Plain bearings - Appearance and characterization of damage to metallic hydrodynamic bearings - Part 2: Cavitation erosion and its countermeasures

This document defines, describes and classifies the characteristics of damage occurring in service in hydrodynamically lubricated metallic plain bearings due to cavitation erosion, together with possible countermeasures. It assists in understanding the various characteristic forms of damage which can occur.
Consideration is restricted to damage which has a well-defined appearance and which can be attributed to particular causes with a high degree of certainty. Various appearances are illustrated with photographs and diagrams.

Paliers lisses - Aspect et caractérisation de l'endommagement des paliers métalliques à couche lubrifiante fluide - Partie 2: Érosion de cavitation et sa contre-mesure

Drsni ležaji - Tekočinski sloj kovinskih ležajev - Izrazi in značilnosti poškodb - 2. del: Kavitacijske poškodbe in ukrepi za njihovo preprečevanje

Ta dokument opredeljuje, opisuje in razvršča značilnosti poškodb, ki se pojavijo med obratovanjem v hidrodinamično mazanih kovinskih drsnih ležajih zaradi kavitacijske erozije, skupaj z možnimi protiukrepi. Pomaga razumeti različne značilne oblike poškodb, ki se lahko pojavijo.
Obravnava je omejena na poškodbe, ki so jasno vidne in jih je mogoče z veliko stopnjo gotovosti pripisati določenim vzrokom. Različni prikazi poškodb so ponazorjeni s fotografijami in diagrami.

General Information

Status
Published
Publication Date
13-Mar-2023
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
08-Mar-2023
Due Date
13-May-2023
Completion Date
14-Mar-2023

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SLOVENSKI STANDARD
SIST ISO 7146-2:2023
01-april-2023
Drsni ležaji - Tekočinski sloj kovinskih ležajev - Izrazi in značilnosti poškodb - 2.
del: Kavitacijske poškodbe in ukrepi za njihovo preprečevanje
Plain bearings - Appearance and characterization of damage to metallic hydrodynamic
bearings - Part 2: Cavitation erosion and its countermeasures
Paliers lisses - Aspect et caractérisation de l'endommagement des paliers métalliques à
couche lubrifiante fluide - Partie 2: Érosion de cavitation et sa contre-mesure
Ta slovenski standard je istoveten z: ISO 7146-2:2019
ICS:
21.100.10 Drsni ležaji Plain bearings
SIST ISO 7146-2:2023 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST ISO 7146-2:2023

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SIST ISO 7146-2:2023
INTERNATIONAL ISO
STANDARD 7146-2
Second edition
2019-05
Plain bearings — Appearance and
characterization of damage to metallic
hydrodynamic bearings —
Part 2:
Cavitation erosion and its
countermeasures
Paliers lisses — Aspect et caractérisation de l'endommagement des
paliers métalliques à couche lubrifiante fluide —
Partie 2: Érosion de cavitation et sa contre-mesure
Reference number
ISO 7146-2:2019(E)
©
ISO 2019

---------------------- Page: 3 ----------------------
SIST ISO 7146-2:2023
ISO 7146-2:2019(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

---------------------- Page: 4 ----------------------
SIST ISO 7146-2:2023
ISO 7146-2:2019(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Cavitation erosion . 1
4.1 Mechanism of cavitation erosion . 1
4.2 Classification of cavitation erosion . 4
4.3 General countermeasures against cavitation erosion . 6
5 Five types of cavitation erosion. 7
5.1 General . 7
5.2 Flow cavitation erosion . 7
5.2.1 Typical damage appearance . 7
5.2.2 Possible causes . 8
5.2.3 Possible countermeasures . 8
5.2.4 Typical examples (see Figures 4 to 8) . 8
5.3 Impact cavitation erosion .10
5.3.1 Typical damage appearance .10
5.3.2 Possible damage causes .10
5.3.3 Possible countermeasures .10
5.3.4 Typical examples (see Figures 9 to 11) .11
5.4 Suction cavitation erosion .12
5.4.1 Typical damage appearance .12
5.4.2 Possible causes .12
5.4.3 Possible countermeasures .12
5.4.4 Typical examples (see Figures 12 to 14) .13
5.5 Discharge cavitation erosion .14
5.5.1 Typical damage appearance .14
5.5.2 Possible causes .14
5.5.3 Possible countermeasures .14
5.5.4 Typical examples (see Figures 15 to 16) .14
5.6 Miscellaneous cavitation erosion (see Figures 17 to 20) .15
5.6.1 Cavitation erosion caused by high-frequency vibration (“Vibration cavitation”) 15
5.6.2 Cavitation erosion by elastic bearing deformation or abnormal combustion .15
5.6.3 Rippling or roughening (see Figures 19 and 20) .15
© ISO 2019 – All rights reserved iii

