Petroleum, petrochemical and natural gas industries - Prevention of corrosion on pipeline systems influenced by stray currents (ISO 21857:2021)

This document 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 pipeline systems. A brief description of
alternating current (a.c.) effects is provided.
The document is intended to offer guidance for:
— the design of cathodic protection systems which may produce stray currents;
— the design of pipeline systems, or elements of pipeline systems, which are to be buried or immersed and which may be subject to stray current corrosion;
— the selection of appropriate protection or mitigation measures.
The effects of a.c. induced voltages are not dealt with in detail in this document because they are
covered in ISO 18086. General principles and guidelines are, however, provided.
Stray current corrosion can also occur internally in systems containing a conducting electrolyte e.g.
near insulating joints or high resistance pipe joints in pipelines transporting conductive fluids.
Internal corrosion risks from stray currents are not dealt with in detail in this document but principles
and measures described here can be applicable for minimizing the interference effects.
Stray currents can also cause other effects such as overheating. These other effects are not covered in
this document.
A.C. currents can induce unacceptable touch voltages on above-ground appurtenances of pipeline
systems. These are not covered in detail in this document. They are covered in EN 50443, EN 61140,
IEC 60364-4-41, IEC TS 60479-1, IEC 60364-5-52, IEC /TS 61201, and IEC TR 60479-5.
Systems which may be affected by stray currents include buried or immersed metal structures such as:
a) pipeline systems;
b) metal sheathed cables;
c) tanks and vessels;
d) earthing systems;
e) steel reinforcement in concrete;
f) sheet steel piling.
This document provides details only for pipeline systems although the principles can be applied to
other buried structures. The EN 50162 series of standards also provide guidance for railway related
structures.

Erdöl-, petrochemische und Erdgasindustrie - Vermeidung von durch Streuströme beeinflusster Korrosion an Rohrleitungssystemen (ISO 21857:2021)

Industries du pétrole, de la pétrochimie et du gaz naturel - Prévention de la corrosion sur les systèmes de conduites soumis à l'influence de courants vagabonds (ISO 21857:2021)

Petrokemična industrija ter industrija za predelavo nafte in zemeljskega plina - Preprečevanje korozije na cevovodnih sistemih zaradi blodečih tokov (ISO 21857:2021)

General Information

Status
Published
Public Enquiry End Date
04-Sep-2021
Publication Date
24-Oct-2021
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
20-Oct-2021
Due Date
25-Dec-2021
Completion Date
25-Oct-2021

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SLOVENSKI STANDARD
SIST EN ISO 21857:2021
01-december-2021
Petrokemična industrija ter industrija za predelavo nafte in zemeljskega plina -
Preprečevanje korozije na cevovodnih sistemih zaradi blodečih tokov (ISO
21857:2021)

Petroleum, petrochemical and natural gas industries - Prevention of corrosion on pipeline

systems influenced by stray currents (ISO 21857:2021)
Erdöl-, petrochemische und Erdgasindustrie - Vermeidung von durch Streuströme
beeinflusster Korrosion an Rohrleitungssystemen (ISO 21857:2021)

Industries du pétrole, de la pétrochimie et du gaz naturel - Prévention de la corrosion sur

les systèmes de conduites soumis à l'influence de courants vagabonds (ISO
21857:2021)
Ta slovenski standard je istoveten z: EN ISO 21857:2021
ICS:
75.200 Oprema za skladiščenje Petroleum products and
nafte, naftnih proizvodov in natural gas handling
zemeljskega plina equipment
77.060 Korozija kovin Corrosion of metals
SIST EN ISO 21857:2021 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN ISO 21857:2021
---------------------- Page: 2 ----------------------
SIST EN ISO 21857:2021
EN ISO 21857
EUROPEAN STANDARD
NORME EUROPÉENNE
October 2021
EUROPÄISCHE NORM
ICS 75.200
English Version
Petroleum, petrochemical and natural gas industries -
Prevention of corrosion on pipeline systems influenced by
stray currents (ISO 21857:2021)

