EN 12954:2019

SLOVENSKI STANDARD
01-januar-2020
Nadomešča:
SIST EN 12954:2003
Splošna načela katodne zaščite vkopanih ali potopljenih kovinskih konstrukcij
General principles of cathodic protection of buried or immersed onshore metallic
structures
Grundlagen des kathodischen Korrosionsschutzes von metallenen Anlagen in Böden
und Wässern
Principes généraux de la protection cathodique des structures métalliques à terre
enterrées ou immergées
Ta slovenski standard je istoveten z: EN 12954:2019
ICS:
25.220.40 Kovinske prevleke Metallic coatings
91.080.10 Kovinske konstrukcije Metal structures
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 12954
EUROPEAN STANDARD
NORME EUROPÉENNE
August 2019
EUROPÄISCHE NORM
ICS 23.040.99; 77.060 Supersedes EN 12954:2001
English Version
General principles of cathodic protection of buried or
immersed onshore metallic structures
Principes généraux de la protection cathodique des Grundlagen des kathodischen Korrosionsschutzes von
structures métalliques à terre enterrées ou immergées metallenen Anlagen in Böden und Wässern
This European Standard was approved by CEN on 28 July 2019.

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, Turkey 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
© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 12954:2019 E
worldwide for CEN national Members.

Contents Page
European foreword . 4
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
4 Abbreviations and symbols . 13
5 Cathodic protection personnel competence . 13
6 Principles and criteria of cathodic protection . 14
6.1 Principles of cathodic protection . 14
6.2 Cathodic protection criteria . 14
Table 1 — Free corrosion potentials, protection potentials and limiting critical potentials of
common metallic materials in soils and waters (except seawater and brackish
water) measured against CSE . 15
6.3 Alternative method . 16
6.3.1 100 mV cathodic potential shift . 16
6.3.2 Other methods . 17
6.4 Criteria in presence of a.c . 17
7 Prerequisites for application of cathodic protection . 17
7.1 General . 17
7.2 Electrical continuity . 17
7.3 Electrical isolation . 17
7.4 External coating . 18
8 Useful data and design considerations . 18
8.1 General . 18
8.2 Structure details . 19
8.3 Service conditions . 19
9 Design . 20
9.1 General . 20
9.2 Design lifetime . 20
9.3 Adjacent structures and external electrical sources . 20
9.4 Electrical continuity/discontinuity . 20
9.5 Protective coatings . 21
9.6 Current demand . 21
9.7 Galvanic anode systems . 22
9.7.1 General considerations . 22
9.7.2 Utilization of galvanic anode systems. 22
9.7.3 Design of a galvanic anode system . 22
9.7.4 Technical considerations and data for the design of a galvanic protection system . 23
Table 2 — Typical chemical compositions of the alloys used for zinc anodes . 24
Table 3 — Typical electrochemical parameters for zinc anodes used in soils. 25
Table 4 — Typical chemical compositions of the alloys used for magnesium anodes . 25
Table 5 — Typical electrochemical parameters for magnesium anodes used in soils . 26
Figure 1 — Current capacity of magnesium alloy versus current density [9] . 27
9.8 A.C. and/or d.c. decoupling devices . 28
9.9 Impressed current cathodic protection (ICCP) system . 28
9.10 Monitoring . 29
9.11 Cable . 29
9.12 Impressed current groundbeds . 30
10 Installation of cathodic protection systems . 31
11 Commissioning . 31
11.1 General . 31
11.2 Preliminary checking . 31
11.3 Start-up . 32
11.4 Assessment of the cathodic protection effectiveness . 32
11.5 Documentations . 33
12 Monitoring, inspection and maintenance . 33
12.1 General . 33
12.2 Monitoring . 34
12.3 Inspection . 35
12.4 Maintenance . 35
Annex A (informative) Corrosion likelihood in soils . 36
Annex B (informative) Reduction of the corrosion rate by using a 100 mV cathodic
polarization — 100 mV cathodic potential shift . 38
B.1 Measurement method during polarization . 38
Figure B.1 — Polarization formation method . 38
B.2 Measurement method during depolarization . 39
Figure B.2 — Polarization decay method . 39
Bibliography . 40

European foreword
This document (EN 12954:2019) has been prepared by 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 February 2020, and conflicting national standards shall
be withdrawn at the latest by February 2020.
