Corrosion of metals and alloys -- Guidelines for the evaluation of pitting corrosion

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.

Corrosion des métaux et alliages -- Lignes directrices pour l’évaluation de la corrosion par piqûres

Le présent document fournit des lignes directrices concernant la sélection de modes opératoires pouvant ętre utilisés dans l'identification et l'examen de piqűres de corrosion ainsi que dans l'évaluation de la corrosion par piqűres et de la vitesse de propagation de piqűre.

Korozija kovin in zlitin - Smernice za ovrednotenje jamičaste korozije

General Information

Status
Published
Publication Date
05-Aug-2020
Current Stage
5060 - Close of voting Proof returned by Secretariat
Start Date
09-Jul-2020
Completion Date
08-Jul-2020

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SLOVENSKI STANDARD
SIST ISO 11463:2021
01-julij-2021
Nadomešča:
SIST ISO 11463:1999
Korozija kovin in zlitin - Smernice za ovrednotenje jamičaste korozije

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
Ta slovenski standard je istoveten z: ISO 11463:2020
ICS:
77.060 Korozija kovin Corrosion of metals
SIST ISO 11463:2021 en

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

---------------------- Page: 1 ----------------------
SIST ISO 11463:2021
---------------------- Page: 2 ----------------------
SIST ISO 11463:2021
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: 3 ----------------------
SIST ISO 11463:2021
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: 4 ----------------------
SIST ISO 11463:2021
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
---------------------- Page: 5 ----------------------
SIST ISO 11463:2021
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
---------------------- Page: 6 ----------------------
SIST ISO 11463:2021
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
---------------------- Page: 7 ----------------------
SIST ISO 11463:2021
---------------------- Page: 8 ----------------------
SIST ISO 11463:2021
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
---------------------- Page: 9 ----------------------
SIST ISO 11463:2021
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
---------------------- Page: 10 ----------------------
SIST ISO 11463:2021
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
---------------------- Page: 11 ----------------------
SIST ISO 11463:2021
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. Re
...

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: 1 ----------------------
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: 2 ----------------------
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
---------------------- Page: 3 ----------------------
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
---------------------- Page: 4 ----------------------
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
---------------------- Page: 5 ----------------------
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
---------------------- Page: 6 ----------------------
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
---------------------- Page: 7 ----------------------
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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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 micr
...

NORME ISO
INTERNATIONALE 11463
Deuxième édition
2020-08
Corrosion des métaux et alliages —
Lignes directrices pour l’évaluation de
la corrosion par piqûres
Corrosion of metals and alloys — Guidelines for the evaluation of
pitting corrosion
Numéro de référence
ISO 11463:2020(F)
ISO 2020
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ISO 11463:2020(F)
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ii © ISO 2020 – Tous droits réservés
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ISO 11463:2020(F)
Sommaire Page

Avant-propos ..............................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Domaine d’application ................................................................................................................................................................................... 1

2 Références normatives ................................................................................................................................................................................... 1

3 Termes et définitions ....................................................................................................................................................................................... 1

4 Identification et examen des piqûres ............................................................................................................................................. 1

4.1 Contrôle visuel préliminaire avec faible grossissement ...................................................................................... 1

4.2 Examen de la taille et de la forme des piqûres par microscopie optique ............................................. 1

4.3 Contrôle non destructif in situ................................................................................................................................................... 3

4.3.1 Généralités ............................................................................................................................................................................ 3

4.3.2 Contrôle radiographique ........................................................................................................................................... 3

4.3.3 Contrôle électromagnétique .................................................................................................................................. 3

4.3.4 Contrôle par ultrasons ................................................................................................................................................ 3

4.3.5 Contrôle par ressuage ................................................................................................................................................. 4

4.3.6 Contrôle par réplique ........................................................................................................................................... ........ 4

4.4 Techniques d’examen ex situ ...................................................................................................................................................... 4

4.4.1 Généralités ............................................................................................................................................................................ 4

4.4.2 Microscopie électronique à balayage ............................................................................................................. 4

4.4.3 Tomodensitométrie (TDM) ..................................................................................................................................... 4

4.4.4 Analyse d’images ............................................................................................................................................................. 4

4.4.5 Profilométrie ....................................................................................................................................................................... 5

5 Étendue des piqûres ......................................................................................................................................................................................... 5

5.1 Perte de masse ........................................................................................................................................................................................ 5

