SIST EN 50162:2005

SLOVENSKI SIST EN 50162:2005

STANDARD
december 2005
Železniške naprave – Zaščita proti koroziji zaradi učinkovanja blodečih tokov
pri enosmernih tokovnih sistemih
Protection against corrosion by stray current from direct current systems
ICS 29.020; 77.060 Referenčna številka
SIST EN 50162:2005(en)
©  Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno

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EUROPEAN STANDARD EN 50162
NORME EUROPÉENNE
EUROPÄISCHE NORM August 2004

ICS 29.020; 77.060


English version


Protection against corrosion by stray current
from direct current systems


Protection contre la corrosion  Schutz gegen Korrosion
due aux courants vagabonds durch Streuströme aus
des systèmes à courant continu Gleichstromanlagen






This European Standard was approved by CENELEC on 2004-05-01. CENELEC 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 CENELEC 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 CENELEC member into its own language and
notified to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees 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.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels


© 2004 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 50162:2004 E

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EN 50162:2004 - 2 -
Foreword
This European Standard has been prepared by CENELEC BTTF 114-1, Protection against corrosion
by stray current from direct current systems.
The text of the draft was submitted to the Unique Acceptance Procedure and was approved by
CENELEC as EN 50162 on 2004-05-01.
The following dates were fixed:
- latest date by which the EN has to be implemented
at national level by publication of an identical national
standard or by endorsement (dop) 2005-05-01
- latest date by which the national standards
conflicting with the EN have to be withdrawn (dow) 2007-05-01

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Contents
Introduction .5
1 Scope .6
2 Normative references.7
3 Definitions.7
4 Information exchange and co-operation.8
5 Identification and measurement of stray current interference.8
5.1 Identification.8
5.2 Measurement .9
6 Criteria for stray-current interference .10
6.1 Anodic interference .10
6.2 Cathodic interference.10
7 Reduction of stray current interference – Modifications to current source.11
7.1 General .11
7.2 Principles.11
7.3 Direct current systems at industrial sites .11
7.4 Direct current systems at ports .11
7.5 Direct current communication systems.12
7.6 Direct current traction systems .12
7.7 High-voltage direct current transmission systems .12
7.8 Cathodic protection systems.13
7.9 Interference caused by electrical drainage (secondary interference).14
8 Reduction of stray current interference – Modifications to the interfered structure .15
8.1 General .15
8.2 Design prerequisites .15
8.3 Installation of mitigation devices .15
9 Inspection and maintenance .18
Annex A (informative) Stray current corrosion, potential measurements and IR-drop .19
Annex B (informative) Principles of anodic and cathodic interference.21

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EN 50162:2004 - 4 -
Annex C (informative) Criteria for maximum acceptable levels of potential shift ΔU of anodic
interference.23
Annex D (informative) The use of current probes to evaluate fluctuating stray current interference on
cathodically protected structures.24
Annex E (informative) Interference situations and protection techniques.27
Bibliography.29

Figures
Figure B.1 - Principle of interference due to d.c. operated railways .21
Figure B.2 - Principle of interference due to cathodic potential gradients (anodic interference) .21
Figure B.3 - Principle of interference due to anodic potential gradients (cathodic interference) .22
Figure D.1 - Measuring method.24
Figure D.2 - Example of the result of a probe current measurement („A“ indicates the period in
which the reference level is measured; „B“ indicates the period with the highest
reduction of the reference level). .25
Figure D.3 - Graphical representation of Table D.1 .26
Figure E.1 - Examples for secondary interference.27
Figure E.2 - Mitigation of interference using a drainage bond .27
Figure E.3 - Mitigation of interference using a unidirectional drainage bond.28
Figure E.4 - Mitigation of interference using a forced drainage bond .28
Figure E.5 - Mitigation of interference using an earthing electrode or a galvanic anode.29
Figure E.6 - Mitigation of interference using an impressed current station.29

Tables
Table 1 – Acceptable positive potential shifts ΔU for buried or immersed metal structures which
are not cathodically protected .10
Table D.1 – Current criteria in case of interference due to d.c. traction systems .26

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Introduction
Stray currents originating from direct current systems may cause severe material damage by
corrosion, stray current corrosion, on buried or immersed metal structures (see Annex A). Particularly,
long buried horizontal structures, e.g. pipelines and metal sheathed cables, may be in danger of this
type of corrosion. Since corrosion damage can appear after only a short time of exposure to stray
current it is important to make provisions for protective measures at an early stage and also to check
the effect of these measures regularly.
This standard describes appropriate measures that can be applied to interfering d.c. systems and, if
necessary, to structures which are, or which can be, exposed to stray current corrosion. The standard
also gives measurement criteria for determining when these measures must be applied. Measurement
techniques used on d.c. interfered structures are described in EN 13509.
The measures described in this standard are aimed for protection against stray current corrosion. For
effective protection against other types of corrosion other measures have to be applied.

