EN ISO 9351:2025
(Main)Galvanic anodes for cathodic protection in seawater and saline sediments (ISO 9351:2025)
Galvanic anodes for cathodic protection in seawater and saline sediments (ISO 9351:2025)
This document defines requirements and gives recommendations for the chemical composition, electrochemical properties, physical tolerances and test and inspection procedures for cast galvanic anodes of aluminium, magnesium and zinc-based alloys for cathodic protection in seawater, saline sediment and brackish water.
Information on salinity ranges can be found in Annex A.
The requirements and recommendations of this document can be applied to any available anode shape for cast anodes, e.g. trapezoid, circular, half-spherical cross sections, bracelet type.
Whilst other metals, such as soft iron, can be used as galvanic anode material to protect more noble metals than iron and steel, these are not covered in this document.
Galvanische Anoden für den kathodischen Schutz in Meerwasser und salzhaltigen Sedimenten (ISO 9351:2025)
Dieses Dokument definiert Anforderungen und gibt Empfehlungen für die chemische Zusammensetzung, elektrochemischen Eigenschaften, physikalischen Toleranzen, Prüf- und Inspektionsverfahren für galvanische Gussanoden aus auf Aluminium, Magnesium und Zink basierenden Legierungen für den kathodischen Korrosionsschutz in Meerwasser, salzhaltigem Sediment und Brackwasser.
Informationen zu Bereichen des Salzgehalts können Anhang A entnommen werden.
Die Anforderungen und Empfehlungen dieses Dokuments können auf jede verfügbare Anodenform für Gussanoden angewendet werden, z. B. trapezförmig, kreisförmig, halbkugelförmig, Querschnitte, Manschettenart.
Obwohl andere Metalle, wie z.B. Weicheisen, als Werkstoffe von galvanischen Anoden verwendet werden können, um edlere Metalle als Eisen und Stahl zu schützen, werden diese in diesem Dokument nicht behandelt.
Anodes galvaniques pour la protection cathodique dans l’eau de mer et les sédiments salins (ISO 9351:2025)
Le présent document définit des exigences et fournit des recommandations pour la composition chimique, les propriétés électrochimiques, les tolérances physiques et les modes opératoires d’essai et d’inspection des anodes galvaniques coulées en alliages à base d’aluminium, de magnésium et de zinc, utilisées pour la protection cathodique dans l’eau de mer, les sédiments salins et les eaux saumâtres.
L’Annexe A fournit des informations sur les plages de salinité.
Les exigences et les recommandations du présent document peuvent s’appliquer à d’autres formes d’anode pour les anodes coulées, par exemple trapézoïdales, circulaires, demi-sphériques, type bracelet.
Bien que d’autres métaux, tels que le fer doux, puissent être utilisés comme matériau d’anode galvanique pour protéger des métaux plus nobles que le fer et l’acier, ces métaux ne sont pas couverts par le présent document.
Galvanske anode za katodno zaščito v slani vodi in slanih usedlinah (ISO 9351:2025)
Ta dokument določa zahteve in podaja priporočila za kemično sestavo, elektrokemične lastnosti, fizične tolerance ter preskusne postopke in postopke pregledovanja za lite galvanske anode iz zlitin aluminija, magnezija in cinka za katodno zaščito v slani vodi, slanih usedlinah in somornici. Informacije o razponih slanosti so navedene v dodatku A. Zahteve in priporočila v tem dokumentu je mogoče uporabiti za katero koli razpoložljivo obliko litih anod, npr. trapezno, krožno, polkrožno, v obliki zapestnice. Kot galvanski anodni material za zaščito plemenitejših kovin, kot sta železo in jeklo, je mogoče uporabiti tudi druge kovine (npr. mehko železo), vendar te niso zajete v tem dokumentu.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-maj-2025
Galvanske anode za katodno zaščito v slani vodi in slanih usedlinah (ISO
9351:2025)
Galvanic anodes for cathodic protection in seawater and saline sediments (ISO
9351:2025)
Galvanische Anoden für den kathodischen Schutz in Seewasser und salzhaltigen
Sedimenten (ISO 9351:2025)
Anodes galvaniques pour la protection cathodique dans l'eau de mer et les boues
salines (ISO 9351:2025)
Ta slovenski standard je istoveten z: EN ISO 9351:2025
ICS:
77.060 Korozija kovin Corrosion of metals
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EN ISO 9351
EUROPEAN STANDARD
NORME EUROPÉENNE
February 2025