---------------------- Page: 5 ----------------------
SIST ISO 7146-2:2023
ISO 7146-2:2019(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation 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 123, Plain bearings, Subcommittee SC 2,
Materials and lubricants, their properties, characteristics, test methods and testing conditions.
This second edition cancels and replaces the first edition (ISO 7146-2:2008), of which it constitutes a
minor revision. The changes compared to the previous edition are as follows:
— Adjustment to the ISO Directives, including the replacement of "may" with "can" throughout.
A list of all parts in the ISO 7146 series can be found on the ISO website.
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 2019 – All rights reserved

---------------------- Page: 6 ----------------------
SIST ISO 7146-2:2023
ISO 7146-2:2019(E)

Introduction
In practice, damage to a bearing can often be the result of several mechanisms operating simultaneously.
The damage can result from improper assembly or maintenance or from faulty manufacture of the
bearing, its housing or the counterface against which it operates. In some instances, damage can be
caused by a design compromise made in the interests of economy or from unforeseen operating
conditions. It is the complex combination of design, manufacture, assembly, operation, maintenance
and possible reconditioning which often causes difficulty in establishing the primary cause of damage.
In the event of extensive damage or destruction of the bearing, the evidence is likely to be lost, in which
case it is impossible to identify how the damage came about.
In all cases, knowledge of the actual operating conditions of the assembly and the maintenance history
is of the utmost importance.
The classification of bearing damage established in this document is based primarily upon the features
visible on the running surfaces and elsewhere, and consideration of each aspect is needed for reliable
determination of the cause of bearing damage.
Since more than one process can cause similar effects on the running surface, a description of
appearance alone is occasionally inadequate in determining the cause of damage. In such cases, the
operating conditions need to be considered.
Cavitation erosion dealt with in ISO 7146-1 is treated in this document in more detail.
© ISO 2019 – All rights reserved v

---------------------- Page: 7 ----------------------
SIST ISO 7146-2:2023

---------------------- Page: 8 ----------------------
SIST ISO 7146-2:2023
INTERNATIONAL STANDARD ISO 7146-2:2019(E)
Plain bearings — Appearance and characterization of
damage to metallic hydrodynamic bearings —
Part 2:
Cavitation erosion and its countermeasures
1 Scope
This document defines, describes and classifies the characteristics of damage occurring in service in
hydrodynamically lubricated metallic plain bearings due to cavitation erosion, together with possible
countermeasures. It assists in understanding the various characteristic forms of damage which can occur.
Consideration is restricted to damage which has a well-defined appearance and which can be
attributed to particular causes with a high degree of certainty. Various appearances are illustrated
with photographs and diagrams.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 4378-1, Plain bearings — Terms, definitions, classification and symbols — Part 1: Design, bearing
materials and their properties
ISO 4378-2, Plain bearings — Terms, definitions, classification and symbols — Part 2: Friction and wear
ISO 4378-3, Plain bearings — Terms, definitions, classification and symbols — Part 3: Lubrication
ISO 7146-1, Plain bearings — Appearance and characterization of damage to metallic hydrodynamic
bearings — Part 1: General
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4378-1, ISO 4378-2, ISO 4378-3,
and ISO 7146-1 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
4 Cavitation erosion
4.1 Mechanism of cavitation erosion
Cavitation erosion is a form of damage to the surface of a solid body in liquid caused by implosion (violent
inward collapse) of cavities or vapour bubbles. When the static pressure in the liquid is decreased under
the vapour pressure of the liquid at a given temperature, evaporation occurs and bubbles of vapour
are generated in the liquid. This phenomenon is called “cavitation”. When these cavities encounter
higher pressure, because they have flowed to a place of higher pressure or the pressure at the place of
© ISO 2019 – All rights reserved 1