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 12954:2001.
This document describes general principles for applying external cathodic protection on onshore metallic
structures in contact with soils, fresh surface waters or underground waters, except those which are
embedded in concrete and those which are in sea-waters or brackish waters.
This edition of EN 12954 does not cover specific applications for on-land pipelines.
NOTE On-land pipeline applications is now completely covered by EN ISO 15589-1 [1].
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, 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, Turkey and the United
Kingdom.
Introduction
Cathodic protection is a technique based on the application of electrochemical principles. It is achieved
by the supply of sufficient direct current to the external surface, such that the metallic structure-to-
electrolyte potential is shifted to more negative values where external corrosion becomes insignificant.
Cathodic protection covers a wide range of materials and equipment and requires a variety of
measurement techniques.
This document is applicable to the protection of external surfaces of all types of buried or immersed
metallic structures. However, in order to allow for structures having specific features with regards to
shape, use, detailed configuration, construction, commissioning or operation, provision has been made
for complementary standards to be used in conjunction with this one to deal with the peculiarities of such
structures.
To achieve effective cathodic protection design installation, commissioning, inspection and maintenance
it is essential that the works are performed by competent personnel.
This document specifies conditions necessary to consider cathodic protection as an efficient method
which can be applied to mitigate corrosion. It is normally used in combination with a coating.
Alternative solutions to those provided in this standard may be applied if it is demonstrated that they
give equivalent effectiveness and they are well documented.
1 Scope
This document describes the general principles for the implementation and management of a system of
cathodic protection against corrosive attacks on structures which are buried or in contact with soils,
surface fresh waters or underground waters, with and without the interference of external electrical
sources. It specifies the protection criteria to be achieved to demonstrate the cathodic protection
effectiveness.
For structures that cannot be electrically isolated from neighbouring influencing structures, it may be
impossible to use the criteria defined in the present document. In this case, EN 14505 will be applied
(see 9.4 “Electrical continuity/discontinuity”).
NOTE To assist in forming a decision whether or not to apply cathodic protection the corrosion likelihood can
be evaluated using informative Annex A which summarizes the requirements of EN 12501-1 [2] and
EN 12501-2 [3].
Cathodic protection of structures immersed in seawater or brackish waters is covered by EN 12473 and
a series of standards more specific for various applications.
Cathodic protection for reinforced concrete structures is covered by EN ISO 12696.
This document is applicable in conjunction with:
— EN ISO 15589-1 for application for buried or immersed cathodically protected pipelines,
— EN 50162 to manage d.c. stray currents,
— EN ISO 18086 to manage corrosion due to a.c. interference from high voltage power sources and a.c.
traction systems,
— EN 13509 for cathodic protection measurement techniques
— EN 50443 to manage protection for touch and step voltage.
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.
EN 12496, Galvanic anodes for cathodic protection in seawater and saline mud
EN 13509, Cathodic protection measurement techniques
EN 14505, Cathodic protection of complex structures
EN 50162, Protection against corrosion by stray current from direct current systems
EN 60079-10-1, Explosive atmospheres – Part 10-1: Classification of areas - Explosive gas atmospheres
(IEC 60079-10-1)
EN ISO 8044, Corrosion of metals and alloys - Basic terms and definitions (ISO 8044)
EN ISO 15257, Cathodic protection - Competence levels of cathodic protection persons - Basis for
certification scheme (ISO 15257)
EN ISO 18086, Corrosion of metals and alloys - Determination of AC corrosion - Protection criteria (ISO
18086)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 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
anaerobic conditions
lack of free oxygen in the electrolyte adjacent to a metallic structure
3.2
anode backfill
added material immediately surrounding a buried anode
3.3
electrical bond
metal conductor, usually copper, connecting two points on the same structure or on different structures
3.4
cathodic protection system
all active and passive components associated with the provision of active external corrosion protection
and its monitoring
Note 1 to entry: Cathodic protection is provided either by impressed current or by galvanic anodes using one or
more stations.
