SIST EN ISO 11463:2020
(Main)Corrosion of metals and alloys - Guidelines for the evaluation of pitting corrosion (ISO 11463:2020)
Corrosion of metals and alloys - Guidelines for the evaluation of pitting corrosion (ISO 11463:2020)
This document gives guidelines for the selection of procedures that can be used in the identification
and examination of corrosion pits and in the evaluation of pitting corrosion and pit growth rate.
Korrosion von Metallen und Legierungen - Richtlinien für die Bewertung der Lochkorrosion (ISO 11463:2020)
Dieses Dokument liefert einen Leitfaden für die Auswahl von Verfahren, die zum Nachweis und zur Untersuchung von Lochkorrosion und zur Bewertung von Lochkorrosion und Lochwachstumsgeschwindigkeit angewendet werden können.
Corrosion des métaux et alliages - Lignes directrices pour l’évaluation de la corrosion par piqûres (ISO 11463:2020)
Le présent document fournit des lignes directrices concernant la sélection de modes opératoires pouvant être utilisés dans l'identification et l'examen de piqûres de corrosion ainsi que dans l'évaluation de la corrosion par piqûres et de la vitesse de propagation de piqûre.
Korozija kovin in zlitin - Smernice za vrednotenje jamičaste korozije (ISO 11463:2020)
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 11463:2020
01-november-2020
Nadomešča:
SIST EN ISO 11463:2008
Korozija kovin in zlitin - Smernice za vrednotenje jamičaste korozije (ISO
11463:2020)
Corrosion of metals and alloys - Guidelines for the evaluation of pitting corrosion (ISO
11463:2020)
Korrosion von Metallen und Legierungen - Richtlinien für die Bewertung der
Lochkorrosion (ISO 11463:2020)
Corrosion des métaux et alliages - Lignes directrices pour l’évaluation de la corrosion par
piqûres (ISO 11463:2020)
Ta slovenski standard je istoveten z: EN ISO 11463:2020
ICS:
77.060 Korozija kovin Corrosion of metals
SIST EN ISO 11463:2020 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN ISO 11463:2020
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SIST EN ISO 11463:2020
EN ISO 11463
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2020
EUROPÄISCHE NORM
ICS 77.060 Supersedes EN ISO 11463:2008
English Version
Corrosion of metals and alloys - Guidelines for the
evaluation of pitting corrosion (ISO 11463:2020)
Corrosion des métaux et alliages - Lignes directrices Korrosion von Metallen und Legierungen - Richtlinien
pour l'évaluation de la corrosion par piqûres (ISO für die Bewertung der Lochkorrosion (ISO
11463:2020) 11463:2020)
This European Standard was approved by CEN on 9 August 2020.
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
© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 11463:2020 E
worldwide for CEN national Members.
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SIST EN ISO 11463:2020
EN ISO 11463:2020 (E)
Contents Page
European foreword . 3
2
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SIST EN ISO 11463:2020
EN ISO 11463:2020 (E)
European foreword
This document (EN ISO 11463:2020) has been prepared by Technical Committee ISO/TC 156
"Corrosion of metals and alloys" in collaboration with Technical Committee CEN/TC 262 “Metallic and
other inorganic coatings, including for corrosion protection and corrosion testing of metals and alloys”
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 March 2021, and conflicting national standards shall
be withdrawn at the latest by March 2021.
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.
This document supersedes EN ISO 11463:2008.
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 11463:2020 has been approved by CEN as EN ISO 11463:2020 without any modification.