Industries du pétrole, de la pétrochimie et du gaz Erdöl-, petrochemische und Erdgasindustrie -

naturel - Prévention de la corrosion sur les systèmes Vermeidung von durch Streuströme beeinflusster

de conduites soumis à l'influence de courants Korrosion an Rohrleitungssystemen (ISO 21857:2021)

vagabonds (ISO 21857:2021)
This European Standard was approved by CEN on 3 October 2021.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this

European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references

concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN

member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by

translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management

Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,

Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and

United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 21857:2021 E

worldwide for CEN national Members.
---------------------- Page: 3 ----------------------
SIST EN ISO 21857:2021
EN ISO 21857:2021 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

---------------------- Page: 4 ----------------------
SIST EN ISO 21857:2021
EN ISO 21857:2021 (E)
European foreword

The text of ISO 21857:2021 has been prepared by Technical Committee ISO/TC 67 "Materials,

equipment and offshore structures for petroleum, petrochemical and natural gas industries” of the

International Organization for Standardization (ISO) and has been taken over as EN ISO 21857:2021 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 April 2022, and conflicting national standards shall be

withdrawn at the latest by April 2022.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

Any feedback and questions on this document should be directed to the users’ national standards body.

A complete listing of these bodies can be found on the CEN website.

According to the CEN-CENELEC Internal Regulations, the national standards organizations of the

following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,

Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,

Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of

North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the

United Kingdom.
Endorsement notice

The text of ISO 21857:2021 has been approved by CEN as EN ISO 21857:2021 without any modification.

---------------------- Page: 5 ----------------------
SIST EN ISO 21857:2021
---------------------- Page: 6 ----------------------
SIST EN ISO 21857:2021
INTERNATIONAL ISO
STANDARD 21857
First edition
2021-03
Petroleum, petrochemical and
natural gas industries — Prevention
of corrosion on pipeline systems
influenced by stray currents
Industries du pétrole, de la pétrochimie et du gaz naturel —
Prévention de la corrosion sur les systèmes de conduites soumis à
l'influence de courants vagabonds
Reference number
ISO 21857:2021(E)
ISO 2021
---------------------- Page: 7 ----------------------
SIST EN ISO 21857:2021
ISO 21857:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
---------------------- Page: 8 ----------------------
SIST EN ISO 21857:2021
ISO 21857:2021(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction ................................................................................................................................................................................................................................vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 2

4 Abbreviations and symbols ....................................................................................................................................................................... 3

4.1 Abbreviations ........................................................................................................................................................................................... 3

4.2 Symbols ......................................................................................................................................................................................................... 4

5 Information exchange and co-operation ..................................................................................................................................... 5

6 Common sources of interference that can affect corrosion ..................................................................................... 6

6.1 General ........................................................................................................................................................................................................... 6

6.2 Direct current ........................................................................................................................................................................................... 7

6.2.1 General...................................................................................................................................................................................... 7

6.2.2 Traction systems .............................................................................................................................................................. 7

6.2.3 Industrial systems .......................................................................................................................................................... 7

6.3 Alternating current.............................................................................................................................................................................. 7

6.3.1 General...................................................................................................................................................................................... 7

6.3.2 Overhead and buried power lines..................................................................................................................... 8

6.4 High-voltage direct current transmission systems .................................................................................................. 8

6.5 Natural interference ........................................................................................................................................................................... 8

6.5.1 General...................................................................................................................................................................................... 8

6.5.2 Geomagnetic (telluric) interference ................................................................................................................ 8

6.5.3 Tidal interference effects .......................................................................................................................................... 9

7 Identification and measurement of stray current interference ..........................................................................9

7.1 Principle ........................................................................................................................................................................................................ 9

7.2 Stray Current interference .........................................................................................................................................................10

7.2.1 Inductive and conductive coupling from remote sources .........................................................10

7.2.2 Conductive coupling from nearby sources .............................................................................................10

7.3 Measurement of electrical parameters ...........................................................................................................................10

7.3.1 Data acquisition systems .......................................................................................................................................10

7.3.2 Possible errors in AC measurements ..........................................................................................................11

7.3.3 Potential measurement ...........................................................................................................................................11

7.3.4 Current measurement on probes ...................................................................................................................11