Note 2 to entry: Impressed current and galvanic anode systems consist of all the equipment necessary for the
application of cathodic protection, such as impressed current stations, galvanic anodes, electrical bonds and
isolating joints.
3.5
coating breakdown factor
fc
ratio of current density required to polarize a coated steel surface as compared to a bare steel surface
3.6
average coating resistance
average structure to soil resistance
r
co
value derived from the ratio of the difference between the ON and OFF potentials to the protection
current and the surface area of the structure in question
Note 1 to entry: It is usually expressed in Ω.m .
Note 2 to entry: It is mainly determined by the size and number of coating defects, coating porosity and the
electrolyte resistivity.
3.7
complex structure
structure composed of the structure to be protected and of one or more foreign electrodes, which, for
safety or technical reason, are not electrically separated from it
3.8
copper/saturated copper sulphate reference electrode
CSE
reference electrode consisting of piece of copper in a saturated solution of copper sulphate
3.9
coupon
representative metal sample with known bare surface area dimensions
Note 1 to entry: A coupon can be electrically connected to the structure.
3.10
d.c. decoupling device
equipment that provides a low-impedance path for a.c. and high resistance for d.c
Note 1 to entry: Polarization cells, capacitors or diodes assemblies are examples.
3.11
depolarization
anodic change of potential of a cathodically polarized electrode after disconnection or loss of the cathodic
protection source
3.12
design current
maximum current necessary to protect a structure for the lifetime of a cathodic protection system
Note 1 to entry: This current can be the result of calculation or test (on existing structure). It can be affected by a
design allowance (according to laying conditions, ageing of coating, environmental conditions, operating
conditions…).
3.13
drainage
electrical drainage
transfer of stray current from the affected structure to its source by mean of a deliberate electrical bond
Note 1 to entry: For drainage devices (direct drainage bond, resistance drainage bond, unidirectional drainage
bond and forced drainage bond) see EN 50162.
3.14
drainage station
equipment and materials required to provide drainage of stray currents from affected systems
3.15
driving voltage
difference between the structure/electrolyte potential and the anode/electrolyte potential when the
cathodic protection is operating
3.16
earthing system
arrangement of connections and devices necessary to earth equipment or a system separately or jointly
3.17
electrical continuity
physical state of a structure such that a current circulating within it does not produce a significant voltage
drop
3.18
electrical isolation
lack of electrical continuity between structures or components
3.19
foreign structure
foreign electrode
metallic structure or electrode (anode or cathode), in contact with the structure under consideration
Note 1 to entry: A foreign anode is a foreign electrode, which has a more negative potential than the structure, a
foreign cathode is a foreign electrode, which has a more positive potential than the structure.
3.20
galvanic anode
electrode that provides current for cathodic protection by means of galvanic action
3.21
groundbed
system of buried or immersed galvanic or impressed current anodes
3.22
holiday
defect in a protective coating at which metal is exposed to the environment
3.23
immersed structure
metal construction, or part of a construction laid in a liquid environment such as fresh water (rivers,
lakes)
3.24
impressed current anode
electrode that supplies current for cathodic protection by means of an impressed current source
3.25
impressed current station
station which comprises the equipment and materials required to provide cathodic protection by
impressed current
Note 1 to entry: Such materials and equipment include impressed current anodes, cables, one or several d.c.
sources (e.g. transformer rectifier) and tests facilities.
3.26
insulated flanges
flanged joint between adjacent lengths of pipe in which the nuts and bolts are electrically insulated from
the flange(s) and the gasket is non-conducting, so that there is an electrical discontinuity in the structure
(e.g. pipeline, piping system) at that point
3.27
interference
phenomenon resulting from conductive, capacitive, or inductive coupling between a structure and a
foreign d.c. or a.c. electrical source or between two structures, and which can cause malfunction,
dangerous voltage, damage, etc
Note 1 to entry: Capacitive and inductive coupling are related to a.c. interference.
