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

Status
Published
Public Enquiry End Date
04-Sep-2019
Publication Date
04-Oct-2020
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
24-Sep-2020
Due Date
29-Nov-2020
Completion Date
05-Oct-2020

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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.

---------------------- Page: 1 ----------------------
SIST EN ISO 11463:2020
---------------------- Page: 2 ----------------------
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

---------------------- Page: 4 ----------------------
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.

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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
---------------------- Page: 7 ----------------------
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
---------------------- Page: 8 ----------------------
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.
© ISO 2020 – All rights reserved 3
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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.

---------------------- Page: 1 ----------------------
oSIST prEN ISO 11463:2019
---------------------- Page: 2 ----------------------
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
---------------------- Page: 3 ----------------------
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
---------------------- Page: 4 ----------------------
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

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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.
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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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