7.3.5 IR-free potential measurement on coupons or probes ................................................................11

7.3.6 Duration of the measurement ...........................................................................................................................11

7.3.7 Specific requirements for coupons or probes......................................................................................12

7.4 Corrosion rate measurement ...................................................................................................................................................12

8 Acceptance criteria for DC interference ....................................................................................................................................12

8.1 Overview of criteria .........................................................................................................................................................................12

8.2 Corrosion rate .......................................................................................................................................................................................13

8.3 Criteria for steel and cast iron ................................................................................................................................................14

8.3.1 Time constant interference .................................................................................................................................14

8.3.2 Time variant interference .....................................................................................................................................15

8.4 Criteria for steel pipes in concrete based on potential measurements without

cathodic protection ..........................................................................................................................................................................16

8.4.1 Time constant anodic interference ...............................................................................................................16

8.4.2 Time variant interference .....................................................................................................................................16

9 Reduction of DC stray current interference ..........................................................................................................................16

9.1 General ........................................................................................................................................................................................................16

9.2 Modifications to the source of interference ................................................................................................................17

9.2.1 Principles .............................................................................................................................................................................17

© ISO 2021 – All rights reserved iii
---------------------- Page: 9 ----------------------
SIST EN ISO 21857:2021
ISO 21857:2021(E)

9.2.2 Direct current systems at industrial sites ...............................................................................................17

9.2.3 Direct current systems at ports........................................................................................................................17

9.2.4 Direct current traction systems .......................................................................................................................17

9.2.5 Cathodic protection systems ..............................................................................................................................18

9.2.6 Telluric interference...................................................................................................................................................19

9.2.7 Direct current communication systems ....................................................................................................19

10 Modifications to the interfered structure ...............................................................................................................................19

10.1 General ........................................................................................................................................................................................................19

10.2 Design prerequisites .......................................................................................................................................................................20

10.2.1 Coatings ................................................................................................................................................................................20

10.2.2 Isolation from other structures ........................................................................................................................20

10.2.3 Distance to be maximized .....................................................................................................................................20

10.2.4 Installation of mitigation devices ...................................................................................................................20

10.2.5 Modifying the electrical continuity of the interfered structure ...........................................21

11 Inspection and maintenance .................................................................................................................................................................22

Annex A (informative) Use of current probes to evaluate fluctuating stray current

interference on cathodically protected structures ........................................................................................................23

Annex B (informative) Determining the relevant position for placing reference electrodes,

coupons and probes in case of any conductive coupling caused by stray currents .....................26

Annex C (informative) Operating principles of electrical resistance probes ..........................................................33

Annex D (informative) Geomagnetic interference ..............................................................................................................................34

Annex E (informative) High voltage direct current interference .........................................................................................43

Annex F (informative) Alternating Current Interference .............................................................................................................45

Annex G (informative) Tidal Effects ....................................................................................................................................................................50

Annex H (informative) Photovoltaic interference ...............................................................................................................................51

Annex I (informative) Modelling the effects of stray current interference on cathodically

protected pipelines .........................................................................................................................................................................................54

Annex J (informative) Assessment of the corrosion risk for steel in concrete or for

cathodically protected structures under time variant interference conditions .............................58

Annex K (informative) Principles of anodic and cathodic interference .......................................................................63

Bibliography .............................................................................................................................................................................................................................66

iv © ISO 2021 – All rights reserved
---------------------- Page: 10 ----------------------
SIST EN ISO 21857:2021
ISO 21857:2021(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/

iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 67, Materials, equipment and offshore

structures for petroleum, petrochemical and natural gas industries, Subcommittee SC 2, Pipeline

transportation systems, in collaboration with the European Committee for Standardization (CEN)

Technical Committee CEN/TC 219, Cathodic protection, in accordance with the Agreement on technical

cooperation between ISO and CEN (Vienna Agreement).

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
© ISO 2021 – All rights reserved v
---------------------- Page: 11 ----------------------
SIST EN ISO 21857:2021
ISO 21857:2021(E)
Introduction

This document provides guidance for the prevention of external corrosion when a pipeline is influenced

by electrical interference. Electrical interference can be from stray currents (defined in ISO 8044) and

from naturally occurring interference caused by geomagnetic or tidal activity.