EUROPÄISCHE NORM
ICS 77.060 Supersedes EN 12496:2013
English Version
Galvanic anodes for cathodic protection in seawater and
saline sediments (ISO 9351:2025)
Anodes galvaniques pour la protection cathodique Galvanische Anoden für den kathodischen Schutz in
dans l'eau de mer et les sédiments salins (ISO Meerwasser und salzhaltigen Sedimenten (ISO
9351:2025) 9351:2025)
This European Standard was approved by CEN on 14 February 2025.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 9351:2025 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
European foreword
This document (EN ISO 9351:2025) has been prepared by Technical Committee ISO/TC 156 "Corrosion
of metals and alloys" in collaboration with Technical Committee CEN/TC 219 “Cathodic protection” the
secretariat of which is held by BSI.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by August 2025, and conflicting national standards shall
be withdrawn at the latest by August 2025.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 12496:2013.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 9351:2025 has been approved by CEN as EN ISO 9351:2025 without any modification.
International
Standard
ISO 9351
First edition
Galvanic anodes for cathodic
2025-02
protection in seawater and saline
sediments
Anodes galvaniques pour la protection cathodique dans l’eau de
mer et les sédiments salins
Reference number
ISO 9351:2025(en) © ISO 2025
ISO 9351:2025(en)
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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ii
ISO 9351:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviations . 4
4.1 Symbols .4
4.2 Abbreviations .5
5 Competence of personnel . 5
6 Galvanic anode materials and their properties . 5
6.1 General .5
6.2 Anode alloy composition .5
6.3 Electrochemical properties . .6
6.4 Electrochemical testing .6
6.4.1 General .6
6.4.2 Performance testing .6
6.4.3 Short-term testing for quality control.7
6.5 Anode consumption rate .7
7 Anode design and acceptance criteria . . 8
7.1 General .8
7.2 Chemical composition .9
7.3 Electrochemical properties . .9
7.4 Anode shape .9
7.5 Physical properties .9
7.6 Anode core materials .10
7.7 Cable connections to anodes .11
8 Environmental impact .11
Annex A (informative) Seawater .13
Annex B (normative) Physical tolerances for galvanic anodes . 14
Annex C (informative) Composition and performance properties for galvanic anodes . 19
Annex D (informative) Description of various electrochemical tests .26
Annex E (informative) Environmental impact considerations .29
Annex F (informative) Inspection and test plan (ITP) .33
Bibliography .40
iii
ISO 9351:2025(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 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 156, Corrosion of metals and alloys, in
collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/TC 219,
Cathodic protection, in accordance with the Agreement on technical cooperation between ISO and CEN
(Vienna Agreement).
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.
iv
ISO 9351:2025(en)
Introduction
This standard defines the minimum requirements for the galvanic anode quality levels and verification
procedures.
The anticipated performance of the cast galvanic anodes for use in seawater and saline mud or sediment is
determined by their composition, anode dimensions and the quality of their manufacture.
In addition, the document provides guidance and recommendations related to the environmental impact.
v
International Standard ISO 9351:2025(en)
Galvanic anodes for cathodic protection in seawater and
saline sediments
1 Scope
This document defines requirements and gives recommendations for the chemical composition,
electrochemical properties, physical tolerances and test and inspection procedures for cast galvanic anodes
of aluminium, magnesium and zinc-based alloys for cathodic protection in seawater, saline sediment and
brackish water.
Information on salinity ranges can be found in Annex A.
The requirements and recommendations of this document can be applied to any available anode shape for
cast anodes, e.g. trapezoid, circular, half-spherical cross sections, bracelet type.
Whilst other metals, such as soft iron, can be used as galvanic anode material to protect more noble metals
than iron and steel, these are not covered in this document.
