ISO 10976:2023

Refrigerated light hydrocarbon fluids — Measurement of cargoes on board LNG carriers

This document establishes all necessary steps to properly measure and account for the quantities of cargoes on liquefied natural gas (LNG) carriers. This includes, but is not limited to, the measurement of liquid volume, vapour volume, temperature and pressure, and accounting for the total quantity of the cargo on board. This document describes the use of common measurement systems on board LNG carriers, the aim of which is to improve the general knowledge and processes in the measurement of LNG for all parties concerned. This document provides general requirements for those involved in the LNG trade on ships and onshore.

Hydrocarbures légers réfrigérés — Mesurage des cargaisons à bord des navires méthaniers

General Information

• Status: Published
• Publication Date: 17-Aug-2023
• 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: 6060 - International Standard published
• Start Date: 18-Aug-2023
• Due Date: 07-Sep-2023
• Completion Date: 18-Aug-2023

Relations

• Revises: ISO 10976:2015 - Refrigerated light hydrocarbon fluids — Measurement of cargoes on board LNG carriers
• Effective Date: 06-Jun-2022

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 10976
Third edition
2023-08
Refrigerated light hydrocarbon
fluids — Measurement of cargoes on
board LNG carriers
Hydrocarbures légers réfrigérés — Mesurage des cargaisons à bord
des navires méthaniers
Reference number
ISO 10976:2023(E)
© ISO 2023

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ISO 10976:2023(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023
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
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ISO 10976:2023(E)
Contents  Page
Foreword .v
Introduction . vi
1 Scope . 1
2  Normative references . 1
3  Terms, definitions and abbreviated terms . 1
3.1 Terms and definitions . 1
3.2 Abbreviated terms . 5
4  General operating safety precautions and regulations . 6
4.1 General . 6
4.2 Electrical equipment classification . 7
4.3 Electromagnetic disturbance . 7
4.4 Maintenance . 7
4.5 Service conditions . 7
4.6 Compatibility . 7
4.7 Personnel protection . . 7
4.8 Procedures . 8
5  Measurement systems and equipment . 8
5.1 General . 8
5.2 Measurement equipment performance . 8
5.3 Calibration and certification of measurement equipment . 9
5.4 V erification of measurement equipment between dry dockings . 9
5.5 Inspection of measurement equipment during transfer operations . 10
5.6 Static measurement systems and equipment . 10
5.6.1 General . 10
5.6.2 Tank capacity tables . 10
5.6.3 Trim and list measurement .12
5.6.4 Tank gassing-up tables or means of determination .13
5.6.5 Tank cool-down tables or means of determination .13
5.6.6 Liquid level measurement equipment . 14
5.6.7 Temperature measurement equipment . 18
5.6.8 Pressure measurement equipment . 19
5.6.9 Custody transfer measurement system . 19
5.7 Dynamic measurement systems and equipment . 20
6  Measurement procedures .20
6.1 General . 20
6.2 Static measurement . 21
6.2.1 General . 21
6.2.2 Measuring liquid level .22
6.2.3 Loading .22
6.2.4 Discharge.22
6.2.5 Shipboard measurements . 22
6.2.6 Liquid level . . .23
6.2.7 Temperature . 24
6.2.8 Pressure . 25
6.2.9 CTMS . 25
6.2.10 Sampling . 25
6.2.11 Vapour return .26
6.3 Gas-up and cool-down quantification . 26
6.3.1 General . 26
6.3.2 Inerting . 26
6.3.3 Gas up and cool down. 26
6.4 Dynamic measurement . 27
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ISO 10976:2023(E)
7  Cargo calculations .27
7.1 General . 27
7.2 LNG volume determination . 27
7.2.1 General . 27
7.2.2 Liquid levels below lower measurable limit .28
7.3 LNG density determination .28
Annex A (informative)  LNGC design and marine operations .29
Annex B (informative)  Additional considerations for measurement on board an LNGC .36
Annex C (informative)  Examples of tank capacity tables for a spherical tank.40
Annex D (informative)  Calculation examples .47
Annex E (informative)  Sampling .57
Annex F (informative)  Marine measurement witnessing checklists .61
Bibliography .64
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ISO 10976:2023(E)
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 10976:2015), which has been technically
revised.