International Standards on cathodic protection (e.g. ISO 15589-1 and ISO 15589-2) refer to a structure-

to- electrolyte potential value that is considered to indicate that cathodic protection is effective. When

the potential is influenced by stray currents, however, it is not always possible to obtain a meaningful

structure-to-electrolyte potential and other methods of assessment are needed. These other methods

can include mathematical analysis of the potentials and/or direct assessment of the corrosion rate

using electrical resistance probes.

An affected structure carrying stray currents, e.g. a pipeline or cable can itself affect other nearby

structures.

This document is not intended to inhibit the use of alternative equipment or engineering solutions for

individual applications. Where an alternative is offered, it is intended that any variations from this

document be identified and documented.
vi © ISO 2021 – All rights reserved
---------------------- Page: 12 ----------------------
SIST EN ISO 21857:2021
INTERNATIONAL STANDARD ISO 21857:2021(E)
Petroleum, petrochemical and natural gas industries —
Prevention of corrosion on pipeline systems influenced by
stray currents
1 Scope

This document establishes the general principles for the evaluation and minimization of the effects of

stray current corrosion on external surfaces of buried or immersed pipeline systems caused by AC and

DC electrical interference.

Other stray current effects such as overheating, and interference with welding operations are not

covered in this document.

A brief description of AC effects, general principles and some guidelines, are provided.

NOTE 1 See ISO 18086 for the effects of alternating current on buried or immersed pipelines.

Systems that can also be affected by stray currents include buried or immersed metal structures such

as the following:
a) pipeline systems;
b) metal sheathed cables;
c) tanks and vessels;
d) earthing systems;
e) steel reinforcement in concrete;
f) sheet steel piling.
This document gives guidelines for
— the design of cathodic protection systems that might produce stray currents,

— the design of pipeline systems, or elements of pipeline systems, which are buried or immersed, and

which can be subject to stray current corrosion, and
— the selection of appropriate protection or mitigation measures.

Internal corrosion risks from stray currents are not dealt with in detail in this document but principles

and measures described here can be applicable for minimizing the interference effects.

NOTE 2 The impact of electromagnetic interference on above-ground appurtenances of pipeline systems is

covered in EN 50443, IEC 61140, IEC 60364-4-41, IEC 60479-1, IEC 60364-5-52, IEC/TS 61201 and IEC/TR 60479-5.

This document can also be used for pipeline systems outside of the petrochemical and natural gas

industries and other buried or immersed structures.
NOTE 3 EN 50162 provides guidance for railway related structures.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

© ISO 2021 – All rights reserved 1
---------------------- Page: 13 ----------------------
SIST EN ISO 21857:2021
ISO 21857:2021(E)

IEC 62128-2:2013, Railway applications - Fixed installations - Electrical safety, earthing and the return

circuit - Part 2: Provisions against the effects of stray currents caused by d.c. traction systems

ISO 15589-1, Petroleum, petrochemical and natural gas industries — Cathodic protection of pipeline

systems — Part 1: On-land pipelines
ISO 8044, Corrosion of metals and alloys — Vocabulary
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 15589-1, IEC 62128-2:2013,

ISO 8044 and the following apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
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
remote earth

theoretical concept that refers to a ground electrode of zero impedance placed an infinite distance

away from the ground under test

Note 1 to entry: In practice, remote earth is approached when the mutual resistance between the ground under

test and the test electrode becomes negligible. Remote earth is normally considered to be at zero potential.

[1]
[SOURCE: IEEE Std 81-2012 ]
3.3
conductive coupling

transfer of energy occurring when a part of the current belonging to the interfering system returns to

the system earth via the interfered system

Note 1 to entry: Also, when the voltage to the reference earth of the ground in the vicinity of the influenced object

rises because of a fault in the interfering system, and the results of which are conductive voltages and currents.

