SIST EN ISO 13174:2013

SLOVENSKI STANDARD
01-maj-2013
1DGRPHãþD
SIST EN 13174:2003
.DWRGQD]DãþLWD]DSULVWDQLãNHQDSHOMDYH,62
Cathodic protection of harbour installations (ISO 13174:2012)
Kathodischer Korrosionsschutz für Hafenbauten (ISO 13174:2012)
Protection cathodique des installations portuaires (ISO 13174:2012)
Ta slovenski standard je istoveten z: EN ISO 13174:2012
ICS:
25.220.40 Kovinske prevleke Metallic coatings
47.020.01 Splošni standardi v zvezi z General standards related to
ladjedelništvom in shipbuilding and marine
konstrukcijami na morju structures
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 13174
NORME EUROPÉENNE
EUROPÄISCHE NORM
December 2012
ICS 77.060; 47.020.99 Supersedes EN 13174:2001
English Version
Cathodic protection of harbour installations (ISO 13174:2012)
Protection cathodique des installations portuaires (ISO Kathodischer Korrosionsschutz für Hafenbauten (ISO
13174:2012) 13174:2012)
This European Standard was approved by CEN on 18 December 2012.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2012 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 13174:2012: E
worldwide for CEN national Members.

Contents Page
Foreword . 3
Foreword
This document (EN ISO 13174:2012) has been prepared by Technical Committee CEN/TC 219 “Cathodic
protection", the secretariat of which is held by BSI, in collaboration with Technical Committee ISO/TC 156
"Corrosion of metals and alloys".
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 June 2013, and conflicting national standards shall be withdrawn at
the latest by June 2013.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 13174:2001.
According to the CEN/CENELEC Internal Regulations, the national standards organisations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech
Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.
INTERNATIONAL ISO
STANDARD 13174
First edition
2012-12-15
Cathodic protection of harbour
installations
Protection cathodique des installations portuaires
Reference number
ISO 13174:2012(E)
©
ISO 2012
ISO 13174:2012(E)
© ISO 2012
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any
means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the
address below or ISO’s member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
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Published in Switzerland
ii © ISO 2012 – All rights reserved

ISO 13174:2012(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
1.1 General . 1
1.2 Structures . 1
1.3 Materials . 1
1.4 Environment . 1
1.5 Safety and environment protection . 2
2 Normative references . 2
3 Terms and definitions . 2
4 Competence of personnel . 4
5 Design basis . 5
5.1 Objectives. 5
5.2 Cathodic protection criteria . 5
5.3 Design parameters . 6
5.4 Electrical current demand . 7
5.5 Cathodic protection systems . 9
5.6 Electrical continuity .11
5.7 Interactions .11
6 Impressed current systems .12
6.1 Objectives.12
6.2 Design considerations.12
6.3 Equipment considerations .13
7 Galvanic anode systems .16
7.1 Objectives.16
7.2 Design .16
7.3 Materials .16
7.4 Location of anodes .17
7.5 Installation .17
8 Commissioning, operation and maintenance .18
8.1 Objectives.18
8.2 Commissioning: galvanic systems .18
8.3 Commissioning: Impressed current systems .18
8.4 Operation and maintenance .19
9 Documentation .20
9.1 Objectives.20
9.2 Impressed current system .20
9.3 Galvanic anodes system .21
Annex A (informative) Guidance for current requirements for cathodic protection of
harbour installations .22
Annex B (informative) Anode resistance, current and life determination .24
Annex C (informative) Typical electrochemical characteristics of impressed current anodes .29
Annex D (informative) Guidance related to the design process .30
Bibliography .32
ISO 13174:2012(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International
Standards adopted by the technical committees are circulated to the member bodies for voting.
Publication as an International Standard requires approval by at least 75 % of the member bodies
casting a vote.
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.
ISO 13174 was prepared by the European Committee for Standardization (CEN) Technical Committee
CEN/TC 219, Cathodic protection, in collaboration with Technical Committee ISO/TC 156, Corrosion of
metals and alloys, in accordance with the Agreement on technical cooperation between ISO and CEN
(Vienna Agreement).
ISO 13174 cancels and replaces EN 13174:2001, which has been technically revised.
iv © ISO 2012 – All rights reserved

ISO 13174:2012(E)
Introduction
Cathodic protection is applied, sometimes in conjunction with protective coatings, to protect the
external surfaces of steel harbour installations and appurtenances from corrosion due to seawater,
brackish water, saline mud or soil fill.