The main changes are as follows:
— Table 1 has been modified,
— in 5.7 and 6.4, new international standards have been cited,
— in Annex D, the example has been updated according to ISO 6578:2017.
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.
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ISO 10976:2023(E)
Introduction
This document provides accepted methods for measuring quantities on board liquefied natural gas
(LNG) carriers, for those involved in the LNG trade on ships and onshore. It includes recommended
methods for measuring, reporting and documenting quantities on board these vessels.
This document is intended to establish uniform practices for measuring the quantity of cargo on board
LNG carriers from which the energy is computed. It details the current, commonly used methods of
cargo measurement, but is not intended to preclude the use or development of any other technologies or
methods, or the revision of the methods presented.
Safety or operating practices can apply, including those recommended by organizations such as
the International Maritime Organization (IMO), the International Chamber of Shipping (ICS), the Oil
Companies International Marine Forum (OCIMF), the International Group of LNG Importers (GIIGNL)
and the Society of International Gas Tanker and Terminal Operators (SIGTTO), or individual operating
companies.
The International System of units (SI) is used throughout this document as the primary units of measure
since this system is commonly used in the industry for these types of cargoes. However, as some LNG
carrier tanks are calibrated in US customary units and some sales and purchase agreements (SPA) are
made in US customary units, both SI and US customary equivalents are shown. Proper unit conversion
is intended to be applied, documented and agreed upon among all parties involved in the LNG custody
transfer.
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INTERNATIONAL STANDARD ISO 10976:2023(E)
Refrigerated light hydrocarbon fluids — Measurement of
cargoes on board LNG carriers
1 Scope
This document establishes all necessary steps to properly measure and account for the quantities of
cargoes on liquefied natural gas (LNG) carriers. This includes, but is not limited to, the measurement
of liquid volume, vapour volume, temperature and pressure, and accounting for the total quantity of
the cargo on board. This document describes the use of common measurement systems on board LNG
carriers, the aim of which is to improve the general knowledge and processes in the measurement of
LNG for all parties concerned. This document provides general requirements for those involved in the
LNG trade on ships and onshore.
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 6578:2017, Refrigerated hydrocarbon liquids — Static measurement — Calculation procedure
ISO 8310, Refrigerated hydrocarbon and non-petroleum based liquefied gaseous fuels — General
requirements for automatic tank thermometers on board marine carriers and floating storage
ISO 8943:2007, Refrigerated light hydrocarbon fluids — Sampling of liquefied natural gas — Continuous
and intermittent methods
ISO 18132-1, Refrigerated hydrocarbon and non-petroleum based liquefied gaseous fuels — General
requirements for automatic tank gauges — Part 1: Automatic tank gauges for liquefied natural gas on
board marine carriers and floating storage
ISO 19970, Refrigerated hydrocarbon and non-petroleum based liquefied gaseous fuels — Metering of gas
as fuel on LNG carriers during cargo transfer operations
ISO 21903, Refrigerated hydrocarbon fluids — Dynamic measurement — Requirements and guidelines for
the calibration and installation of flowmeters used for liquefied natural gas (LNG) and other refrigerated
hydrocarbon fluids
IEC 60533, Electrical and electronic installations in ships — Electromagnetic compatibility (EMC) — Ships
with a metallic hull
ISO 16903, Petroleum and natural gas industries — Characteristics of LNG, influencing the design, and
material selection
IACS, Unified Requirements E10
3  Terms, definitions and abbreviated terms
3.1  Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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ISO 10976:2023(E)
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
absolute pressure
total of the gauge pressure plus the pressure of the surrounding atmosphere
3.1.2
aerating
introduction of fresh air with an acceptable dew point into the
tank to purge inert gases and to increase the oxygen content to approximately 21 % of volume so as to
ensure a breathable atmosphere
3.1.3
approved equipment
