CEN/TS 15280:2006

Evaluation of a.c. corrosion likelihood of buried pipelines - Application to cathodically protected pipelines

This Technical Specification is applicable to buried or immersed cathodically protected metallic structures and influenced by a.c. traction systems and/or a.c. power lines.
   In the presence of a.c. interference, the criteria given in EN 12954:2001, Table 1, are not sufficient to demonstrate that the steel is being protected against corrosion.
   This Technical Specification provides limits, measurements procedures and information to deal with long term a.c. interference and evaluating a.c. corrosion likelihood.
   Even though short term interference can cause damage to buried pipelines (e.g. arc fusion), this Technical Specification does not deal with short term interference.

Beurteilung der Korrosionswahrscheinlichkeit durch Wechselstrom an erdverlegten Rohrleitungen - Anwendung für kathodisch geschützte Rohrleitungen

Diese Technische Spezifikation gilt für erdverlegte oder unterirdische bzw. unter Wasser befindliche metallische Anlagen, die kathodisch geschützt sind und durch Wechselstrom-Fahrleitungen und/oder Wechselstrom-Überlandleitungen beeinflusst werden.
Eine erdverlegte Rohrleitung (oder Anlage) im Sinne dieses Dokuments ist eine Rohrleitung (oder Anlage) in Böden oder Wässern, wie in EN 12954 festgelegt.
Bei Anwesenheit einer Wechselstrombeeinflussung sind die in EN 12954:2001, Tabelle 1, gegebenen Kriterien nicht ausreichend, um nachzuweisen, dass der Stahl gegen Korrosion geschützt ist.
Diese Technische Spezifikation gibt Grenzwerte, Messverfahren und Information zum Umgang mit Langzeitwechselstromeinfluss und zur Beurteilung der Wahrscheinlichkeit von Korrosion durch Wechselstrom verursachten Korrosion an.
Obwohl bereits kurze Beeinflussung Schäden an erdverlegten Rohrleitungen bewirken kann (z. B. Verschmelzung durch Lichtbogen), gilt diese Technische Spezifikation nicht für Kurzzeitbeeinflussung.

Evaluation du risque de corrosion des canalisations enterrées occasionné par les courants alternatifs - Application aux canalisations protégées cathodiquement

La présente Spécification technique est applicable aux structures métalliques enterrées qui sont protégées cathodiquement et influencées par des systèmes de traction à courant alternatif et/ou des lignes électriques haute tension en courant alternatif.
Dans le présent document, une canalisation (ou une structure) enterrée est une canalisation (ou une structure) enterrée ou immergée au sens de l’EN 12954.
En présence d’une  influence due aux courants alternatifs, les critères spécifiés dans le tableau 1 de l’EN 12954 sont insuffisants pour démontrer que l’acier est protégé contre la corrosion.
La présente Spécification technique spécifie les limites, les modes opératoires de mesure et les informations relatives à l’influence permanente par les courants alternatifs et à l’évaluation du risque de corrosion engendré par ces courants.
   Bien qu’une perturbation accidentelle puisse provoquer des dommages sur les canalisations enterrées (par exemple une fusion par arc électrique), la présente Spécification technique ne traite pas de ces phénomènes.

Vrednotenje verjetnosti nastanka korozije vkopanih cevovodov – Uporaba pri katodno zaščitenih cevovodih

General Information

• Status: Withdrawn
• Publication Date: 14-Mar-2006
• Withdrawal Date: 13-Aug-2013
• ICS: 23.040.03 - Pipeline and its parts for external water conveyance systems
• ICS: 23.040.99 - Other pipeline components
• ICS: 77.060 - Corrosion of metals
• Technical Committee: CEN/TC 219 - Cathodic protection (provisional)
• Drafting Committee: CEN/TC 219/WG 1 - Cathodic protection of buried and immersed metallic structures
• Current Stage: 9960 - Withdrawal effective - Withdrawal
• Start Date: 14-Aug-2013
• Completion Date: 14-Aug-2013
• Ref Project: SIST-TS CEN/TS 15280:2006 - Evaluation of a.c. corrosion likelihood of buried pipelines - Application to cathodically protected pipelines

Relations

• Replaced By: EN 15280:2013 - Evaluation of a.c. corrosion likelihood of buried pipelines applicable to cathodically protected pipelines
• Effective Date: 08-Jun-2022

Standards Content (Sample)