---------------------- Page: 9 ----------------------
SIST ISO 7146-2:2023
ISO 7146-2:2019(E)

cavitation has increased in the meantime, they condense instantaneously and implode, causing a very
high and local pressure and high temperature in the liquid. It can lead, after repeated implosion, to
“cavitation erosion” of the surface of the solid body near the place of implosion.
Because of the high intensity of cavity implosion, a chemical reaction called “cavitation corrosion”
can take place. The damage can also occur together with “fluid erosion” and “cavitation erosion”. A
phenomenon known as the “micro-Diesel effect”, where the imploding cavities release electrical charge,
is also detected in plain bearing oil.
When a bearing surface is eroded by cavitation, the colour of the surface changes slightly due to
roughening. Then small pores form, and cracks initiate on the surface, especially at grain boundaries.
These cracks with sharp edges are spread first on the surface and then deepen according to the
properties of the underlying material (see Figure 1). The cracks are joined together leading to break-out
and wash-away of small particles of bearing materials.
When the damage
...

INTERNATIONAL ISO
STANDARD 7146-2
Second edition
2019-05
Plain bearings — Appearance and
characterization of damage to metallic
hydrodynamic bearings —
Part 2:
Cavitation erosion and its
countermeasures
Paliers lisses — Aspect et caractérisation de l'endommagement des
paliers métalliques à couche lubrifiante fluide —
Partie 2: Érosion de cavitation et sa contre-mesure
Reference number
ISO 7146-2:2019(E)
©
ISO 2019

---------------------- Page: 1 ----------------------
ISO 7146-2:2019(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 7146-2:2019(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Cavitation erosion . 1
4.1 Mechanism of cavitation erosion . 1
4.2 Classification of cavitation erosion . 4
4.3 General countermeasures against cavitation erosion . 6
5 Five types of cavitation erosion. 7
5.1 General . 7
5.2 Flow cavitation erosion . 7
5.2.1 Typical damage appearance . 7
5.2.2 Possible causes . 8
5.2.3 Possible countermeasures . 8
5.2.4 Typical examples (see Figures 4 to 8) . 8
5.3 Impact cavitation erosion .10
5.3.1 Typical damage appearance .10
5.3.2 Possible damage causes .10
5.3.3 Possible countermeasures .10
5.3.4 Typical examples (see Figures 9 to 11) .11
5.4 Suction cavitation erosion .12
5.4.1 Typical damage appearance .12
5.4.2 Possible causes .12
5.4.3 Possible countermeasures .12
5.4.4 Typical examples (see Figures 12 to 14) .13
5.5 Discharge cavitation erosion .14
5.5.1 Typical damage appearance .14
5.5.2 Possible causes .14
5.5.3 Possible countermeasures .14
5.5.4 Typical examples (see Figures 15 to 16) .14
5.6 Miscellaneous cavitation erosion (see Figures 17 to 20) .15
5.6.1 Cavitation erosion caused by high-frequency vibration (“Vibration cavitation”) 15
5.6.2 Cavitation erosion by elastic bearing deformation or abnormal combustion .15
5.6.3 Rippling or roughening (see Figures 19 and 20) .15
© ISO 2019 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO 7146-2:2019(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation 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 123, Plain bearings, Subcommittee SC 2,
Materials and lubricants, their properties, characteristics, test methods and testing conditions.
This second edition cancels and replaces the first edition (ISO 7146-2:2008), of which it constitutes a
minor revision. The changes compared to the previous edition are as follows:
— Adjustment to the ISO Directives, including the replacement of "may" with "can" throughout.
A list of all parts in the ISO 7146 series can be found on the ISO website.
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 2019 – All rights reserved

---------------------- Page: 4 ----------------------
ISO 7146-2:2019(E)