equipment of a design approved by a recognized authority, such as a governmental agency, classification
society or other accredited agency which certifies the particular equipment as safe for use in a specified
hazardous atmosphere
3.1.4
automatic tank gauge
ATG
instrument that automatically measures and displays liquid levels or ullages in one or more tanks,
either continuously, periodically or on demand
3.1.5
automatic tank thermometer
ATT
instrument that automatically measures and displays the temperature of the contents in a tank,
continuously, periodically or on demand
3.1.6
boil off
process of evaporation of a liquid resulting from heat ingress or a drop in pressure
3.1.7
boil-off gas
vapour produced by boil off (3.1.6)
3.1.8
cool down
process of reducing the temperature of equipment, such as piping, transfer arms and tanks associated
with custody transfer cargo movements, to required operating temperatures
3.1.9
constant pressure/floating piston sample container
CP/FP sample container
sample container, usually used for intermittent sampling (3.1.19), capable of maintaining constant
pressure during the sampling of gas from the process line into the gas cylinder
[SOURCE: ISO 8943:2007, 3.4]
3.1.10
continuous sampling
sampling from gasified liquid natural gas (LNG) with constant flow rate
[SOURCE: ISO 8943:2007, 3.5]
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ISO 10976:2023(E)
3.1.11
drying
process of reducing the moisture in the ship tank by displacement or dilution with an inert gas or by
using a drying system
3.1.12
filling limit
quantity to which a tank may be safely filled, taking into account the possible expansion (and change in
density) of the liquid
Note 1 to entry: Filling limit (i.e. volume) and filling ratio are expressed as a percentage of the total capacity of a
tank.
3.1.13
full range
range between the maximum and minimum measurable value
3.1.14
gas code
regulation on the construction of ships carrying liquefied gases developed by the International
Maritime Organization
Note 1 to entry: These include the IMO International Code for the Construction and Equipment of Ships Carrying
Liquefied Gases in Bulk (IGC Code) (generally applies to ships built after 17 July 1986), the IMO Code for Construction
and Equipment of Ships Carrying Liquefied Gases in Bulk (GC Code) (generally applies to ships built on or after 31
December 1976 but prior to 17 July 1986) and the IMO Code for Existing Ships Carrying Liquefied Gases in Bulk
(generally applies to ships delivered before 31 December 1976), as applicable to each vessel.
3.1.15
gas sample container
sample container, usually used for continuous sampling (3.1.10) and used for the retention of the gas
sample and for its transfer to an analysing instrument
[SOURCE: ISO 8943:2007, 3.6]
3.1.16
gassing up
process of replacing an inert atmosphere in a cargo tank with the vapour from the shore or from another
cargo tank to a suitable level, to allow cooling down and subsequent loading to achieve a specified
environment with at least a defined methane (CH ), carbon dioxide (CO ) and oxygen (O ) content
4 2 2
3.1.17
heel
amount of cargo retained in a cargo tank prior to loading or after discharge
3.1.18
inerting
introduction of inert gas into a tank with the objective of attaining the inert condition
3.1.19
intermittent sampling
sampling from gasified liquid natural gas (LNG) with predetermined intervals or with predetermined
flow amount intervals
[SOURCE: ISO 8943:2007, 3.9]
3.1.20
letter of protest
letter issued by any participant in a custody transfer citing any condition with which issue is taken and
which serves as a written record that a particular action or finding was observed/questioned at the
time of occurrence
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ISO 10976:2023(E)
3.1.21
liquid natural gas carrier
LNG carrier
cargo ship specifically constructed and used for the carriage of liquid natural gas (LNG) in bulk
3.1.22
liquid natural gas sample vaporizer
LNG sample vaporizer
apparatus to completely gasify the liquid natural gas (LNG) sample collected from the LNG transfer line
[SOURCE: ISO 8943:2007, 3.11]
3.1.23
multiple-spot automatic tank thermometer
multiple-spot ATT
automatic tank thermometer (ATT) (3.1.5) consisting of multiple spot temperature element sensors to
measure the temperature(s) at selected liquid level(s)
Note 1 to entry: The readout equipment for a multiple-point averaging ATT averages the readings from the
submerged temperature elements sensors to compute the average temperature of the liquid in the tank, and can
also display the temperature profile in the tank.