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EN 50162:2004 - 6 -
1 Scope
This standard establishes the general principles to be adopted to minimize the effects of stray current
corrosion caused by direct-current (d.c.) on buried or immersed metal structures.
The standard is intended to offer guidance for:
– the design of direct current systems which may produce stray currents;
– the design of metal structures, which are to be buried or immersed and
– which may be subject to stray current corrosion;
– the selection of appropriate protection measures.
The standard mainly deals with external stray current corrosion on buried or immersed structures.
However stray current corrosion may also occur internally in systems containing an electrolyte e.g.
near insulating joints or high resistance pipe joints in a water pipeline.
These situations are not dealt with in detail in this standard but principles and measures described
here are generally applicable for minimizing the interference effects.
Stray currents may also cause other effects such as overheating. These are not covered in this
standard.
D.C. systems that can cause currents to flow in the earth or any other electrolyte, whether intentional
or unintentional, include:
– d.c. traction systems;
– trolley bus systems;
– d.c. power systems;
– d.c. equipment at industrial sites;
– d.c. communication systems ;
– cathodic protection systems;
– high voltage d.c. (HVDC) transmission systems;
– d.c. track circuit signalling systems. For stray currents from traction systems EN 50122-2 gives
requirements for minimizing their production and for the effects within the railroad.
Systems which may be affected by stray currents include buried or immersed metal structures such
as:
a) pipelines;
b) metal sheathed cables;
c) tanks and vessels;
d) earthing systems;
e) steel reinforcement in concrete;
f) steel piling.

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An affected structure carrying stray currents, e.g. a pipeline or cable may itself affect other nearby
structures (see Clause 8).
This standard does not address the effect of a.c. stray current. Where a.c. stray current is suspected,
care should be taken when taking measurements on any components due to risk of large induced
voltages. If a.c. stray current interference is present the criteria described in this standard will not
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.
EN 50122-2:1998, Railway applications - Fixed installations - Part 2: Protective provisions against the
effects of stray currents caused by d.c. traction systems
EN 12954:2001, Cathodic protection of buried or immersed metallic structures – General principles
and application for pipelines
EN 13509:2003, Cathodic protection measurement techniques
3 Definitions
For the purposes of this European Standard, the terms and definitions given in EN 12954, EN 50122-2
and the following apply.
3.1
coating
electrically insulating covering bonded to a metal surface for protection against corrosion by
preventing contact between the electrolyte and the metal surface
3.2
drainage (electrical drainage)
transfer of stray current from an affected structure to the current source by means of a deliberate bond
NOTE For drainage devices see direct drainage bond, unidirectional drainage bond and forced drainage bond
3.3
direct drainage bond
device that provides electrical drainage by means of a direct bond between an affected structure and
the stray current source. The bond may include a series resistor to limit current
3.4
forced drainage bond
device that provides electrical drainage by means of a bond between an affected structure and the
stray current source. The bond includes a separate source of d.c. power to augment the transfer of
current
3.5
unidirectional drainage bond
device that provides electrical drainage by means of a unidirectional bond between the affected
structure and the stray current source. The bond includes a device such as a diode to ensure that
current can only flow in one direction

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EN 50162:2004 - 8 -
4 Information exchange and co-operation
During the design stage of buried or immersed metallic structures the possibility of both causing and
suffering from stray current interference shall be taken into consideration in order to meet the criteria
mentioned in Clause 6.
Electrical interference problems on buried or immersed metallic structures shall be considered with the
following points in mind:
– the owner of the metallic structure may protect a structure against corrosion with the method that
he considers to be the most suitable. However, electrical interference to neighbouring structures
shall be maintained within the defined limits;
– stray currents, especially from d.c. traction systems are directly related to the design of the return
circuits. This means that it is possible to limit the stray current but not to remove it entirely;
– where other structures that may be affected are present, the requirement to maintain interference
within the defined limits applies to all affected structures.
This goal is best achieved by agreement, co-operation and information exchange between the parties
involved. Information exchange and co-operation are important and shall be carried out both at the
design stage and during operation of the systems. In this way possible effects, suitable precautions
and remedies can be assessed.
The following information shall be exchanged:
1) details of new buried metallic structures;
2) cathodic protection installations or significant modifications;
3) d.c. traction system installations or significant modifications;
4) HVDC transmission line installation or modification.
Agreement and co-operation may be more effectively achieved and maintained by periodic meetings
between interested parties, committees or other associations who can establish information exchange
procedures and protocols.
5 Identification and measurement of stray current interference
5.1 Identification
In cases where there is a possible corrosion risk due to d.c. interference analysis of the situation shall
consider electrical properties and the location of the possible source of interference as well as
anomalies recorded during routine cathodic protection measurements.
There are four principal ways to identify stray-current interference. These are to measure one or more
of the following:
– structure to electrolyte potential fluctuations;
– deviations from normal structure to electrolyte potentials;
– voltage gradients in the electrolyte;
– line currents in pipelines coupons or metallic cable sheaths.
NOTE The measurement of current fluctuations and current polarity changes is particularly useful for identifying interference in
complex networks.

