ISO/PRF 6578

Refrigerated hydrocarbon liquids — Static measurement — Calculation procedure

ISO 6578:2017 specifies the calculation procedure to convert the volume of liquefied petroleum gas (LPG) and liquefied natural gas (LNG) under the conditions at the time of measurement to the equivalent volume of liquid or vapour at the standard condition, i.e. 15 °C and 101,325 kPaA, or to the equivalent mass or energy (calorific content). It applies to the quantities of refrigerated hydrocarbon liquids stored in or transferred to/from tanks and measured under static storage conditions. Calculation of pressurized gases is out of the scope of ISO 6578:2017.

Hydrocarbures liquides réfrigérés — Mesurage statique — Procédure de calcul

General Information

• Status: Not Published
• ICS: 75.180.30 - Volumetric equipment and measurements
• Technical Committee: ISO/TC 28/SC 5 - Measurement of refrigerated hydrocarbon and non-petroleum based liquefied gaseous fuels
• Drafting Committee: ISO/TC 28/SC 5 - Measurement of refrigerated hydrocarbon and non-petroleum based liquefied gaseous fuels
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 03-Sep-2025
• Completion Date: 06-Sep-2025

Relations

• Revises: ISO 6578:2017 - Refrigerated hydrocarbon liquids — Static measurement — Calculation procedure
• Effective Date: 13-May-2023

Standards Content (Sample)

International
Standard
ISO 6578
Third edition
Refrigerated hydrocarbon liquids —
Static measurement — Calculation
procedure
Hydrocarbures liquides réfrigérés — Mesurage statique —
Procédure de calcul
PROOF/ÉPREUVE
Reference number
ISO 6578:2025(en) © ISO 2025
ISO 6578:2025(en)
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
PROOF/ÉPREUVE
ii
ISO 6578:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
3.1 Terms and definitions .1
3.2 Symbols .2
4 Outline of the calculation . 3
4.1 Liquefied petroleum gas .3
4.2 Liquefied natural gas .4
4.3 Data for calculation .5
5 Mass . 5
5.1 Mass of liquid phase .5
5.2 Correction for vapour phase .6
5.3 Mass in vacuum to mass in air .6
6 Energy content (calorific content) . 7
7 Inter-conversion of liquid mass and vapour volume at standard conditions . 8
8 Calculation of liquid density from composition . 8
8.1 General .8
8.2 Liquid petroleum gas .8
8.3 Liquid natural gas .9
9 Calculation of calorific value from composition . 9
9.1 Volumetric basis .9
9.2 Mass basis .9
Annex A (informative) Molar volume of individual component .10
Annex B (informative) Correction factors for volume reduction of LNG mixtures .11
Annex C (informative) Gross calorific values for individual components.12
Annex D (informative) Molar mass, compression factor and summation factor of individual
component .13
Annex E (informative) Calculation examples . 14
Bibliography . 19
PROOF/ÉPREUVE
iii
ISO 6578:2025(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 28, Petroleum and related products, fuels and
lubricants from natural or synthetic sources, Subcommittee SC 5, Measurement of refrigerated hydrocarbon
and non-petroleum based liquefied gaseous fuels.
This third edition cancels and replaces the second edition (ISO 6578:2017), which has been technically
revised.
The main changes are as follows:
— Table D.1 has been aligned with ISO 6976:2016;
— calculation examples have been moved from the main body to Annex E.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
PROOF/ÉPREUVE
iv
ISO 6578:2025(en)
Introduction
Large quantities of refrigerated hydrocarbon liquids such as liquefied natural gas (LNG) and liquefied
petroleum gas (LPG), are transported by marine carriers especially designed for these applications. These
gases are traded based on the static measurement on board marine carriers rather than the measurement at
shore tanks or pipelines, mainly due to the nature of the tank operation.
The measurement on board involves determining the liquid/vapour interface, i.e. liquid level, average
temperatures of liquid and vapour, and the vapour pressure in the tanks of marine carriers. The volumetric
quantity of the liquid and gas is then computed with the tank capacity tables.
This document specifies calculations for the volume at standard conditions, the liquid density from chemical
composition and the mass and energy content of fully refrigerated hydrocarbon liquids at a vapour pressure
near to atmospheric pressure from the results of custody transfer measurement. This document also
specifies calculations for ascertaining the inventory in shore tanks. This document does not cover calculation
procedures for refrigerated hydrocarbon liquids consisting predominantly of ethane or ethylene or partially
refrigerated hydrocarbon liquids at pressures substantially above atmospheric. No recommendations are
given for the measurement of small parcels of refrigerated liquids, which are directly weighed.
Aspects of safety are not dealt with in this document. It is the responsibility of the user to ensure that the
procedure of measurement meets applicable safety regulations.
Basic data and source references used in the calculation procedures are given in Annexes A to E.
PROOF/ÉPREUVE
v
International Standard ISO 6578:2025(en)
Refrigerated hydrocarbon liquids — Static measurement —
Calculation procedure
1 Scope
This document specifies the calculation procedure for converting the volume of liquefied petroleum gas
(LPG) and liquefied natural gas (LNG) under the conditions at the time of measurement to the equivalent
volume of liquid or vapour at the standard condition (i.e. 15 °C and 101,325 kPa absolute), or to the equivalent
mass or energy (calorific content). This document applies to the quantities of refrigerated hydrocarbon
liquids that are stored in or transferred to or from tanks and measured under static storage conditions. This
document does not cover the calculation of pressurized gases.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 91:2017, Petroleum and related products — Temperature and pressure volume correction factors (petroleum
measurement tables) and standard reference conditions
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1.1
compression factor
actual (real) volume of a given amount of gas at a specified pressure and temperature divided by its volume,
under the same conditions as calculated from the ideal gas law
[SOURCE: ISO 6976:2016, 3.10]
3.1.2
gross calorific value
amount of heat that would be released by the complete combustion with oxygen of a specified quantity of
gas, in such a way that the pressure, p , at which the reaction takes place remains constant, and all the
products of combustion are returned to the same specified temperature, T , as that of the reactants, all of
these products being in the gaseous state except for water, which is condensed to the liquid state at T
Note 1 to entry: T and p are the combustion reference temperature and combustion reference pressure, respectively.
1 1
[SOURCE: ISO 6976:2016, 3.1, modified — Note 1 to entry has been replaced; t has been replaced by T .]
1 1
PROOF/ÉPREUVE
ISO 6578:2025(en)
3.1.3
liquefied natural gas
LNG
liquid composed predominan
...