Cathodic protection works by supplying sufficient direct current to the immersed external surface of
the structure to change the steel to electrolyte potential to values where corrosion is insignificant.
The general principles of cathodic protection in seawater are detailed in ISO 12473. The general
principles of cathodic protection in soils are detailed in EN 12954.
INTERNATIONAL STANDARD ISO 13174:2012(E)
Cathodic protection of harbour installations
1 Scope
1.1 General
This International Standard defines the means to be used to ensure that cathodic protection is efficiently
applied to the immersed and driven/buried metallic external surfaces of steel port, harbour, coastal and flood
defence installations and appurtenances in seawater and saline mud to provide protection from corrosion.
1.2 Structures
This International Standard specifies cathodic protection of fixed and floating port and harbour
structures. This includes piers, jetties, dolphins (mooring and berthing), sheet or tubular piling, pontoons,
buoys, floating docks, lock and sluice gates. It also specifies cathodic protection of the submerged areas
of appurtenances, such as chains attached to the structure, when these are not electrically isolated from
the structure.
This International Standard is to be used in respect of cathodic protection systems where the anodes are
exposed to water or saline mud. For buried areas, typically in soil or sand filled areas behind piled walls
or within filled caissons, which may be significantly affected by corrosion, specific cathodic protection
design and operation requirements are defined in EN 12954, the anodes being exposed to soils.
This International Standard does not cover the cathodic protection of fixed or floating offshore structures
(including offshore loading buoys), submarine pipelines or ships.
This International Standard does not include the internal protection of surfaces of any components such
as ballast tanks, internals of floating structures flooded compartments of lock and sluice gates or the
internals of tubular steel piles.
1.3 Materials
This International Standard covers the cathodic protection of structures fabricated principally from
bare or coated carbon and carbon manganese steels.
As some parts of the structure may be made of metallic materials other than carbon steels, the cathodic
protection system should be designed to ensure that there is a complete control over any galvanic coupling
and minimize risks due to hydrogen embrittlement or hydrogen-induced cracking (see ISO 12473).
This International Standard does not address steel reinforced concrete structures (see ISO 12696).
1.4 Environment
This International Standard is applicable to the whole submerged zone in seawater, brackish waters and
saline mud and related buried areas which can normally be found in port, harbour, coastal and flood
defence installations wherever these structures are fixed or floating.
For surfaces which are alternately immersed and exposed to the atmosphere, the cathodic protection
is only effective when the immersion time is long enough for the steel to become polarized. Typically,
effective cathodic protection is achieved for all surfaces below mid tide.
For structures such as sheet steel and tubular steel piles that are driven into the sea bed or those that
are partially buried or covered in mud, this International Standard is also applicable to the surfaces
buried, driven and exposed to mud which are intended to receive cathodic protection along with surfaces
immersed in water.
ISO 13174:2012(E)
Cathodic protection may also be applied to the rear faces of sheet steel piled walls and the internal
surfaces of filled caissons. Cathodic protection of such surfaces is specified by EN 12954.
This International Standard is applicable to those structures which are, or may be in the future, affected
by “Accelerated Low Water Corrosion” (ALWC) and other more general forms of microbial corrosion
(MIC) or other forms of so-called “concentrated corrosion” associated with galvanic couples, differential
aeration and other local corrosion influencing parameters
NOTE Information is available in BS 6349-1:2000, Clause 59 and CIRIA C634 (see Bibliography)
1.5 Safety and environment protection
This International Standard does not address safety and environmental protection aspects associated
with cathodic protection to which national or international regulations apply.
2 Normative references
The following referenced documents are indispensable for the application 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 12473, General principles of cathodic protection in sea water
EN 12496, Galvanic anodes for cathodic protection in seawater and saline mud
ISO 12696, Cathodic protection of steel in concrete
EN 12954, Cathodic protection of buried or immersed metallic structures – General principles and application
for pipelines
EN 13509, Cathodic protection measurement techniques
EN 50162, Protection against corrosion by stray current from direct current systems
3 Terms and definitions
For the purposes of this document, the terms and definitions in ISO 12473 and the following apply.