SLOVENSKI STANDARD
01-maj-2006
9UHGQRWHQMHYHUMHWQRVWLQDVWDQNDNRUR]LMHYNRSDQLKFHYRYRGRY±8SRUDEDSUL
NDWRGQR]DãþLWHQLKFHYRYRGLK
Evaluation of a.c. corrosion likelihood of buried pipelines - Application to cathodically
protected pipelines
Beurteilung der Korrosionswahrscheinlichkeit durch Wechselstrom an erdverlegten
Rohrleitungen - Anwendung für kathodisch geschützte Rohrleitungen
Evaluation du risque de corrosion des canalisations enterrées occasionné par les
courants alternatifs - Application aux canalisations protégées cathodiquement
Ta slovenski standard je istoveten z: CEN/TS 15280:2006
ICS:
23.040.01 Deli cevovodov in cevovodi Pipeline components and
na splošno pipelines in general
77.060 Korozija kovin Corrosion of metals
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL SPECIFICATION
CEN/TS 15280
SPÉCIFICATION TECHNIQUE
TECHNISCHE SPEZIFIKATION
March 2006
ICS 23.040.99; 77.060
English Version
Evaluation of a.c. corrosion likelihood of buried pipelines -
Application to cathodically protected pipelines
Evaluation du risque de corrosion des canalisations Beurteilung der Korrosionswahrscheinlichkeit durch
enterrées occasionné par les courants alternatifs - Wechselstrom an erdverlegten Rohrleitungen - Anwendung
Application pour les canalisations protégées für kathodisch geschützte Rohrleitungen
cathodiquement
This Technical Specification (CEN/TS) was approved by CEN on 8 November 2005 for provisional application.
The period of validity of this CEN/TS is limited initially to three years. After two years the members of CEN will be requested to submit their
comments, particularly on the question whether the CEN/TS can be converted into a European Standard.
CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/TS available
promptly at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in parallel to the CEN/TS)
until the final decision about the possible conversion of the CEN/TS into an EN is reached.
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, Romania,
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
© 2006 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TS 15280:2006: E
worldwide for CEN national Members.

Contents Page
Foreword .3
1 Scope .4
2 Normative references .4
3 Terms and definitions.4
4 A. c. interference sources .5
5 Simplified description of a.c. corrosion process .6
6 Evaluation of a.c. corrosion likelihood.8
6.1 Prerequisite .8
6.2 General .8
6.3 Installation / use of coupons.9
6.4 Influence of a.c. voltage on the structure.9
6.5 Off potential influence .11
6.6 Influence of a.c. current density .12
6.7 Influence of the on potential toward a.c. corrosion likelihood.13
6.8 Influence of current ratio "I /I ".16
a.c. d.c.
6.9 Influence of soil characteristics on a.c. corrosion likelihood.16
6.10 Assessment of the a.c. corrosion likelihood of the pipeline by using corrosion coupons.17
7 Design consideration.18
7.1 General .18
7.2 New interference cases (pipelines/power lines/traction systems in the design phase) -
Condition for calculation.18
8 Interpretation of data, limits and relevant aspects.20
9 Mitigation measures .20
10 Monitoring .21
Annex A (informative) Assessment of the corrosion condition by using the electric resistance
technique.22
Annex B (informative) Coulometric oxidation of corrosion products formed by a.c. corrosion.24
Bibliography.25

Foreword
This Technical Specification (CEN/TS 15280:2006) has been prepared by Technical Committee CEN/TC 219
“Cathodic Protection”, the secretariat of which is held by BSI.
Long term a.c. interference on buried metallic pipelines may cause corrosion due to an exchange of
alternating current between the soil and the bare metal at unavoidable coating faults in the structure.
a.c. corrosion is more likely on pipelines which are not cathodically protected. To reduce it, it is advisable to
consider the application of cathodic protection and to follow the present Technical Specification.
Danger to people in contact with the pipeline or connected equipment, malfunction of connected equipment
and other damages to the pipeline or connected equipment are dealt with in relevant CENELEC standards.
This Technical Specification refers to EN 12954 and may be used in place of its Annex A.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to announce this CEN Technical Specification: Austria, Belgium, Cyprus, Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden,
Switzerland and United Kingdom.

