SIST EN 14505:2005
(Main)Cathodic protection of complex structures
Cathodic protection of complex structures
This document should be used for the cathodic protection of complex structures. It is applicable to structures, which are to be cathodically protected, but cannot be electrically isolated, whether for technical or safety reasons, from foreign metallic structures situated in the same electrolyte as the structure to be protected. Such a structure is referred to as a "complex structure".
This document is not applicable to structures that can be protected in accordance with EN 12954. When contacts with foreign structures or defective isolation from foreign structures exist, but can be corrected, the EN 12954 should be used instead of this document. As an example pipeline network distribution systems are not considered to be complex structures
It is assumed in this document that the design, installation, commissioning, inspection and maintenance are entrusted to adequately trained, experienced, competent and reliable personnel in order to achieve effective and efficient cathodic protection.
Annexes A and B show the principle scheme of a complex structure with examples.
Kathodischer Korrosionsschutz komplexer Anlagen
Dieses Dokument ist für den kathodischen Korrosionsschutz von komplexen Anlagen anzuwenden. Sie gilt für Anlagen, bei denen ein kathodischer Korrosionsschutz erforderlich ist, die jedoch entweder aus technischen oder aus sicherheitsbezogenen Gründen nicht elektrisch von Fremdanlagen aus Metall getrennt werden können, die sich in demselben Elektrolyt befinden wie das Schutzobjekt. Eine derartige Anlage wird als "komplexe Anlage" bezeichnet.
Dieses Dokument gilt nicht für Anlagen, die nach EN 12954 geschützt werden können. Wenn eine Verbindung zu Fremdanlagen oder eine fehlerhafte Trennung von Fremdanlagen vorliegt, jedoch behoben werden kann, ist EN 12954 an Stelle der vorliegenden Europäischen Norm anzuwenden. Rohrleitungsverteilungssysteme gelten zum Beispiel nicht als komplexe Anlagen.
In diesem Dokument wird davon ausgegangen, dass die Planung, Installation, Inbetriebnahme, Prüfung und Wartung von entsprechend ausgebildetem Personal mit einem geeigneten Maß an Erfahrung, Kompetenz und Verlässlichkeit durchgeführt wird, um einen wirksamen kathodischen Korrosionsschutz zu erreichen.
In den Anhängen A und B wird der prinzipielle Aufbau einer komplexen Anlage anhand von Beispielen erläutert.
Protection cathodique des structures complexes
La présente Norme européenne s'applique lorsque l'isolation électrique des structures, pour des raisons techniques ou de sécurité, n'est pas possible. Elle décrit des principes pour l'étude des systemes de protection cathodique des structures complexes, en soulignant les étapes pratiques de mise en oeuvre de ces études, les méthodes de mesure et les criteres d'évaluation de la protection cathodique.
La présente norme n'est pas applicable aux structures couvertes par le prEN 12954 ou en cas de contacts non désirés avec des structures étrangeres ou d'isolation défectueuse.
Il est toujours préférable d'observer les exigences telles qu'elles sont décrites dans le prEN 12954 avant d'appliquer la présente norme.
L'annexe A illustre le principe et présente un exemple simplifié d'une structure complexe.
Katodna zaščita kompleksne zgradbe
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN 14505:2005
01-julij-2005
.DWRGQD]DãþLWDNRPSOHNVQH]JUDGEH
Cathodic protection of complex structures
Kathodischer Korrosionsschutz komplexer Anlagen
Protection cathodique des structures complexes
Ta slovenski standard je istoveten z: EN 14505:2005
ICS:
77.060 Korozija kovin Corrosion of metals
SIST EN 14505:2005 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN 14505:2005
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SIST EN 14505:2005
EUROPEAN STANDARD
EN 14505
NORME EUROPÉENNE
EUROPÄISCHE NORM
April 2005
ICS 77.060
English version
Cathodic protection of complex structures
Protection cathodique des structures complexes Kathodischer Korrosionsschutz komplexer Anlagen
This European Standard was approved by CEN on 15 March 2005.
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 Central Secretariat 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 Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36 B-1050 Brussels
© 2005 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 14505:2005: E
worldwide for CEN national Members.