3.1
accelerated low water corrosion
ALWC
localised corrosion generally found on the sea side at or just below the LAT level of structures, but can
be present at all immersed levels
Note 1 to entry: This phenomenon is associated with microbiologically influenced corrosion (MIC) and generally
quiescent conditions. (See CIRIA C634.) Corrosion rates, without cathodic protection, can be as high as 2 mm/side/
year and the corrosion is typically localized as large, open pitting
3.2
atmospheric zone
zone located above the splash zone, i.e. above the level reached by the normal swell, whether the
structure is moving or not
3.3
buried zone
zone located under the mud line or in soil or fill
3.4
cathodic protection zone
that part of the structure which can be considered independently with respect to cathodic protection design
2 © ISO 2012 – All rights reserved

ISO 13174:2012(E)
3.5
coating breakdown factor
F
ratio of cathodic current density for a coated metallic material to the cathodic current density of the
bare material
3.6
driving voltage
difference between the structure/electrolyte potential and the anode/electrolyte potential when the
cathodic protection is operating
3.7
HAT
level of highest astronomical tide
3.8
immersed zone
zone located above the mud line and below the extended tidal zone or the water line at a draught
corresponding to the normal working conditions
3.9
LAT
level of lowest astronomical tide
3.10
MTL
mean tide level (also known as MSL mean sea level or MWL mean water level)
3.11
microbial corrosion
corrosion associated with the action of micro-organisms present in the corrosion system
Note 1 to entry: Also called microbiologically influenced corrosion (MIC).
3.12
ROV
remotely operated vehicle
3.13
piling
foundation, tubular or sheet steel element forming part or whole of a harbour structure
3.14
splash zone
the elevation of the structure which is intermittently wet and dry due to the wave action just above the HAT
3.15
submerged zone
zone including the buried zone, the immersed zone, the transition
zone and the lower part of the tidal zone under the MWL
See Figure 1.
3.16
transition zone
zone located below LAT and including the possible level inaccuracy of the structure installation which is
affected by a higher oxygen content due to normal swell or tidal movement
ISO 13174:2012(E)
Figure 1 — Schematic representation of levels and zones in seawater environment
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 appropriate level of competence for the tasks undertaken. This competence should be
independently assessed and documented.
NOTE 1 EN 15257 constitutes a suitable method of assessing and certifying competence of cathodic protection
personnel which may be utilized.
NOTE 2 Competence of cathodic protection personnel to the appropriate level for tasks undertaken should be
demonstrated by certification in accordance with EN 15257 or by another equivalent prequalification procedure.
4 © ISO 2012 – All rights reserved

ISO 13174:2012(E)
5 Design basis
5.1 Objectives
The objective of a cathodic protection system is to deliver sufficient current to each part of the structure
and appurtenances and to distribute this current so that the steel/water potential of each part of the
structure is within the limits given by the protection criteria (see 5.2).
Steel/water potentials should be as uniform as possible over the whole structure. This may be achieved
only if distribution of the protective current over the structure during normal service conditions allows.
Uniform levels of cathodic protection may be difficult to achieve in some areas or parts of structures
such as chains, for which a supplementary cathodic protection system may be considered if it is intended
to attempt to provide full cathodic protection to them.
The cathodic protection system for a fixed or floating structure belonging to harbour installations may
be combined with a coating system, even though some appurtenances, such as chains, may not benefit
from the use of coatings. Extensive coating damage may also occur to buried areas of piles and steel
sheet pile walls which are driven into position during installation.
Dielectric shields may be used in conjunction with anodes; particularly impressed current anodes, to
minimize the risk of local over-protection and to improve the distribution of current from the anodes.
The cathodic protection system should be designed either for the life time of the structure or for a period
corresponding to a planned maintenance or (if applicable) dry-docking interval. Alternatively when it
is not feasible to design the cathodic protection system for the life of the structure or if dry-docking is
not possible, the system should be designed for easy replacement of cathodic protection components,
typically using divers or a ROV.
The above objectives should be achieved by the design of a cathodic protection system using impressed
current or galvanic anode systems or a combination of both.
The design, the installation, the energising, the commissioning, the long-term operation and the
documentation of all of the elements of cathodic protection systems shall be fully recorded.
Each step shall be undertaken in accordance with a fully documented quality plan.
NOTE ISO 9001 constitutes a suitable Quality Management Systems Standard which may be utilized.