[SOURCE: ISO 4266-5:2002, 3.4, modified — the definition and note 1 to entry have been modified; the
term has been changed from "multiple-point" to "multiple-spot".]
3.1.24
notice of apparent discrepancy
notice issued by any participant in a custody transfer citing any discrepancy in cargo quantities and
which serves as a written record that such a discrepancy was found
3.1.25
offline analysis
procedure of analysis implemented on the representative sample gas that is once charged into a gas
sample container (3.1.15) or a constant pressure/floating piston sample container (3.1.9)
[SOURCE: ISO 8943:2007, 3.13]
3.1.26
online analysis
procedure of analysis implemented using analytical equipment that is directly connected through
pipelines or other means to the sampling device
[SOURCE: ISO 8943:2007, 3.14]
3.1.27
online gas chromatograph
gas chromatograph that is directly connected to the pipelines or sampling device to implement online
analysis (3.1.26)
[SOURCE: ISO 8943:2007, 3.15]
3.1.28
seal water
water used in the water-seal-type gas sample holder (3.1.35) to preclude contact of the gas sample with
the atmosphere
[SOURCE: ISO 8943:2007, 3.19]
3.1.29
tank capacity table
numeric tables that relate the liquid level in a tank to the volume contained in that tank
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ISO 10976:2023(E)
3.1.30
vapour
fluid in the gaseous state that is transferred to/from or contained within the cargo tank
3.1.31
vapour pressure
pressure at which a liquid and its vapour are in equilibrium at a given temperature
3.1.32
verification
process of confirming the accuracy of an instrument by comparing to a source with known uncertainty
3.1.33
warming up
process of warming the cargo tanks from the cargo carriage temperature to the required temperature
3.1.34
waterless-type gas sample holder
holder without seal water (3.1.28) (typically using an expandable/contractible, transformable rubber
membrane) and used for collecting gasified liquid natural gas (LNG)
[SOURCE: ISO 8943:2007, 3.22]
3.1.35
water-seal-type gas sample holder
holder with seal water (3.1.28) used for collecting gasified liquid natural gas (LNG)
[SOURCE: ISO 8943:2007, 3.23]
3.1.36
working range
range of an instrument in normal operation
3.2  Abbreviated terms
API American Petroleum Institute
ATG automatic tank gauge
ATT automatic tank thermometer
BOG boil-off gas
CP/FP constant pressure/floating piston
CTMS custody transfer measurement system
EMC electromagnetic compatibility
FSRU floating storage and re-gasification unit
GCU gas combustion unit
GIIGNL International Group of Liquefied Natural Gas Importers
GNG gaseous natural gas
GPA Gas Processors Association
IACS International Association of Classification Societies
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ISO 10976:2023(E)
IAPH International Association of Ports and Harbors
ICS International Chamber of Shipping
IEC International Electrotechnical Commission
IGC Code International Gas Carrier Code
IMO International Maritime Organization
ISGOTT International Safety Guide for Oil Tankers and Terminals
LNGC liquefied natural gas carrier
MPMS Manual of Petroleum Measurement Standards
MSDS material safety data sheet
OBQ on board quantity
OCIMF Oil Companies International Marine Forum
ROB quantity remaining on board
SI International System of Units
SIGTTO Society of International Gas Tanker and Terminal Operators Limited
SPA sales and purchase agreement
VEF vessel experience factor
4  General operating safety precautions and regulations
4.1 General
This clause applies to all types of measurement on board LNG carriers. While these precautions
represent safe operating practices, they should not be considered complete or comprehensive. In
addition to those listed in this document, reference should be made to all safety precautions contained
in relevant operating guidelines.