Introduction
In practice, damage to a bearing can often be the result of several mechanisms operating simultaneously.
The damage can result from improper assembly or maintenance or from faulty manufacture of the
bearing, its housing or the counterface against which it operates. In some instances, damage can be
caused by a design compromise made in the interests of economy or from unforeseen operating
conditions. It is the complex combination of design, manufacture, assembly, operation, maintenance
and possible reconditioning which often causes difficulty in establishing the primary cause of damage.
In the event of extensive damage or destruction of the bearing, the evidence is likely to be lost, in which
case it is impossible to identify how the damage came about.
In all cases, knowledge of the actual operating conditions of the assembly and the maintenance history
is of the utmost importance.
The classification of bearing damage established in this document is based primarily upon the features
visible on the running surfaces and elsewhere, and consideration of each aspect is needed for reliable
determination of the cause of bearing damage.
Since more than one process can cause similar effects on the running surface, a description of
appearance alone is occasionally inadequate in determining the cause of damage. In such cases, the
operating conditions need to be considered.
Cavitation erosion dealt with in ISO 7146-1 is treated in this document in more detail.
© ISO 2019 – All rights reserved v

---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 7146-2:2019(E)
Plain bearings — Appearance and characterization of
damage to metallic hydrodynamic bearings —
Part 2:
Cavitation erosion and its countermeasures
1 Scope
This document defines, describes and classifies the characteristics of damage occurring in service in
hydrodynamically lubricated metallic plain bearings due to cavitation erosion, together with possible
countermeasures. It assists in understanding the various characteristic forms of damage which can occur.
Consideration is restricted to damage which has a well-defined appearance and which can be
attributed to particular causes with a high degree of certainty. Various appearances are illustrated
with photographs and diagrams.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 4378-1, Plain bearings — Terms, definitions, classification and symbols — Part 1: Design, bearing
materials and their properties
ISO 4378-2, Plain bearings — Terms, definitions, classification and symbols — Part 2: Friction and wear
ISO 4378-3, Plain bearings — Terms, definitions, classification and symbols — Part 3: Lubrication
ISO 7146-1, Plain bearings — Appearance and characterization of damage to metallic hydrodynamic
bearings — Part 1: General
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4378-1, ISO 4378-2, ISO 4378-3,
and ISO 7146-1 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
4 Cavitation erosion
4.1 Mechanism of cavitation erosion
Cavitation erosion is a form of damage to the surface of a solid body in liquid caused by implosion (violent
inward collapse) of cavities or vapour bubbles. When the static pressure in the liquid is decreased under
the vapour pressure of the liquid at a given temperature, evaporation occurs and bubbles of vapour
are generated in the liquid. This phenomenon is called “cavitation”. When these cavities encounter
higher pressure, because they have flowed to a place of higher pressure or the pressure at the place of
© ISO 2019 – All rights reserved 1

---------------------- Page: 6 ----------------------
ISO 7146-2:2019(E)

cavitation has increased in the meantime, they condense instantaneously and implode, causing a very
high and local pressure and high temperature in the liquid. It can lead, after repeated implosion, to
“cavitation erosion” of the surface of the solid body near the place of implosion.
Because of the high intensity of cavity implosion, a chemical reaction called “cavitation corrosion”
can take place. The damage can also occur together with “fluid erosion” and “cavitation erosion”. A
phenomenon known as the “micro-Diesel effect”, where the imploding cavities release electrical charge,
is also detected in plain bearing oil.
When a bearing surface is eroded by cavitation, the colour of the surface changes slightly due to
roughening. Then small pores form, and cracks initiate on the surface, especially at grain boundaries.
These cracks with sharp edges are spread first on the surface and then deepen according to the
properties of the underlying material (see Figure 1). The cracks are joined together leading to break-out
and wash-away of small particles of bearing materials.
When the damage is caused solely by collapsing cavities, the attacked areas show a rough texture.
Metallurgical section often shows signs of local work-hardening and fatigue cracking due to hammer
blows caused by cavity collapse. But if particles are trapped in the damage pockets, the surface can
be eroded and exhibits a smooth and polished appearance. The place of cavitation erosion is usually
limited locally and spreads seldom to a broader region. The cavitation erosion
...

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