3
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SIST EN ISO 11463:2020
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SIST EN ISO 11463:2020
INTERNATIONAL ISO
STANDARD 11463
Second edition
2020-08
Corrosion of metals and alloys —
Guidelines for the evaluation of pitting
corrosion
Corrosion des métaux et alliages — Lignes directrices pour
l’évaluation de la corrosion par piqûres
Reference number
ISO 11463:2020(E)
©
ISO 2020
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SIST EN ISO 11463:2020
ISO 11463:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
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 2020 – All rights reserved
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SIST EN ISO 11463:2020
ISO 11463:2020(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Identification and examination of pits . 1
4.1 Preliminary low magnification visual inspection . 1
4.2 Optical microscopic examination of pit size and shape . 1
4.3 In situ non-destructive inspection . 3
4.3.1 General. 3
4.3.2 Radiographic . 3
4.3.3 Electromagnetic . 3
4.3.4 Ultrasonics. 3
4.3.5 Penetrants . . 3
4.3.6 Replication . 4
4.4 Ex situ examination techniques . 4
4.4.1 General. 4
4.4.2 Scanning electron microscopy . 4
4.4.3 X-ray computed tomography . 4
4.4.4 Image analysis . 4
4.4.5 Profilometry . 4
5 Extent of pitting . 5
5.1 Mass loss . 5
5.2 Pit depth measurement . 5
5.2.1 Metallography . 5
5.2.2 Machining . 5
5.2.3 Micrometer or depth gauge . 6
5.2.4 Microscopy . 6
6 Evaluation of pitting . 6
6.1 General . 6
6.2 Standard charts . 7
6.3 Metal penetration . 9
6.4 Statistical . 9
7 Test report .10
8 Additional information .11
Bibliography .12
© ISO 2020 – All rights reserved iii
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SIST EN ISO 11463:2020
ISO 11463:2020(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 156, Corrosion of metals and alloys, in
collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/
TC 262, Metallic and other inorganic coatings, including for corrosion protection and corrosion testing of
metals and alloys, in accordance with the Agreement on technical cooperation between ISO and CEN
(Vienna Agreement).
This second edition cancels and replaces the first edition (ISO 11463:1995), which has been technically
revised. The main changes compared with the previous edition are as follows:
— modern surface analysis and characterization techniques for ex situ examination have been
included.
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.
iv © ISO 2020 – All rights reserved
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SIST EN ISO 11463:2020
ISO 11463:2020(E)
Introduction
It is important to be able to determine the extent of pitting and its characteristics, either in a service
application, where it is necessary to estimate the remaining life in a metal structure, or in laboratory
test programmes that are used to select pitting-resistant materials for a particular service. Corrosion
pits can also act as the precursor to other damage modes such as stress corrosion cracking and
corrosion fatigue.
The application of the materials to be tested will determine the minimum pit size to be evaluated and
whether total area covered, average pit depth, maximum pit depth or another criterion is the most
important to measure.
© ISO 2020 – All rights reserved v
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SIST EN ISO 11463:2020
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SIST EN ISO 11463:2020
INTERNATIONAL STANDARD ISO 11463:2020(E)
Corrosion of metals and alloys — Guidelines for the
evaluation of pitting corrosion
1 Scope
This document gives guidelines for the selection of procedures that can be used in the identification
and examination of corrosion pits and in the evaluation of pitting corrosion and pit growth rate.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
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/
4 Identification and examination of pits
4.1 Preliminary low magnification visual inspection
4.1.1 A visual examination of the corroded metal surface with or without the use of a low-power
magnifying glass may be used to determine the extent of corrosion and the apparent location of pits. It
is often advisable to photograph the corroded surface so that it can be compared with the clean surface
after the removal of corrosion products or with a fresh unused piece of material.
4.1.2 If the metal specimen has been exposed to an unknown environment, the composition of the
corrosion products may be of value in determining the cause of corrosion. Recommended procedures for
the removal of particulate corrosion products should be followed and the material removed should be
preserved for future identification.
4.1.3 To expose the pits fully, it is recommended that cleaning procedures should be used to remove the
corrosion products. Rinsing with water followed by light mechanical cleaning can be sufficient for lightly
[1]
adhered corrosion products. Chemical cleaning is required for more adherent products. ISO 8407
provides a range of chemical cleaning processes. Preliminary testing should be undertaken to ensure
that attack of the base metal is avoided.
