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

ISO 10976:2015 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.

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

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Status
Published
Publication Date
09-Dec-2015
Current Stage
9092 - International Standard to be revised
Start Date
07-Sep-2021
Completion Date
07-Sep-2021
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INTERNATIONAL ISO
STANDARD 10976
Second edition
2015-12-15
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 10976:2015(E)
ISO 2015
---------------------- Page: 1 ----------------------
ISO 10976:2015(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2015, Published in Switzerland

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form

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ii © ISO 2015 – All rights reserved
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ISO 10976:2015(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 .................................................................................................................................................................................................. 7

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 ........................................................ 9

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 .......................................................................12

5.6.5 Tank cool-down tables or means of determination ........................................................................13

5.6.6 Liquid level measurement equipment .......................................................................................................13

5.6.7 Temperature measurement equipment ....................................................................................................17

5.6.8 Pressure measurement equipment ..............................................................................................................18

5.6.9 Custody transfer measurement system.....................................................................................................18

5.7 Dynamic measurement systems and equipment ...................................................................................................19

6  Measurement procedures ........................................................................................................................................................................19

6.1 General ........................................................................................................................................................................................................19

6.2 Static measurement .........................................................................................................................................................................20

6.2.1 General...................................................................................................................................................................................20

6.2.2 Measuring liquid level ..............................................................................................................................................21

6.2.3 Loading ..................................................................................................................................................................................21

6.2.4 Discharge .............................................................................................................................................................................21

6.2.5 Shipboard measurements .....................................................................................................................................21

6.2.6 Liquid level .........................................................................................................................................................................22

6.2.7 Temperature .....................................................................................................................................................................23

6.2.8 Pressure ................................................................................................................................................................................24

6.2.9 CTMS .......................................................................................................................................................................................24

6.2.10 Sampling...............................................................................................................................................................................24

6.2.11 Vapour return ..................................................................................................................................................................25

6.3 Gas-up and cool-down quantification ..............................................................................................................................25

6.3.1 General...................................................................................................................................................................................25

6.3.2 Inerting ..................................................................................................................................................................................25

6.3.3 Gas up and cool down ...............................................................................................................................................25

6.4 Dynamic measurement .................................................................................................................................................................26

© ISO 2015 – All rights reserved iii
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ISO 10976:2015(E)

7  Cargo calculations ............................................................................................................................................................................................26

7.1 General ........................................................................................................................................................................................................26

7.2 LNG volume determination .......................................................................................................................................................26

7.2.1 General...................................................................................................................................................................................26

7.2.2 Liquid levels below lower measurable limit .........................................................................................27

7.3 LNG density determination .......................................................................................................................................................27

Annex A (informative) LNGC design and marine operations....................................................................................................28

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

iv © ISO 2015 – All rights reserved
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ISO 10976:2015(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 second edition cancels and replaces the first edition (ISO 10976:2012), of which it constitutes a

minor revision.
© ISO 2015 – All rights reserved v
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ISO 10976:2015(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 intended 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.
vi © ISO 2015 – All rights reserved
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INTERNATIONAL STANDARD ISO 10976:2015(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

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.
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
© ISO 2015 – All rights reserved 1
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ISO 10976:2015(E)
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
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.
2 © ISO 2015 – All rights reserved
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ISO 10976:2015(E)
3.1.13
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.

3.1.14
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]
3.1.15
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
3.1.16
heel
amount of cargo retained in a cargo tank prior to loading or after discharge
3.1.17
inerting

introduction of inert gas into a tank with the object of attaining the inert condition

3.1.18
intermittent sampling

sampling from gasified LNG with predetermined intervals or with predetermined flow amount intervals

[SOURCE: ISO 8943:2007, 3.9]
3.1.19
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
3.1.20
LNG carrier
cargo ship specifically constructed and used for the carriage of LNG in bulk
3.1.21
LNG sample vaporizer

apparatus to completely gasify the LNG sample collected from the LNG transfer line

[SOURCE: ISO 8943:2007, 3.11]
© ISO 2015 – All rights reserved 3
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ISO 10976:2015(E)
3.1.22
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.
3.1.23
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
3.1.24
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]
3.1.25
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]
3.1.26
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]
3.1.27
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]
3.1.28
tank capacity table

numeric tables that relate the liquid level in a tank to the volume contained in that tank

3.1.29
vapour

fluid in the gaseous state that is transferred to/from or contained within the cargo tank

3.1.30
vapour pressure

pressure at which a liquid and its vapour are in equilibrium at a given temperature

3.1.31
verification

process of confirming the accuracy of an instrument by comparing to a source with known accuracy

4 © ISO 2015 – All rights reserved
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ISO 10976:2015(E)
3.1.32
warming up

process of warming the cargo tanks from cargo carriage temperature to required temperature

3.1.33
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]
3.1.34
water-seal-type gas sample holder
holder with seal water used for collecting gasified LNG
[SOURCE: ISO 8943:2007, 3.23]
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 Electrotechnical Commission
IGC Code International Gas Carrier Code
IMO International Maritime Organization
ISGOTT International Safety Guide for Oil Tankers and Terminals
ISO International Organization for Standardization
LNG Liquefied natural gas
LNGC Liquefied natural gas carrier
MPMS Manual of Petroleum Measurement Standards
© ISO 2015 – All rights reserved 5
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ISO 10976:2015(E)
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 (Système International d’Unités)
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 regulatory requirements
4.1 General

This Clause applies to all types of measurement on board LNG carriers. However, while these precautions

represent safe operating practices, they should not be considered complete or comprehensive. In

addition to those listed in this International Standard, reference should be made to all safety precautions

contained in any relevant governmental, local or company operating guidelines.

IMPORTANT — Anyone working with the vessel’s measurement equipment shall be, at all times,

under the direction and supervision of the Master of the vessel or its designated representative

and be properly trained in its use.

Personnel involved in the handling of liquefied natural gas should be familiar with its physical and

chemical characteristics, including potential for fire, explosion, cryogenic burns (frostbite) and

reactivity, as well as the appropriate emergency procedures. These procedures should comply with

the individual company’s safe operating practices, in addition to local, state and federal regulations,

including those covering the use of proper protective clothing and equipment. Personnel should be alert

in order to avoid potential sources of ignition.

SIGTTO publications Liquefied Gas Fire Hazard Management and Liquefied Gas Handling Principles on

Ships and in Terminals should be consulted to ensure familiarity with the characteristics and hazards

of LNG, all fire protection and firefighting equipment on board LNG carriers along with the appropriate

fire hazard management plan.

API Standard 2217A and any applicable regulations should be consulted where entering into

confined spaces.

Information regarding particular material safety and conditions should be obtained from the employer,

manufacturer or supplier of that material or the material safety data sheet (MSDS).

LNG is carried and handled at extremely low temperatures. The very nature of liquids at very low

temperatures is a hazard, added to which LNG itself has properties that shall be taken into account

...

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