5.2 Mesurage de la profondeur de piqûre ................................................................................................................................. 5

5.2.1 Métallographie ................................................................................................................................................................... 5

5.2.2 Usinage ..................................................................................................................................................................................... 5

5.2.3 Micromètre ou jauge de profondeur ............................................................................................................... 6

5.2.4 Microscopie .......................................................................................................................................................................... 6

6 Évaluation des piqûres ................................................................................................................................................................................... 7

6.1 Généralités .................................................................................................................................................................................................. 7

6.2 Clichés-étalons ........................................................................................................................................................................................ 7

6.3 Pénétration du métal ......................................................................................................................................................................... 8

6.4 Statistiques ................................................................................................................................................................................................. 9

7 Rapport d’essai ....................................................................................................................................................................................................10

8 Informations complémentaires .........................................................................................................................................................11

Bibliographie ...........................................................................................................................................................................................................................12

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ISO 11463:2020(F)
Avant-propos

L’ISO (Organisation internationale de normalisation) est une fédération mondiale d’organismes

nationaux de normalisation (comités membres de l’ISO). L’élaboration des Normes internationales est

en général confiée aux comités techniques de l’ISO. Chaque comité membre intéressé par une étude

a le droit de faire partie du comité technique créé à cet effet. Les organisations internationales,

gouvernementales et non gouvernementales, en liaison avec l’ISO participent également aux travaux.

L’ISO collabore étroitement avec la Commission électrotechnique internationale (IEC) en ce qui

concerne la normalisation électrotechnique.

Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont

décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier, de prendre note des différents

critères d’approbation requis pour les différents types de documents ISO. Le présent document a été

rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2 (voir www

.iso .org/ directives).

L’attention est attirée sur le fait que certains des éléments du présent document peuvent faire l’objet de

droits de propriété intellectuelle ou de droits analogues. L’ISO ne saurait être tenue pour responsable

de ne pas avoir identifié de tels droits de propriété et averti de leur existence. Les détails concernant

les références aux droits de propriété intellectuelle ou autres droits analogues identifiés lors de

l’élaboration du document sont indiqués dans l’Introduction et/ou dans la liste des déclarations de

brevets reçues par l’ISO (voir www .iso .org/ brevets).

Les appellations commerciales éventuellement mentionnées dans le présent document sont données

pour information, par souci de commodité, à l’intention des utilisateurs et ne sauraient constituer un

engagement.

Pour une explication de la nature volontaire des normes, la signification des termes et expressions

spécifiques de l’ISO liés à l’évaluation de la conformité, ou pour toute information au sujet de l’adhésion

de l’ISO aux principes de l’Organisation mondiale du commerce (OMC) concernant les obstacles

techniques au commerce (OTC), voir www .iso .org/ avant -propos.

Le présent document a été élaboré par le comité technique ISO/TC 156, Corrosion des métaux et alliages,

en collaboration avec le comité technique CEN/TC 262, Revêtements métalliques et inorganiques, incluant

ceux pour la protection contre la corrosion et les essais de corrosion des métaux et alliages, du Comité

européen de normalisation (CEN) conformément à l’Accord de coopération technique entre l’ISO et le

CEN (Accord de Vienne).

Cette deuxième édition annule et remplace la première édition (ISO 11463:1995), qui a fait l’objet d’une

révision technique. Les principales modifications par rapport à l’édition précédente sont les suivantes:

— intégration de techniques modernes d’analyse et de caractérisation des surfaces pour l’examen

ex situ.

Il convient que l’utilisateur adresse tout retour d’information ou toute question concernant le présent

document à l’organisme national de normalisation de son pays. Une liste exhaustive desdits organismes

se trouve à l’adresse www .iso .org/ fr/ members .html.
iv © ISO 2020 – Tous droits réservés
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ISO 11463:2020(F)
Introduction

Il importe d’être en mesure de déterminer l’étendue et les caractéristiques des piqûres, que ce soit

dans une application en service, où il est nécessaire d’évaluer la durée de vie restante d’une structure

métallique, ou au cours de programmes d’essais en laboratoire visant à sélectionner des matériaux

résistants aux piqûres pour une exploitation particulière. Les piqûres de corrosion peuvent également

agir comme précurseur à d’autres types de dommages, tels que la corrosion sous contrainte ou la fatigue

corrosion.