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Contents
Page
Foreword .3
1 Scope .4
2 Normative references .4
3 Terms and definitions.4
4 Criteria for the cathodic protection of complex structures .4
5 Prerequisites for the application of cathodic protection to a complex structure .5
6 Base data for design.6
7 Design and prerequisites .7
8 Installation of cathodic protection systems.10
9 Commissioning .11
10 Inspection and maintenance.12
Annex A (informative) Principle scheme of a complex structure .14
Annex B (informative) Example of an industrial complex structure.15
Annex C (informative) Reinforced concrete data in complex structures .16
Annex D (informative) Increasing soil potential .17
Annex E (informative) Groundbed data .21
Bibliography.24
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Foreword
This European Standard (EN 14505:2005) 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 October 2005, and conflicting national standards shall be withdrawn at
the latest by October 2005.
It may be difficult to obtain complete cathodic protection of certain structures when following the general
guidelines in EN 12954. This may be due to an electrical connection to one or more metal structures
(electrodes) situated in the same electrolyte as the structure, which is to be protected. In particular, the
structure may be earthed in order to mitigate electrical hazards or the connection to the other structures may
be dictated by construction or operational requirements.
An electrical connection to a foreign structure can result in a significantly increased cathodic protection current
demand, since the current flows not only to the structure to be protected but also to the foreign structure. This
unwanted increased current demand is enhanced when the foreign structure consists of a metal, which is
more noble (having a more positive resting potential) than the metal in the structure to be protected.
Connection to a copper earthing electrode or to the steel reinforcement in a concrete structure are examples
of the latter.
These difficulties can mean that a significantly increased cathodic protection current is required because of
structures electrically connected to the structure to be protected, resulting in inadequate cathodic protection,
current distribution and shielding effects.
For this reason, the term “complex structure” has been used. It does not refer to the complexity of the structure or
to the complexity of the cathodic protection system.
In such conditions the prerequisites, the criteria and the methods described in the present document expand
those given in EN 12954.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland
and United Kingdom.
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1 Scope
This European Standard applies to the cathodic protection of complex structures. It is applicable to structures,
which are to be cathodically protected, but cannot be electrically isolated, whether for technical or safety
reasons, from foreign metallic structures situated in the same electrolyte as the structure to be protected.
Such a structure is referred to as a “complex structure”.
This European Standard is not applicable to structures that can be protected in accordance with EN 12954.
When contacts with foreign structures or defective isolation from foreign structures exist, but can be corrected,
EN 12954 is applicable instead of this document. As an example pipeline network distribution systems are not
considered to be complex structures
It is assumed in this document that the design, installation, commissioning, inspection and maintenance are
entrusted to adequately trained, experienced, competent and reliable personnel in order to achieve effective
and efficient cathodic protection.
Annexes A and B show the principle scheme of a complex structure with examples.
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.
EN 12954:2001, Cathodic protection of buried or immersed metallic structures — General principles and
application for pipelines.
EN 50162, Protection against corrosion by stray current from direct current systems.
3 Terms and definitions
For the purposes of this European Standard, the terms and definitions given in EN 12954:2001 and the following
apply.
NOTE For other definitions related to corrosion, refer to EN ISO 8044:1999.
3.1
complex structure
structure composed of the structure to be protected and of one or more foreign electrodes, which, for safety or
technical reasons, cannot be electrically separated from it
3.2
foreign electrode
electrode (anode or cathode), in contact with the structure under consideration
NOTE 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.
4 Criteria for the cathodic protection of complex structures
For complex structures, the cathodic protection criteria defined in EN 12954 should be used where possible.
Indeed, the characteristics of complex structures and the special influential factors (see Clause 5) which can occur
means that it is not always possible on every part of the complex structure to determine by measurement whether
these criteria of cathodic protection are met. In this case alternative methods of verification may be selected to
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ensure an adequate reduction of the corrosion rate. Particular attention should be paid to the selection of these
alternative methods, and these will depend upon the structure and the soil characteristics.
The following three alternative methods may be used as criteria. They are based upon practical experience
and are widely used. All structure to electrolyte potential measurements are stated with respect to a
copper/saturated copper sulphate reference electrode.
a) Potential measurement method
An on potential E equal to or more negative than –1,2 V, if the measuring point is outside the area of
on
influence of the large foreign cathode (e.g. reinforced concrete or copper earthing system) and if the soil
resistivity is sufficiently low (less than about 100 Ω⋅m) with the exception that an on potential E more
on
negative than –0,8 V could be acceptable at entries to, and in the vicinity (within 0,5 m) of large foreign
cathodes (demonstrating that the effect of a galvanic cell with the large foreign cathode is mitigated).
b) Current method
The purpose of this method is to demonstrate that current is able to enter the structure at critical locations
either:
1) directly (i.e. when the protection current is switched on, a negative shift from the free corrosion
potential E by at least 0,3 V indicating that probably sufficient current is entering the structure); or
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2) by means of either current density or potential shift measurements at test probes or coupons.