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After stray current interference has been identified further measurements must be carried out to
assess the risk of corrosion.
5.2 Measurement
5.2.1 General
In order to assess the risk of corrosion to which any metal structure is exposed as a result of stray
current, the positive potential shift of the affected structure shall be considered (see 6.1). If cathodic
corrosion (see Annex A and EN 12954) of the metallic structure is likely to occur corrosion risks shall
also be assessed by reference to the negative shift of the potential of the structure (see 6.2).The
structure to soil potential should be measured with respect to a reference electrode, which is placed
directly above the interfered structure.
In order to identify stray current polarity and/or magnitude potential gradient measurements using two
reference electrodes may be carried out. One of the two electrodes shall be placed immediately above
the structure exposed to the interference and the other one at a distance of, ideally, not less than
10 m.
Measuring the magnitude and direction of current flow and/or the potential shift at coupons or test
probes will help to assess a possible corrosion risk.
Measurement techniques, sample periods and the number of readings shall be selected to provide
representative data. In order to ensure accurate measurements care should be taken to select suitable
voltage recording equipment and due consideration given to input impedance, sample period (or chart
speed) and signal conditioning and filtering.
Measurement techniques are described in EN 13509.
5.2.2 Non fluctuating interference
In case of non fluctuating interference structure-to-electrolyte potentials or voltage gradients in the
electrolyte shall be measured while the stray current source is in and out of operation. The measured
values during these two conditions shall be compared with each other. If the stray current source
cannot be temporarily switched off, the interference should be extrapolated from tests made under
different stray current source operation conditions.
5.2.3 Fluctuating interference
Where the potentials or voltage drops measured fluctuate, e.g. as a result of interference from a d.c.
traction system, measurements should be made using a continuous chart recorder or digital data
logger. The recording shall include the period of time when maximum interference is expected as well
as a period of no interference if possible. Many sources of interference exhibit the maximum and
minimum levels over a 24 h period.
It is advisable to record the measured values of the affected system and an operating parameter of the
stray current source simultaneously to allow a clear association of the stray current to the source.
Values recorded during the non operational period of the interfering system shall be considered as the
normal or unaffected potentials.
NOTE A judgment should be made where the interfering system is not de-energised during non operational periods.

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EN 50162:2004 - 10 -
6 Criteria for stray-current interference
6.1 Anodic interference
A positive shift in potential on the structure constitutes anodic interference (see Annex A).
6.1.1 Structures without cathodic protection
Anodic interference (see Annex B) on structures without cathodic protection is acceptable if the
positive potential shift ΔU is lower than the criterion given in Table 1.
NOTE 1 The acceptable positive potential shift ΔU (ohmic voltage drop, i.e. IR-drop, included) is related to the electrolyte
resistivity since the IR-drop part of the measured potential shift increases with increasing resistivity (see Annex C).
NOTE 2 It is difficult to assess whether anodic interference meets the acceptance criterion of Table 1 where the potentials are
rapidly fluctuating. A judgement should be made regarding the duration and extent of the potential excursions beyond the
criterion as to whether or not the excursions are acceptable. This judgement may be based on the duration and frequency of the
excursions or upon the average potential shift. If the results of the judgement are inconclusive then IR free potential
measurements should be made and the criterion of Table 1 column three should be applied (∆U/mV excluding IR drop)
Table 1 – Acceptable positive potential shifts ΔU for buried or immersed
metal structures which are not cathodically protected
Structure metal Resistivity of the Maximum positive potential Maximum positive potential
electrolyte
shift ΔU (mV) shift ΔU (mV)
(including IR-drop) (excluding IR-drop)
ρ (Ωm)
Steel, cast iron > 200 300 20
15 to 200 20
1,5 x ρ*
< 15 20 20
Lead
1 x ρ*
Steel in buried concrete 200
structures
*ρ in Ωm
6.1.2 Structures with cathodic protection
Structures protected against corrosion by cathodic protection shall be deemed to be exposed to
unacceptable stray current interference if the IR free potential is outside the protective potential range
(see EN 12954).
To evaluate the acceptability of stray current interference the installation of test probes and coupons
should be considered.
In situations with fluctuating interference current probe measurements as described in Annex D can
also be used to evaluate the acceptability of interference.
If in special situations (e.g. under d.c. traction influence) there are reasons to doubt the accuracy of
the measurement method used other measurement techniques (e.g. weight loss coupons) can be
used to establish that the structure is cathodically protected.
Measurements should be carried out during a period of normal operation of the interfering system.
6.2 Cathodic interference
Cathodic interference (see Annex B) by stray currents shall be deemed to be unacceptably high if the
interference causes the IR free potential to be more negative than the limiting IR-free potential (see
EN 12954).