4.2 Optical microscopic examination of pit size and shape
4.2.1 Examine the cleaned metal surface to determine the approximate size and distribution of pits.
Follow this procedure by a more detailed examination through a microscope using a low magnification
(approximately × 20). Pits can have various sizes and shapes. A visual examination of the metal surface
can show a round, elongated or irregular opening, but it seldom provides an accurate indication of the
© ISO 2020 – All rights reserved 1
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SIST EN ISO 11463:2020
ISO 11463:2020(E)
extent of corrosion beneath the surface. Thus, it is often necessary to cross-section the pit to determine
its actual shape. Several common variations in the cross-sectioned shape of pits are shown in Figure 1.
Key
(a) narrow, deep (e) undercutting
(b) elliptical (f) microstructural orientation (horizontal)
(c) wide, shallow (g) microstructural orientation (vertical)
(d) sub-surface
Figure 1 — Variations in the cross-sectional shape of pits
4.2.2 It is difficult to determine pit density by counting pits through a microscope eyepiece, but the
task can be made easier by the use of a plastic grid. Place the grid, containing 3 mm to 6 mm squares,
on the metal surface. Count and record the number of pits in each square and move across the grid in a
systematic manner until all the surface has been covered. This approach minimizes eyestrain because the
eyes can be taken from the field of view without fear of losing the area of interest. Enlarged photographs
of the area of interest may also be used to reduce eyestrain. An alternative approach is to mount the
specimen on an x-y stage and measure both the number and spatial distribution of pits. When coupled
with optical depth measurement, where applicable, the number, depth and spatial distribution of pits
can be determined.
4.2.3 Advanced optical microscopy techniques, such as infinite focus microscopy and confocal laser
microscopy may be used to obtain three-dimensional images of the pit surface, within the constraints
of optical observations [most relevant to Figure 1 a) to c) but not applicable to undercut]. Such
measurements can be used to view the surface features and quantify surface roughness, pit depth,
surface profile, etc.
4.2.4 To carry out a metallographic examination, select and cut out a representative portion of the
metal surface containing the pits and prepare a metallographic specimen. If corrosion products are to
be examined in cross-section, it may be necessary to fix the surface in a mounting compound before
cutting. Examine microscopically to determine whether there is a relation between pits and inclusions
or microstructure, or whether the cavities are true pits or might have resulted from metal loss caused by
intergranular corrosion, dealloying, etc.
2 © ISO 2020 – All rights reserved
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SIST EN ISO 11463:2020
ISO 11463:2020(E)
4.3 In situ non-destructive inspection
4.3.1 General
Several techniques have been developed to assist in the detection of cracks or cavities in a metal surface
without destroying the material (see Reference [2]). These methods are less effective for locating and
defining the shape of pits than some of those described previously, but they merit consideration because
they are often used in situ, and thus they are more applicable to field applications.
4.3.2 Radiographic
Radiation, such as X-rays, passes through the object. The intensity of the emergent rays decreases
with increasing thickness of the material. Imperfections can be detected if they cause a change in the
absorption of X-rays. Detectors or films are used to provide an image of interior imperfections. The
metal thickness that can be inspected is dependent on the available energy output. Pits must be as
large as 0,5 % of the metal thickness to be detected and care should be taken to ensure that pits are not
confused with pre-existing pores.
4.3.3 Electromagnetic
4.3.3.1 Eddy currents may be used to detect defects or irregularities in the structure of electrically
conductive materials. When a specimen is exposed to a varying magnetic field, produced by connecting
an alternating current to a coil, eddy currents are induced in the specimen and they in turn produce a
magnetic field of their own. Materials with defects will produce a magnetic field that is different from
that of a reference material without defects, and an appropriate detection instrument is required to
determine these differences.
4.3.3.2 The induction of a magnetic field in ferromagnetic materials is another approach that is used.
Discontinuities that are transverse to the direction of the magnetic field cause a leakage field to form
above the surface of the part. Ferromagnetic particles are placed on the surface to detect the leakage
field and to outline the size and shape of the discontinuities. Rather small imperfections can be detected
by this method. However, the method is limited by the required directionality of defects to the magnetic
field, by the possible need for demagnetization of the material, and by the limited shapes of parts that
can be examined.