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 630 (all parts), Structural steels
ISO 1461, Hot dip galvanized coatings on fabricated iron and steel articles — Specifications and test methods
ISO 8501-1, Preparation of steel substrates before application of paints and related products — Visual
assessment of surface cleanliness — Part 1: Rust grades and preparation grades of uncoated steel substrates and
of steel substrates after overall removal of previous coatings
ISO 9606-1, Qualification testing of welders — Fusion welding — Part 1: Steels
EN 10025, Hot rolled products of structural steels (all parts)
ISO 10474:2013, Steel and steel products — Inspection documents
ISO 15607, Specification and qualification of welding procedures for metallic materials — General rules
ISO 15609-1, Specification and qualification of welding procedures for metallic materials — Welding procedure
specification — Part 1: Arc welding
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/
ISO 9351:2025(en)
3.1
anode consumption rate
mass consumption rate
amount of anode material consumed for a current output of one ampere during one year
Note 1 to entry: The anode consumption rate is expressed in kilograms per amp year [kg/(A·y)].
3.2
batch
group of anodes all produced from a single furnace cast
Note 1 to entry: Multiple batches of different anodes can be produced from a single cast.
3.3
bracelet anode
anode shaped as half-shells (annular castings) to be positioned on tubular items
Note 1 to entry: Two half-shell castings fit together to become a bracelet anode. These are typically used for submarine
pipelines and occasionally used for marine structure tubulars.
Note 2 to entry: Bracelet anodes can be fabricated as half or part shell castings with the structural core within the
casting, or as cast segments with only the supporting core within the casting and the structural steel elements
external to the castings. Segmental bracelets comprise individual castings attached to external steel bands to fit
around the pipeline or tubular structure.
3.4
cast
charge
heat
single furnace load with a unique, analysed chemical composition from which anodes are produced
3.5
closed circuit potential
potential of an electrode measured with respect to a reference electrode or another electrode when a
current is flowing in the circuit
3.6
cold shut
surface discontinuity in the cast anode alloy caused by solidification of a portion of a meniscus during the
progressive filling of a mould, which is later covered with more solidifying metals as the molten metal level rises
Note 1 to entry: Cold shuts often occur remote from the point of pour.
3.7
crack
imperfection produced by a local rupture in the solid state, which can arise from the effect of cooling or
stresses
3.8
driving voltage
voltage between the galvanic anode to electrolyte potential and the structure to electrolyte potential
Note 1 to entry: For design purposes, the driving voltage refers to the difference between the closed-circuit potential
of the anode and the design protective potential of the structure. This value is used to determine the maximum
available anode current for a given circuit resistance.
3.9
electrochemical capacity
total amount of electric charge that is produced when a fixed mass of anode alloy is consumed
electrochemically
Note 1 to entry: Electrochemical capacity is expressed in ampere hours per kg (A·h/kg).
ISO 9351:2025(en)
Note 2 to entry: This represents the practical amount of charge per unit mass available, which is less than the
theoretical, Faradaic value.
Note 3 to entry: An alternative, not preferred, term is alloy capacity.
Note 4 to entry: Electrochemical capacity is not a material constant but can vary with electrolyte conditions.
3.10
electrochemical property
property of potential and electrochemical capacity that characterises a galvanic alloy and can be assessed
by quantitative tests
3.11
flush mounted anode
anode fitted to a structure with one face in contact with or very close to the structure
3.12
free-running test
electrochemical test where potential and current are not controlled
3.13
gas hole
blow hole, channel or porosity produced by gas evolution during solidification or entrapped air
Note 1 to entry: Gas holes can indicate:
— contamination of the mould or core prior to casting;
— poor mould or insert design;
— casting process permitting entrapped air during the pour.
3.14
gross mass
mass of a cast anode, including the mass of the steel core and any integral attachments on completion of casting
3.15
insert
core
structural item over which the anode is cast and which supports the alloy and can be used to connect the
anode to the structure requiring protection
Note 1 to entry: The insert (core) is generally made of steel. Its design helps determine the utilization factor of the anodes.
3.16
ladle sample
specimen taken from the molten metal
3.17
net mass
mass of cast anode, excluding the mass of the steel core and any integral attachments on completion of casting
Note 1 to entry: Net mass represents the mass of the galvanic alloy material and is used in cathodic protection design.
