ISO 23668:2022

INTERNATIONAL ISO
STANDARD 23668
First edition
2022-11
Ships and marine technology —
Marine environment protection —
Continuous on-board pH monitoring
method
Navires et technologie maritime — Protection de l'environnement
marin — Méthode de surveillance continue du pH à bord
Reference number
ISO 23668:2022(E)
© ISO 2022

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ISO 23668:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
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ISO 23668:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 S c op e . 1
2 Nor m at i ve r ef er enc e s . 1
3 Terms and definitions . 1
4 pH buffer solution . 2
4.1 General . 2
4.2 C ertified pH buffer solution . 3
4.3 P ractical-use pH buffer solution . 3
5 P erformance requirements for the combination electrode . 3
5.1 G eneral . 3
5 . 2 S lop e f or c e . 3
5.2.1 R equirement . 3
5.2.2 Verification . 3
5.3 R epeatability . 3
5.3.1 Requirement . 3
5.3.2 Verification . 3
5.4 L inearity . 3
5.4.1 R equirement . 3
5.4.2 Verification . 4
6 I nt er f er enc e s . 4
6.1 General . 4
6.2 S ample conductivity . 4
6 . 3 E le c t r o de f ou l i n g . 4
6.4 E lectrical noise . 4
6 . 5 A i r bubble s . 4
7 Re quirements for pH meters for continuous on-board monitoring .5
7.1 G eneral . 5
7.2 A pparatus . 5
7.2.1 G eneral . 5
7.2.2 p H combination electrode . 5
7.2.3 Transmitter . 6
7.2.4 Electrode mounting . 7
7.2.5 C leaning device . 7
7.3 Pl acement . 7
7.4 Report . 7
8
Calibration . 7
9 Ma i nt en a nce . 8
9.1 G eneral . 8
9.2 M anual cleaning . . 8
9.3 A utomatic cleaning . 9
9.3.1 General . 9
9.3.2 U ltrasonic cleaning . . . 9
9.3.3 Mechanical cleaning . 9
9.3.4 Air/water cleaning . 9
9.4 S torage of the pH combination electrode . 9
Bibliography .10
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ISO 23668:2022(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).
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www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 8, Ships and marine technology,
Subcommittee SC 2, Marine environment protection.
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 23668:2022(E)
Introduction
The pH of water is an important indicator of water quality. Continuous pH monitoring of water served
in marine equipment/systems installed on-board ships for various applications, such as exhaust gas
cleaning systems (scrubbers) and boilers, is essential. “Continuous” describes a monitoring situation.
The pH meter for continuous monitoring is situated in a fixed position on-board to monitor a stream,
as opposed to batched-based deployment in a laboratory. This situation imparts some challenges that
should be addressed. For installation of systems such as scrubbers to remove sulfur oxide from the
exhaust gas by using seawater or freshwater, pH monitoring of the processed water is important not
only for the process control of the systems but also for ensuring compliance with regulations when
discharging the processed water [see IMO Resolution MEPC. 340(77)]. It is expected that reliable pH
meters are robust over time, and suitable for processed water that can contain sea salts and/or oily
substances or can exhibit a wide range of pH.
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INTERNATIONAL STANDARD ISO 23668:2022(E)
Ships and marine technology — Marine environment
protection — Continuous on-board pH monitoring method
1 S cope
This document specifies the performance requirements and the test procedures for a pH meter used for
continuous on-board monitoring using combination electrodes. The pH meter applies to measuring the
pH of the following water for on-board consumption and research purposes:
a) natural seawater and freshwater,
b) freshwater produced from freshwater generators,
c) the used process water for running machinery on-board ships.
This document also specifies the method for evaluating performance, calibration, and maintenance of a
pH meter used for continuous on-board monitoring.
2 Normat ive 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.
ASTM D6569-14, Standard Test Method for On-Line Measurement of pH
IEC 60746-2:2003, Expression of Performance of Electrochemical Analyzers — Part 2 — pH value
3 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
pH value
value derived from the potential difference between the glass electrode (3.5) and the reference electrode
(3.6) and compensated using temperature measured with the temperature sensor (3.7)
Note 1 to entry: This is based on a measure of the relative hydrogen ion activity in an aqueous solution given in
IEC 60746-2:2003, 3.1
3.2
continuous monitoring
measurement using fixed equipment that continually and automatically takes a reading at a
predetermined interval and then returns a result
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ISO 23668:2022(E)
3.3
pH meter for continuous on-board monitoring
on-board equipment composed of a pH combination electrode (3.4), a transmitter (3.9), and an electrode
mounting (3.10), which automatically and continuously measures pH and contains a cleaning device
(3.11), if needed
3.4
pH combination electrode
electrode holding a glass electrode (3.5) and a reference electrode (3.6) in a single unit
3.5
glass electrode
electrode measuring the electromotive force that corresponds to hydrogen ion concentration
3.6
reference electrode
electrode measuring reference potential to determine the electromotive force of the glass electrode
(3.5)
3.7
temperature sensor
sensor that measures the actual temperature of a sample solution to compensate for changes in the
slope force (3.8) of the glass electrode (3.5) due to temperature variations
3.8
slope force
electromotive force per a unit pH of the glass electrode (3.5)
Note 1 to entry: Theoretical Nernstian slope, which is temperature dependent, is 59,16 mV at 25 °C. The
temperature dependency of theoretical Nernstian slope is specified in IEC 60746-2:2003, Table A.1.
3.9
transmitter
device capable of outputting the potential difference as pH value (3.1), temperature, and state signal
3.10
electrode mounting
equipment to hold in place the pH combination electrode (3.4) when used for continuous monitoring (3.2),
which may contain a cleaning device (3.11), if needed
3.11
...