ISO 4266-2:2023

INTERNATIONAL ISO
STANDARD 4266-2
Second edition
2023-11
Petroleum and liquid petroleum
products — Measurement of level
and temperature in storage tanks by
automatic methods —
Part 2:
Measurement of level in marine
vessels
Pétrole et produits pétroliers liquides — Mesurage du niveau et de
la température dans les réservoirs de stockage par des méthodes
automatiques —
Partie 2: Mesurage du niveau dans les citernes de navire
Reference number
© 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: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Precautions . 3
4.1 Safety precautions . 3
4.1.1 General . 3
4.1.2 Equipment precautions . 3
4.2 General recommendations . 3
4.2.1 Accuracy and performance . 3
4.2.2 Speed of response . 3
4.2.3 Protection from mechanical damage . 4
4.2.4 Manual gauging . 4
4.2.5 Minimum measurable level . 4
4.2.6 Trim and list . 4
4.2.7 Product temperatures . 4
4.2.8 Compatibility . 4
4.2.9 Entrained air and vapour . 4
4.2.10 Vessel motion . 4
4.3 Use of marine ALGs in fiscal/custody transfer . 5
5 Accuracy . 5
5.1 Intrinsic error of ALGs . 5
5.2 Calibration prior to installation . 5
5.3 Initial shipyard adjustment . 5
5.4 Error caused by operating conditions . 5
5.5 Overall accuracy . . 6
5.5.1 General . 6
5.5.2 Use of ALGs for fiscal/custody transfer purposes . 6
6 Installation of marine ALGs .6
6.1 General . 6
6.2 Location of ALG . 6
6.3 Location of manual calibration check point . 6
6.4 Gauging of inerted tanks . 6
7 Onboard verification of marine ALGs . .7
7.1 General precautions . 7
7.1.1 Check for smooth operation of level-sensing elements— at the shipyard . 7
7.1.2 ALG technology-specific considerations . 7
7.2 Verification by innage gauging or ullage gauging . 7
7.3 Initial verification . 7
7.4 Subsequent verification . 7
7.4.1 General . 7
7.4.2 Agreement between ALG reading and manual gauge reading . 7
7.4.3 Use of average gauge readings . 7
7.4.4 Adjustment of the ALG . 8
7.5 Verification by alternate methods . 8
7.6 Schedule for regular ALG verification . 8
7.7 Record keeping . 8
8 Data communication and receiving . 8
8.1 General . 8
8.2 Use of remote readout in fiscal or custody transfer . 8
iii
8.3 Telemetry and readout equipment . 9
Annex A (informative) Accuracy limitations of marine level measurement .10
Annex B (informative) Accuracy limitations of marine volume measurement .11
Bibliography .12
iv
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 2, Measurement of petroleum and
related products.
This second edition cancels and replaces the first edition (ISO 4266-2:2002), which has been technically
revised.
The main changes are as follows:
— in Clause 2, the reference to ISO 8697 has been removed as it is a withdrawn document;
— in 4.2.7, it has been clarified that the tank level should be measured and recorded simultaneously
with the temperature;
— in 7.4.4.1, it has been clarified regarding the procedure prior to making adjustments against manual
measurements;
— added addition documents in Bibliography.
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.
v
Introduction
Marine automatic level gauges (ALGs) are not normally used in fiscal or custody transfer applications
because of the limitations described in Annexes A and B. However, level measurement by marine ALGs
may be used in fiscal or custody transfer when no other alternative, reliable measurement is available.
The use of marine-vessel-based ALGs in fiscal or custody transfer normally requires mutual contractual
agreement between the buyer and the seller and can be subject to government regulations.
vi
INTERNATIONAL STANDARD ISO 4266-2:2023(E)
Petroleum and liquid petroleum products — Measurement
of level and temperature in storage tanks by automatic
methods —
Part 2:
Measurement of level in marine vessels
1 Scope
This document gives guidance on the accuracy, installation, calibration and verification of automatic
level gauges (ALGs), both intrusive and non-intrusive, for measuring the level of petroleum and liquid
petroleum products having a Reid vapour pressure less than 100 kPa, transported aboard marine
vessels (i.e. tankers and barges).