3.28
interference test
test to determine the electrical interaction between two structures
3.29
IR drop
voltage, due to any current, developed in any part of the circuit, such as the electrolyte (typically soil), in
accordance with Ohm's Law
Note 1 to entry: In this standard, when IR Drop is discussed, it is mainly the one present in the electrolyte
(typically soil), between the reference electrode and the metal of the structure.
Note 2 to entry: IR drops in the electrolyte can affect the accuracy of the structure-to-electrolyte potential.
3.30
IR free potential
E
IR free
structure-to-electrolyte potential measured without the voltage error caused by the IR drop due to the
protection current or any other current
3.31
isolating joint
electrically-insulating component between two parts of a structure, in order to provide electrical
discontinuity between them
EXAMPLE Monobloc/monolithic isolating joint, insulated flange, isolating coupling.
3.32
limiting critical potential
IR free potential below which there is a risk of detrimental effect on the protected material
3.33
OFF-potential
E
OFF
structure-to-electrolyte potential measured immediately after synchronous interruption of all sources of
applied cathodic protection current and before significant depolarization of the structure
Note 1 to entry: EOFF can be misleading in presence of d.c. or a.c. interference.
3.34
ON-potential
E
ON
structure-to-electrolyte potential measured with the cathodic protection current and/or any other
current flowing
3.35
polarization
electrode polarization
change in the structure-to-electrolyte potential as the result of current flow to or from that structure
3.36
protected structure
structure to which cathodic protection is applied
3.37
protection current
current made to flow onto a metallic structure from its electrolytic environment in order to effect
cathodic protection of the structure
3.38
protection potential
structure-to-electrolyte potential at which the metal corrosion rate is acceptable for the structure
3.39
remote earth
part of the electrolyte in which no noticeable voltage, caused by current flow, occur between any two
points
Note 1 to entry: This situation generally prevails outside the zone of influence of an earth electrode, an earthing
system, an impressed current groundbed or a protected structure.
3.40
remote monitoring
measurement made using telecommunication systems for transmission of data
Note 1 to entry: It can include an automatic reporting system when pre-set upper and lower limits are exceeded.
3.41
standard hydrogen electrode
reference electrode, used as a standard in laboratories, consisting of an inert metal, such as platinum, in
an electrolyte containing hydrogen ions at unit activity and saturated with hydrogen gas at one standard
atmosphere
3.42
stray current
current flowing through paths other than the intended circuits
3.43
structure
metallic construction, whether coated or not, which is in contact with an electrolyte
Note 1 to entry: Examples of electrolyte are soil or water.
Note 2 to entry: The structure can represent a construction of great length, such as underground electric cables,
as well as constructions on a smaller scale such as piles, sheet pilings, tanks or other underground constructions.
3.44
structure-to-electrolyte potential
difference in potential between the metallic surface of a structure in contact with an electrolyte and a
reference electrode in contact with the electrolyte at a point sufficiently close to, but not touching the
structure
3.45
sulphate reducing bacteria
SRB
group of bacteria found in most soils and natural waters, but active only in conditions of near neutrality
and freedom from oxygen
Note 1 to entry: Sulphate reducing bacteria reduce sulphates in their environment, with the production of
sulphides and accelerate the corrosion.
3.46
test point
location where the potential measurement is carried out
Note 1 to entry: This can be at a test station, but can be at any location where potential can be measured.
Note 2 to entry: It corresponds to the location where the reference electrode is placed.
3.47
probe
device incorporating a coupon that provides measurements of key parameters to assess the effectiveness
of cathodic protection and/or corrosion likelihood
3.48
test station
installation that provides measuring and test facilities for the buried or immersed structure
Note 1 to entry: Such installations can include cabling and structure connections or can be a direct contact for
measurement purposes.
3.49
transformer rectifier
device that transforms the a.c. voltage and rectifies it to d.c. voltage
Note 1 to entry: d.c. voltage derived in this way is used as a power source for impressed current cathodic
protection systems.