3.18
nominal value
designated or intended value
Note 1 to entry: Examples of nominal values are length, width and mass.
3.19
non-metallic inclusions
particles of oxides and other refractory materials entrapped in liquid metal during the melting or casting
sequences
ISO 9351:2025(en)
3.20
pitting
localised corrosion resulting in cavities extending from the surface into the metal
3.21
polarization
change in the potential of an electrode as a result of current flow to or from that electrode
3.22
shrinkage depressions
natural concave surfaces which can be produced when liquid metal is allowed to solidify in a mould without
the provision of extra liquid metal to compensate for the reduction in volume that occurs during the liquid
and liquid–solid (solidification) contractions on cooling the liquid-solid transformation
3.23
stand-off anode
anode which is offset a certain distance from the object on which it is positioned
3.24
surface morphology
description of the features or structure of the anode surface
3.25
undercutting
formation of subsurface cavities which can be caused by pitting corrosion or inter-granular corrosion
3.26
utilization factor
fraction of the galvanic alloy mass in an anode which can be used for cathodic protection current before
the galvanic material is no longer supported by the core or the anode can no longer deliver the minimum
required current
Note 1 to entry: Utilization factor is generally expressed numerically (e.g. 0,80) and is dependent on the detailed anode
design and location of the insert.
Note 2 to entry: Utilization factor is critical in the determination of anode mass requirements for a cathodic
protection design.
3.27
void
lack of bond between the steel core and the cast alloy of an anode that can be formed by movement of the
anode core in the mould as the alloy solidifies
4 Symbols and abbreviations
4.1 Symbols
y year
E anode consumption rate, kg/(A·y)
Q electrochemical capacity of the alloy, A·h/kg
CE carbon equivalent
ISO 9351:2025(en)
4.2 Abbreviations
CP cathodic protection
EPD environmental product declaration
ITP inspection and test plan
LCA life cycle assessment
QC quality control
5 Competence of personnel
It is the responsibility of personnel performing the design of the anode and the anode core to ensure that the
anode, including its core, is suitable to deliver the utilization factor, see Clause 7. Those responsible for the
core design shall have the appropriate level of competence for the tasks undertaken. Those responsible for
all other aspects of the anode manufacture, inspection and testing shall also have the appropriate level of
competence for the tasks undertaken. These should be the subject of the necessary training, assessment and
documentation by the anode manufacturer to ensure that the requirements of this document are met.
NOTE Competence of CP personnel to the appropriate level for tasks undertaken can be demonstrated by
certification in accordance with ISO 15257 or by another equivalent prequalification procedure.
6 Galvanic anode materials and their properties
6.1 General
In this document, alloys used for galvanic anodes in seawater or saline sediment shall be based on aluminium
(Al), magnesium (Mg) or zinc (Zn). The performance, and therefore the suitability of a particular alloy for a
specific application, depends on the composition and characteristics of both the anode alloy, the electrolyte
and operation conditions of the polarized anode.
The performance of an anode alloy will vary in different environmental conditions. The performance data
shall include the electrochemical capacity in ampere-hours per kilogram (A·h /kg), and the closed-circuit
anode to electrolyte potential of a working anode measured against a calibrated standard reference
electrode (see 6.3 and Annex D).
Each anode shall be uniquely marked by hard stamping with the cast number during production. Other
markings can be added by agreement between purchaser and manufacturer and may include for example, a
manufacturer identification, an alloy designation, anode mass and a sequential production number within
the cast. Marking should be by hard stamping on the anode surface located where it is visible when the
anodes are stacked or palleted for storage or delivery.
6.2 Anode alloy composition
The performance of an alloy is dependent on the specific alloy composition. Variations in composition from
established specifications can result in variations in activation, resistance to passivation, electrochemical
capacity and corrosion surface morphology. Some elements are known to have a detrimental effect on anode
performance and their content is normally subject to strict control.
The most common galvanic anode generic compositions for aluminium, magnesium and zinc-based anode
alloys are given in Annex C.
Strict control of the alloy chemical composition, both alloying elements and impurities, is essential and shall
be carried out on each cast.