3.4
drainage
electrical drainage

transfer of stray current from an affected structure to the current source by means of a deliberate bond

Note 1 to entry: For drainage devices see direct drainage bond (3.5), unidirectional drainage bond (3.7) and forced

drainage bond (3.6).
3.5
direct drainage bond

device that provides electrical drainage (3.4) by means of a bi-directional, metallic bond between an

affected structure and the stray current source
Note 1 to entry: The bond can include a series resistor to reduce the current.
2 © ISO 2021 – All rights reserved
---------------------- Page: 14 ----------------------
SIST EN ISO 21857:2021
ISO 21857:2021(E)
3.6
forced drainage bo
...

SLOVENSKI STANDARD
oSIST prEN ISO 21857:2021
01-september-2021
Petrokemična industrija ter industrija za predelavo nafte in zemeljskega plina -
Preprečevanje korozije na cevovodnih sistemih zaradi neurejenih tokov (ISO
21857:2021)

Petroleum, petrochemical and natural gas industries - Prevention of corrosion on pipeline

systems influenced by stray currents (ISO 21857:2021)
Erdöl-, petrochemische und Erdgasindustrie - Vermeidung von durch Streuströme
beeinflusster Korrosion an Rohrleitungssystemen (ISO 21857:2021)

Industries du pétrole, de la pétrochimie et du gaz naturel - Prévention de la corrosion sur

les systèmes de conduites soumis à l'influence de courants vagabonds (ISO
21857:2021)
Ta slovenski standard je istoveten z: prEN ISO 21857
ICS:
75.200 Oprema za skladiščenje Petroleum products and
nafte, naftnih proizvodov in natural gas handling
zemeljskega plina equipment
77.060 Korozija kovin Corrosion of metals
oSIST prEN ISO 21857:2021 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
oSIST prEN ISO 21857:2021
---------------------- Page: 2 ----------------------
oSIST prEN ISO 21857:2021
INTERNATIONAL ISO
STANDARD 21857
First edition
2021-03
Petroleum, petrochemical and
natural gas industries — Prevention
of corrosion on pipeline systems
influenced by stray currents
Industries du pétrole, de la pétrochimie et du gaz naturel —
Prévention de la corrosion sur les systèmes de conduites soumis à
l'influence de courants vagabonds
Reference number
ISO 21857:2021(E)
ISO 2021
---------------------- Page: 3 ----------------------
oSIST prEN ISO 21857:2021
ISO 21857:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
---------------------- Page: 4 ----------------------
oSIST prEN ISO 21857:2021
ISO 21857:2021(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction ................................................................................................................................................................................................................................vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 2

4 Abbreviations and symbols ....................................................................................................................................................................... 3

4.1 Abbreviations ........................................................................................................................................................................................... 3

4.2 Symbols ......................................................................................................................................................................................................... 4

5 Information exchange and co-operation ..................................................................................................................................... 5

6 Common sources of interference that can affect corrosion ..................................................................................... 6

6.1 General ........................................................................................................................................................................................................... 6

6.2 Direct current ........................................................................................................................................................................................... 7

6.2.1 General...................................................................................................................................................................................... 7

6.2.2 Traction systems .............................................................................................................................................................. 7

6.2.3 Industrial systems .......................................................................................................................................................... 7

6.3 Alternating current.............................................................................................................................................................................. 7

6.3.1 General...................................................................................................................................................................................... 7

6.3.2 Overhead and buried power lines..................................................................................................................... 8

6.4 High-voltage direct current transmission systems .................................................................................................. 8

6.5 Natural interference ........................................................................................................................................................................... 8

6.5.1 General...................................................................................................................................................................................... 8

6.5.2 Geomagnetic (telluric) interference ................................................................................................................ 8

6.5.3 Tidal interference effects .......................................................................................................................................... 9

7 Identification and measurement of stray current interference ..........................................................................9

7.1 Principle ........................................................................................................................................................................................................ 9

7.2 Stray Current interference .........................................................................................................................................................10

7.2.1 Inductive and conductive coupling from remote sources .........................................................10

7.2.2 Conductive coupling from nearby sources .............................................................................................10

7.3 Measurement of electrical parameters ...........................................................................................................................10

7.3.1 Data acquisition systems .......................................................................................................................................10

