Plain bearings - Appearance and characterization of damage to metallic hydrodynamic bearings - Part 1: General

This document defines, describes and classifies the characteristics of damage occurring in service to hydrodynamically lubricated metallic plain bearings and journals. It assists in the understanding of the various characteristic forms of damage which can occur.
Consideration is restricted to damage characteristics which have a well-defined appearance and which can be attributed to particular damage 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

Drsni ležaji - Tekočinski sloj kovinskih ležajev - Izrazi in značilnosti poškodb - 1. del: Splošno

General Information

Status
Published
Publication Date
20-Jul-2020
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
24-Jun-2020
Due Date
29-Aug-2020
Completion Date
21-Jul-2020

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SLOVENSKI STANDARD
SIST ISO 7146-1:2020
01-oktober-2020

Drsni ležaji - Tekočinski sloj kovinskih ležajev - Izrazi in značilnosti poškodb - 1.

del: Splošno

Plain bearings - Appearance and characterization of damage to metallic hydrodynamic

bearings - Part 1: General

Paliers lisses -- Aspect et caractérisation de l'endommagement des paliers métalliques à

couche lubrifiante fluide
Ta slovenski standard je istoveten z: ISO 7146-1:2019
ICS:
21.100.10 Drsni ležaji Plain bearings
SIST ISO 7146-1:2020 en,fr,de

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

---------------------- Page: 1 ----------------------
SIST ISO 7146-1:2020
---------------------- Page: 2 ----------------------
SIST ISO 7146-1:2020
INTERNATIONAL ISO
STANDARD 7146-1
Second edition
2019-05
Plain bearings — Appearance and
characterization of damage to metallic
hydrodynamic bearings —
Part 1:
General
Paliers lisses — Aspect et caractérisation de l'endommagement des
paliers métalliques à couche lubrifiante fluide —
Partie 1: Généralités
Reference number
ISO 7146-1:2019(E)
ISO 2019
---------------------- Page: 3 ----------------------
SIST ISO 7146-1:2020
ISO 7146-1:2019(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 7146-1:2020
ISO 7146-1:2019(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction ................................................................................................................................................................................................................................vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Descriptions, causes and features of damage ........................................................................................................................ 2

4.1 Damage .......................................................................................................................................................................................................... 2

4.1.1 General...................................................................................................................................................................................... 2

4.1.2 Indicators of damage .................................................................................................................................................... 2

4.2 Damage causes ........................................................................................................................................................................................ 2

4.3 Damage appearances ......................................................................................................................................................................... 2

4.4 Damage characterization ............................................................................................................................................................... 3

4.4.1 General...................................................................................................................................................................................... 3

4.4.2 Static overload ................................................................................................................................................................... 3

4.4.3 Dynamic overload ........................................................................................................................................................... 3

4.4.4 Wear by friction ................................................................................................................................................................ 3

4.4.5 Overheating .......................................................................................................................................................................... 3

4.4.6 Insufficient lubrication (starvation) ............................................................................................................... 3

4.4.7 Contamination ................................................................................................................................................................... 3

4.4.8 Cavitation erosion ........................................................................................................................................................... 3

4.4.9 Electroerosion .................................................................................................................................................................... 3

4.4.10 Hydrogen diffusion ........................................................................................................................................................ 4

4.4.11 Bond failure .......................................................................................................................................................................... 4

4.5 Relationship between damage appearance and damage characterizations ...................................... 4

5 Guidelines for damage analysis ............................................................................................................................................................ 5

5.1 General ........................................................................................................................................................................................................... 7

5.2 Step 1 ............................................................................................................................................................................................................... 7

5.3 Step 2 ............................................................................................................................................................................................................... 7

5.4 Step 3 ............................................................................................................................................................................................................... 7

5.5 Step 4 ............................................................................................................................................................................................................... 7

5.6 Step 5 ............................................................................................................................................................................................................... 7

6 Damage to the bearing surface — Damage characteristics, typical damage

appearances and possible damage causes ................................................................................................................................ 7

6.1 General ........................................................................................................................................................................................................... 7

6.2 Static overload ......................................................................................................................................................................................... 8

6.2.1 Typical damage appearances ................................................................................................................................ 8

6.2.2 Possible damage causes ............................................................................................................................................. 8

6.2.3 Typical examples ............................................................................................................................................................ 8

6.3 Dynamic overload ................................................................................................................................................................................. 9

6.3.1 Typical damage appearances ................................................................................................................................ 9

6.3.2 Possible damage causes ............................................................................................................................................. 9

6.3.3 Typical examples ............................................................................................................................................................ 9

