EN ISO 17864:2008

SLOVENSKI STANDARD
01-julij-2008
.RUR]LMDNRYLQLQ]OLWLQ'RORþDQMHNULWLþQHWHPSHUDWXUH]D]DþHWHNWRþNDVWH
NRUR]LMHSULSRWHQFLRVWDWLþQLNRQWUROL,62
Corrosion of metals and alloys - Determination of the critical pitting temperature under
potientiostatic control (ISO 17864:2005)
Corrosion des métaux et alliages - Determination de la température critique de piquration
des aciers inoxydables sous contrôle potentiostatique (ISO 17864:2005)
Ta slovenski standard je istoveten z: EN ISO 17864:2008
ICS:
77.060 Korozija kovin Corrosion of metals
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 17864
NORME EUROPÉENNE
EUROPÄISCHE NORM
April 2008
ICS 77.060
English Version
Corrosion of metals and alloys - Determination of the critical
pitting temperature under potientiostatic control (ISO
17864:2005)
Corrosion des métaux et alliages - Determination de la Korrosion von Metallen und Legierungen - Bestimmung der
température critique de piqûration des aciers inoxydables kritischen Lochkorrosionstemperatur bei potentiostatischer
sous contrôle potentiostatique (ISO 17864:2005) Belastung (ISO 17864:2005)
This European Standard was approved by CEN on 21 March 2008.
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 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 Management Centre has the same status as the
official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, 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
© 2008 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 17864:2008: E
worldwide for CEN national Members.

Contents Page
Foreword.3

Foreword
The text of ISO 17864:2005 has been prepared by Technical Committee ISO/TC 156 “Corrosion of metals and
alloys” of the International Organization for Standardization (ISO) and has been taken over as EN ISO
17864:2008 by Technical Committee CEN/TC 262 “Metallic and other inorganic coatings” the secretariat of
which is held by BSI.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by October 2008, and conflicting national standards shall be withdrawn at
the latest by October 2008.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
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, 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 the United Kingdom.
Endorsement notice
The text of ISO 17864:2005 has been approved by CEN as a EN ISO 17864:2008 without any modification.

INTERNATIONAL ISO
STANDARD 17864
First edition
2005-08-01
Corrosion of metals and alloys —
Determination of the critical pitting
temperature under potientiostatic control
Corrosion des métaux et alliages — Determination de la température
critique de piqûration des aciers inoxydables sous contrôle
potentiostatique
Reference number
ISO 17864:2005(E)
©
ISO 2005
ISO 17864:2005(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

©  ISO 2005
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2005 – All rights reserved

ISO 17864:2005(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Principle. 1
5 Apparatus . 2
6 Specimens . 3
7 Calibration of specimen temperature vs. solution temperature . 4
8 Procedure . 4
9 Assessment of results. 5
10 Test report . 6
Annex A (informative) Guidelines for selecting the test parameters. 7
Annex B (informative) Method of preventing a crevice attack. 9
Annex C (informative) Potential difference of selected reference electrodes at 25 °C with respect
to the standard hydrogen electrode (SHE) . 13

ISO 17864:2005(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 17864 was prepared by Technical Committee ISO/TC 156, Corrosion of metals and alloys.
iv © ISO 2005 – All rights reserved

ISO 17864:2005(E)
Introduction
Stainless steel is susceptible to pitting corrosion, crevice corrosion, and stress-corrosion cracking, etc.,
although it is used as generally a corrosion-resistant material. Pitting phenomenon is generally of a random
nature, therefore its measurement requires at least a couple of values. Critical pitting temperature defines the
lowest potential-independent temperature, below which pitting does not occur.
The basic methodology was first standardized in ASTM G150, Standard test method for electrochemical
critical pitting temperature testing of stainless steels.

INTERNATIONAL STANDARD ISO 17864:2005(E)