7.3.2 Possible errors in AC measurements ..........................................................................................................11

7.3.3 Potential measurement ...........................................................................................................................................11

7.3.4 Current measurement on probes ...................................................................................................................11

7.3.5 IR-free potential measurement on coupons or probes ................................................................11

7.3.6 Duration of the measurement ...........................................................................................................................11

7.3.7 Specific requirements for coupons or probes......................................................................................12

7.4 Corrosion rate measurement ...................................................................................................................................................12

8 Acceptance criteria for DC interference ....................................................................................................................................12

8.1 Overview of criteria .........................................................................................................................................................................12

8.2 Corrosion rate .......................................................................................................................................................................................13

8.3 Criteria for steel and cast iron ................................................................................................................................................14

8.3.1 Time constant interference .................................................................................................................................14

8.3.2 Time variant interference .....................................................................................................................................15

8.4 Criteria for steel pipes in concrete based on potential measurements without

cathodic protection ..........................................................................................................................................................................16

8.4.1 Time constant anodic interference ...............................................................................................................16

8.4.2 Time variant interference .....................................................................................................................................16

9 Reduction of DC stray current interference ..........................................................................................................................16

9.1 General ........................................................................................................................................................................................................16

9.2 Modifications to the source of interference ................................................................................................................17

9.2.1 Principles .............................................................................................................................................................................17

© ISO 2021 – All rights reserved iii
---------------------- Page: 5 ----------------------
oSIST prEN ISO 21857:2021
ISO 21857:2021(E)

9.2.2 Direct current systems at industrial sites ...............................................................................................17

9.2.3 Direct current systems at ports........................................................................................................................17

9.2.4 Direct current traction systems .......................................................................................................................17

9.2.5 Cathodic protection systems ..............................................................................................................................18

9.2.6 Telluric interference...................................................................................................................................................19

9.2.7 Direct current communication systems ....................................................................................................19

10 Modifications to the interfered structure ...............................................................................................................................19

10.1 General ........................................................................................................................................................................................................19

10.2 Design prerequisites .......................................................................................................................................................................20

10.2.1 Coatings ................................................................................................................................................................................20

10.2.2 Isolation from other structures ........................................................................................................................20

10.2.3 Distance to be maximized .....................................................................................................................................20

10.2.4 Installation of mitigation devices ...................................................................................................................20

10.2.5 Modifying the electrical continuity of the interfered structure ...........................................21

11 Inspection and maintenance .................................................................................................................................................................22

Annex A (informative) Use of current probes to evaluate fluctuating stray current

interference on cathodically protected structures ........................................................................................................23

Annex B (informative) Determining the relevant position for placing reference electrodes,

coupons and probes in case of any conductive coupling caused by stray currents .....................26

Annex C (informative) Operating principles of electrical resistance probes ..........................................................33

Annex D (informative) Geomagnetic interference ..............................................................................................................................34

Annex E (informative) High voltage direct current interference .........................................................................................43

Annex F (informative) Alternating Current Interference .............................................................................................................45

Annex G (informative) Tidal Effects ....................................................................................................................................................................50

Annex H (informative) Photovoltaic interference ...............................................................................................................................51

Annex I (informative) Modelling the effects of stray current interference on cathodically

protected pipelines .........................................................................................................................................................................................54

Annex J (informative) Assessment of the corrosion risk for steel in concrete or for

cathodically protected structures under time variant interference conditions .............................58

Annex K (informative) Principles of anodic and cathodic interference .......................................................................63

Bibliography .............................................................................................................................................................................................................................66

iv © ISO 2021 – All rights reserved
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oSIST prEN ISO 21857:2021
ISO 21857:2021(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/

iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 67, Materials, equipment and offshore

structures for petroleum, petrochemical and natural gas industries, Subcommittee SC 2, Pipeline

transportation systems, in collaboration with the European Committee for Standardization (CEN)

Technical Committee CEN/TC 219, Cathodic protection, in accordance with the Agreement on technical

cooperation between ISO and CEN (Vienna Agreement).