6.4 Wear by friction ...................................................................................................................................................................................15

6.4.1 Typical damage appearances .............................................................................................................................15

6.4.2 Possible damage causes ..........................................................................................................................................16

6.4.3 Typical examples .........................................................................................................................................................16

6.5 Overheating.............................................................................................................................................................................................18

6.5.1 Typical damage appearances .............................................................................................................................18

6.5.2 Possible damage causes ..........................................................................................................................................19

6.5.3 Typical examples .........................................................................................................................................................19

6.6 Insufficient lubrication (starvation) ..................................................................................................................................21

6.6.1 Typical damage appearances .............................................................................................................................21

© ISO 2019 – All rights reserved iii
---------------------- Page: 5 ----------------------
SIST ISO 7146-1:2020
ISO 7146-1:2019(E)

6.6.2 Possible damage causes ..........................................................................................................................................21

6.6.3 Typical examples .........................................................................................................................................................21

6.7 Contamination ......................................................................................................................................................................................25

6.7.1 Contamination with particles ............................................................................................................................25

6.7.2 Contamination with chemicals .........................................................................................................................32

6.8 Cavitation erosion .............................................................................................................................................................................37

6.8.1 General...................................................................................................................................................................................37

6.8.2 Typical damage appearances .............................................................................................................................37

6.8.3 Possible damage causes ..........................................................................................................................................37

6.8.4 Typical examples ..........................................................................................................................................................37

6.9 Electro-erosion ....................................................................................................................................................................................39

6.9.1 Typical damage appearance ................................................................................................................................39

6.9.2 Possible damage causes ..........................................................................................................................................39

6.9.3 Typical examples ..........................................................................................................................................................39

6.10 Hydrogen diffusion ...........................................................................................................................................................................40

6.10.1 Typical damage appearances .............................................................................................................................40

6.10.2 Possible damage cause ............................................................................................................................................41

6.10.3 Typical examples .........................................................................................................................................................41

6.11 Bond failure ............................................................................................................................................................................................42

6.11.1 Typical damage appearances .............................................................................................................................42

6.11.2 Possible damage causes ..........................................................................................................................................42

6.11.3 Typical example ............................................................................................................................................................42

7 Damage to the bearing back ..................................................................................................................................................................43

7.1 General ........................................................................................................................................................................................................43

7.2 Dynamic overload on the bearing back ..........................................................................................................................43

7.2.1 Typical damage appearance ................................................................................................................................43

7.2.2 Possible damage causes ..........................................................................................................................................43

7.2.3 Typical examples .........................................................................................................................................................43

7.3 Wear by friction on the bearing back ...............................................................................................................................45

7.3.1 Typical damage appearances .............................................................................................................................45

7.3.2 Possible damage causes ..........................................................................................................................................45

7.3.3 Typical examples .........................................................................................................................................................45

7.4 Contamination with particles on the bearing back ..............................................................................................46

7.4.1 Typical damage appearances .............................................................................................................................46

7.4.2 Possible damage cause ............................................................................................................................................46

7.4.3 Typical examples .........................................................................................................................................................47

8 Special position of damage appearances .................................................................................................................................48

Annex A (informative) Example of use of Table 1.................................................................................................................................51

Bibliography .............................................................................................................................................................................................................................53

iv © ISO 2019 – All rights reserved
---------------------- Page: 6 ----------------------
SIST ISO 7146-1:2020
ISO 7146-1:2019(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 7146-1:2008), 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.
© ISO 2019 – All rights reserved v
---------------------- Page: 7 ----------------------
SIST ISO 7146-1:2020
ISO 7146-1:2019(E)
Introduction

In practice, damage to a bearing can often be the result of several mechanisms operating simultaneously.

The complex combination of design, manufacture, assembly, operation, maintenance and possible

reconditioning 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. Thus Clause 4 is

subdivided into several subclauses including damage appearance and damage characteristics.

For the procedure of damage analysis, Clause 5 can be a helpful guide.

In Clauses 6 and 7, examples of all damage characteristics with typically associated damage appearance

are given.
vi © ISO 2019 – All rights reserved
---------------------- Page: 8 ----------------------
SIST ISO 7146-1:2020
INTERNATIONAL STANDARD ISO 7146-1:2019(E)
Plain bearings — Appearance and characterization of
damage to metallic hydrodynamic bearings —
Part 1:
General
1 Scope

This document defines, describes and classifies the characteristics of damage occurring in service to

hydrodynamically lubricated metallic plain bearings and journals. It assists in the understanding of the

various characteristic forms of damage which can occur.