IMPORTANT — Anyone working with the vessel's measurement equipment shall be, at all times,
under the direction and s
...

DRAFT INTERNATIONAL STANDARD
ISO/DIS 10976
ISO/TC 28/SC 5 Secretariat: JISC
Voting begins on: Voting terminates on:
2022-07-25 2022-10-17
Refrigerated light hydrocarbon fluids — Measurement of
cargoes on board LNG carriers
Hydrocarbures légers réfrigérés — Mesurage des cargaisons à bord des navires méthaniers
ICS: 75.180.30
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
This document is circulated as received from the committee secretariat.
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 10976:2022(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
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NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION. © ISO 2022

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ISO/DIS 10976:2022(E)
DRAFT INTERNATIONAL STANDARD
ISO/DIS 10976
ISO/TC 28/SC 5 Secretariat: JISC
Voting begins on: Voting terminates on:

Refrigerated light hydrocarbon fluids — Measurement of
cargoes on board LNG carriers
Hydrocarbures légers réfrigérés — Mesurage des cargaisons à bord des navires méthaniers
ICS: 75.180.30
COPYRIGHT PROTECTED DOCUMENT
THIS DOCUMENT IS A DRAFT CIRCULATED
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© ISO 2022
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All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
NOT BE REFERRED TO AS AN INTERNATIONAL
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on STANDARD UNTIL PUBLISHED AS SUCH.
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IN ADDITION TO THEIR EVALUATION AS
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STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
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NATIONAL REGULATIONS.
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RECIPIENTS OF THIS DRAFT ARE INVITED
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RIGHTS OF WHICH THEY ARE AWARE AND TO
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PROVIDE SUPPORTING DOCUMENTATION. © ISO 2022

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ISO/DIS 10976:2022(E)
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and abbreviated terms . 1
3.1 Terms and definitions . 1
3.2 Abbreviated terms . 5
4 General operating safety precautions and regulatory requirements .6
4.1 General . 6
4.2 Electrical equipment classification . 7
4.3 Electromagnetic disturbance . 7
4.4 Maintenance . 7
4.5 Service conditions . 7
4.6 Compatibility . 7
4.7 Personnel protection . . 7
4.8 Procedures . 8
5 Measurement systems and equipment . 8
5.1 General . 8
5.2 Measurement equipment performance . 8
5.3 Calibration and certification of measurement equipment . 9
5.4 Verification of measurement equipment between dry dockings . 9
5.5 Inspection of measurement equipment during transfer operations . 10
5.6 Static measurement systems and equipment . 10
5.6.1 General . 10
5.6.2 Tank capacity tables . 10
5.6.3 Trim and list measurement .12
5.6.4 Tank gassing-up tables or means of determination .13
5.6.5 Tank cool-down tables or means of determination .13
5.6.6 Liquid level measurement equipment . 14
5.6.7 Temperature measurement equipment . 18
5.6.8 Pressure measurement equipment . 19
5.6.9 Custody transfer measurement system . 19
5.7 Dynamic measurement systems and equipment . 20
6 Measurement procedures .20
6.1 General . 20
6.2 Static measurement . 21
6.2.1 General . 21
6.2.2 Measuring liquid level .22
6.2.3 Loading .22
6.2.4 Discharge.22
6.2.5 Shipboard measurements . 22
6.2.6 Liquid level . . .23
6.2.7 Temperature . 24
6.2.8 Pressure . 25
6.2.9 CTMS . 25
6.2.10 Sampling . 25
6.2.11 Vapour return .26
6.3 Gas-up and cool-down quantification . 26
6.3.1 General . 26
6.3.2 Inerting . 26
6.3.3 Gas up and cool down. 26
6.4 Dynamic measurement . 27
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ISO/DIS 10976:2022(E)
7 Cargo calculations .27
7.1 General . 27
7.2 LNG volume determination . 27
7.2.1 General . 27
7.2.2 Liquid levels below lower measurable limit .28
7.3 LNG density determination .28
Annex A (informative) LNGC design and marine operations .29
Annex B (informative) Additional considerations for measurement on board an LNGC .36
Annex C (informative) Examples of tank capacity tables for a spherical tank .40
Annex D (informative) Calculation examples .46
Annex E (informative) Sampling .55
Annex F (informative) Marine measurement witnessing checklists .59
Bibliography .62
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ISO/DIS 10976:2022(E)
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 documents 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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO's adherence to the WTO principles in the Technical
Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 28, Petroleum products and lubricants,
Subcommittee SC 5, Measurement of refrigerated hydrocarbon and non-petroleum based liquefied gaseous
fuels.