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
© ISO 2021 – All rights reserved v
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oSIST prEN ISO 21857:2021
ISO 21857:2021(E)
Introduction

This document provides guidance for the prevention of external corrosion when a pipeline is influenced

by electrical interference. Electrical interference can be from stray currents (defined in ISO 8044) and

from naturally occurring interference caused by geomagnetic or tidal activity.

International Standards on cathodic protection (e.g. ISO 15589-1 and ISO 15589-2) refer to a structure-

to- electrolyte potential value that is considered to indicate that cathodic protection is effective. When

the potential is influenced by stray currents, however, it is not always possible to obtain a meaningful

structure-to-electrolyte potential and other methods of assessment are needed. These other methods

can include mathematical analysis of the potentials and/or direct assessment of the corrosion rate

using electrical resistance probes.

An affected structure carrying stray currents, e.g. a pipeline or cable can itself affect other nearby

structures.

This document is not intended to inhibit the use of alternative equipment or engineering solutions for

individual applications. Where an alternative is offered, it is intended that any variations from this

document be identified and documented.
vi © ISO 2021 – All rights reserved
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oSIST prEN ISO 21857:2021
INTERNATIONAL STANDARD ISO 21857:2021(E)
Petroleum, petrochemical and natural gas industries —
Prevention of corrosion on pipeline systems influenced by
stray currents
1 Scope

This document establishes the general principles for the evaluation and minimization of the effects of

stray current corrosion on external surfaces of buried or immersed pipeline systems caused by AC and

DC electrical interference.

Other stray current effects such as overheating, and interference with welding operations are not

covered in this document.

A brief description of AC effects, general principles and some guidelines, are provided.

NOTE 1 See ISO 18086 for the effects of alternating current on buried or immersed pipelines.

Systems that can also be affected by stray currents include buried or immersed metal structures such

as the following:
a) pipeline systems;
b) metal sheathed cables;
c) tanks and vessels;
d) earthing systems;
e) steel reinforcement in concrete;
f) sheet steel piling.
This document gives guidelines for
— the design of cathodic protection systems that might produce stray currents,

— the design of pipeline systems, or elements of pipeline systems, which are buried or immersed, and

which can be subject to stray current corrosion, and
— the selection of appropriate protection or mitigation measures.

Internal corrosion risks from stray currents are not dealt with in detail in this document but principles

and measures described here can be applicable for minimizing the interference effects.

NOTE 2 The impact of electromagnetic interference on above-ground appurtenances of pipeline systems is

covered in EN 50443, IEC 61140, IEC 60364-4-41, IEC 60479-1, IEC 60364-5-52, IEC/TS 61201 and IEC/TR 60479-5.

This document can also be used for pipeline systems outside of the petrochemical and natural gas

industries and other buried or immersed structures.
NOTE 3 EN 50162 provides guidance for railway related structures.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

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oSIST prEN ISO 21857:2021
ISO 21857:2021(E)

IEC 62128-2:2013, Railway applications - Fixed installations - Electrical safety, earthing and the return

circuit - Part 2: Provisions against the effects of stray currents caused by d.c. traction systems

ISO 15589-1, Petroleum, petrochemical and natural gas industries — Cathodic protection of pipeline

systems — Part 1: On-land pipelines
ISO 8044, Corrosion of metals and alloys — Vocabulary
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 15589-1, IEC 62128-2:2013,

ISO 8044 and the following apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
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
remote earth

theoretical concept that refers to a ground electrode of zero impedance placed an infinite distance

away from the ground under test

Note 1 to entry: In practice, remote earth is approached when the mutual resistance between the ground under

test and the test electrode becomes negligible. Remote earth is normally considered to be at zero potential.

[1]
[SOURCE: IEEE Std 81-2012 ]
3.3
conductive coupling

transfer of energy occurring when a part of the current belonging to the interfering system returns to

the system earth via the interfered system

Note 1 to entry: Also, when the voltage to the reference earth of the ground in the vicinity of the influenced object

rises because of a fault in the interfering system, and the results of which are conductive voltages and currents.