L’application des matériaux à soumettre à essai déterminera la taille minimale de piqûre à évaluer et

le paramètre le plus important à mesurer, à savoir l’aire totale couverte, les profondeurs de piqûre

moyenne et maximale, ou tout autre critère.
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NORME INTERNATIONALE ISO 11463:2020(F)
Corrosion des métaux et alliages — Lignes directrices pour
l’évaluation de la corrosion par piqûres
1 Domaine d’application

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.
2 Références normatives
Le présent document ne contient aucune référence normative.
3 Termes et définitions
Aucun terme n’est défini dans le présent document.

L’ISO et l’IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en

normalisation, consultables aux adresses suivantes:

— ISO Online browsing platform: disponible à l’adresse https:// www .iso .org/ obp

— IEC Electropedia: disponible à l’adresse http:// www .electropedia .org/
4 Identification et examen des piqûres
4.1 Contrôle visuel préliminaire avec faible grossissement

4.1.1 Afin de déterminer l’étendue de la corrosion et l’emplacement visible des piqûres, il est admis

de procéder à un examen visuel de la surface de métal corrodée en utilisant ou non une loupe à faible

pouvoir grossissant. Il est généralement recommandé de photographier la surface corrodée afin de

pouvoir la comparer avec la surface propre, après élimination des produits de corrosion, ou avec une

pièce de matériau neuve.

4.1.2 Si l’éprouvette de métal a été exposée à un environnement inconnu, la composition des produits

de corrosion peut être utile pour déterminer la cause de la corrosion. Il convient de suivre les modes

opératoires recommandés pour l’élimination des produits de corrosion particulaires et il convient de

conserver les matériaux éliminés pour de futures identifications.

4.1.3 Afin d’exposer totalement les piqûres, il convient d’appliquer des modes opératoires de nettoyage

pour éliminer les produits de corrosion. Un rinçage à l’eau suivi d’un léger nettoyage mécanique peut

se révéler suffisant pour les produits de corrosion à faible adhérence, mais un nettoyage chimique est

[1]

nécessaire pour les produits à plus forte adhérence. L’ISO 8407 décrit plusieurs méthodes de nettoyage

chimique, mais il convient de procéder à des essais préliminaires afin de s’assurer d’éviter l’attaque du

métal de base.
4.2 Examen de la taille et de la forme des piqûres par microscopie optique

4.2.1 Examiner la surface du métal nettoyée pour déterminer la taille et la répartition approximatives

des piqûres. Procéder ensuite à un examen plus détaillé au microscope, en utilisant un faible grossissement

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ISO 11463:2020(F)

(environ × 20). Les piqûres peuvent être de tailles et de formes variées. Un examen visuel de la surface

du métal peut montrer une ouverture ronde, oblongue ou irrégulière, mais il ne fournira que rarement

une indication exacte de l’étendue de la corrosion sous la surface. Il est donc souvent nécessaire de faire

une coupe transversale de la piqûre pour déterminer sa forme réelle. La Figure 1 présente plusieurs

variantes communes de la forme des piqûres en coupe transversale.
Légende
(a) étroite, profonde (e) sous-jacente
(b) elliptique (f) orientation de la microstructure (horizontale)
(c) large, superficielle (g) orientation de la microstructure (verticale)
(d) cachée
Figure 1 — Variantes de la forme des piqûres en coupe transversale

4.2.2 Il est difficile de déterminer la densité des piqûres en les comptant par l’oculaire d’un microscope,

mais la tâche peut être facilitée en utilisant une grille en plastique. Placer la grille, formée de carrés de

3 mm à 6 mm, sur la surface métallique. Compter et consigner le nombre de piqûres par carré, et déplacer

la grille de manière systématique jusqu’à ce que toute la surface ait été couverte. Cette approche réduit

la fatigue visuelle, car les yeux peuvent quitter le champ optique sans craindre de perdre la zone étudiée.

Des agrandissements photographiques de cette zone peuvent également être utilisés pour diminuer la

fatigue visuelle. Une autre approche consiste à monter l’échantillon sur une platine XY et à mesurer à la

fois le nombre et la répartition spatiale des piqûres. Lorsqu’elle est couplée à un mesurage optique de

la profondeur, si cela est possible, alors le nombre, la profondeur et la répartition spatiale des piqûres

peuvent être déterminés.

4.2.3 Des techniques avancées de microscopie optique, telles que la microscopie à foyer à l’infini et la

microscopie confocale à balayage laser, peuvent être utilisées pour obtenir des images tridimensionnelles

de la surface de la piqûre, en tenant compte des contraintes inhérentes aux observations optiques (plus

appropriées aux variantes a) à c) de la Figure 1, mais non-pertinentes pour les piqûres sous-jacentes).