1 Scope
This Technical Specification is applicable to buried cathodically protected metallic structures and influenced
by a.c. traction systems and/or a.c. power lines.
In this document, a buried pipeline (or structure) is intended as buried or immersed pipeline (or structure), as
defined in the Standard EN 12954.
In the presence of a.c. interference, the criteria given in EN 12954, Table 1, are not sufficient to demonstrate
that the steel is being protected against corrosion.
This Technical Specification provides limits, measurements procedures and information to deal with long term
a.c. interference and the evaluation of a.c. corrosion likelihood.
Even though short term interference can cause damages to buried pipelines (e.g. arc fusion), this standard
does not deal with short term interference.
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 13509:2003, Cathodic protection measurement techniques
EN 12954:2001, Cathodic protection of buried or immersed metallic structures – General principles and
application for pipelines.
3 Terms and definitions
For the purposes of this Technical Specification, the following terms and definitions apply
3.1
a.c. traction system
an a.c. electrical system of a railway, i.e. the electric train units and their feeding and return systems
NOTE The lines used to feed the railway substations (three-phase lines or, sometimes, two-phase lines in case of
16,7 Hz systems) are a.c. power supply systems, and it is suggested to take them into consideration together with the a.c.
traction system.
3.2
cathodic protection system
the entire installation, including active and passive elements, that provides cathodic protection
(See EN 12954:2001 clause 3.2.9)
NOTE It includes for example the following: cathodic protection stations and relevant accessories as remote control
systems, drainages, insulating joints, resistors, diodes, test points, groundings, a.c. discharge / d.c. decoupling devices etc.
3.3
incubation time
period of time before the leakage resistance of exposed metal, at coating faults or coupons, stabilizes due to
electrochemical reactions
3.4
instantaneous measurement
reading of electrical parameters by an operator
3.5
leakage resistance
local resistance to earth of metal exposed to the environment
3.6
long term a.c. interference
interference on a pipeline during normal operating conditions of a.c. power systems (e.g. traction systems or
electricity power lines)
3.7
long term measurements
measurements of electrical parameters taken by an operator having a duration of more than 1 hour using
equipment to store the data
3.8
reference electrical status
electrical status to be used as a reference in subsequent cathodic protection measurements and checks which
conform to protection requirements
NOTE The “electrical status” refers to a well defined cathodic protection system and its electrical configuration
3.9
remote monitoring
supervision of the state of operational equipment by means of telecommunication techniques
3.10
selected test point
test point which allows comparison of present and past parameters to be recorded in the reference electric
status where a cathodic protection system still maintains its efficiency and effectiveness
3.11
short term a.c. interference
interference on a pipeline during a fault condition of a.c. traction systems or electricity power lines
3.12
short measurements
measurements of electrical parameters taken by an operator having a duration of about 5 min using
equipment to store the data
4 A. c. interference sources
Main long term a. c. interfering sources on buried metallic pipelines are:
- a.c. overhead or underground power lines;
- a.c. traction systems (usually fed by a parallel high voltage feeding line which may be 50 Hz or 16,7Hz).
Long term a.c. interference on a buried pipeline may cause corrosion due to an exchange of a.c. current
between the exposed metal of the pipeline and the surrounding electrolyte.
This exchange of current depends on a.c. voltage whose amplitude is related to various parameters such as:
- the configuration of a.c. power line phase conductors and shield wires;
- the distance between the a.c. power line / traction system and the pipeline;
- the current flowing in the a.c. power line / traction system phase conductors;
- the average coating resistance of the pipeline (Ω.m²);
- the thickness of the coating;
- the soil resistivity.
5 Simplified description of a.c. corrosion process
The cathodic protection of pipelines forces current to enter the pipeline through the metal surface in contact
with soil where the coating is damaged. This current prevents corrosion from taking place.
The corrosion reaction is associated with a current leaving the metal surface.
When an a.c. voltage is present on the cathodically protected pipeline, current will flow through the metal
surface at defects in the coating. This current depends on the impedance of the system. During the positive
half wave of the a.c. voltage, the current will leave the metal surface if the a.c. voltage is sufficiently large.
The current leaving the metal surface can cause charging of the double layer capacitance, oxidation of
hydrogen and reduced corrosion products due to the cathodic protection, and oxidation of the pipeline. Since
the current leaving the metal surface is consumed by several non-corrosive processes, generally higher
voltages than between 4V and 10 V are required to result in a significant corrosion attack on the pipeline.
Various additional parameters influence this process, such as leakage resistance of the defect, soil
composition, cathodic protection level etc.
The processes taking place are schematically illustrated in Figure 1. During the positive half wave the bare
metal surface is oxidized resulting in the formation of a passive film. This is due to the current that leaves the
metal surface. During the negative half wave, when the current enters the metal surface this passive film is
reduced to iron hydroxide. In the following anodic cycle a new passive film grows. Upon reduction of the
passive film the amount of iron hydroxide is increased. Hence every a.c. cycle results in some oxidation of the
metal. In the long term this can result in a significant metal loss.
For comparison, the situation without a.c. interference is shown in Figure 2 In this case no metal loss is
observed, since the current always enters the metal surface.
+
t
-
23 4
key
1 Current
2 Metal
3 Passive film (eg. Fe O )
3 4
4 Iron hydroxide (eg. Fe(OH) )
t Time
Figure 1 - Graph of cathodic protection current with a.c. influence - Schematic description of the a.c.
corrosion process with cathodic protection