A minimum of two samples from each cast (ladle sample) shall be taken for chemical analysis. The samples
shall be taken in the beginning and at the end of casting from the pouring stream. The sample shall be taken
ISO 9351:2025(en)
at the beginning of the first cast and at the end of the second cast, then in the beginning of the third cast
and so on. The samples shall be analysed to verify the required chemical composition. All samples shall be
identified with the cast number. All anodes from that particular cast shall be similarly identified with the
cast number (see 6.1).
The samples shall be analysed to prove conformity with the agreed chemical composition limits of the
alloy being produced. Additional sample(s) may be taken and stored for future determination of chemical
composition.
NOTE Spark emission spectrometry is an appropriate method of analysis in a production environment but
requires regular calibration against known and certified reference alloy samples.
Where a small holding furnace is used to continue topping up the cooling and solidifying anode after
pouring from the main furnace has ceased, the holding furnace shall be supplied from the same cast as in the
main furnace. A sample should be taken from the holding furnace for chemical analysis to ensure that the
composition remains within limits.
The chemical composition of all samples analysed shall be documented. Anodes from casts which do not
meet the required chemical composition shall be rejected.
6.3 Electrochemical properties
Cathodic protection (CP) is electrochemical in nature. The anode material’s electrochemical properties are
primary factors in cathodic protection design and therefore shall be documented.
These properties are:
— closed circuit potential;
— practical electrochemical capacity.
These properties can vary with electrolyte conditions. They can also vary over time, even when exposed
to constant conditions. This is due to the corrosion products and layers of marine growth that form on the
anode surface as well as variations in current demand. Caution should be exercised when considering these
parameters for CP-specific design purposes (see 6.4.2).
NOTE 1 ISO 15589-2 and References [11] and [12] give further information on the impact of capacity variations of
temperature and environment on cathodic protection design for pipelines.
NOTE 2 Due to self-corrosion, all anode materials have a practical electrochemical capacity lower than the capacity
calculated by considering the theoretical electrical equivalence determined by Faraday’s Law (i.e. some of the anode
mass is consumed through self-corrosion, not current supply, and is not available for cathodic protection). The
practical electrochemical capacity is used in cathodic protection design.
6.4 Electrochemical testing
6.4.1 General
There are two principal reasons for carrying out electrochemical tests: to determine alloy electrochemical
performance and to conduct production quality control. Testing can also be carried out for research
purposes, but such tests are generally customised and not considered in this document.
The principal methods of electrochemical testing are described in Annex D.
6.4.2 Performance testing
To determine alloy performance, there is no substitute for prolonged field testing of alloys in practical
situations. Experience with different anode applications can be drawn upon, where possible.
ISO 9351:2025(en)
In some cases, there are no reliable historical or laboratory data relating to the performance of a specific
anode alloy composition range in a particular environment. In these cases, electrochemical testing shall be
carried out to indicate the relevant alloy closed circuit potential and electrochemical capacity.
Long-term laboratory test procedures shall be selected to best represent the expected operating conditions
(including electrolyte, temperature and anode current density). These test procedures shall be carried
out over a period that is long enough to provide a realistic assessment of alloy performance in a practical
application.
The test period should not be less than one year. One year is a relatively short period compared to most CP
design lives. See Annex D.
A long-term test to an agreed common procedure can be used to qualify alloys for specific purposes. It can
be useful to rank alloys on a relative scale. A related procedure is described in Reference [11].
These laboratory tests produce alloy performance data. However, these data only reflect the particular test
parameters used in the test, e.g. exposure period, temperature and anode current density and its variation
over time. Free running tests have current density variations in time, but galvanostatic tests cannot show
risk of passivation. Even data from long-term free running tests should be used with caution, since it is
possible they do not reflect the particular application intended. In addition, it is not necessarily safe to adopt
the test results for CP design in all applications (see Annex D).
Samples for electrochemical testing should be representative of the specified alloy composition range, the
process route and the target chemical analysis.
Where performance tests are to be used to determine anode alloy performance properties for design
purposes, they should be conducted by or witnessed, assessed and approved by an independent certified
authority. The certified authority shall be experienced in and accredited to conduct the tests they are
assessing. The accreditation shall be by a national accreditation body.