De tels mesurages peuvent être utilisés pour visualiser les caractéristiques de surface et quantifier la

rugosité de surface, la profondeur de piqûre, le profil de surface, etc.

4.2.4 Pour réaliser un examen métallographique, choisir et découper une partie représentative de la

surface métallique contenant les piqûres et préparer une éprouvette métallographique. Si les produits

de corrosion sont à examiner sur une coupe transversale, il peut s’avérer nécessaire de fixer la surface

sur un support composite avant de faire la coupe. L’examiner au microscope afin de déterminer s’il existe

une relation entre les piqûres et les inclusions ou la microstructure, ou si les cavités sont de véritables

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ISO 11463:2020(F)

piqûres ou pourraient être le résultat d’une perte de métal due à une corrosion intergranulaire, à une

corrosion sélective, etc.
4.3 Contrôle non destructif in situ
4.3.1 Généralités

Diverses techniques ont été élaborées pour aider à détecter les fissures ou cavités dans une surface

métallique sans détruire le matériau (voir la Référence [2]). Pour localiser les piqûres et définir

leur forme, ces méthodes sont moins efficaces que certaines décrites ci-avant, mais elles méritent

d’être prises en considération car elles sont souvent utilisées in situ et conviennent donc mieux à des

applications sur le terrain.
4.3.2 Contrôle radiographique

On fait passer un rayonnement, par exemple des rayons X, au travers de l’objet. L’intensité des rayons

émergents diminue à mesure que l’épaisseur du matériau augmente. Les imperfections peuvent être

détectées si elles provoquent une modification de l’absorption des rayons X. Des détecteurs ou des films

sont utilisés pour fournir une image des imperfections internes. L’épaisseur de métal susceptible d’être

contrôlée dépend du rendement énergétique disponible. Pour être détectées, les piqûres doivent avoir

une taille équivalente à au moins 0,5 % de l’épaisseur du métal, et il convient de s’assurer que des pores

préexistants ne soient pas pris pour des piqûres.
4.3.3 Contrôle électromagnétique

4.3.3.1 Des courants de Foucault peuvent être utilisés pour détecter les défauts ou les irrégularités

dans la structure de matériaux conducteurs. Lorsqu’une éprouvette est exposée à un champ magnétique

variable, créé en branchant une bobine en courant alternatif, des courants de Foucault sont induits

dans l’éprouvette et produisent à leur tour leur propre champ magnétique. Des matériaux présentant

des défauts produiront un champ magnétique différent de celui d’un matériau de référence exempt de

défauts; un instrument de détection approprié est nécessaire pour déterminer ces différences.

4.3.3.2 Une autre approche utilisée est l’induction d’un champ magnétique dans des matériaux

ferromagnétiques. Les discontinuités perpendiculaires au sens du champ magnétique provoquent la

formation d’un champ de dispersion au-dessus de la surface de la pièce. Des particules ferromagnétiques

sont placées à la surface pour détecter le champ de dispersion et esquisser la taille et la forme des

discontinuités. Cette méthode permet de détecter d’assez petites imperfections. Toutefois, cette méthode

est limitée par la nécessaire directionnalité des défauts par rapport au champ magnétique, par la

nécessité éventuelle de démagnétiser le matériau et par les formes limitées des pièces qui peuvent être

examinées.
4.3.4 Contrôle par ultrasons

Avec la méthode par ultrasons, des vibrations acoustiques sont transmises par un milieu de couplage, tel

que l’huile ou l’eau, à la surface du métal où des ondes sont produites. Les échos réfléchis sont convertis

en signaux électriques qui peuvent être interprétés pour montrer l’emplacement des défauts ou des

piqûres. Les méthodes par contact et par immersion sont utilisées, et diverses techniques peuvent

être adoptées. Il convient que l’essai soit effectué sur la surface non piquée. L’essai est influencé par la

morphologie des piqûres, par la technique ultrasonique adoptée et par les performances de la sonde et

du détecteur de défauts. Des informations relatives à la taille et à l’emplacement des défauts peuvent

être obtenues. Toutefois, il convient d’évaluer l’adéquation de la technique par rapport au type de piqûre

attendu et de produire des étalons de référence aux fins de comparaison. Il convient que les opérateurs

soient formés à l’application de la technique et à l’interprétation des résultats.