Corrosion of metals and alloys — Determination of the critical
pitting temperature under potientiostatic control
1 Scope
This International Standard describes the procedure for determining the critical pitting temperature for
stainless steels (austenitic, ferritic/austenitic, ferritic stainless steel) under potentiostatic control.
The principal advantage of the test is the rapidity with which the critical pitting temperature can be measured
in a single test.
The critical pitting temperature, as determined in this International Standard, can be used as a relative index
of performance, for example, to compare the relative performance of different grades of stainless steel. The
test described in this International Standard is not intended to determine the temperature at which pitting will
occur in service.
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.
ISO 8044:1999, Corrosion of metals and alloys — Basic terms and definitions
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
critical pitting temperature
CPT
lowest temperature on the surface of the specimen at which stable propagating pitting occurs under specified
test conditions
3.2
temperature ramp rate
rate at which the temperature of the surface of the specimen is increased during the test
−1
NOTE The temperature ramp rate is expressed in degrees Celsius per second (°C s ).
4 Principle
4.1 The test involves increasing the temperature of the surface of the specimen at a specified rate, whilst
exposing the specimen to a specified environment and maintaining the potential of the specimen at a specified
value. The temperature of the surface of the specimen is increased by heating the solution.
ISO 17864:2005(E)
4.2 The critical pitting temperature is defined as the temperature of the specimen at which the current
density exceeds a specified value for 60 s. A 60 s delay is used in order to ensure that the observed current
increase originates from stable propagating pitting, and not short-lived current peaks originating from
metastable pitting.
4.3 The specimen holder is designed to ensure that crevice corrosion does not occur at the seal between
the specimen and the holder.
4.4 There may be a temperature gradient between the bulk of the solution and the surface of the specimen,
the magnitude of which will depend on the geometry and dimensions of the specimen. Guidelines for
calibrating the temperature of the surface of the specimen relative to the temperature of the solution are given
in Clause 7.
4.5 The temperature ramp rate, environment and applied potential may be varied, depending on the
material. Guidelines for selecting the test parameters for austenitic and duplex stainless steels are given in
Annex A.
4.6 The critical pitting temperature is specific to the method of testing and should only be used as a
comparative measure of performance.
5 Apparatus
5.1 Potentiostat
The potentiostat shall be capable of controlling the electrode potential to within ± 1 mV of a preset value.
5.2 Electrode potential-measuring instrument
11 14
The instrument should have a high input impedance of the order of 10 Ω to 10 Ω, to minimize current
drawn from the system during measurement. The sensitivity and accuracy of the instrument should be
sufficient to detect a change of 1,0 mV.
5.3 Current-measuring instruments
The current in the circuit is evaluated from the potential drop measured across a known resistor. In many
potentiostats, this measurement is made internally, but measurements can also be made externally by
locating a resistor in the current line from the auxiliary electrode to the auxiliary connection on the potentiostat.
The instrument shall be capable of measuring a current to within 2 % of the actual value.
5.4 Temperature controller
The temperature controller shall be capable of increasing the temperature of the surface of the specimen from
0 °C to 100 °C at a controlled rate. This is achieved by heating or cooling the solution. Above 10 °C, the
average rate of temperature change of the specimen shall be controlled to within ± 30 % of the desired value,
where the average is calculated over a temperature range of 10 °C. Guidelines for calculating the temperature
of the specimen relative to the temperature of the solution are given in Clause 7.
5.5 Temperature-measurement instrumentation
The temperature-measurement instrumentation shall be capable of measuring the temperature of the test
solution with an accuracy of ± 0,4 °C.
2 © ISO 2005 – All rights reserved

ISO 17864:2005(E)
5.6 Specimen holder
5.6.1 Any part of the specimen holder coming into contact with the test solution shall be made of an inert
material.
5.6.2 The specimen holder shall be designed to ensure that crevice corrosion does not occur at the contact
area between the specimen holder and the specimen. A method of preventing such crevice attack, using a
flushed-port cell or a flushed specimen holder, is outlined in Annex B.
5.7 Test cell
5.7.1 The test cell shall contain the test specimen, a Luggin capillary probe connected to an external
reference electrode for measuring the electrode potential, an auxiliary electrode, a port for insertion of a
temperature-measuring device and a facility for stirring the solution in a repeatable manner. This can be
achieved using a mechanical stirring device or simply by bubbling gas through the solution at a controlled rate.
5.7.2 A double-walled cell is commonly used to enable the solution to be cooled or heated by recirculating a
liquid from an external heating bath to the outer chamber of the cell.
5.7.3 The tip of the Luggin capillary probe shall be positioned so that it is at a distance from the specimen of
about, but not closer than, twice the diameter of the tip.
5.7.4 Any part of the test cell or specimen holder that comes into contact with the solution shall be
constructed from an inert material. Polycarbonate, glass and polytetrafluoroethylene (PTFE) are suitable
materials.
5.7.5 The ratio of the volume of solution in the test cell to the specimen area shall be at least 100 ml/cm .
5.8 Auxiliary electrode
The auxiliary electrode is commonly prepared from high-purity platinum. Other materials may be used provided
they are inert. The auxiliary electrode may be constructed in the form of sheet or rod, or in the form of a gauze
supported on a glass frame. The area of the auxiliary electrode should be at least the area of the specimen.
NOTE Graphite may be used as a auxiliary electrode but care must be taken to avoid contamination; desorption of
species retained in the graphite may be necessary prior to use.
5.9 Reference electrode
5.9.1 The reference electrode shall be maintained at ambient temperature external to the test cell and
connected to the test cell via a Luggin capillary probe.
5.9.2 Commonly used electrodes include the silver/silver chloride electrode and the saturated calomel
electrode. The potentials of these electrodes at 25 °C relative to the standard hydrogen electrode at 25 °C are
given in Annex C.
6 Specimens
6.1 Any specimen geometry compatible with the specimen holder may be used.
6.2 A minimum test area of 1 cm shall be used.
6.3 The surface finish shall be reproducible.
-
...