NOTE A critical location is location where the probability to have an anodic current leaving the structure to be protected
is high (e.g., vicinity of foreign cathode due to galvanic couple, heterogeneity of the soil or shielding effect).
c) Depolarisation measurement method
A positive shift (depolarisation) on test probes or coupons of at least 0,1 V measured from immediately after
disconnection (E ) to 1 h after disconnection from the structure indicates that the structure is polarized. These
off
test probes/coupons are disconnected only for measurements.
One of these alternative criteria shall be used as a minimum. More than one of these alternative criteria may
be required to verify adequate protection over the entire complex structure. Other criteria can be used if they
can be shown to reduce the external corrosion rate to an acceptable level.
5 Prerequisites for the application of cathodic protection to a complex structure
5.1 General
The cathodic protection system depends on the size and shape of the complex structure, the type of coating,
the aggressive action of the soil and its resistivity, d.c. and a.c interference, national regulations, and also on
the technical and economic criteria.
To achieve cathodic protection, the conditions given in 5.2 to 5.4 should be satisfied.
5.2 Electrical continuity
In the case of a complex structure, all metallic parts of the structure to be protected should be electrically
continuous. Foreign electrodes should also be electrically continuous.
5.3 Electrical isolation
For the cathodic protection system to be properly designed, the form and extent of the structure should be clearly
defined in terms of its location and electrical isolation from foreign structures.
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If the electrical isolation is ineffective and cannot be restored to its original condition, then the extent of the
complex structure should be revised to take this into account.
5.4 External coating
Protective coatings are not always applied to components in a complex structure (e.g. earthing systems).
Uncoated components significantly increase protection current demands and thus add to the difficulties of the
application of cathodic protection and increase the risk of interference. Wherever possible, buried metallic
components should be suitably coated.
6 Base data for design
6.1 General
In addition to following the principles laid out in EN 12954, other specific data, as given in 6.2 to 6.8, should be
used when dealing with complex structures.
6.2 Structure details
The surface area of all buried or immersed components of a complex structure should be ascertained as well
as the status of the coating (if any).
6.3 Coatings
Types of the different coating applied on all components of a complex structure should be taken into account.
6.4 Environment
Depending on the composition of some parts of a complex structure, particular environmental conditions
should be considered, for example, the chloride content of the electrolyte when an integral part of a complex
structure is made of stainless steel, or reinforcement steel in concrete (rebar).
6.5 Shielding
All relevant information should be obtained on any feature that might act as a shield to the cathodic protection
current or its distribution, e.g. reinforced concrete foundations, pits, ducts, any geotextiles, and pipe sleeves. The
location of the anodes with respect to the shields should be selected such that shielding is minimized.
A shield can be either conductive or non-conductive.
A conductive shield can be either a part of the complex structure itself or a foreign structure such as steel
sleeves for pipes, large conducting structures (sheet piling and reinforced concrete foundations) close to the
structure to be protected.
Non-conductive shields can be either a non-conductive object (e.g. plastic or a well coated steel sleeve pipe)
or a mechanical protective material or a localized area with a higher resistivity (e.g. drained sands, gravels,
sealed concrete).
6.6 Electrical isolation
The location and efficiency of electrical isolation should be taken into account at the defined complex structure
limits and, if necessary, within the complex structure.
For example, isolation is ineffective if it is bypassed by metallic components or equipment that provide a
parallel electrical path. Electrical earthing systems, instrumentation and/or telemetry cables, control pipework,
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and supporting structures are examples of possible parallel paths. Electrical isolation is also ineffective when
pipelines carrying low resistivity liquids (e.g. brine) are equipped with inappropriate isolating joints.
NOTE Details concerning isolating joints are given in EN 12954.
6.7 Foreign electrodes
Details of the type, location and other detailed characteristics of foreign electrodes should be obtained.
In a complex structure, the presence of foreign electrodes which act as an anode (e.g. zinc or zinc-coated
(galvanized) steel) or as a cathode (e.g. steel reinforcement in concrete (see Annex C), copper, stainless steel
or silicon iron in carbonaceous backfill earthing systems) increases the protection current demand.
Zinc earthing systems should be used because they consume less current from the cathodic protection
system than copper, stainless steel or silicon iron.
Electrical earthing systems associated with complex structures should utilize zinc or zinc-coated (galvanized)
steel electrodes.
NOTE The connection of copper or cathodic earthing systems to buried steel not only increases cathodic protection
current demand but, if cathodic protection is not applied, it will increase the corrosion risk to the buried steel.