4.3.4 Ultrasonics
In the use of ultrasonics, pulses of sound energy are transmitted through a couplant, such as oil or water,
on to the metal surface where waves are generated. The reflected echoes are converted to electrical
signals that can be interpreted to show the location of flaws or pits. Both contact and immersion
methods are used and various techniques can be applied. The test should be carried out from the non-
pitted face. The test is affected by the morphology of the pits, the ultrasonic technique selected and the
performance of the probe and flaw detector. Information about the size and location of flaws can be
established. However, the capability of the technique for the pitting expected should be assessed and
reference standards produced for comparison. Operators should be trained in the application of the
technique and the interpretation of the results.
4.3.5 Penetrants
Defects opening to the surface can be detected by the application of a penetrating liquid that
subsequently exudes from the surface after the excess penetrant has been removed. Defects are located
by spraying the surface with a developer that reacts with a dye in the penetrant, or the penetrant may
contain a fluorescent material that is viewed under ultraviolet light. The size of the defect is shown by
the intensity of the colour and the rate of bleed-out. This technique provides only an approximation of
the depth and size of pits.
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SIST EN ISO 11463:2020
ISO 11463:2020(E)
4.3.6 Replication
Images of a pitted surface can be created by applying a material to the surface that conforms to the
shape of the pits and can be removed without damaging its shape. This method will not work, however,
for pits of subsurface or undercut type. The removed material contains a replica of the original surface
that, in some cases, is easier to analyse than the original. Replication is particularly useful for the
analysis of very small pits.
4.4 Ex situ examination techniques
4.4.1 General
Several sophisticated ex-situ techniques are available for examining the size, shape and distribution of
pits in metallic samples. Their application would involve transport of the specimens to a laboratory or
dedicated analytical facility. Some of these techniques are described in 4.4.2 to 4.4.5.
4.4.2 Scanning electron microscopy
Scanning electron microscopy (SEM) can be used to obtain images containing topographic and phase
contrast information. It is a very useful technique for obtaining images of pits in surfaces and the
technique can be used to determine the dimensions of the pit and any relationships with different
phases within the microstructure of the metal. By combining electron-dispersive X-ray spectroscopy
(EDS) or wavelength-dispersive X-ray spectroscopy (WDS), elemental composition and distribution
of any corrosion products in pits can be determined. However, in deeper pits and where subsurface
undercutting of the pit mouth has occurred, electron emission is shielded from the detector and this
can limit the effectiveness of the technique for imaging the pit morphology.
4.4.3 X-ray computed tomography
X-ray computed tomography (CT) is a non-destructive technique that, coupled with reconstruction
software, can enable 3D imaging of pits. The images are constructed by taking slices through the sample
using high intensity X-ray sources, which may be X-ray tubes in conventional laboratories or derived
from synchrotron X-ray sources. The thickness of specimen can be limited due to X-ray attenuation.
Sectioning parallel to the surface can be required to reduce the thickness. Nevertheless, the technique
is a powerful tool for 3D imaging of pits of complex shape.
4.4.4 Image analysis
Image analysis is the technique whereby images that have been taken using a measurement technique
such as optical microscopy or X-ray computed tomography are post-processed to extract quantitative
information. The technique can be used to automate the analysis or post-processing of images to
reduce time and cost. It also permits the analysis of a greater number of images, thereby improving the
statistical reliability of the measurements. Image analysis allows micrographs to be processed rapidly
and can produce data that are more accurate and statistically robust than manual methods.
4.4.5 Profilometry
Profilometry measures the physical surface geometry or topography of a sample. It may be classed as
“contact” or “non-contact”. Contact profilometry involves a stylus, with known tip dimensions, being
brought into contact with the sample surface, and then rastered over the surface. The displacement
of the stylus tip as it comes into contact with high and low features on the surface is monitored and
recorded as a function of its position. From this data, the physical characteristics of the surface, such
as roughness, can be measured, and any features of interest, such as pitting, can be identified and
quantified.
Non-contact methods record the same type of information, although they usually employ laser-based
optical methods, such as an infinite focus microscope, and they do not require direct physical contact
with the sample surface. Such techniques develop a 3D surface profile through the accumulation of
4 © ISO 2020 – All rights reserved
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SIST EN ISO 11463:2020
ISO 11463:2020(E)
images at different optical focal planes, and white
...