Each stage of the design shall be checked and the checking shall be documented.
Each stage of the installation, energising, commissioning and operation shall be the subject of appropriate
visual, mechanical and/or electrical testing and all testing shall be documented.
All test instrumentation shall have valid calibration certificates traceable to national or International
Standards of calibration.
The documentation shall constitute part of the permanent records for the works.
5.2 Cathodic protection criteria
The criteria for cathodic protection are detailed in ISO 12473.
The criterion for protection of steel in aerobic seawater is a polarized potential more negative than
−0,80 V measured with respect to silver/silver chloride/seawater reference electrode (Ag/AgCl/seawater
reference electrode). This corresponds approximately to + 0,23 V when measured with respect to pure
zinc electrode (e.g. alloy type Z2 as defined in EN 12496) or + 0,25 V when measured with respect to zinc
electrode made with galvanic anode alloy types Z1, Z3 or Z4 as specified in EN 12496.
The criterion for protection of steel in anaerobic environments in seawater and sea bed muds which
contain active sulfate reducing bacteria or support other microbial corrosion (MIC) species, including
those associated with Accelerated Low Water Corrosion (ALWC), is a polarized potential more negative
ISO 13174:2012(E)
than −0,90 V measured with respect to silver/silver chloride/seawater reference electrode (Ag/AgCl/
seawater reference electrode).
A negative limit of −1,10 V (Ag/AgCl/seawater reference electrode) is generally recommended to prevent
coating disbondment and/or increase in fatigue propagation rates.
Where there is a possibility of hydrogen embrittlement of steels or other metals which may be adversely
affected by cathodic protection to excessively negative values, an additional less negative potential limit
shall be defined and observed. If not enough documented for a given material, this specific negative
potential limit shall be determined relative to the metallurgical and mechanical conditions by mechanical
testing at the limit polarized potential. For conventional steels, this limit is −1,10 V (Ag/AgCl/seawater
reference electrode). Refer to ISO 12473 for more details.
These values also apply to steel in brackish waters but the errors due to variations in salinity when
using Ag/AgCl/seawater reference electrodes shall be corrected when necessary as detailed in 6.3.4.
The recommended metal/water potential limits for a range of metals and alloys in seawater are listed
in ISO 12473.
NOTE The protection criteria and limit values are polarized potentials without IR errors. IR errors, caused
by cathodic protection current flowing though resistive electrolyte and surface films on the protected surface,
are generally considered insignificant in marine applications. Potential measurements using “Instant OFF”
techniques or “coupon Instant OFF” techniques may be necessary in applications described in this International
Standard to demonstrate the achievement of the above protection criteria (see EN 13509). Particular attention
should be given to this in brackish waters and mud applications or close to impressed current anodes.
5.3 Design parameters
5.3.1 General
The design of a cathodic protection system should be made in order that each structure subdivision and
anode zone is supplied with the cathodic protection current necessary to provide cathodic protection to
meet the criteria in 5.2 for all service conditions.
5.3.2 Structure subdivision
Structures to be protected should be divided into different cathodic protection zones, which can be
considered independently with respect to cathodic protection design, although they may not necessarily
be electrically isolated.
NOTE 1 For a non-floating structure such as a dolphin, the area of piling can be divided into two main cathodic
protection zones: the immersed or wetted cathodic protection zone and the buried cathodic protection zone. This
division is related to the different current demands of the two zones. The high current demand of the immersed
or wetted cathodic protection zone is due to the velocity of water movement, salinity, oxygen content and
temperature. In the buried cathodic protection zone the current demand will be reduced due to the environment.
NOTE 2 For buoys, a single zone is generally considered sufficient to cover the immersed body of the buoy and
the influenced part of the mooring chain(s).
5.3.3 Description of cathodic protection zone
Each cathodic protection zone may consist of several components, the parameters of which should be
fully described including material (steel, cast iron, etc.), surface area and coating characteristics (type,
lifetime and coating breakdown factor).
6 © ISO 2012 – All rights reserved

ISO 13174:2012(E)
5.3.4 Service conditions
The design of the cathodic protection system(s) depends on service conditions which include lifetime,
environment and operating conditions.
— Lifetime: Either the whole design life of the structure or the planned maintenance period(s)
should be used.