6.4.3 Short-term testing for quality control
The objectives of short-term quality control (QC) tests are very different from those of the long-term tests
described in 6.4.2. Short-term tests are designed to produce measurable results in a relatively short period
consistent with production release and delivery requirements. This is performed by adopting relatively high
anode current densities, which can lie outside reasonable expectations of actual anode applications. These
tests are primarily intended to demonstrate consistency of production within a particular alloy chemical
compositional range.
Data from such short-term quality control tests shall not be relied on for system design or be interpreted as
an indicator of the long-term performance of the alloy.
Short-term tests for quality control should be carried out to an agreed standardised procedure. Suitable
tests in common use are those described in References [11] and [13] (see also Annex D). For anode
production quality control, short-term high current density tests should be carried out on each charge of
production or otherwise at a frequency to be agreed and consistent with the contract delivery requirement.
Acceptance criteria for quality control testing shall be agreed. Test results should form part of the contract
documentation.
Other short-term tests for QC purposes, such as closed-circuit potential tests, may be carried out by
agreement.
6.5 Anode consumption rate
The anode consumption rate for a galvanic alloy anode is expressed in kilograms per ampere year (kg/(A·y))
and is the total amount of anode material consumed in practice for a current output of one ampere during
one year. Like electrochemical capacity (see 6.4.2), all anode materials have a practical consumption rate
different from their theoretical consumption rate. In this case, the anode consumption rate is higher than
that calculated by Faraday’s Law.
ISO 9351:2025(en)
The anode consumption rate and the current capacity are related by:
E · Q = 8 760
where
E is the anode consumption rate (kg/(A·y));
Q is the electrochemical capacity (A·h/kg);
8 760 is the number of hours in one year.
7 Anode design and acceptance criteria
7.1 General
The chemical composition of any alloy used for galvanic anodes shall be specified by either the CP designer
or the purchaser. The corresponding electrochemical properties shall be determined and documented
against defined test procedures (see 6.4).
The anodes, including cores and associated supports, shall be designed to give the specified performance
during fabrication, transport, installation and operation. The dimensions and shape of the anodes, their steel
core and any integral extensions shall be designed to withstand the mechanical forces that can act on the
anodes, e.g. waves, currents, pile driving or vibration. For all anodes, the anode and anode core dimensions
shall be designed to be compatible with the proposed installation method and any structural material
requirements. However, the steel core shall be designed to support the anode alloy for its full design life
consistent with the utilization factor appropriate for the anode design.
Anodes shall not be manufactured without cores or inserts.
In subsea areas where divers or remote operated vehicles are likely to operate, stand-off type anodes should
be provided so that the support cores protrude through the end-faces of the anode. This is to reduce the
danger of entangling wires, ropes, umbilical cables, etc.
For open moulds, over-pouring to fill shrinkage depressions shall be kept to a minimum. All pouring of
molten anode alloy shall be finished smooth before the surface of the cast anode solidifies. The surface of
the anode may be kept in a liquid state for a while by applying heat, for example, from gas burners, but
once solidified, no re-melting shall be allowed, not even to fill shrinkage depressions. The term "shrinkage
depression" also applies to the free surface area of an open mould casting, where the final solidification
occurs and where, before final solidification, additional molten alloy can be added to top up any shrinkage
depressions to maintain final mass and dimension requirements.
NOTE The term "shrinkage depression" can also apply to the concave surfaces produced when liquid metal is
solidified in a closed mould in such a manner that the area is not “fed” by the liquid metal provided by the mould design.
The exposed (external) surfaces of the anode shall not be subject to any coating except for flush mounted
and bracelet anodes where the anode surface facing, and immediately adjacent to the structure surface to be
protected, should be coated.
The manufacturers shall produce anode castings in which the presence of defects, such as shrinkage
depressions and cracks, shall conform to the limits specified in Annex B.
Physical tolerances of anodes shall be confirmed in accordance with the requirements of Annex B. An
inspection and test plan (ITP) shall be agreed upon between anode producer and purchaser before
commencing anode casting. The ITP shall define all requirements to the production, including alloy
composition, testing, dimensions etc., and which level of inspection the purchaser requires during the
production. An example of an ITP is given in Annex F.