Consideration is restricted to damage characteristics which have a well-defined appearance and which

can be attributed to particular damage 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 4378-4, Plain bearings — Terms, definitions, classification and symbols — Part 4: Basic symbols

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,

ISO 4378-4 and the following 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/
3.1
damage to plain bearings
bearing damage

change in appearance occurring on the bearing surface and/or on the bearing back during operation

that adversely affect the performance of the bearing
© ISO 2019 – All rights reserved 1
---------------------- Page: 9 ----------------------
SIST ISO 7146-1:2020
ISO 7146-1:2019(E)
4 Descriptions, causes and features of damage
4.1 Damage
4.1.1 General

Damage to plain bearings is a phenomenon that adversely changes their tribological function and is

usually accompanied with a change in appearance. The damage is initiated by the damage cause and

develops to the end of service life.

As long as no abnormal conditions occur, service life of the plain bearing relates to the service life of the

machine.
4.1.2 Indicators of damage

Typical indicators observed during machine operation are: continuously increasing service temperature,

decline of lubricant pressure, noise, vibration and bad smell.
4.2 Damage causes

The cause is the practical event that initiates and leads to damage. The majority of damage causes are

found outside the bearing.
4.3 Damage appearances

Damage appearance is a defined visible picture of the bearing surface and/or of the bearing back.

Damage appearances are clearly different from each other.

A plain bearing failure can show various damage appearances. Usually, damage appearances are

directly associated with damage characteristics, but not directly with the damage cause (for exceptions,

see 6.8 and 6.9).
Damage appearances include:
a) depositions;
b) creep deformation;
c) deformation due to temperature cycles;
d) thermal cracks;
e) fatigue cracks;
f) material relief (loss of bond);
g) frictional corrosion;
h) melting out, seizure;
i) polishing, scoring;
j) traces of mixed lubrication, worn material;
k) discolouration (blue, black colour);
l) corrosion, fluid erosion;
m) embedded particles, particle-migration tracks, formation of wire wool;
n) electric arc craters;
2 © ISO 2019 – All rights reserved
---------------------- Page: 10 ----------------------
SIST ISO 7146-1:2020
ISO 7146-1:2019(E)
o) cavitation erosion appearance: worn-out material.
4.4 Damage characterization
4.4.1 General

A damage characterization is a description of what has happened based on a detected typical

combination of damage appearances. Defined characteristics provide the basis for establishing the

cause of damage.

Damage characterizations are clearly different from each other, as specified in 4.4.2 to 4.4.11.

4.4.2 Static overload

Material is loaded above compressive yield strength corresponding to actual operation temperature.

4.4.3 Dynamic overload

Material is loaded above fatigue strength corresponding to actual operation temperature. Intensive

dynamic load also favours damage by weakening the fit.
4.4.4 Wear by friction

Wear by friction is confined to changes in microgeometry and to the loss of material as a result of

interaction between journal and bearing. Movement between backing and housing also favours wear

by friction.
4.4.5 Overheating

The heat balance in the lubricant, the bearing, the environment and the cooling system as required

at design stage is not realized resulting in a higher temperature than anticipated. The viscosity and,

therefore, the load capacity decrease with increasing temperature. This results again in temperature

increase. The bearing, therefore, cannot operate stably if cooling cannot stop further temperature

increase.
4.4.6 Insufficient lubrication (starvation)
This affects the tribological system.
4.4.7 Contamination

Contamination of lubricant with foreign particles or reaction products can result in damage to a

bearing. Foreign particles embedded between bearing backing and housing also favour damage.

4.4.8 Cavitation erosion

Decreased pressure in liquids leads to evaporation of liquids and formation of vapour bubbles, which,

when liquid pressure increases, implode, generating locally very high pressure, and cause erosion on

sliding surfaces.
4.4.9 Electroerosion

A potential difference between journal and bearing can lead to an electric arc with locally high current

flow which damages journal and bearing surface.
© ISO 2019 – All rights reserved 3
---------------------- Page: 11 ----------------------
SIST ISO 7146-1:2020
ISO 7146-1:2019(E)
4.4.10 Hydrogen diffusion

Hydrogen can be incorporated in the steel backing or in an electroplated layer of the bearing. If

hydrogen diffusion is blocked by a layer, blisters occur.
4.4.11 Bond failure

Bond failure is delamination between lining and backing or between layers. A metallographic

examination is required to distinguish it from other damage characterizations.
4.5 Relationship between damage appearance and damage characterizations
Damage characterization and damage appearance alter with the progress of damage
...

