11.5.3 specifies a formula for making this conversion, which is reproduced below.




e. Correct the GOV to standard temperature. This is done by multiplying the GOV by the CTPL to arrive at the GSV.

f. Adjust for any measured amount of S&W. This is done by multiplying GSV by the CSW. g. If net standard weight [NSW] is required, multiply the result from Item f. the density in air



e. Correct the GOV to mass or weight. This is done by multiplying the GOV by the density in air at observed temperature to arrive at the weight or density in vacuum at observed temperature to arrive at the mass.

standard weight [NSW] is required. Should this be required, the density at standard temperature should be applied to the mass or weight, as appropriate, to arrive at gross standard volume [GSV].




necessary to establish unique calculation procedures for lease tanks. This procedure is applicable to lease tanks of 5,000 barrels (795 m3) or less and assumes that the clearance sample has verified merchantable oil at least 4 inches below the tank outlet. The CTSh is not significant to these situations



b. After the transfer, the incoming product has been blended with whatever was in the tank. In order for the CTPL and FRA to be correct, they will have to be based on the density of the product as found in the tank.

c. The tank’s FW level must be left the same on the closing report as on the opening report. All deducted water volumes should come from the sampler and be accounted for in the form of correction for S&W (CSW).


conversions and this standard does not attempt to define any specific routines for converting from one unit to another; however, the user should be guided by the following:

Conversion units that are “exact by definition” are to be considered primary and shall be used whenever possible

The use of multiple conversion factors should be avoided if possible. If this cannot be avoided the process that uses the least number of conversion factors shall be used.

Quantity from the tank capacity table using the liquid level gauge to enter the table. For this example, it is assumed that any correction to the gauge, due to expansion or contraction of the tape itself, has already been made. This issue is not addressed in this standard. The user should refer to the tape manufacturer’s instructions for specific details.

As displayed on a 12-digit calculator. Actual discrimination is determined by the calculating capacity of the calculation hardware.

Sediment and water percent 0.17% Forward draft 36’ 06” After draft 38’ 00” Trim (by the stern) 1’ 06” List (vessel upright) No list

Not all trim (or list) corrections are volumetric. Many are linear adjustments that are made to the observed ullage. In this case, the adjustment would be made before entering the vessel’s capacity table and a volumetric adjustment would not be necessary. If a volumetric list correction was applicable, it would be applied at this point in the calculation.


The volumetric value for sediment and water is determined by subtracting the net standard volume from the gross standard volume.

Free water gauge 10 mm Density at 15ºC kg/l (air) 0.8643 kg/l Liquid temperature ºC 22.3ºC Ambient temperature ºC 18.0ºC

that any correction to the gauge, due to expansion or contraction of the tape itself, has already been made. This issue is not addressed in this standard. The user should refer to the tape manufacturer’s instructions for specific details.


(From Table 5 in Section 12.3) Density at 15ºC kg/l (vacuum) 0.7440


Chapter 11.1/Adjunct to ASTM D1250/Adjunct to IP 200 “C” Tables; however, this example is applicable to any CTPL/VCF that derives form these “C” tables.


Liquid level gauge 5810 mm Free water gauge None Found Density at 15ºC (air) kg/l 0.8831 kg/l (air) Thermal Density Coefficient / ºC 0.00100 kg/l per ºC Liquid temperature ºC 22.5ºC

is assumed that any correction to the gauge, due to expansion or contraction of the tape itself, has already been made. This issue is


Such expansion or contraction in tank volume may be computed once the tank shell temperature is determined.

). For tanks that are not insulated, the shell temperature is a weighted average of the ambient and the product temperature based the following equation:

) CTSh = 1 + (2 x 0.0000062 x ΔT) + (0.0000062 x 0.0000062 x ΔT x ΔT)

) CTSh = 1 + (2 x 0.0000062 x ΔT) + (0.0000062 x 0.0000062 x ΔT x ΔT)

) that was used to compute the capacity table volumes. If the tank is insulated, it can be assumed that the Tank Shell Reference Temperature (TShREF) is the same as the product operating temperature. If the tank is not insulated, the user should contact the company that generated the capacity table to determine what tank shell reference temperature (TSh REF) was used.

calculated ala tank shell reference temperature (TShREF) of 60°F. For temperatures outside the range of this table use the formula in API MPMS Chapter 12, Section 1, Part 1, Subpart 9.1.3.