SLOVENSKI STANDARD
oSIST prEN ISO 11463:2019
01-september-2019
Korozija kovin in zlitin - Vrednotenje jamičaste korozije (ISO/DIS 11463:2019)
Corrosion of metals and alloys - Evaluation of pitting corrosion (ISO/DIS 11463:2019)
Korrosion von Metallen und Legierungen - Bewertung der Lochkorrosion (ISO/DIS
11463:2019)
Corrosion des métaux et alliages - Évaluation de la corrosion par piqûres (ISO/DIS
11463:2019)
Ta slovenski standard je istoveten z: prEN ISO 11463
ICS:
77.060 Korozija kovin Corrosion of metals
oSIST prEN ISO 11463:2019 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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oSIST prEN ISO 11463:2019
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oSIST prEN ISO 11463:2019
DRAFT INTERNATIONAL STANDARD
ISO/DIS 11463
ISO/TC 156 Secretariat: SAC
Voting begins on: Voting terminates on:
2019-06-13 2019-09-05
Corrosion of metals and alloys — Evaluation of pitting
corrosion
Corrosion des métaux et alliages — Évaluation de la corrosion par piqûres
ICS: 77.060
THIS DOCUMENT IS A DRAFT CIRCULATED
This document is circulated as received from the committee secretariat.
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
ISO/CEN PARALLEL PROCESSING
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 11463:2019(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
©
PROVIDE SUPPORTING DOCUMENTATION. ISO 2019
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oSIST prEN ISO 11463:2019
ISO/DIS 11463:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2019
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
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved
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oSIST prEN ISO 11463:2019
ISO/DIS 11463:2019(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Identification and examination of pits . 1
4.1 Preliminary low magnification visual inspection . 1
4.2 Optical microscopic examination of pit size and shape . 1
4.3 In situ non-destructive inspection . 3
4.3.1 General. 3
4.3.2 Radiographic . 3
4.3.3 Electromagnetic . 3
4.3.4 Ultrasonics. 3
4.3.5 Penetrants . . 3
4.3.6 Replication . 4
4.4 Ex situ examination techniques . 4
4.4.1 General. 4
4.4.2 Scanning electron microscopy . 4
4.4.3 X-ray Computed Tomography (XCT) . 4
4.4.4 Image analysis . 4
4.4.5 Profilometry . 4
5 Extent of pitting . 5
5.1 Mass loss . 5
5.2 Pit depth measurement . 5
5.2.1 Metallography . 5
5.2.2 Machining . 5
5.2.3 Micrometer or depth gauge . 6
5.2.4 Microscopy . 6
6 E valuation of pitting . 7
6.1 General . 7
6.2 Standard Charts . 7
6.3 Metal Penetration . 8
6.4 Statistical . 9
7 Report .10
8 Additional information .11
Bibliography .12
© ISO 2019 – All rights reserved iii
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oSIST prEN ISO 11463:2019
ISO/DIS 11463:2019(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 on 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 the following URL: www .iso .org/iso/foreword .html.
The committee responsible for this document is ISO/TC 156, Corrosion of metals and alloys. WG 6,
General principles of testing and data interpretation.
This third edition cancels and replaces the first edition (ISO 11463:1995), which has been technically
revised.
iv © ISO 2019 – All rights reserved
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oSIST prEN ISO 11463:2019
ISO/DIS 11463:2019(E)
Introduction
It is important to be able to determine the extent of pitting and its characteristics, either in a service
application, where it is necessary to estimate the remaining life in a metal structure, or in laboratory
[1]
test programmes that are used to select pitting-resistant materials for a particular service (see
in Bibliography). Corrosion pits can also act as the precursor to other damage modes such as stress
corrosion cracking and corrosion fatigue.
The application of the materials to be tested will determine the minimum pit size to be evaluated and
whether total area covered, average pit depth, maximum pit depth or another criterion is the most
important to measure.