4 Abbreviations and symbols
I Current
ICCP Impressed current cathodic protection
E Potential
R Resistance
j Current density
a.c. Alternating current
d.c. Direct current
E Metal or structure-to-electrolyte potential with respect to a copper/saturated copper
Cu
sulphate reference electrode
E IR free potential
IR Free
E Limiting critical potential
l
E Off potential
OFF
E On potential
ON
E Protection potential
p
E Free corrosion potential
cor
E Metal or structure-to-electrolyte potential with respect to a standard hydrogen electrode
H
f Coating breakdown factor
c
f Final coating breakdown factor
f
f Initial coating breakdown factor
i
Δf Average yearly increase in the coating breakdown factor
I Protection current demand
p
t Total current demand
tot
k Contingency factor
S Surface area
SPD Surge protective device
T Temperature
t Time
t Design life time
dl
ρ Resistivity
5 Cathodic protection personnel competence
Personnel who undertake the design, supervision of installation, commissioning, supervision of
operation, measurements, monitoring inspection, and supervision of maintenance of cathodic protection
systems shall have the appropriate level of competence for the tasks undertaken.
EN ISO 15257 constitutes a suitable method of assessing competence of cathodic protection personnel.
Competence of cathodic protection personnel to the appropriate level for tasks undertaken can be
demonstrated by certification in accordance with prequalification procedures such as EN ISO 15257 or
by another equivalent scheme.
6 Principles and criteria of cathodic protection
6.1 Principles of cathodic protection
The corrosion rate of a metal in soil or water is a function of the electrode potential, E, of the material in
its surrounding media. Except in the case of metals or alloys which can passivate or can be corroded at
high pH, the corrosion rate decreases as the potential is shifted in the negative direction. This negative
potential shift is achieved by applying sufficient direct current from anodes via the soil or water to the
metal surface of the structure to be protected. In the case of coated structures, the current flows to the
metal surface at holidays. The protection current can be provided by impressed current stations or
galvanic anodes.
Cathodic protection is effective if the surface current density is sufficient to lower the potential to a level
capable of achieving an acceptable residual corrosion rate of the structure. Detrimental conditions that
can cause shielding of the cathodic protection current typically include disbonded coatings, thermal
insulating coatings, insulating objects or electrolytes with a high resistivity.
6.2 Cathodic protection criteria
The criteria are most often based on the potential of the metal to be protected in the corrosive electrolyte
(soil or water). The metal protection potential, Ep, corresponds to a threshold at which the corrosion rate
of the metal is reduced to a level considered as acceptably low for practical purposes. The cathodic
protection criteria is therefore:
E ≤ E (1)
p
The cathodic protection system shall be capable of polarizing all parts of the buried structure to potentials
more negative than E , and to maintain such potentials throughout the design life of the structure.
p
The protection potential E depends on the metal in its environment.
p
For carbon steel, low alloyed steels and cast iron, the residual corrosion rate corresponding to E is
p
considered to be 0,01 mm per year.
Some metals may be subject to corrosion damage at very negative potentials. For such metals, the
potential shall therefore not be more negative than a limiting critical potential E. In such cases the
l
criterion for cathodic protection is:
E ≤ E ≤ E (2)
p
l
E and E potentials are those which exist at the metal–to-electrolyte interface, i.e. they shall be considered
p l
IR free, IR being the ohmic drop in the electrolyte between the reference electrode and the metal at the
location where the potential is measured (e.g. at a coating defect).
Procedures for measuring the metal-to-electrolyte potentials are detailed in EN 13509.
The protection, and any limiting critical potentials, of the most common metals to be cathodically
protected in soils and waters are listed in Table 1. For all materials not listed in Table 1, the protection
and limiting critical potentials shall be documented or determined experimentally.
The IR Free potential, E , shall meet the criteria given by Formula (1) and, if applicable, Formula (2).
IR Free
Table 1 presents free corrosion potentials E , protection potentials E and limiting critical potentials E
cor p l
for different metals in different environmental conditions.