3.4
drainage
electrical drainage

transfer of stray current from an affected structure to the current source by means of a deliberate bond

Note 1 to entry: For drainage devices see direct drainage bond (3.5), unidirectional drainage bond (3.7) and forced

drainage bond (3.6).
3.5
direct drainage bond

device that provides electrical drainage (3.4) by means of a bi-directional, metallic bond between an

affected structure and the stray current source
Note 1 to entry: The bond can include a series resistor to reduce the current.
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oSIST prEN ISO 21857:2021
ISO 21857:2021(E)
3.6
forced drainage bond

device that provides electrical drainage (3.4) by means of a bond between an affected structure and the

stray current source

Note 1 to entry: The bond includes a separate source of DC power to augment the transfer of current.

3.7
unidirectional drainage bond

device that provides electrical drainage (3.4) by means of a unidirectional bond between the affected

structure and the stray current source

Note 1 to entry: The bond includes a device such as a diode to ensure that current can only flow in one direction.

3.8
telluric interference

voltages generated by geomagnetic field variations that cause variations in the observed pipe-to-soil

potentials
3.9
electrical resistance probe
ER probe

device that measures metal loss by comparison of the calibrated resistance value of a piece of metal

with known physical characteristics
3.10
sampling rate
measuring interval set by the operator
3.11
alternating current interference
AC interference

electrical disturbance generated by AC systems that affects buried or immersed pipelines by conduction

and/or induction
Note 1 to entry: Powerlines, railway traction systems.
3.12
direct current interference
DC interference

disturbance, generated by DC systems, that affects buried or immersed metallic structures primarily

by conduction
4 Abbreviations and symbols
4.1 Abbreviations
AC Alternating current
ACVG Alternating current voltage gradient
CP Cathodic protection
DC Direct current
DCVG Direct current voltage gradient
emf Electromotive force
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oSIST prEN ISO 21857:2021
ISO 21857:2021(E)
GIC Geomagnetically induced currents
HVAC High voltage alternating current
HVDC High Voltage Direct Current

IR Product of the current and resistance (I and R) that indicates the voltage drop error in a

potential measurement
PV Photovoltaic
r.m.s. Root mean square
4.2 Symbols
a Per annum
B Magnetic field
E Structure/soil potential for non cathodically protected structures
E Anodic potential
E Cathodic potential

ΔE Potential difference due to operation / non-operation of the interfering source

ΔE Anodic potential shift (IR drop included)
ΔE Average anodic potential shift
a,avg
ΔE Anodic potential shift (IR drop excluded)
a,IR free
ΔE Cathodic potential shift
ΔE Measured interference
ΔE Average cathodic potential shift
c,avg
E Structure potential of a metal in a given corrosion system (ISO 8044)
cor

E Structure potential without measurement error due to current flowing in the circuit

IR-free
E ON potential
E Average ON potential
on,avg
E Protection potential according to ISO 15589-1
E On potential required to achieve effective cathodic protection
ref
F Electric field
I Coupon current
cpn
J Current density
J Anodic current density
J Cathodic current density
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oSIST prEN ISO 21857:2021
ISO 21857:2021(E)
J Coupon current density
cpn
J Reference value for current density (analogous to I )
ref ref
ρ Soil resistivity (Ω·m)
Q Anodic charge during the period of anodic interference
Q Cathodic charge during the period of cathodic interference
R Coupon element resistance
R Isolation resistance, usually of a cable insulation
iso
s Seconds
S⋅km Siemens per unit length
t Time

T Interval when the structure is anodic with respect to the selected value of E or J

a ref ref
T Maximum duration of the anodic period
a,max

T Interval when the structure is cathodic with respect to the selected value of E or J

c ref ref
v Corrosion rate
cor
V Voltage with respect to a copper/copper sulfate reference electrode
CSE
5 Information exchange and co-operation

Common sources of interference that can cause stray current corrosion are given in Clause 6. During

the design stage of buried or immersed metallic pipeline systems, the possibility of both causing and

suffering from stray current interference shall be taken into consideration and documented. The

pipeline system should achieve the acceptance criteria identified in Clause 8. Construction work, major

changes on existing structures, regenerative braking, etc. can require a detailed consideration of the

interference situation.
Electri
...

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