— Environment: The seawater, sea bed, or estuarine environment properties to which the structure is
exposed should be established (see ISO 12473 and Annex A).
— Operating conditions: The cathodic protection design normally considers only the static conditions
of the structure because the durations when dynamic conditions prevail are generally negligible.
5.4 Electrical current demand
5.4.1 General
The current density for each component shall be selected to achieve the protection criteria specified in
5.2 for the conditions outlined in 5.3.
The current demand of each metallic component of the structure is the result of the product of its surface
area exposed to the electrolyte multiplied by the selected current density (see Annex A).
5.4.2 Protection current density for bare steel
The selected current density may not be the same for all components of the structure as the materials,
coatings, environment and service conditions may be variable.
The selection of design current densities should be based on experiences gained from similar structures
in a similar environment or from specific tests and measurements.
NOTE 1 The current density depends on the kinetics of electrochemical reactions and varies with parameters
such as the protection potential, surface condition, seawater resistivity, dissolved oxygen in seawater, seawater
velocity at the steel surface, temperature.
For optimising the design, the following should be specified:
— initial current density necessary to achieve initial polarization of the structure;
— maintenance current density necessary to maintain polarization of the structure;
— final current density for possible repolarisation of the structure, e.g. after severe storms or
cleaning operations.
NOTE 2 As the initial polarization preceding steady-state conditions is normally short compared to the design life,
the average current density over the lifetime of the structure is usually very close to the maintenance current density.
If the structure has established ALWC or microbial corrosion the initial current density necessary for
polarization may be greater than that necessary to polarize steel unaffected by microbial corrosion. In
addition, the time to reach steady-state polarization may be considerably extended by the presence of
previously active ALWC/microbial corrosion colonies. The design of cathodic protection of structures
affected by ALWC shall take these factors into account (see Annex A).
The (average) maintenance current density shall be used to calculate the minimum mass of galvanic
anode material or the capacity (anode current output x life) of impressed current anodes necessary
to maintain cathodic protection throughout the design life. The initial or final current density values
will normally determine the peak current output of the cathodic protection system; for galvanic anode
systems the anode numbers and shape will generally be determined by these parameters and for
impressed current systems the maximum output rating of anodes and power supplies will generally be
determined by these parameters.
ISO 13174:2012(E)
Typical values of current densities as used for bare steel are given in Annex A.
5.4.3 Protection current density for coated steel
The cathodic protection system may be combined with suitable coating systems. Effective coatings can
significantly reduce current density and improve the current distribution over the surface. The cathodic
protection design shall reflect the increase in current demand as the coating deteriorates.
Coatings are not necessary for effective cathodic protection.
The reduction of necessary current density for coated steel compared with bare steel may be in a ratio of
100 to 1 or even more. However, the current density will increase with time as the coating deteriorates.
For harbour installations cathodic protection of bare steel may present a lower full life cost than cathodic
protection of coated steel. Corrosion protection above the mid tide level is not possible by cathodic
protection; coatings may be necessary above the mid tide level to deliver the required structure design
life or aesthetics.
An initial coating breakdown factor related mainly to mechanical damage occurring during the
fabrication and installation of the structure should be included in the design. A coating deterioration
rate (i.e. an increase of the coating breakdown factor) should be selected to take into account the coating
ageing and possible mechanical damage occurring to the coating during the design life of the cathodic
protection system which should itself be related to the lifetime of the structure or corresponding to the
dry-docking or maintenance period(s).
These values are strongly dependent on the actual coating selection, surface preparation, coating
application, construction and operational conditions.
Due to possible interactions between the cathodic protection and the coating, all coatings to be used in
combination with cathodic protection should be tested beforehand to establish that they have acceptable
resistance to cathodic disbondment.
Guidelines for the values of coating breakdown factors ( f ) are given in Annex A.
c
The current density needed for the protection of coated steel is equal to the product of the current
density for the bare steel and the coating breakdown factor.
JJ=⋅ f
cb c
where
J is the protection current density for coated steel, in amperes per square metre;
c
J is the protection current density for bare steel, in amperes per square metre;
b
f is the coating breakdown factor which varies with time due to ageing and mechanical damage:
c
f = 0 for a perfectly insulating coating.
c
f = 1 for a bare structure.
c
This formula should be applied for each individual component or zone as defined in 5.3 where the
coating, or the current density for bare steel, may be different.