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DRAFT INTERNATIONAL STANDARD ISO/DIS 11463:2019(E)
Corrosion of metals and alloys — Evaluation of pitting
corrosion
1 Scope
This document provides guidance on the selection of procedures that can be used in the identification
and examination of corrosion pits and in the evaluation of pitting corrosion and pit growth rate.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 8407, Corrosion of metals and alloys — Removal of corrosion products from corrosion test specimens
ISO 14802, Corrosion of metals and alloys — Guidelines for applying statistics to analysis of corrosion data
3 Terms and definitions
No terms and definitions are listed in this document.
4 Identification and examination of pits
4.1 Preliminary low magnification visual inspection
4.1.1 A visual examination of the corroded metal surface with or without the use of a low-power
magnifying glass may be used to determine the extent of corrosion and the apparent location of pits. It
is often advisable to photograph the corroded surface so that it can be compared with the clean surface
after the removal of corrosion products or with a fresh unused piece of material.
4.1.2 If the metal specimen has been exposed to an unknown environment, the composition of the
corrosion products may be of value in determining the cause of corrosion. Recommended procedures for
the removal of particulate corrosion products should be followed and the material removed should be
preserved for future identification.
4.1.3 To expose the pits fully, it is recommended that cleaning procedures should be used to remove
the corrosion products. Rinsing with water followed by light mechanical cleaning can be sufficient for
lightly adhered corrosion product but for more adherent product chemical cleaning is required. ISO 8407
provides a range of chemical cleaning processes, but preliminary testing should be undertaken to ensure
that attack of the base metal is avoided.
4.2 Optical microscopic examination of pit size and shape
4.2.1 Examine the cleaned metal surface to determine the approximate size and distribution of pits.
Follow this procedure by a more detailed examination through a microscope using low magnification
(approximately ×20). Pits may have various sizes and shapes. A visual examination of the metal surface
may show a round, elongated or irregular opening, but it seldom provides an accurate indication of the
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extent of corrosion beneath the surface. Thus, it is often necessary to cross-section the pit to determine
its actual shape. Several common variations in the cross-sectioned shape of pits are shown in Figure 1.
Figure 1 — Variations in the Cross-sectional shape of pits
4.2.2 It is difficult to determine pit density by counting pits through a microscope eyepiece, but the
task may be made easier by the use of a plastic grid. Place the grid, containing 3 mm to 6 mm squares,
on the metal surface. Count and record the number of pits in each square and move across the grid in a
systematic manner until all the surface has been covered. This approach minimizes eye-strain because the
eyes can be taken from the field of view without fear of losing the area of interest. Enlarged photographs
of the area of interest may also be used to reduce eyestrain. An alternative approach is to mount the
specimen on an x-y stage and measure both the number and spatial distribution of pits. When coupled
with optical depth measurement, where applicable, the number, depth and spatial distribution of pits
can be determined.
4.2.3 Advanced optical microscopy techniques, such as infinite focus microscopy and confocal laser
microscopy may be used to obtain three-dimensional images of the pit surface, within the constraints of
optical observations (most relevant to Fig. 1 a-c but not applicable to undercut). Such measurements can
be used to view the surface features and quantify surface roughness, pit depth, surface profile, etc.
4.2.4 To carry out a metallographic examination, select and cut out a representative portion of the
metal surface containing the pits and prepare a metallographic specimen. If corrosion products are to
be examined in cross-section, it may be necessary to fix the surface in a mounting compound before
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cutting. Examine microscopically to determine whether there is a relation between pits and inclusions
or microstructure, or whether the cavities are true pits or might have resulted from metal loss caused by
intergranular corrosion, dealloying, etc.
4.3 In situ non-destructive inspection
4.3.1 General
Several techniques have been developed to assist in the detection of cracks or cavities in a metal surface
[1]
without destroying the material (see reference in Bibliography). These methods are less effective
for locating and defining the shape of pits than some of those previously described, but they merit
consideration because they are often used in situ, and thus they are more applicable to field applications.
4.3.2 Radiographic
Radiation, such as X-rays, passes through the object. The intensity of the emergent rays decreases
with increasing thickness of the material. Imperfections may be detected if they cause a change in the
absorption of X-rays. Detectors or films are used to provide an image of interior imperfections. The
metal thickness that can be inspected is dependent on the available energy output. Pits must be as
large as 0,5 % of the metal thickness to be detected and care should be taken to ensure that pits are not
confused with pre-existing pores.
