ISO 20313:2018

Ships and marine technology — Cathodic protection of ships

ISO 20313:2018 specifies protection criteria, and makes recommendations for design and specifications for both impressed current and galvanic anode cathodic protection systems for ships. Cathodic protection of external hull and ballast tanks are included. ISO 20313:2018is applicable to the immersed sections of hulls and tanks containing seawater for ships, boats, and other self-propelled floating vessels. It includes fixtures generally encountered on ship hulls such as: - rudders; - propellers; - shafts; - stabilizers; - thrusters; - sea chests; - water intakes (up to the first valve). ISO 20313:2018 does not cover protection of floating structures that are not self-propelled. ISO 20313:2018 is applicable to the cathodic protection of ship hulls fabricated principally from carbon manganese or low-alloy steels including fixtures of other ferrous or non-ferrous alloys such as stainless steels and copper alloys, etc. ISO 20313:2018 is applicable to both coated and bare hulls and tanks; most hulls and tank internals are coated. ISO 20313:2018 is not applicable to the cathodic protection of hulls principally made of other materials such as aluminium alloys, stainless steels or concrete. ISO 20313:2018 is applicable to the hull and fixtures in seawater and all waters which could be encountered during a ship's world-wide deployment.

Navires et technologie maritime — Protection cathodique des navires

General Information

• Status: Published
• Publication Date: 07-Jan-2018
• ICS: 47.020.10 - Hulls and their structure elements
• Technical Committee: ISO/TC 8/SC 8 - Ship design
• Drafting Committee: ISO/TC 8/SC 8 - Ship design
• Current Stage: 9093 - International Standard confirmed
• Completion Date: 21-Jul-2023

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 20313
First edition
2018-01
Ships and marine technology —
Cathodic protection of ships
Navires et technologie maritime — Protection cathodique des navires
Reference number
ISO 20313:2018(E)
©
ISO 2018

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ISO 20313:2018(E)

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© ISO 2018, Published in Switzerland
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ISO 20313:2018(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Competence of personnel . 3
5 Design basis . 3
5.1 General . 3
5.2 Cathodic protection criteria . 4
5.3 Design process. 5
5.4 Design considerations. 6
5.4.1 Cathodic protection zones of ship hull (external) . 6
5.4.2 Internal cathodic protection zones . 6
5.4.3 Component characteristics . 7
5.4.4 Service conditions . . . 7
5.5 Current demand . 7
5.5.1 General. 7
5.5.2 Design current density for bare steel . 8
5.5.3 Design current density for coated steel . 8
5.5.4 Current demand . 9
5.6 Cathodic protection systems .11
5.7 Electrical continuity .12
5.8 Fitting out period .12
6 Impressed current system .12
6.1 Objectives.12
6.2 Design considerations.12
6.3 Equipment considerations .13
6.3.1 Power source, monitoring and control systems .13
6.3.2 Anodes .15
6.3.3 Dielectric shields . . .16
6.3.4 Permanent reference and measurement electrodes .16
6.3.5 Cables and terminations.16
6.3.6 Cofferdams .17
7 Galvanic anode systems .17
7.1 Objectives.17
7.2 Design considerations.18
7.3 Anode materials .18
7.4 Factors determining the anode current output and operating life .19
7.5 Location of anodes .19
7.5.1 External hull surfaces .19
7.5.2 Internal surfaces .20
8 Commissioning, operation and maintenance .23
8.1 Objectives.23
8.2 Measurement procedures.23
8.3 Commissioning: Galvanic systems .24
8.4 Commissioning: Impressed current systems .24
8.4.1 Visual inspection .24
8.4.2 Pre-energizing measurements .25
8.4.3 Initial energizing .25
8.4.4 Performance assessment .25
8.5 Operation and maintenance .26
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ISO 20313:2018(E)

8.5.1 General.26
8.5.2 Galvanic anode systems .26
8.5.3 Impressed current systems .26
8.5.4 Interaction with adjacent structures .27
8.6 Dry-docking period .27
9 The protection of ships' hulls during fitting out and when laid up .28
9.1 Fitting out period .28
9.2 Lay-up period .28
10 Documentation .28
10.1 Objectives.28
10.2 Galvanic anode systems .29
10.3 Impressed current system .29
Annex A (informative) Impressed current system for external hulls of ships based on two
cathodic protection zones .31
Annex B (informative) Guidance on design current density values for cathodic protection of
ship’s hulls and tanks .32
Annex C (informative) Anode resistance, current and life duration formulae .34
Annex D (informative) Electrical bonding systems .39
Annex E (informative) Monitoring of electrical bonding of a ship's propeller .41
Annex F (informative) Impressed current system for ships based on an aft (stern) system only .42
Annex G (informative) Location of galvanic anodes in the stern area .43
Annex H (informative) Electrochemical characteristics of impressed current anodes .44
Annex I (informative) Cofferdam arrangements .46
Annex J (informative) Cathodic protection of a moored ship using suspended galvanic anodes .49
Annex K (informative) Anode/cathode separation (dielectric shield) calculations .51
Annex L (Informative) Galvanic anode specifications .52
Annex M (informative) Use of portable coupons .55
Bibliography .56
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ISO 20313:2018(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
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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).
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URL: www.iso.org/iso/foreword.html.
This document was prepared by ISO/TC 8 Ships and marine technology, SC 8, Ship design.
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ISO 20313:2018(E)