Table 1 — Free corrosion potentials, protection potentials and limiting critical potentials of
common metallic materials in soils and waters (except seawater and brackish water) measured
against CSE
Limiting
Protection
Free corrosion
critical
potential: E
p
Metals or potential: E
cor
potential:
Environmental conditions
(V)
alloys (V) Indicative
El (V)
values
(IR Free)
(IR Free)
Soils and waters in all conditions
a
−0,65 to −0,40 −0,85
except those hereunder described
b a
Soils and waters at 40°C < T < 60°C -
c c a
Soils and waters at T > 60°C −0,80 to −0,50 −0,95
Soils and waters in aerobic conditions
Carbon steels,
a
at T < 40°C with −0,50 to −0,30 −0,75
low alloyed
100 Ω.m < ρ < 1 000 Ω.m
steels and cast
iron
Soils and waters in aerobic conditions
a
at T < 40°C with
−0,40 to −0,20 −0,65
ρ > 1 000 Ω.m
Soils and waters in anaerobic
a
conditions and with a risk of Sulphate −0,80 to −0,65 −0,95
Reducing Bacteria activity
Austenitic
stainless steels
d
with Pitting −0,10 to +0,20 −0,50
Resistance
Equivalent < 40
Austenitic
stainless steels Neutral and alkaline soils and waters
with Pitting at ambient temperatures −0,10 to +0,20 −0,30 -
Resistance
Equivalent > 40
Martensitic or
austeno-ferritic
e
- 0,10 to +0,20 −0,50
(duplex)
stainless steels
All stainless Acid soils and waters at ambient
e e
−0,10 to +0,20
steels temperatures
Limiting
Protection
Free corrosion
critical
potential: E
Metals or potential: E p
cor
potential:
Environmental conditions
(V)
alloys (V) Indicative
E (V)
l
values
(IR Free)
(IR Free)
Copper or
−0,20 to 0,00 −0,20 -
copper alloys
Lead - 0,50 to - 0,40 −0,65 −0,95
Soils and waters at ambient
temperatures
Aluminium
g
- 0,70 to - 0,50 −0,8 −1,15
f
alloys
Galvanized steel - 1,10 to - 0,90 - 1,20 -
During the lifetime of the structure any possible changes of resistivity of the medium around the
structure shall be taken into account.
NOTE All potentials are IR free and refer to a copper/saturated copper sulphate reference electrode,
E = E – 0,32 V.
Cu H
a
To prevent hydrogen embrittlement on high strength non alloyed and low alloyed steels with designed yield
−2
strength exceeding 550 N.mm , the limiting critical potential shall be documented or determined experimentally.
b
For temperatures 40°C ≤ T ≤ 60°C, the protection potential can be interpolated linearly between the potential
value determined for 40 °C (−0,65 V, −0,75 V, −0,85 V or –0,95 V) and the potential value for 60°C (−0,95 V).
c
The risk of high pH stress corrosion cracking increases with increase of temperature.
d
In case of presence of any martensitic or ferritic phase (e.g. due to hardening), the risk of hydrogen
embrittlement should be determined by documentation or experimentally.
e
To be determined by documentation or determined experimentally.
f
These values are only valid for aluminium alloys without Zn and Cu (e.g. AIMgSi-alloys). For all other
aluminium alloys the protection potential may be different.
g
Corrosion risk because of alkalinity caused by cathodic protection which dissolves the passive layer.
Protective coatings can become damaged or disbonded under the influence of cathodic protection. Coated
structures should not generally be cathodically polarized beyond −1,2 V Cu/CuSO (IR Free). Values more
negative than −1,2 V Cu/CuSO (IR Free) can be used if experience or data for the particular coating
system and its application demonstrate that more negative values do not cause significant detrimental
coating damage or disbondment in the field.
For steels with a specified minimum yield strength greater than 550 MPa and for corrosion-resistant
alloys such as martensitic and duplex stainless steels, the limiting critical potential shall be determined
with respect to the detrimental effects in the material due to hydrogen formation at the metal surface.