+
t
-
23 4
Key
1 Current
2 Metal
3 Passive film (eg. Fe O )
3 4
4 Iron hydroxide (eg. Fe(OH) )
t Time
Figure 2 – Graph of cathodic protection current without a.c. influence
6 Evaluation of a.c. corrosion likelihood
6.1 Prerequisite
The a.c. voltage on a pipeline is considered as the most important parameter to be taken into account when
evaluating the adversely influences by a.c. system.
Therefore, before beginning any evaluation of the a.c. corrosion likelihood, the a.c. voltage of the pipeline
should be lowered if necessary, according to 6.4.4.
6.2 General
The factors which mainly influence the a.c. corrosion phenomena are:
- induced a.c. voltage;
- a.c. current density on the exposed metal;
- d.c. polarisation;
- size of coating faults;
- local soil resistivity;
- local soil chemical composition.
The corrosion likelihood due to a.c. voltage can be evaluated by taking into account different factors which are
generally used in conjunction, such as:
- a.c. voltage on the structure; (See 6.4)
- pipe to soil off potential; (See 6.5)
- a.c. current density; (See 6.6)
- On potential; (See 6.7)
- a.c./d.c. current ratio; (See 6.8)
- soil characteristics; (See 6.9)
- corrosion condition of coupons. (See 6.10)
Other techniques are available to evaluate corrosion. Some of these techniques are described in the annexes
A and B.
In the following, the conditions for evaluating the likelihood of corrosion, either by measurements or by
calculation, are clarified.
For existing pipelines, measuring procedures are also suggested.
Routine direct short measurements on pipelines rarely reflect worst case conditions while calculation gives
more reliable information on the a.c. interference.
For this purpose, measurements shall be related to worst established conditions during normal operation of
interfering systems.
As a first approach, the general evaluation of the likelihood of a.c. corrosion can be by measurement of the a.c.
voltage of the structure (see 6.4).
To evaluate the different factors influencing the a.c. corrosion, the use of coupons is necessary (see EN
13509:2003 Clause 4, and EN 12954). For coupons, an incubation time has to be considered when evaluating
measurement results.
The evaluation of more than one factor is necessary to better assess the a.c. corrosion likelihood. The more
factors considered, the better the assessment.
6.3 Installation / use of coupons
Due to the fact that many electrical and electrochemical parameters cannot be measured directly on the
pipeline itself, the use of coupons is particularly recommended for evaluating the likelihood of a.c. corrosion.
A.c. corrosion coupons are usually made of a steel plate having a known bare surface area (preferably 1 cm
round), simulating a coating fault. They are buried close to the pipeline and connected to it through a test post.
These coupons can either be used for measuring and/or for verifying local protection conditions. In this last
option, three coupons may be installed at the same place (it is recommended to keep at least one meter
between each coupon). The coupons should be excavated at the same time for the purpose of statistical
examination.
Coupons have to be used where the worst conditions have been found in accordance with the calculation or
the measurement described in 7.2.
A reference electrode can either be used during the measurement or permanently installed.
6.4 Influence of a.c. voltage on the structure
6.4.1 General
The a.c. voltage on a structure subjected to interference by a.c. systems should be considered as the most
important parameter to be taken into account when evaluating the likelihood of corrosion on buried pipelines.
The a.c. voltage on a structure subjected to interference by a.c. systems can either be calculated or directly
measured on the structure itself. To evaluate if a calculation or measurements are needed, see 6.4.2.
6.4.2 Voltage calculation
People’s safety and the malfunction of apparatus should be calculated in accordance with CIGRE Technical
Brochure N°95 published in 1995 “Guide on the Influence of High Voltage A.C. Power Systems on Metallic
Pipelines”.
The same algorithms can be used to calculate the pipeline a.c. voltage by taking into account the worst case
under normal operating conditions of the interfering systems.
The limits indicated in 6.4.4 apply.
6.4.3 A.c. voltage measurements
6.4.3.1 General
A.c. interference can be determined by measurement of the a.c. voltage on the pipeline.
While taking measurements on an existing pipeline, the following should be taken into account:
- high voltage power line; variations during time, according to the charge;
- a.c. traction systems; variations during time in accordance with the power absorbed by the traction
system and along the pipeline.
A.c. measurements should be performed on pipelines or sections of them where unacceptable a.c.
interference is suspected or may be expected based on map observation, calculation, or routine
measurements.
The a.c. voltage measurements should be performed in a first instance on all test points, CP stations,
insulating joints and casings, wherever an accessible measuring cable is connected to the pipeline or section.
The following should be included in these measurements:
- instantaneous measurement of a.c. voltage;
- verification of the possible industrial frequencies (mainly 16,7 Hz and 50 Hz).
At a later stage, these measurements may be restricted to a few particular positions, chosen along the most
influenced areas.
NOTE These can be short measurements, provided that they are related to a known electrical behaviour of the
pipeline during a 24 h duration under the influence of the interfering source.
Measurements should be made with the following procedure:
- for routine measurements, short duration a.c. voltage measurements are sufficient and are
carried out between the metal structure and an electrode (which may be a copper / copper
sulfate reference electrode, or any metallic low resistance in contact with the soil) placed over
the pipe;
- for more correct measurements, the electrode should be located at the “remote earth”.
6.4.3.2 Procedure for a.c. voltage measurements
A high input impedance a.c. voltmeter is connected with one pole to a reference electrode (copper/copper
sulfate), which is placed on the soil above the pipeline, and with one pole to the pipeline at a test station. The
voltmeter indicates the instantaneous rms (effective) value of the induced a.c. voltage on the pipeline.
NOTE For long-term evaluation, a data recorder instead of a voltmeter should be used.
V
key
1 Soil
2 a.c voltmeter or recorder
3 Reference electrode
4 Pipe
Figure 3 - Measurement of induced a.c. voltage along the pipeline