INTERNATIONAL ISO
STANDARD 7146-1
Second edition
2019-05
Plain bearings — Appearance and
characterization of damage to metallic
hydrodynamic bearings —
Part 1:
General
Paliers lisses — Aspect et caractérisation de l'endommagement des
paliers métalliques à couche lubrifiante fluide —
Partie 1: Généralités
Reference number
ISO 7146-1:2019(E)
ISO 2019
---------------------- Page: 1 ----------------------
ISO 7146-1:2019(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 7146-1:2019(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction ................................................................................................................................................................................................................................vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Descriptions, causes and features of damage ........................................................................................................................ 2

4.1 Damage .......................................................................................................................................................................................................... 2

4.1.1 General...................................................................................................................................................................................... 2

4.1.2 Indicators of damage .................................................................................................................................................... 2

4.2 Damage causes ........................................................................................................................................................................................ 2

4.3 Damage appearances ......................................................................................................................................................................... 2

4.4 Damage characterization ............................................................................................................................................................... 3

4.4.1 General...................................................................................................................................................................................... 3

4.4.2 Static overload ................................................................................................................................................................... 3

4.4.3 Dynamic overload ........................................................................................................................................................... 3

4.4.4 Wear by friction ................................................................................................................................................................ 3

4.4.5 Overheating .......................................................................................................................................................................... 3

4.4.6 Insufficient lubrication (starvation) ............................................................................................................... 3

4.4.7 Contamination ................................................................................................................................................................... 3

4.4.8 Cavitation erosion ........................................................................................................................................................... 3

4.4.9 Electroerosion .................................................................................................................................................................... 3

4.4.10 Hydrogen diffusion ........................................................................................................................................................ 4

4.4.11 Bond failure .......................................................................................................................................................................... 4

4.5 Relationship between damage appearance and damage characterizations ...................................... 4

5 Guidelines for damage analysis ............................................................................................................................................................ 5

5.1 General ........................................................................................................................................................................................................... 7

5.2 Step 1 ............................................................................................................................................................................................................... 7

5.3 Step 2 ............................................................................................................................................................................................................... 7

5.4 Step 3 ............................................................................................................................................................................................................... 7

5.5 Step 4 ............................................................................................................................................................................................................... 7

5.6 Step 5 ............................................................................................................................................................................................................... 7

6 Damage to the bearing surface — Damage characteristics, typical damage

appearances and possible damage causes ................................................................................................................................ 7

6.1 General ........................................................................................................................................................................................................... 7

6.2 Static overload ......................................................................................................................................................................................... 8

6.2.1 Typical damage appearances ................................................................................................................................ 8

6.2.2 Possible damage causes ............................................................................................................................................. 8

6.2.3 Typical examples ............................................................................................................................................................ 8

6.3 Dynamic overload ................................................................................................................................................................................. 9

6.3.1 Typical damage appearances ................................................................................................................................ 9

6.3.2 Possible damage causes ............................................................................................................................................. 9

6.3.3 Typical examples ............................................................................................................................................................ 9

6.4 Wear by friction ...................................................................................................................................................................................15

6.4.1 Typical damage appearances .............................................................................................................................15

6.4.2 Possible damage causes ..........................................................................................................................................16

6.4.3 Typical examples .........................................................................................................................................................16

6.5 Overheating.............................................................................................................................................................................................18

6.5.1 Typical damage appearances .............................................................................................................................18

6.5.2 Possible damage causes ..........................................................................................................................................19

6.5.3 Typical examples .........................................................................................................................................................19

6.6 Insufficient lubrication (starvation) ..................................................................................................................................21

6.6.1 Typical damage appearances .............................................................................................................................21

© ISO 2019 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 7146-1:2019(E)

6.6.2 Possible damage causes ..........................................................................................................................................21

6.6.3 Typical examples .........................................................................................................................................................21

6.7 Contamination ......................................................................................................................................................................................25

6.7.1 Contamination with particles ............................................................................................................................25

6.7.2 Contamination with chemicals .........................................................................................................................32

6.8 Cavitation erosion .............................................................................................................................................................................37

6.8.1 General...................................................................................................................................................................................37

6.8.2 Typical damage appearances .............................................................................................................................37

6.8.3 Possible damage causes ..........................................................................................................................................37

6.8.4 Typical examples ..........................................................................................................................................................37

6.9 Electro-erosion ....................................................................................................................................................................................39

6.9.1 Typical damage appearance ................................................................................................................................39

6.9.2 Possible damage causes ..........................................................................................................................................39

6.9.3 Typical examples ..........................................................................................................................................................39

6.10 Hydrogen diffusion ...........................................................................................................................................................................40