COF) Factor COF)

calculated ala tank shell reference temperature (TShREF) of 15°C. For temperatures outside the range of this table use the formula in API MPMS Chapter 12, Section 1, Part 1, Subpart 9.1.3.

and the observed density when the primary roof correction is built into the capacity table using reference density.

A total of 4,088.2662 barrels was deducted from this table between 4 feet 00 inches and 5 feet 00 inches for floating roof displacement based on a weight of 1,215,000 pounds and a gravity of 35.0 API. Gauged quantities above 5 feet 00 inches reflect this deduction but shall be adjusted for varying API gravities at tank temperature according to the following.”

Chapter 11.1/Adjunct to ASTM D1250/Adjunct to IP 200, Table 5A (or 5B if the tank content is a petroleum product) as shown in Table 4.

between gravities to arrive at the correct observed gravity. For example, the API @ 60 F to be corrected to observed, is 40.3. Looking up the gravity on Table 4 indicates the gravity falls between




Table B-1 - Correction Factors for Effect of Temperature on the Tank Shell – Reference Temp 60ºF Table B-2 - Correction Factors for Effect of Temperature on the Tank Shell – Reference Temp 15ºC Table B-3 - Linear Thermal Expansion Coefficients of Steel











is organized into Chapters covering general measurement areas and several of these Standards are interrelated, in particular Chapters 11 and 12. If there is uncertainty amongst users as to which takes precedence the following criteria should be applied.

is the primary standard for the determination of the temperature (CTL), pressure (CPL), and combined temperature and pressure (CTPL) correction factors for crude oil, refined products, and lubricating oils, either by presentation of specific implementation procedures or by reference to other publications.

discrimination levels (rounding) required for each input variable and correction factor in a specific volume calculation procedure, and the sequence and manner in which to apply the appropriate parameters (RHO b, APIb, RDb, CTL, Fp, CPL, and CTPL).




“The standard for determining CTL factors is the computer subroutine implementation procedures of API MPMS Chapter 11.1, Volume X. When fully implemented, this generates a CTL factor of five significant digits. That is, five decimal digits at temperatures above standard temperature (60ºF and 15ºC) and four decimal digits at temperatures below standard temperature. Use of the printed table limits the user to

. In the event of dispute, the computer-generated CTL should take preference.”






Innage or ullage or liquid level Innage or ullage of liquid level Innage or ullage of free water level Innage or ullage of free water level



















are not uncommon, especially in the chemical industry. When adjusting a density in vacuum to its corresponding density in air, the correction is subtracted. When adjusting a density in air to its corresponding density in vacuum, the







) or less and assumes that the clearance sample has verified merchantable oil at least 4 inches below the tank outlet. The CTSh is not significant to these situations





Not all trim (or list) corrections are volumetric. Many are linear adjustments that are made to the observed ullage. In this case, the adjustment would be made before entering the vessel’s capacity table and a volumetric adjustment would not be necessary. If a volumetric list correction was applicable, it would be applied at this point in the calculation.


Chapter 11.1/Adjunct to ASTM D1250/Adjunct to IP 200 “C” Tables; however, this example is applicable to any CTPL/VCF that derives form these “C” tables.

kg/l 0.8831 kg/l (air) Thermal Density Coefficient / ºC 0.00100 kg/l per ºC Liquid temperature ºC 22.5ºC


). For tanks that are not insulated, the shell temperature is a weighted average of the ambient and the product temperature based the following equation:

) is the same as the product operating temperature. If the tank is not insulated, the user should contact the company that generated the capacity table to determine what tank shell reference temperature (TSh REF) was used.


Chapter 11.1/Adjunct to ASTM D1250/Adjunct to IP 200, Table 5A (or 5B if the tank content is a petroleum product) as shown in Table 4.











Innage or ullage or liquid level Innage or ullage of liquid level Innage or ullage of free water level Innage or ullage of free water level








are not uncommon, especially in the chemical industry. When adjusting a density in vacuum to its corresponding density in air, the correction is subtracted. When adjusting a density in air to its corresponding density in vacuum, the







) is the same as the product operating temperature. If the tank is not insulated, the user should contact the company that generated the capacity table to determine what tank shell reference temperature (TSh REF) was used.


















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