6.8 Interference assessment
Interference:
- from any d.c. operated equipment to the complex structures or
- from the complex structure to foreign structures
should be assessed in accordance with EN 50162.
If necessary, appropriate measures should be taken to mitigate the effects of interference to maintain effective
cathodic protection of the complex structure.
Particular attention should be paid to interference that can occur between the cathodic protection system(s) of
the complex structure and the incoming/outgoing pipelines. Pipelines in the vicinity of the complex structure
and their cathodic protection should be taken into account both in the design and the commissioning of the
cathodic protection system of the complex structure to limit, or preferably, eliminate adverse interference
effects.
7 Design and prerequisites
7.1 General
Complex structures include foreign electrodes that are often large cathodic surfaces (such as reinforcement steel
and earthing systems). The result is that the cathodic protection current requirement is high and the effective
distribution of the current is difficult to obtain.
Even though all known influences are taken into account in the design of the cathodic protection system,
experience has shown that subsequent adjustments and additional cathodic protection installations can be
necessary after the system has been switched on and a certain polarization time has elapsed. This is due to
the characteristics of the structure to be protected, shielding effects and interference with foreign structures.
For these reasons, the protection current requirements and current distribution cannot always be accurately
determined during the design stage.
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When a complex structure includes reinforcement steel in concrete that is bonded to the structure to be
protected, efficient current distribution can be achieved by the application of an insulating coating to the buried
concrete surface at entries or points of close proximity of the protected structure to the reinforced concrete
(see 7.2 item b) and Annex D). This method may be applied whether local anodes to increase the soil
potential are used or not.
A coating is used to reduce the effect of the local voltage gradient from the reinforced concrete structure and
improve the current distribution.
The coating should extend on the concrete surface at least 1 m around the protected structure (e.g. pipeline)
and up to the soil surface.
If pipelines are laid in soil parallel to steel reinforced concrete foundations and the spacing is less than twice
the pipe diameter or less than 0,5 m, the coating should extend for the length of the parallelism from 1 m
below the bottom of the pipe to ground level.
Test stations connected to reinforcement steel should be located in these areas (see also 7.8).
7.2 Cathodic protection methods for complex structures
To achieve the protection criteria detailed in Clause 4, cathodic protection can be achieved by three methods. The
choice of the method depends on the complex structure in question.
a) By the use of impressed current groundbed(s) sufficiently remote from the complex structure to be
protected (conventional groundbed). By using this method, high levels of cathodic protection current are
often required because all components of the complex structure receive and consume current.
b) By the use of distributed or continuous groundbed(s) located along and close to the structure to be
protected. The purpose of this method is to localize the application of cathodic protection current to the
structure to be protected. (Complementary information is given in Annex D).
c) By a combination of the above two methods.
Effective cathodic protection is usually achieved by a combination of these methods. Complex structures vary
considerably in size and complexity and it is not possible to be prescriptive as to which single method will be
successful.
NOTE Annex E covers groundbed data.
7.3 Electrical isolation of structures
If electrical isolation from the adjacent structures exists or is planned, this information should be used to
determine the extent and limits of the complex structure.
Isolating joints in incoming or outgoing pipelines should be located outside the zone of influence of the
cathodically protected complex structure so that unacceptable interference by the cathodically protected
complex structure (due to voltage gradient) is avoided.
7.4 Safety
7.4.1 General
The design should not cause any additional hazards, (e.g. explosion, safety, personnel and interference).
7.4.2 Electrical earthing systems
Generally, earthing systems are electrically connected directly to the structure to be protected and are part of the
complex structure. In order to prevent excessive drain of cathodic protection current to copper earthing systems,
they can be separated from the structure to be protected by the use of decoupling devices.
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7.4.3 Electrical safety bonding
7.4.3.1 Permanent bonding
Structures such as building frames, reinforcement steel in concrete, access platforms and stairways are often
bonded to the complex structure to be protected and therefore become a part of the complex structure.
Permanent bonding should be taken into account when designing the cathodic protection system.
7.4.3.2 Temporary bonding
Temporary bonds are made when vehicles (road/rail) or ships are engaged in loading or unloading hazardous
products.
All necessary safety precautions should be taken before transfer operations start e.g. equipotential bonding which
may be by conductive hoses or cables (see EN 50162).
Temporary bonding should be taken into account when designing the cathodic protection system.
In hazardous installations, current may be flowing in both buried and above ground sections of pipework and
so to avoid possible sparking when pipework modifications are made, the cathodic protection system should
be switched off and a heavy duty cable bond should be applied across the pipe section to be separated. The
bond should be maintained until the pipe is reconnected or the area declared safe.