4.3.3 Electromagnetic
4.3.3.1 Eddy currents may be used to detect defects or irregularities in the structure of electrically
conductive materials. When a specimen is exposed to a varying magnetic field, produced by connecting
an alternating current to a coil, eddy currents are induced in the specimen and they in turn produce a
magnetic field of their own. Materials with defects will produce a magnetic field that is different from
that of a reference material without defects, and an appropriate detection instrument is required to
determine these differences.
4.3.3.2 The induction of a magnetic field in ferromagnetic materials is another approach that is used.
Discontinuities that are transverse to the direction of the magnetic field cause a leakage field to form
above the surface of the part. Ferromagnetic particles are placed on the surface to detect the leakage
field and to outline the size and shape of the discontinuities. Rather small imperfections can be detected
by this method. However, the method is limited by the required directionality of defects to the magnetic
field, by the possible need for demagnetization of the material, and by the limited shape of parts that can
be examined.
4.3.4 Ultrasonics
In the use of ultrasonics, pulses of sound energy are transmitted through a couplant, such as oil or water,
on to the metal surface where waves are generated. The reflected echoes are converted to electrical
signals that can be interpreted to show the location of flaws or pits. Both contact and immersion
methods are used and various techniques can be applied. The test should be carried out from the non-
pitted face. The test is affected by the morphology of the pits, the ultrasonic technique selected and the
performance of the probe and flaw detector. Information about the size and location of flaws can be
established. However, the capability of the technique for the pitting expected should be assessed and
reference standards produced for comparison. Operators should be trained in the application of the
technique and the interpretation of the results.
4.3.5 Penetrants
Defects opening to the surface can be detected by the application of a penetrating liquid that
subsequently exudes from the surface after the excess penetrant has been removed. Defects are located
by spraying the surface with a developer that reacts with a dye in the penetrant, or the penetrant may
contain a fluorescent material that is viewed under ultra-violet light. The size of the defect is shown by
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the intensity of the colour and the rate of bleed-out. This technique provides only an approximation of
the depth and size of pits.
4.3.6 Replication
Images of a pitted surface can be created by applying a material to the surface which conforms to the
shape of the pits and can be removed without damaging its shape. This method will not work however,
for pits of subsurface or undercut type. The removed material contains a replica of the original surface
which, in some cases, is easier to analyze than the original. Replication is particularly useful for analysis
of very small pits.
4.4 Ex situ examination techniques
4.4.1 General
Several sophisticated ex-situ techniques are available for examining the size, shape and distribution of
pits in metallic samples. Their application would involve transport of the specimens to a laboratory or
dedicated analytical facility. Some of these techniques are described in the following sections.
4.4.2 Scanning electron microscopy
Scanning electron microscopy (SEM) can be used to obtain images containing topographic and phase
contrast information. It is a very useful technique for obtaining images of pits in surfaces and the
technique can be used to determine the dimensions of the pit and any relationships with different
phases within the microstructure of the metal. By combining electron-dispersive X-ray spectroscopy
(EDS) or wavelength-dispersive X-ray spectroscopy (WDS), elemental composition and distribution
of any corrosion products in pits can be determined. However, in deeper pits and where subsurface
undercutting of the pit mouth has occurred, electron emission is shielded from the detector and this
may limit the effectiveness of the technique for imaging the pit morphology.
4.4.3 X-ray Computed Tomography (XCT)
X-ray Computed Tomography (CT) is a non-destructive technique that coupled with reconstruction
software can enable 3D imaging of pits. The images are constructed by taking ‘slices’ through the sample
using high intensity X-ray sources, which may be X-ray tubes in conventional laboratories or derived
from synchrotron X-ray sources. The thickness of specimen can be limited due to X-ray attenuation;
sectioning parallel to the surface may be required to reduce this. Nevertheless, the technique is a
powerful tool for 3D imaging of pits of complex shape.