This third edition cancels and replaces the second edition (ISO 10976:2015), which has been technically
revised.
The main changes are as follows
— in 5.2, modify Table 1,
— in 5.7 and 6.4, add new international standard to refer,
— in Annex D, update the example according to the update of ISO 6578
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ISO/DIS 10976:2022(E)
Introduction
This International Standard provides accepted methods for measuring quantities on liquefied natural
gas (LNG) carriers for those involved in the LNG trade on ships and onshore. It includes recommended
methods for measuring, reporting and documenting quantities on board these vessels.
This International Standard is intFended to establish uniform practices for the measurement of the
quantity of cargo on board LNG carriers from which the energy is computed. It details the commonly
used current methods of cargo measurement, but is not intended to preclude the use or development
of any other technologies or methods or the revision of the methods presented. It is intended that the
reader review, in detail, the latest editions of the publications, standards and documents referenced in
this International Standard in order to gain a better understanding of the methods described.
This International Standard is not intended to supersede any safety or operating practices recommended
by organizations, such as the International Maritime Organization (IMO), the International Chamber of
Shipping (ICS), the Oil Companies lnternational Marine Forum (OCIMF), the International Group of LNG
Importers (GIIGNL) and the Society of International Gas Tanker and Terminal Operators (SIGTTO), or
individual operating companies. This International Standard is not intended to supersede any other
safety or environmental considerations, local regulations or the specific provisions of any contract.
The International System of units (SI) is used throughout this International Standard as the primary
units of measure since this system is commonly used in the industry for these types of cargoes.
However, as some LNG carrier tanks are calibrated in US customary units and some sales and purchase
agreements (SPA) are made in US customary units, both SI and US customary equivalents are shown.
Proper unit conversion is intended to be applied, documented and agreed upon among all parties
involved in the LNG custody transfer.