6.4.4 a.c. voltage limits on buried pipelines
a.c. corrosion likelihood is linked to the a.c. current density at the coating fault and the consequent flowing
between the metallic pipeline and the environment.
The driving force for this is the pipeline a.c. voltage. Therefore, a.c. corrosion likelihood can be primarily
mitigated by reducing the a.c. voltage.
To reduce the a.c. corrosion likelihood on a buried pipeline, the pipeline a.c. voltage, measured at selected
test points according to the procedure described in 6.4.3.2, should not exceed at any time:
- 10 V where the local soil resistivity is greater than 25 Ω.m;
- 4 V where the local soil resistivity is less than 25 Ω.m.
These values should be considered as the threshold limits which significantly reduce a.c. corrosion likelihood;
they are based on long term practical experience of European operators.
6.4.5 Evaluation of a.c. voltage influence on corrosion likelihood
The a.c. voltage values measured or calculated in accordance with 6.4.2 and 6.4.3 shall be compared with the
threshold limits specified in 6.4.4.
To better evaluate a.c. corrosion likelihood on buried pipelines, due consideration is also to be given to other
factors (defined in 6.2).
6.5 Off potential influence
6.5.1 General
The ordinary on / off measurement techniques (rectifier switching) are not appropriate to evaluate a.c.
corrosion likelihood because they do not allow for elimination of a.c. and d.c. interferences.
To evaluate the a.c. corrosion likelihood, IR free potential measurements on coupons are necessary.
This procedure is called “off potential” because it refers to a test coupon disconnected from the pipeline, thus
without interference from a.c. and/or d.c. currents on the coupon itself.
All the measurements indicated in the following shall be related to worst case conditions, in location and on
the time, during normal operation of the interfering systems.
6.5.2 Coupon off potential measurements
Off potential shall be measured in accordance with EN 13509.
6.5.3 Interpretation of coupon off potential
As a.c. corrosion phenomena are linked to the switching, according to the pH, between immunity, and
passivity condition, and vice versa (see Clause 5), the coupon-to-soil off potential should be more negative
than, but as close as possible to, the limiting critical potential (which is E = –850 mV for iron or steel in
Cu
aerobic or –950 mV in anaerobic soil containing sulfate reducing bacteria).
To fully evaluate the a.c. corrosion likeliho
...