4.4.4 Image analysis
Image analysis is the technique whereby images that have been taken using a measurement technique
such as optical microscopy or X-ray computed tomography are post processed to extract quantitative
information. The technique can be used to automate the analysis or post-processing of images to
reduce time and cost. It also permits the analysis of a greater number of images, thereby improving the
statistical reliability of the measurements. Image analysis allows micrographs to be processed rapidly
and can produce data that is more accurate and statistically robust than manual methods.
4.4.5 Profilometry
Profilometry measures the physical surface geometry or topography of a sample. It may be classed as
‘contact’ or ‘non-contact’. Contact profilometry involves a stylus, with known tip dimensions, being
brought into contact with the sample surface, and then ‘rastered’ over the surface. The displacement
of the stylus tip as it comes into contact with high and low features on the surface is monitored and
recorded as a function of its position. From this data the physical characteristics of the surface, such
as roughness, can be measured, and any features of interest, such as pitting may be identified and
quantified.
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Non-contact methods record the same type of information, although they usually employ optical
methods, such as an infinite focus microscope, and they do not require direct physical contact with
the sample surface. Such techniques develop a surface profile through the accumulation of images at
different optical focal planes, and white-light interferometry, where the phase difference between light
reflected from the sample surface and light from a reference mirror are compared, and differences in
the path length due to the surface morphology may be recorded. Confocal laser microscopes can give
similar information.
The disadvantage of these techniques is that they characterise only what they can detect optically and
are applicable mainly to pit types such as Fig 1 a-c (see also Section 4.2.3).
5 Extent of pitting
5.1 Mass loss
Metal mass loss is not ordinarily recommended for use as a measure of the extent of pitting unless
general corrosion is slight and pitting is fairly severe. If uniform corrosion is significant, the contribution
of pitting to total metal loss is small, and pitting damage cannot be determined accurately from mass
loss. In any case, mass loss can only provide information about total metal loss due to pitting but
nothing about density of pits and depth of penetration. However, mass loss should not be neglected in
every case because it may be of value; for example, mass loss along with a visual comparison of pitted
surfaces may be adequate to evaluate the pitting resistance of alloys in laboratory tests. Mass loss may
also be useful to detect the existence of subsurface metal loss.
5.2 Pit depth measurement
5.2.1 Metallography
Pit depth may be determined by sectioning vertically through a preselected pit, mounting the cross-
sectioned pit metallographically and polishing the surface. A better or alternative way is to section
slightly away from the pit and slowly grind until the pit is in the cross-section. Sectioning through a
pit can be difficult and one may miss the deepest portion. The depth of the pit is measured on the flat,
polished surface using a microscope with a calibrated eyepiece. The method is very accurate, but it
requires good operator skill and good judgment in the selection of the pit and good technique in cutting
through the pit. Its limitations are that it is time-consuming, the deepest pit may not have been selected
and the pit may not have been sectioned at the deepest point of penetration. The method, however,
is the only suitable for the evaluation of the pit shape as in Figure 1. This technique will result in the
destruction of the specimen.
5.2.2 Machining
[3]
See references [2l and in Bibliography.
5.2.2.1 This method requires a sample that is fairly regular in shape, and it usually involves the
destruction of the specimen. Measure the thickness of the specimen between two areas that have not
been affected by general corrosion. Select a portion of the surface on one side of the specimen that is
relatively unaffected; then machine the opposite surface where the pits are located on a precision lathe,
grinder or mill until all signs of corrosion have disappeared. Some difficulty from galling and smearing
may be encountered with soft metals and pits may be obliterated. Conversely, inclusions may be
removed from the metal thus confusing examination. Measure the thickness of the specimen between
the unaffected surface and subtract from the original thickness to give the maximum depth of pitting.
Repeat this procedure on the unmachined surface unless the thickness has been reduced by 50 % or
more during the machining of the first side.
5.2.2.2 This method is equally suitable for determining the distribution of pit depths in a sample. Count
the visible pits then machine away the surface of the metal in measured stages (the amount of material
removed in each step will determine the uncertainty in pit depth). Continue this process noting for each
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pit the depth of materia
...
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