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DRAFT INTERNATIONAL STANDARD ISO/DIS 10976:2022(E)
Refrigerated light hydrocarbon fluids — Measurement of
cargoes on board LNG carriers
1 Scope
This International Standard establishes all of the steps needed to properly measure and account for
the quantities of cargoes on liquefied natural gas (LNG) carriers. This includes, but is not limited to, the
measurement of liquid volume, vapour volume, temperature and pressure, and accounting for the total
quantity of the cargo on board. This International Standard describes the use of common measurement
systems used on board LNG carriers, the aim of which is to improve the general knowledge and
processes in the measurement of LNG for all parties concerned. This International Standard provides
general requirements for those involved in the LNG trade on ships and onshore.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 8310, Refrigerated hydrocarbon and non-petroleum based liquefied gaseous fuels — General
requirements for automatic tank thermometers on board marine carriers and floating storage
ISO 8943, Refrigerated light hydrocarbon fluids — Sampling of liquefied natural gas — Continuous and
intermittent methods
ISO 18132-1, Refrigerated hydrocarbon and non-petroleum based liquefied gaseous fuels — General
requirements for automatic tank gauges — Part 1: Automatic tank gauges for liquefied natural gas on
board marine carriers and floating storage
ISO 19636, Ships and marine technology — General requirements for inclinometers used for the
determination of trim and list of LNG carriers
ISO 19970, Refrigerated hydrocarbon and non-petroleum based liquefied gaseous fuels — Metering of gas
as fuel on LNG carriers during cargo transfer operations
ISO 21903, Refrigerated hydrocarbon fluids — Dynamic measurement — Requirements and guidelines for
the calibration and installation of flowmeters used for liquefied natural gas (LNG) and other refrigerated
hydrocarbon fluids
IEC 60533, Electrical and electronic installations in ships — Electromagnetic compatibility
EN 1160, Installations and equipment for liquefied natural gas — General characteristics of liquefied
natural gas
IACS, Unified Requirements E10
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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ISO/DIS 10976:2022(E)
3.1.1
absolute pressure
total of the gauge pressure plus the pressure of the surrounding atmosphere
3.1.2
aerating
introduction of fresh air with an acceptable dew point into the
tank to purge inert gases and to increase the oxygen content to approximately 21 % of volume so as to
ensure a breathable atmosphere
3.1.3
approved equipment
equipment of a design approved by a recognized authority, such as a governmental agency, classification
society or other accredited agency which certifies the particular equipment as safe for use in a specified
hazardous atmosphere
3.1.4
automatic tank gauge
ATG
instrument that automatically measures and displays liquid levels or ullages in one or more tanks,
either continuously, periodically or on demand
3.1.5
automatic tank thermometer
ATT
instrument that automatically measures and displays the temperature of the contents in a tank,
continuously, periodically or on demand
3.1.6
boil off
process of evaporation of a liquid resulting from heat ingress or a drop in pressure
3.1.7
boil-off gas
vapour produced by boil off
3.1.8
cool down
process of reducing the temperature of equipment, such as piping, transfer arms and tanks associated
with custody transfer cargo movements, to required operating temperatures
3.1.9
constant pressure/floating piston sample container
CP/FP sample container
sample container, usually used for intermittent sampling, capable of maintaining constant pressure
during the sampling of gas from the process line into the gas cylinder
[SOURCE: ISO 8943:2007, 3.4, modified]
3.1.10
continuous sampling
sampling from gasified LNG with constant flow rate
[SOURCE: ISO 8943:2007, 3.5]
3.1.11
drying
process of reducing the moisture in the ship tank by displacement or dilution with an inert gas or by the
use of a drying system
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ISO/DIS 10976:2022(E)
3.1.12
filling limit
filling ratio
quantity to which a tank may be safely filled, taking into account the possible expansion (and change in
density) of the liquid
Note 1 to entry: Filling limit (i.e. volume) and filling ratio are expressed as a percentage of the total capacity of a
tank.
3.1.13
full range
range between the maximum and minimum measurable value
3.1.14
gas codes
regulations on the construction of ships carrying liquefied gases developed by the International
Maritime Organization
Note 1 to entry: These include the IMO International Code for the Construction and Equipment of Ships Carrying
Liquefied Gases in Bulk (IGC Code) (generally applies to ships built after 17 July 1986), the IMO Code for Construction
and Equipment of Ships Carrying Liquefied Gases in Bulk (GC Code) (generally applies to ships built on or after 31
December 1976 but prior to 17 July 1986) and the IMO Code for Existing Ships Carrying Liquefied Gases in Bulk
(generally applies to ships delivered before 31 December 1976), as applicable to each vessel.