7.5 Electrical continuity
Metallic bonds are installed to ensure electrical continuity of the complex structure and also to avoid interference
and excessive voltage drops in the cathodic protection circuit.
7.6 Negative connections
To achieve optimum current distribution in the complex structure, several transformer rectifiers and/or several
negative connections should be used.
7.7 Transformer–rectifiers
The rating of transformer–rectifiers should be designed with sufficient capacity to allow for the initial higher current
requirement during the polarization period and for changing conditions. The output voltage should be kept as low
as possible to help limit the interference levels (see also 7.9).
7.8 Test stations and measuring points
Test stations and measuring points should be located at sufficient locations to adequately represent the cathodic
protection status of the structure.
Where measuring points are located in concrete or gravel areas, provision should be made for reference
electrode contact to the soil beneath the concrete/gravel.
Measuring points should be located at critical points, permanently marked to ensure reproducible
measurements. These critical points should take into account the presence of:
a) sleeve pipes;
b) sheet piling;
c) reinforced concrete structures;
d) entries to reinforced concrete structures;
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e) electrical earthing systems;
f) foreign structures, especially when they are close to (or crossing) the considered structure;
g) potentially shielded locations;
h) locations most affected by galvanic couples;
i) locations closest to and most remote from groundbeds;
j) limits of the complex structure.
The use of probes, coupons and permanently installed reference electrodes at suitable locations should be
considered, particularly if the verification of the cathodic protection effectiveness is to be performed in accordance
with methods b) and c) of Clause 4.
7.9 Anode groundbeds
The current output of galvanic anodes is limited directly by the soil resistivity. For complex structures, magnesium
anodes are not used when the electrolyte resistivity is greater than 50 Ω⋅m and zinc anodes are not used when
the electrolyte resistivity is greater than 10 Ω⋅m. This limits their use in many cases.
Impressed current cathodic protection systems are generally used in complex structure applications.
Depending on the method chosen in 7.2, several configurations of groundbed may be considered (remote or
close groundbeds: single point, distributed or continuous groundbeds) (see Annex E).
a) when designing a groundbed system the following shall be considered: Groundbed lifetime;
b) groundbed locations are selected to avoid inadmissible interference to foreign structures (see EN 50162)
and shielding effects;
c) groundbed resistance to earth which should be kept as low as possible;
d) individual anodes and groundbed current control;
e) gas evolution from the groundbed.
7.10 Design document
Design documents should be prepared in sufficient detail to satisfy the requirements of safety, design,
verification, installation procedures and future inspection.
8 Installation of cathodic protection systems
8.1 General
Installation procedures should be in accordance with EN 12954:2001, Clause 8.
8.2 Cables
If cables in ducts pass through hazardous areas, national regulations apply. These regulations may require that
the ducts are sealed by adequate means to prevent inflammable liquids and gases from being carried into
non-hazardous areas.
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9 Commissioning
9.1 General
Commissioning procedures are described in EN 12954. For complex structures, cathodic polarization can require
extended periods of time, during which adjustments are usually necessary to both the protection current and its
distribution.
In some circumstances, the polarization rate may be enhanced by initially providing more current than is
subsequently necessary to maintain protection.
9.2 Preliminary checking
Before a cathodic protection system is activated, care shall be taken to check that all installations are in
accordance with the design. In particular, bonding, connections and safety measures (contact protection, lightning
protection, explosion proofing) shall be confirmed and d.c. connections to the transformer rectifiers shall be
checked for correct polarity.
The following measurements should be made and the values compared with the design requirements.
a) Resistance measurements:
1) groundbed resistance to remote earth;
2) resistance between the structure to be protected and the groundbed;
3) resistance between the complex structure and foreign structures.
b) Potential measurements:
1) free corrosion potential E of the structure at all measuring points;
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2) interference due to stray currents;
3) structure to electrolyte potential of foreign structures;
4) potential difference between the complex structure and foreign structures.
When an existing cathodic protection system is already operating and the criterion b)1 in Clause 4 is to be applied,
the system should be switched off for a sufficiently long period of time to enable the structure to depolarize to a
constant value approximating to E before commissioning.
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9.3 Start up
The following steps shall be carried out.
a) Switch on the impressed current station and confirm that it is functioning correctly.
b) Adjust the current output in order to achieve the design values. If major deviations occur, ascertain the
causes by further investigation.
c) Make the following measurements:
1) rectifier output voltage on impressed current station;
2) protective current output;
3) on p
...
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