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ISO/FDIS 6578:2025(en)
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Date: 2025-07-0109-02
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ISO TC 28/SC 5/WG 3
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Secretariat: JISC
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Refrigerated hydrocarbon liquids — Static measurement — Calculation procedure
Style Definition: ANNEX
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Hydrocarbures liquides réfrigérés — Mesurage statique — Procédure de calcul
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at 0.7 cm + 1.4 cm + 2.1 cm + 2.8 cm + 3.5 cm + 4.2 cm
+ 4.9 cm + 5.6 cm + 6.3 cm + 7 cm
Formatted: Centered
ISO 6578:2025(en) Formatted: Centered
Formatted
Formatted: No page break before
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or
utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be
requested from either ISO at the address below or ISO's member body in the country of the
requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11 Formatted: English (United Kingdom)
Fax + 41 22 749 09 47
E-mail [e-mail]
Web www.iso.orgwww.iso.org
Published in Switzerland.
Formatted: Normal, Centered, Space After: 24 pt, Tab stops:
17.2 cm, Right
Formatted: Font: 9 pt
iii
ISO/FDIS 6578:2025 (en)
Formatted: (none)
Contents
Foreword . v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
3.1 Terms and definitions . 1
3.2 Symbols . 2
4 Outline of the calculation . 3
4.1 Liquefied petroleum gas . 3
4.2 Liquefied natural gas . 5
4.3 Data for calculation . 5
5 Mass . 5
5.1 Mass of liquid phase . 5
5.2 Correction for vapour phase . 6
5.3 Mass in vacuum to mass in air . 7
6 Energy content (calorific content) . 7
7 Inter-conversion of liquid mass and vapour volume at standard conditions . 8
8 Calculation of liquid density from composition . 9
8.1 General . 9
8.2 Liquid petroleum gas . 9
8.3 Liquid natural gas . 9
9 Calculation of calorific value from composition . 10
9.1 Volumetric basis . 10
9.2 Mass basis . 10
Annex A (normative) Molar volume of individual component . 11
iv
ISO 6578:2025(en) Formatted: Centered
Annex B (normative) Correction factors for volume reduction of LNG mixtures . 12
Annex C (normative) Gross calorific values for individual components . 13
Annex D (normative) Molar mass, compression factor and summation factor of individual
component . 14
Annex E (informative) Calculation examples . 15
E.1 Calculation for LPG . 15
E.2 LNG . 17
Bibliography . 20

Foreword . vii
Introduction . viii
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
3.1 Terms and definitions . 1
3.2 Symbols . 2
4 Outline of the calculation . 3
4.1 Liquefied petroleum gas . 3
4.2 Liquefied natural gas . 5
4.3 Data for calculation . 5
5 Mass . 6
5.1 Mass of liquid phase . 6
5.2 Correction for vapour phase . 7
5.3 Mass in vacuum to mass in air . 8
6 Energy content (calorific content) . 8
7 Inter-conversion of liquid mass and vapour volume at standard conditions . 10
8 Calculation of liquid density from composition . 10
8.1 General . 10
Formatted: Normal, Centered, Space After: 24 pt, Tab stops:
17.2 cm, Right
8.2 Liquid petroleum gas . 11
Formatted: Font: 9 pt
v
ISO/FDIS 6578:2025 (en)
Formatted: (none)
8.3 Liquid natural gas . 11
9 Calculation of calorific value from composition . 12
9.1 Volumetric basis . 12
9.2 Mass basis . 12
Annex A (informative) Molar volume of individual component . 13
Annex B (informative) Correction factors for volume reduction of LNG mixtures . 14
Annex C (informative) Gross calorific values for individual components . 15
Annex D (informative) Molar mass, compression factor and summation factor of individual
component . 16
Annex E (informative) Calculation examples . 17
Bibliography . 23

vi
ISO 6578:2025(en) Formatted: Centered
Formatted: Don't adjust space between Latin and Asian text,
Foreword
Don't adjust space between Asian text and numbers
ISO (the International Organization for Standardization) is a worldwide federation of national
standards bodies (ISO member bodies). The work of preparing International Standards is normally
carried out through ISO technical committees. Each member body interested in a subject for which a
technical committee has been established has the right to be represented on that committee.
International organizations, governmental and non-governmental, in liaison with ISO, also take part in
the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all
matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directiveswww.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of
(a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed
patent rights in respect thereof. As of the date of publication of this document, ISO had not received Formatted: Font color: Auto
notice of (a) patent(s) which may be required to implement this document. However, implementers are
cautioned that this may not represent the latest information, which may be obtained from the patent
database available at www.iso.org/patents.www.iso.org/patents. ISO shall not be held responsible for
identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/forewo
...