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Negative potential shifts due to cathodic interference on a certain part of a structure (usually) implies
that there exist other parts which are subject to anodic interference (see 6.1). If very negative potential
shifts (e.g. ΔU > 500 mV, IR-drop included) are measured, it is recommended to identify areas with
anodic potential shifts to confirm compliance with 6.1.
Values recorded during the non operational period of the interfering system shall be considered as the
normal or unaffected potentials.
7 Reduction of stray current interference – Modifications to current source
7.1 General
Measures taken to minimise the effects of stray current interference should commence with the source
of the interference. If these are impractical or ineffective, then attention should be turned to the
interfered structure. In some cases it may be necessary to introduce interference mitigation measures
at both, to achieve an acceptable interference level.
In some cases the source of interference originates from a structure that is itself interfered with. This is
known as secondary interference. Where such cases of secondary interference exist it is advised to
modify the original source of interference first. The source of secondary interference may have to be
modified if it is not possible to modify the original source.
7.2 Principles
Under normal operating conditions the earth shall not be used to carry any direct currents. For
exceptions to this principle see 7.5, 7.7, 7.8.
Structures which are a source of interference shall not be connected to foreign buried or immersed
metal structures unless it is necessary for safety or stray current corrosion protection reasons.
7.3 Direct current systems at industrial sites
All conductors of direct current systems (such as direct current power systems and direct current
welding equipment) shall be insulated from earth. When for some reasons, for instance by personnel
safety, earthing or equipotential bonding is necessary, special care shall be taken in order to avoid
stray currents, for instance earthing at only one point.
The weld current circuit shall be as short as possible. Earthed metal structures such as railroad or
crane tracks, overhead pipe crossings or buried pipelines shall not be used to conduct current.
7.4 Direct current systems at ports
7.4.1 Cranes
New crane installations at ports should be designed for alternating current operation with any direct
current required for crane operation generated locally at the point of use. Each conductor carrying
direct current should be insulated from earth.
If a direct current crane system cannot be operated without an earth connection, as in the case of an
existing installation, special measures shall be taken in order to avoid stray currents e.g. by installing
an insulated return conductor. A stray current drainage system shall be provided if stray current
interference to buried metal structures is unacceptably high.

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EN 50162:2004 - 12 -
7.4.2 Quayside direct current welding stations
Each ship shall be served by one or several independent quayside welding stations. A single direct
current welding system serving several ships may be a source of stray currents between the ships
causing severe dolphin or fender corrosion damage as stray current interference is not significantly
reduced by equipotential bonds between ships.
Connections for the operation of welding equipment shall be directly bonded to the ships' hulls, e.g. by
welding.
NOTE Such problems can be overcome by placing the welding station(s) on board.
7.4.3 Direct current power supply to ships
Direct-current power systems on ships featuring complete earth insulation and earth protective relays
may be supplied with d.c. electric power from shore.
If a direct-current power system on a ship features single phase earthing, alternating current power
shall be supplied to the ship and rectified on board for use in the direct-current power systems.
7.5 Direct current communication systems
All communication systems shall be designed such that no direct current normally flows through the
earth. Direct-current pulses such as pulses for dialling or earthing may flow through the earth. Direct
currents shall not be the source of any stray-current interference with nearby pipeline or cables.
Pipelines or cables shall not be used for earthing connections.
Traffic signals shall be designed such that direct currents do not normally flow through the earth.
7.6 Direct current traction systems
The traction system should be designed to reduce the stray currents flowing into the ground in order to
reduce or eliminate the effects on foreign structures. Direct current traction systems are generally
operated with the negative pole connected to the rails. In rare cases the positive pole is connected to
the rails. Modern d.c. operated railways use a current feedback system during braking. The methods
to be carried out shall comply with requirements given in EN 50122-2. They mainly consist of
– adjustment of the power supply system,
– improvement of the return circuit,
– isolation of the return circuit from ground, grounded metallic structures (pipelines, cables, bridges
and tunnels) and other rail systems.
It is necessary to consider the requirements and the methods for suppressing stray current from the
earliest stages of a d.c. railway project, so that the suppression of stray current is taken into account
when the positions and the sizes of the substations are decided.
7.7 High-voltage direct current transmission systems
7.7.1 General
There are two main configurations for high voltage direct current (HVDC) transmission systems,
monopolar and
...