NOTE A tolerably low rate of corrosion of stainless steels and other corrosion resistant alloys can generally be
achieved without polarizing to −850 mV (Cu/CuSO ). Specific grades of stainless steel may be damaged by polarizing
to −850 mV (Cu/CuSO ). For grades of Corrosion Resistant Alloy that are not susceptible to damage by excessive
-
polarization (e.g. resulting from H2 or OH ), it is generally acceptable to polarize them to the protection potential
defined for carbon steel.
6.3 Alternative method
6.3.1 100 mV cathodic potential shift
If the criteria defined in Table 1 cannot be achieved, a cathodic protection shift of 100 mV is considered
as an acceptable alternative method to reduce the corrosion rate (see NACE Publication n°35108 [3]). A
residual corrosion rate less than 0,01 mm/y might not be achieved.
NOTE Informative Annex B provides guidance for measurement of the formation or decay of potential shift.
The application of the 100 mV potential shift shall be avoided at operating temperatures above 40°C, in
soils containing sulfate reducing bacteria; or when interference currents, equalizing currents or telluric
currents might be present. Furthermore, the potential shift method shall not be used in the case of
pipelines connected to or consisting of mixed metal components.
6.3.2 Other methods
Alternative methods may be used if it can be demonstrated that the control of corrosion is achieved.
NOTE The use of corrosion or ER probe are an alternative method that can be used.
6.4 Criteria in presence of a.c
In locations where a.c. interference is suspected, measurements of a.c. voltage and current density shall
be carried out to evaluate the level of the a.c. interference.
In the presence of a.c. voltage on the structure, the protection potentials defined in Table 1 shall be
maintained as a minimum.
For pipelines, EN ISO 18086 gives guidelines for the a.c. corrosion likelihood and defines detailed criteria
to respect.
7 Prerequisites for application of cathodic protection
7.1 General
The effective application of cathodic protection will depend on the size and shape of the structure, the
effectiveness of any coating, the corrosivity of the surrounding medium (e.g. soil, water), a.c. or d.c.
interference, specific requirements in national regulations, and also on the technical and economic
criteria.
To achieve cathodic protection the following conditions shall be satisfied.
7.2 Electrical continuity
The structure, or a section of the whole structure, to be protected, shall be electrically continuous.
Continuity testing can be performed to confirm that the intended continuity has been achieved.
The resistance of the structure to be protected may affect the design of the CP system. Lowering the
electrical resistance of a structure is generally beneficial to uniformity of current distribution. For a
pipeline or a piping system, lowering the longitudinal resistance of the pipe and associated welds will
allow the cathodic protection system to be more efficient. Components (e.g. flanges or expanders) which
may increase the longitudinal resistance of the structure should have low resistance metal bonds.
The resistance of electrical bonds should be low to avoid voltage drops within the structure. Bonds can
be made using metallic conductors such as electrical cables as defined in 9.11 or structural connections.
If cathodic protection is to be applied on non-welded longitudinal structures (e.g. sheet steel piling), the
electrical continuity of the longitudinal structures shall be ensured. Tests of the electrical continuity of
the structure should be performed. When necessary or if problems during the operational lifetime of the
structure are foreseen, permanent electrical bonds (or additional welding) shall be installed.
7.3 Electrical isolation
Whenever possible, the structure to be protected should be electrically isolated from any foreign
structure that will have an adverse effect on the effectiveness of the cathodic protection (e.g. copper
earthing system, rebar in concrete, foreign piping). It is especially important if the structure to be
protected is coated.
If the structure to be protected cannot be electrically isolated from any foreign structure, then it is
required to adequately design the cathodic protection system, and the structure will be considered as
complex one (see EN 14505).
If the structure requires to be earthed, this can be made compatible with the cathodic protection by
installing d.c. decoupling devices and they shall be suitably specified and rated for the purpose. If the
safety earthing circuit is used, the decoupling shall conform to national electrical regulations.
Electrical earth systems can interact with CP systems and can drain current from them. Depending on
national regulations, the following techniques can be used to limit the drain on a CP system:
a) electrically isolate the protected structure from the earth connection and from any items electrically
connected to the earth system;
b) ensure that electrical safety for equipment connected to the CP system is achieved by isolation
(e.g. classes II or III as defined in EN 61140);
c) earth the it
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