CEN/TS 15280:2006

SLOVENSKI STANDARD
01-maj-2006
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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,
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© 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 d
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