Introduction
Cathodic protection is applied to ships to protect the immersed sections of the vessel from corrosion.
This includes the external hull surface and the internal surfaces of tanks containing seawater, e.g.
ballast tanks.
Cathodic protection, often in conjunction with coatings, can be applied by impressed current, galvanic
anode techniques or a combination of both.
Cathodic protection works by applying direct current to the immersed surface to change the steel-to-
electrolyte potential to values where the rate of corrosion is considered insignificant.
The General Principles of Cathodic Protection in Seawater are described in ISO 12473.
Hull penetrations and cofferdams necessary for cathodic protection generally require Classification
Society approval.
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INTERNATIONAL STANDARD ISO 20313:2018(E)
Ships and marine technology — Cathodic protection of ships
1 Scope
This document specifies protection criteria, and makes recommendations for design and specifications
for both impressed current and galvanic anode cathodic protection systems for ships. Cathodic
protection of external hull and ballast tanks are included.
This document is applicable to the immersed sections of hulls and tanks containing seawater for ships,
boats, and other self-propelled floating vessels. It includes fixtures generally encountered on ship hulls
such as:
— rudders;
— propellers;
— shafts;
— stabilizers;
— thrusters;
— sea chests;
— water intakes (up to the first valve).
It does not cover protection of floating structures that are not self-propelled.
This document is applicable to the cathodic protection of ship hulls fabricated principally from carbon
manganese or low-alloy steels including fixtures of other ferrous or non-ferrous alloys such as stainless
steels and copper alloys, etc.
This document is applicable to both coated and bare hulls and tanks; most hulls and tank internals
are coated.
This document is not applicable to the cathodic protection of hulls principally made of other materials
such as aluminium alloys, stainless steels or concrete.
This document is applicable to the hull and fixtures in seawater and all waters which could be
encountered during a ship’s world-wide deployment.
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 8044, Corrosion of metals and alloys — Basic terms and definitions
ISO 9606-1, Qualification testing of welders — Fusion welding — Part 1: Steels
ISO 12944-1, Paints and varnishes — Corrosion protection of steel structures by protective paint systems —
Part 1: General introduction
ISO 12944-2, Paints and varnishes — Corrosion protection of steel structures by protective paint systems —
Part 2: Classification of environments
ISO 15607, Specification and qualification of welding procedures for metallic materials — General rules
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ISO 20313:2018(E)

ISO 15609-1, Specification and qualification of welding procedures for metallic materials — Welding
procedure specification — Part 1: Arc welding
ASTM B418, Type 1 Standard specification for cast and wrought galvanic zinc anodes
EN 12496, Galvanic anodes for cathodic protection in seawater and saline mud
EN 50162, Protection against corrosion by stray current from direct current systems
IMCA DO45, Code of Practice for Safe Use of Electricity Underwater
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 8044 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at http://www.iso.org/obp
3.1
system life
design life of the cathodic protection system
3.2
anode design life
stated period for which the anode is required to be fully functional
3.3
immersed zone
zone located below the water line at draught corresponding to normal working conditions
3.4
underwater hull
immersed surface area of the hull at any given time
Note 1 to entry: Used to calculate current demand.
3.5
boot topping
section of the hull between light and fully loaded conditions
Note 1 to entry: Boot topping may be intermittently an immersed part of the structure which can be considered
independently with respect to the cathodic protection design. A single zone can comprise a variety of components
with differing design parameters.
3.7
submerged zone
zone including the immersed zone and the boot topping
3.8
driving voltage
difference between the steel-to-electrolyte potential and the sacrificial anode-to-electrolyte potential
when the cathodic protection is operating
3.9
closed circuit potential
potential measured at a galvanic anode when a current is flowing between the anode and the surface
being protected
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ISO 20313:2018(E)