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ISO 11463:2020(F)
4.3.5 Contrôle par ressuage

Les défauts apparaissant à la surface peuvent être détectés en appliquant un liquide pénétrant qui

exsude de la surface une fois que l’excès de liquide a été éliminé. Les défauts sont localisés en pulvérisant

sur la surface un révélateur qui réagit à un colorant du liquide pénétrant, ou ce dernier peut contenir

une matière fluorescente qui se détecte aux ultraviolets. La taille du défaut est traduite par l’intensité

de la couleur et par la vitesse de ressuage. Cette technique ne donne qu’une idée approximative de la

profondeur et de la taille des piqûres.
4.3.6 Contrôle par réplique

Des images de surface piquée peuvent être créées en appliquant à la surface un matériau qui épouse la

forme des piqûres et peut être retiré sans endommager sa forme. Toutefois, cette méthode ne fonctionne

pas dans le cas de piqûres cachées ou sous-jacentes. Le matériau retiré comporte une réplique de la

surface originale qui, dans certains cas, est plus facile à analyser que l’original. Le contrôle par réplique

est particulièrement utile pour l’analyse de très petites piqûres.
4.4 Techniques d’examen ex situ
4.4.1 Généralités

Il existe plusieurs techniques ex situ sophistiquées pour analyser la taille, la forme et la répartition

des piqûres dans des échantillons métalliques. Leur mise en application nécessite le transport des

éprouvettes vers un laboratoire ou un centre d’analyse spécialisé. Quelques-unes de ces techniques sont

décrites aux 4.4.2 à 4.4.5.
4.4.2 Microscopie électronique à balayage

La microscopie électronique à balayage (MEB) peut être utilisée pour obtenir des images contenant

des informations topographiques et de contraste de phase. Il s’agit d’une technique très utile pour

obtenir des images de piqûres en surface et elle peut être utilisée pour déterminer les dimensions de

la piqûre ainsi que les relations éventuelles avec différentes phases dans la microstructure du métal.

En la combinant avec la spectroscopie de rayons X à dispersion d’énergie (EDS) ou la spectroscopie

de rayons X à dispersion de longueur d’onde (WDS), il est possible de déterminer la composition

élémentaire et la répartition des éventuels produits de corrosion dans les piqûres. Cependant, dans le

cas de piqûres plus profondes et lorsqu’une piqûre sous-jacente cachée s’est formée sous l’ouverture,

cela obstrue l’émission d’électrons pour le détecteur, et l’efficacité de la technique pour représenter la

morphologie de la piqûre peut s’en trouver diminuée.
4.4.3 Tomodensitométrie (TDM)

La tomodensitométrie (TDM) est une technique non destructive qui, associée à un logiciel de

reconstitution, permet d’obtenir une imagerie 3D des piqûres. Les images sont construites à partir de

« tranches » de l’échantillon obtenues à l’aide de sources de rayons X à haute intensité, qui peuvent

être des tubes à rayons X dans des laboratoires classiques ou être dérivées de sources de rayons X

synchrotron. L’épaisseur de l’éprouvette peut être restreinte en raison de l’atténuation des rayons X;

une coupe parallèle à la surface peut s’avérer nécessaire pour réduire l’épaisseur. Néanmoins, cette

technique est un outil performant pour l’imagerie 3D de piqûres de forme complexe.

4.4.4 Analyse d’images

L’analyse d’images est une technique qui consiste à post-traiter les images obtenues au moyen d’une

technique de mesure telle que la microscopie optique ou la tomodensitométrie pour en extraire des

données quantitatives. Cette technique peut être utilisée en vue d’automatiser l’analyse ou le post-

traitement des images afin d’en réduire le temps et les coûts. Elle permet également l’analyse d’un plus

grand nombre d’images, améliorant ainsi la fiabilité statistique des mesures. L’analyse d’images permet

un traitement rapide des micrographies et peut produire des données plus exactes et statistiquement

plus fiables que les méthodes manuelles.
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ISO 11463:2020(F)
4.4.5 Profilométrie

La profilométrie consiste à mesurer la géométrie ou la topographie de la surface physique d’un

échantillon. Elle peut être à contact ou sans contact. La profilométrie à contact implique qu’un stylet,

dont les dimensions de la pointe sont connues, soit mis en contact avec la surface de l’échantillon, puis

la « balaye ». Le déplacement de la pointe du stylet, lorsque celle-ci entre en contact avec des éléments

saillants et creux à la surface, est observé et enregistré en fonction de sa position. À partir de ces

données, les caractéristiques physiques de la surface, telles que la rugosité, peuvent être mesurées, et

toutes les caractéristiques pertinentes, telles que les piqûres, peuvent être identifiées et quantifiées.