ISO 9351:2025(en)
7.2 Chemical composition
Galvanic anode alloys can have reduced ductility due to their inherent mechanical properties and/or the
nature of the as-cast material. This should be considered when designing anode shape and size. Alloying
additions commonly used to strengthen aluminium, zinc and magnesium engineering castings shall not be
used for galvanic anodes because of their detrimental effect on electrochemical properties. Annex C provides
limits for some of these detrimental elements in various galvanic alloys.
7.3 Electrochemical properties
Anode design is a compromise between the current required from an anode and the net mass of the as-
cast anode.
Anode alloy electrochemical capacity is a primary factor in determining the anode net mass requirements
of a CP design. The correct value of anode alloy electrochemical capacity appropriate for any particular
application of cathodic protection is of paramount importance (see 6.3, 6.4.2 and Annex D).
The closed-circuit potential determines the driving voltage between the anode and the protected structure.
The driving voltage and the anode to electrolyte resistance (ohmic resistance) of the anode are used to
determine the available current at various stages of the anode life.
NOTE Standard anode resistance formulae for various anode shapes are included in many other CP design
standards such as ISO 13174, EN 17243, ISO 15589-2, ISO 24656 and Reference [11].
For applications in seawater outside a salinity range between 30 g dissolved salts/kg seawater (30 ‰) and
35 g dissolved salts/kg seawater (35 ‰), the electrochemical properties, capacity and potential should be
determined. Some indications are available in Reference [14] but detailed assessments and testing should be
completed prior to selection of anode shape and composition limits.
7.4 Anode shape
Anode shape is determined by many factors including the shape or nature of the object to be protected, for
example, pipeline, subsea structure with confined spaces etc. CP specifications advise on the preferred or
possible configurations of anodes required in those circumstances.
Other important factors to be taken into account when deciding on anode size and shape are:
— anode distribution, which determines the extent of protection of the structure and therefore the number
and size of the anodes;
— alloy cover over core, which determines the initial mass of the anode and any propensity to cracking of
the as-cast anode, in addition to the end of life current output;
— anode current output, which is calculated using Ohm's Law from a knowledge of driving voltage and
anode to electrolyte resistance.
There are formulae for the calculation of anode to electrolyte (seawater) resistance. All require a knowledge
of the electrolyte resistivity which is governed by the seawater salinity.
Most marine CP applications are in waters with a salinity from 30 g dissolved salts/kg seawater (30 ‰) to
35 g dissolved salts/kg seawater (35 ‰) or their sediment. For CP applications outside this salinity area, the
full range of salinity shall be determined over full tidal and annual variations and the impacts of these on
the anode performance shall be determined by specialists. This covers areas in which salinity is known to be
widely variable such as the Baltic, Caspian and Black Seas. Annex A provides information on ocean salinity.
7.5 Physical properties
The physical and dimensional tolerances shall meet the anode design requirements. Any specific tolerances
required by any CP design shall be agreed between purchaser and manufacturer. These tolerances shall be
clearly marked on an approved drawing.
ISO 9351:2025(en)
Physical and dimensional tolerances that can be used as default parameters are given in Annex B.
No anode or its steel core shall have any defect either on its surface or within its body that affects the
transportation, installation and future performance of the anode. Any protrusions either on the anode body
or insert surfaces shall be examined and removed if potentially a safety hazard.
7.6 Anode core materials
Anode cores shall be fabricated from weldable structural steel tubes/plates/sections in accordance with
the ISO 630 series, the EN 10025 series with a maximum carbon equivalent (CE) value of 0,45. For circular
[15], [16]
hollow sections, ASTM A106 and API 5L may apply.
The CE value shall be calculated using Formula (1):
%%Mn Cr ++%%Mo VN% i% + Cu
CE =+%C + + (1)
65 15
where,
C is carbon;
Mn is manganese;
Cr is chromium;
Mo is molybdenum;
V is vanadium;
Cu is copper.
If the full chemical composition is not reported, the alternative CE Formula (2) may be used.
+%Mn
CE =+%C + 00, 4 (2)
The material certificate for the anode cores shall meet at least the requirements for a declaration of
compliance with the order (doc
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