3.10
light ballast draught
draught when the ship is in light ballast conditions
4 Competence of personnel
Personnel who undertake the design, supervision of installation, commissioning, supervision of
operation, measurements, monitoring and supervision of maintenance of cathodic protection systems
shall have the relevant level of competence for the tasks to be undertaken. This competence shall be
independently assessed and documented. On-board routine measurements can be performed by non-
specialists but the results interpreted by a cathodic protection specialist.
NOTE ISO 15257 and the NACE training and Certification Programme constitute suitable methods of
assessing and certifying competence of cathodic protection specialists.
5 Design basis
5.1 General
5.1.1 The objective of a cathodic protection system is to deliver sufficient current to protect each part
of the structure and fixtures and distribute this current so that the structure-to-electrolyte potential of
each part of the structure is within the limits given by the protection criteria. Electrolytic anti-fouling
systems cannot be assumed to provide cathodic protection to the sea chest and internal pipework. The
impact of these systems on the overall cathodic protection design and control shall not be neglected. The
designer shall consider the location of anti-fouling system anodes, current outputs, current attenuation,
structure isolation (if any), local sacrificial anodes and current exchange across any hull grating in the
overall cathodic protection design.
5.1.2 Potentials should be as uniform as possible over the whole submerged surface. This objective is
best achieved by adequate distribution of the protective current over the structure during the vessel’s
normal operating service conditions. This can be difficult to achieve in some areas of the structure (e.g.
water intakes, thrusters, and sea chests) where specific provisions can be required.
5.1.3 Cathodic protection for a ship is generally combined with a protective coating system. Although
some fixtures, (e.g. propellers), are not usually coated.
5.1.4 The cathodic protection system should be designed to mitigate galvanic coupling. The minimum
protection potentials (most positive potential) listed in Table 1 shall be achieved on all steel surfaces
adjacent to more noble materials.
5.1.5 Cathodic protection within sea chests can adversely affect, by stray current interaction, box
coolers in sea chests if the box coolers are electrically isolated from the sea chest. Box coolers are
often manufactured from copper nickel alloy tubes. The possibility of interaction shall be considered
when designing the cathodic protection requirements for the sea chest. These considerations should
include methods of controlling corrosion on steel surfaces shielded by the cooler, whether the cooler is
electrically isolated or not. The designer should also resolve the adequacy of any cooler manufacturer
installed anodes. These may not last the intended service interval. The principles of concern for sea chest
coolers shall be extended to copper-nickel keel coolers that are similarly installed.
Electrochemical anti-fouling systems are often used within sea chests to prevent the fouling of seawater
intake systems. The possibility of interaction between the anti-fouling system and the cathodic
protection system should be considered in the design and installation of the anti-fouling system.
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ISO 20313:2018(E)

5.1.6 The cathodic protection system shall be designed either for the life of the ship or on the basis of
proposed dry-docking or maintenance intervals. The design life should be agreed between the cathodic
protection system designer and the ship operator/owner.
NOTE Galvanic anodes can be sized for short periods such as dry-docking intervals. Impressed current
materials can last longer, but not necessarily for the whole of the working life of the vessel, without replacement.
5.1.7 Design, installation, energizing, commissioning, and long-term operation of all the elements of
the cathodic protection system shall be fully documented.
5.1.8 Every element of the work shall be undertaken in accordance with an approved, fully documented,
quality plan.
5.1.9 Each stage of the design shall be verified and the checking shall be documented.
5.1.10 ISO 9001 is a suitable Quality Management Systems Standard that can be used.
5.2 Cathodic protection criteria
5.2.1 The accepted criterion for the protection of bare steel in aerated seawater is a protection
potential more negative than:
— −0,80 V measured with respect to a Ag/AgCl seawater reference electrode;
— +0,23 V measured with respect to a pure zinc electrode;
— +0,25 V measured with respect to a zinc electrode (made with alloy ASTM B418 Type 1 or US
MIL-A-18 001K).
These three values are approximately equivalent.
5.2.2 While Ag/AgCl/Seawater reference electrodes can be used on sea-going vessels, the use of zinc
reference electrodes is an acceptable alternative. Zinc reference electrodes are considered sufficiently
accurate and reliable. (See ISO 12473) (See 6.3.4)
5.2.3 To avoid coating cathodic disbondment a negative limit of −1,1 V with respect to
Ag/AgCl/Seawater reference electrode is recommended for hull coatings. Areas around dielectric shields
and dielectric shields themselves shall be separately qualified to a maximum allowable limit. This limit
can be varied provided that technical justification is provided.
5.2.4 Where there is a possibility of hydrogen embrittlement of steels, or other metals, which may be
adversely affected by cathodic protection at excessively negative values, a less negative potential limit
shall be adopted (See Table 1). If there is insufficient documentation available for a given material,
this specific negative potential limit relative to the metallurgical and mechanical conditions shall be
determined by mechanical testing at the limit polarized potential.
5.2.5 The potential criteria and limit potentials are “polarized” and are expressed without IR errors. IR
errors are a consequence of cathodic protection current flowing in the resistive electrolyte and surface
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ISO 20313:2018(E)

films on the protected structure and are generally considered insignificant in marine cathodic protection
applications that use galvanic anodes.
Table 1 — Cathodic protection limits for materials commonly encountered on ship hulls and
fixtures
Material Most positive potential Most negative potential
(V vs. Ag/AgCl/seawater) (V vs. Ag/AgCl/seawater)
Carbon-manganese and low-alloy steels
with specified minimum yield stress
2
(SMYS) equal or lower than 550 N/mm
  In aerobic environment −0,80 −1,10
  In anaerobic environment and/or steel −0,90 −1,10
temperature >60°C
High strength steels (SMYS higher than −0,80 −0,83 to −0,95 (see NOTE 1)
550 MPa)
Aluminium alloys −0,80 (negative potential swing −1,10
(Al Mg and Al Mg Si) 0,10 V) (See NOTE
...