Les méthodes sans contact enregistrent le même type d’information, bien qu’elles recourent

généralement à des méthodes optiques au laser, telles que la microscopie à foyer à l’infini, et elles ne

nécessitent pas de contact physique direct avec la surface de l’échantillon. Ces techniques génèrent

un profil de surface en 3D grâce à l’accumulation d’images dans différents plans focaux optiques et à

l’interférométrie en lumière blanche, où la différence de phase entre la lumière réfléchie par la surface

de l’échantillon et celle d’un miroir de référence est comparée, et les variations dans la distance du trajet

dues à la morphologie de surface peuvent-être enregistrées. Des microscopes confocaux à balayage

laser peuvent donner des informations similaires.

L’inconvénient de ces techniques est qu’elles ne caractérisent que ce qu’elles peuvent détecter

optiquement, ce qui les rend applicables principalement aux types de piqûres a) à c) de la Figure 1 (voir

également 4.2.3).
5 Étendue des piqûres
5.1 Perte de masse

La perte de masse de métal n’est d’ordinaire pas recommandée pour mesurer l’étendue des piqûres,

à moins que la corrosion générale ne soit légère et les piqûres assez sévères. Si la corrosion uniforme

est importante, la contribution des piqûres à la perte totale de métal est faible et les dommages dus

aux piqûres ne peuvent être déterminés avec exactitude à partir de la perte de masse. En tout état

de cause, la perte de masse ne peut renseigner que sur la perte totale de métal liée aux piqûres, mais

aucunement sur la densité des piqûres et la profondeur de pénétration. Il convient toutefois de ne pas

systématiquement négliger la perte de masse, car cette information peut se révéler utile; par exemple,

la perte de masse assortie d’une comparaison visuelle des surfaces piquées peut permettre d’évaluer

la résistance aux piqûres des alliages dans des essais de laboratoire. La perte de masse peut également

être utile pour détecter la perte de métal par piqûres cachées.
5.2 Mesurage de la profondeur de piqûre
5.2.1 Métallographie

La profondeur de piqûre peut être déterminée en sectionnant verticalement une piqûre présélectionnée,

en procédant à un montage métallographique de la piqûre en coupe et en polissant la surface. Une

autre/meilleure façon de procéder consiste à sectionner en s’éloignant quelque peu de la piqûre et à

meuler doucement jusqu’à ce que celle-ci apparaisse en coupe. La section d’une piqûre peut s’avérer

difficile et il est possible de manquer la partie la plus profonde. La profondeur de piqûre est mesurée

sur la surface polie plane au moyen d’un microscope à oculaire étalonné. Cette méthode présente une

grande exactitude, mais exige une bonne habileté de la part de l’opérateur, un bon jugement pour la

sélection de la piqûre et une bonne technique pour réaliser la coupe. Ses limites sont les suivantes: elle

prend du temps, la piqûre la plus profonde peut ne pas avoir été sélectionnée et la section peut ne pas

avoir été effectuée au point de pénétration le plus profond. Cette technique conduit nécessairement à la

destruction de l’éprouvette.
5.2.2 Usinage
NOTE Voir les Références [3] et
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 11463
ISO/TC 156
Corrosion of metals and alloys —
Secretariat: SAC
Guidelines for the evaluation of pitting
Voting begins on:
2020­05­13 corrosion
Voting terminates on:
Corrosion des métaux et alliages — Lignes directrices pour
2020­07­08
l’évaluation de la corrosion par piqûres
ISO/CEN PARALLEL PROCESSING
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 SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
ISO/FDIS 11463:2020(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN­
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. ISO 2020
---------------------- Page: 1 ----------------------
ISO/FDIS 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

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Published in Switzerland
ii © ISO 2020 – All rights reserved
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ISO/FDIS 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 non­destructive 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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ISO/FDIS 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 non­governmental, 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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ISO/FDIS 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 pitting­resistant 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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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 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

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ISO/FDIS 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 cross­sectioned 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) sub­surface
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.
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ISO/FDIS 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 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 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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ISO/FDIS 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
...

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