8 © ISO 2012 – All rights reserved

ISO 13174:2012(E)
5.4.4 Protection current demand
The current demand shall be calculated to optimize the mass and size of galvanic anodes, or the capacity
of impressed current systems. The protection current demand I of each component (element) of the
e
structure to be cathodically protected is equal to:
IA=⋅ J
ee ce
where
A is the surface area of the individual zone, in square metres;
e
J is the individual protection current density for the component considered, in amperes per
ce
square metre.
The protection current demand I of each cathodic protection zone is therefore equal to the sum of
z
current demand of each component included in the cathodic protection zone:
z
II=
ze∑
where I is the protection current demand of each component included in the cathodic protection
e
zone, in amperes.
NOTE 1 For current demand determination, the full range of astronomical tide should be considered but it
is normal to consider the immersed zone of the cathodic protection (CP) system to extend from mean sea level
(mid tide) to sea bed. In the design of galvanic anode systems, due to their ability to increase current output as
the structure/electrolyte potentials become less negative and due to the averaging effect of high and low tides
on current demand, the area used in the calculation of I above may be limited to the area below mean sea level
e
(MSL). In the design of impressed current systems, due to their need to be sized for the maximum current demand,
the area used in the calculation of I above may include the area to HAT.
e
NOTE 2 For sheet steel piled walls without cathodic protection of the rear face, allowances should be made if
the anodes are placed at locations where current will flow to the rear faces. Particular consideration should be
given to ends of sheet steel piled walls which are not connected to other cathodically protected piles. See Annex A.
NOTE 3 Allowances should be made for metallic components connected to the structure which may receive some
cathodic protection current, such as electrical earthing systems or utility service pipes (water and gas). See Annex A.
An estimate of the current demand of chains which are not electrically insulated from the structure
should be made and added to I when applicable. This is necessary to ensure an efficient cathodic
z
protection design, even if the potential achieved on the chains (and their protection) will depend on the
actual quality of the electrical continuity between the chains and the structure, and between the links
of each chain.
Current demand determination calculations shall include steel items such as fenders and ladders which
are part of the structure and within the submerged zones of the structure.
5.5 Cathodic protection systems
Two types of cathodic protection systems are used:
— impressed current,
— galvanic anode.
Sometimes a combination of both systems is used (hybrid).
ISO 13174:2012(E)
The choice of the most appropriate system depends on a series of factors (see ISO 12473).
NOTE In general, for harbour installations, galvanic anode systems are preferred for their proven reliability,
simple robust construction, low maintenance requirements and minimal interaction with berthed vessels.
Impressed current systems are preferred only for those structures that will be provided with a dedicated cathodic
protection monitoring, control and maintenance resource, which have available electrical power and generally to
those where there is a high current demand. Harbours in brackish water may require impressed current systems
if the water resistivity is frequently above that in which galvanic anodes can operate reliably and effectively. It
is recommended that the structure Owner/Operator is appraised of the full life personnel demands and costs of
cathodic protection monitoring, control and maintenance during the choice between galvanic anode systems and
impressed current systems. For the protection of the rear face of sheet steel piled walls and caisson internals
impressed current can be both reliable and the most practical system.
For a cathodic protection system using galvanic anodes, the size and shape of the anodes shall be
determined using Ohm’s law.
ΔU
I =
a
R
where
I is the anode current output (A);
a
ΔU is the driving voltage (V);
R is the circuit resistance (Ω).
The circuit resistance is assumed to be approximately equal to the electrolyte resistance, which is called
“anode resistance” as the cathode (structure) resistance to the electrolyte is generally very small.
The anode resistance is a function of the resistivity of the anodic environment and of the geometry
(form and size) of the anode. Empirical formulae may be used for the evaluation of the anode resistance
such as those given in B.1.
For an impressed current system, the direct current (DC) output voltage of the power source shall
be higher than the sum of the voltage drops in all the components of the circuit; cables, electrolyte
(generally considered as the anode resistance) and the anode/cathode back EMF (i.e. the potential
difference between anode and cathode in the electrolyte without current).
The voltage between anode and electrolyte should not exceed a maximum acceptable value depending
on the material of the anode.
NOTE Recommended figures for maximum acceptable voltages are given in Annex C.
Minimum anodic current densities may be necessary in some cases (see Annex C).
The number and location of the anodes shall
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