This document gives guidance for buyers and sellers who mutually agree to use marine ALGs for either
fiscal and/or custody transfer applications.
This document is not applicable to the measurement of level in refrigerated cargo tanks.
NOTE For information on the measurement of level in refrigerated cargo tanks, please see ISO 18132-1 and
ISO 18132-3.
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 1998-1, Petroleum industry — Terminology — Part 1: Raw materials and products
ISO 1998-2, Petroleum industry — Terminology — Part 2: Properties and tests
ISO 1998-3, Petroleum industry — Terminology — Part 3: Exploration and production
ISO 1998-4, Petroleum industry — Terminology — Part 4: Refining
ISO 1998-5, Petroleum industry — Terminology — Part 5: Transport, storage, distribution
ISO 1998-6, Petroleum industry — Terminology — Part 6: Measurement
ISO 1998-7, Petroleum industry — Terminology — Part 7: Miscellaneous terms
ISO 1998-99, Petroleum industry — Terminology — Part 99: General and index
ISO 4512, Petroleum and liquid petroleum products — Equipment for measurement of liquid levels in
storage tanks — Manual methods
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 1998-1, ISO 1998-2, ISO 1998-3,
ISO 1998-4, ISO 1998-5, ISO 1998-6, ISO 1998-7, ISO 1998-99 and the following 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
automatic level gauge
ALG
automatic tank gauge
ATG
instrument that continuously measures liquid height [dip (3.2) or ullage (3.5)] in storage tanks
3.2
dip
innage
vertical distance between the dipping datum point and the liquid level
3.3
innage-based automatic level gauge
automatic level gauge (3.1) designed and installed to measure the liquid dip (3.2) directly
3.4
still-pipe
stilling-well
stand pipe
guide pole
vertical, perforated pipe built into a tank to contain the liquid-level-detecting element in order to
reduce measurement errors arising from liquid turbulence, surface flow or agitation of the liquid, and
to provide a stable mounting point for an automatic level gauge
3.5
ullage
outage
distance between the liquid level and the upper reference point, measured along the vertical
measurement axis
3.6
ullage-based automatic level gauge
automatic level gauge (3.1) designed and installed to measure the distance from the ALG reference point
to the liquid surface
3.7
intrusive automatic level gauge
automatic level gauge (3.1) where the level-sensing device intrudes within the tank and makes physical
contact with the liquid, e.g. a float and servo-operated-type automatic tank gauge
3.8
non-intrusive automatic level gauge
automatic level gauge (3.1) where the level-sensing device can intrude within the tank, but does not
make physical contact with the liquid, e.g. a microwave or radar-type automatic tank gauge
4 Precautions
4.1 Safety precautions
4.1.1 General
In addition, the manufacturers' recommendations on the use and installation of the equipment should
be followed.
NOTE International Standards and government regulations, classification societies and ISGOTT on safety
and material-compatibility precautions can apply when using marine ALG equipment.
4.1.2 Equipment precautions
4.1.2.1 All marine ALGs should be capable of withstanding the pressure, temperature and other
environmental conditions likely to be encountered in marine service. When an ALG is installed in a
corrosive service, any parts exposed to the liquid or vapours should be of durable, corrosion-resistant
construction.
4.1.2.2 All ALGs should be sealed to withstand the vapour pressure of liquid in the tank. ALGs
mounted on vessels with an inert gas system (IGS) should be designed to withstand the operating
pressure of the IGS.
4.1.2.3 All marine ALGs should be specified and installed in accordance with the appropriate national
and/or international (IMO, IEC, CENELEC, ISGOTT, ISO, etc.) marine electrical safety standards. ALGs
should be certified for use in the hazardous-area classification appropriate to their installation.
All ALG equipment should be maintained in safe operating condition and the manufacturers'
maintenance instructions should be complied with.
NOTE 1 The design and installation of ALGs can be subject to the approval of the national measurement
organization and classification societies, who can have issued a general type approva
...