3.1.15
gas sample container
sample container, usually used for continuous sampling and used for the retention of the gas sample
and for its transfer to an analysing instrument
[SOURCE: ISO 8943:2007, 3.6]
3.1.16
gassing up
process of replacing an inert atmosphere in a cargo tank with the vapour from shore or from another
cargo tank to a suitable level to allow cooling down and subsequent loading to achieve a specified
environment with at least a defined methane (CH ), carbon dioxide (CO ) and oxygen (O ) content
4 2 2
3.1.17
heel
amount of cargo retained in a cargo tank prior to loading or after discharge
3.1.18
inerting
introduction of inert gas into a tank with the object of attaining the inert condition
3.1.19
intermittent sampling
sampling from gasified LNG with predetermined intervals or with predetermined flow amount
intervals
[SOURCE: ISO 8943:2007, 3.9]
3.1.20
letter of protest
letter issued by any participant in a custody transfer citing any condition with which issue is taken and
which serves as a written record that a particular action or finding was observed/questioned at the
time of occurrence
3.1.21
LNG carrier
cargo ship specifically constructed and used for the carriage of LNG in bulk
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ISO/DIS 10976:2022(E)
3.1.22
LNG sample vaporizer
apparatus to completely gasify the LNG sample collected from the LNG transfer line
[SOURCE: ISO 8943:2007, 3.11]
3.1.23
multiple-spot ATT
multiple-point ATT
ATT consisting of multiple spot temperature element sensors to measure the temperature(s) at selected
liquid level(s)
[SOURCE: ISO 4266-5:2002, 3.4, modified]
Note 1 to entry: The readout equipment for a multiple-point averaging ATT averages the readings from the
submerged temperature elements sensors to compute the average temperature of the liquid in the tank, and can
also display the temperature profile in the tank.
3.1.24
notice of apparent discrepancy
notice issued by any participant in a custody transfer citing any discrepancy in cargo quantities and
which serves as a written record that such a discrepancy was found
3.1.25
offline analysis
procedure of analysis implemented on the representative sample gas that is once charged into a gas
sample container or a CP/FP sample container
[SOURCE: ISO 8943:2007, 3.13]
3.1.26
online analysis
procedure of analysis implemented using analytical equipment that is directly connected through
pipelines or other means to the sampling device
[SOURCE: ISO 8943:2007, 3.14, modified]
3.1.27
online gas chromatograph
gas chromatograph that is directly connected to the pipelines or sampling device to implement online
analysis
[SOURCE: ISO 8943:2007, 3.15]
3.1.28
seal water
water used in the water seal type gas sample holder to preclude contact of the gas sample with the
atmosphere
[SOURCE: ISO 8943:2007, 3.19]
3.1.29
tank capacity table
numeric tables that relate the liquid level in a tank to the volume contained in that tank
3.1.30
vapour
fluid in the gaseous state that is transferred to/from or contained within the cargo tank
3.1.31
vapour pressure
pressure at which a liquid and its vapour are in equilibrium at a given temperature
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ISO/DIS 10976:2022(E)
3.1.32
verification
process of confirming the accuracy of an instrument by comparing to a source with known accuracy
3.1.33
warming up
process of warming the cargo tanks from cargo carriage temperature to required temperature
3.1.34
waterless-type gas sample holder
holder without seal water (typically using an expandable/contractible, transformable rubber
membrane) and used for collecting gasified LNG
[SOURCE: ISO 8943:2007, 3.22]
3.1.35
water-seal-type gas sample holder
holder with seal water used for collecting gasified LNG
[SOURCE: ISO 8943:2007, 3.23]
3.1.36
Working range
Range of an instrument in normal operation
3.2 Abbreviated terms
API American Petroleum Institute
ATG Automatic tank gauge
ATT Automatic tank thermometer
BOG Boil-off gas
CTMS Custody transfer measurement system
EMC Electromagnetic compatibility
FSRU Floating storage and re-gasification unit
GCU Gas combustion unit
GIIGNL Groupe International des Importateurs de Gaz Naturel Liquéfié
GNG Gaseous natural gas
GPA Gas Processors Association
IACS International Association of Classification Societies
IAPH International Association of Ports and Harbors
ICS International Chamber of Shipping
IEC International El
...