6.10.1 Typical damage appearances .............................................................................................................................40

6.10.2 Possible damage cause ............................................................................................................................................41

6.10.3 Typical examples .........................................................................................................................................................41

6.11 Bond failure ............................................................................................................................................................................................42

6.11.1 Typical damage appearances .............................................................................................................................42

6.11.2 Possible damage causes ..........................................................................................................................................42

6.11.3 Typical example ............................................................................................................................................................42

7 Damage to the bearing back ..................................................................................................................................................................43

7.1 General ........................................................................................................................................................................................................43

7.2 Dynamic overload on the bearing back ..........................................................................................................................43

7.2.1 Typical damage appearance ................................................................................................................................43

7.2.2 Possible damage causes ..........................................................................................................................................43

7.2.3 Typical examples .........................................................................................................................................................43

7.3 Wear by friction on the bearing back ...............................................................................................................................45

7.3.1 Typical damage appearances .............................................................................................................................45

7.3.2 Possible damage causes ..........................................................................................................................................45

7.3.3 Typical examples .........................................................................................................................................................45

7.4 Contamination with particles on the bearing back ..............................................................................................46

7.4.1 Typical damage appearances .............................................................................................................................46

7.4.2 Possible damage cause ............................................................................................................................................46

7.4.3 Typical examples .........................................................................................................................................................47

8 Special position of damage appearances .................................................................................................................................48

Annex A (informative) Example of use of Table 1.................................................................................................................................51

Bibliography .............................................................................................................................................................................................................................53

iv © ISO 2019 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 7146-1:2019(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 7146-1:2008), 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.
© ISO 2019 – All rights reserved v
---------------------- Page: 5 ----------------------
ISO 7146-1:2019(E)
Introduction

In practice, damage to a bearing can often be the result of several mechanisms operating simultaneously.

The complex combination of design, manufacture, assembly, operation, maintenance and possible

reconditioning 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. Thus Clause 4 is

subdivided into several subclauses including damage appearance and damage characteristics.

For the procedure of damage analysis, Clause 5 can be a helpful guide.

In Clauses 6 and 7, examples of all damage characteristics with typically associated damage appearance

are given.
vi © ISO 2019 – All rights reserved
---------------------- Page: 6 ----------------------
INTERNATIONAL STANDARD ISO 7146-1:2019(E)
Plain bearings — Appearance and characterization of
damage to metallic hydrodynamic bearings —
Part 1:
General
1 Scope

This document defines, describes and classifies the characteristics of damage occurring in service to

hydrodynamically lubricated metallic plain bearings and journals. It assists in the understanding of the

various characteristic forms of damage which can occur.

Consideration is restricted to damage characteristics which have a well-defined appearance and which

can be attributed to particular damage 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 4378-4, Plain bearings — Terms, definitions, classification and symbols — Part 4: Basic symbols

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,

ISO 4378-4 and the following 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/
3.1
damage to plain bearings
bearing damage

change in appearance occurring on the bearing surface and/or on the bearing back during operation

that adversely affect the performance of the bearing
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ISO 7146-1:2019(E)
4 Descriptions, causes and features of damage
4.1 Damage
4.1.1 General

Damage to plain bearings is a phenomenon that adversely changes their tribological function and is

usually accompanied with a change in appearance. The damage is initiated by the damage cause and

develops to the end of service life.

As long as no abnormal conditions occur, service life of the plain bearing relates to the service life of the

machine.
4.1.2 Indicators of damage

Typical indicators observed during machine operation are: continuously increasing service temperature,

decline of lubricant pressure, noise, vibration and bad smell.
4.2 Damage causes

The cause is the practical event that initiates and leads to damage. The majority of damage causes are

found outside the bearing.
4.3 Damage appearances

Damage appearance is a defined visible picture of the bearing surface and/or of the bearing back.

Damage appearances are clearly different from each other.

A plain bearing failure can show various damage appearances. Usually, damage appearances are

directly associated with damage characteristics, but not directly with the damage cause (for exceptions,

see 6.8 and 6.9).
Damage appearances include:
a) depositions;
b) creep deformation;
c) deformation due to temperature cycles;
d) thermal cracks;
e) fatigue cracks;
f) material relief (loss of bond);
g) frictional corrosion;
h) melting out, seizure;
i) polishing, scoring;
j) traces of mixed lubrication, worn material;
k) discolouration (blue, black colour);
l) corrosion, fluid erosion;
m) embedded particles, particle-migration tracks, formation of wire wool;
n) electric arc craters;
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ISO 7146-1:2019(E)
o) cavitation erosion appearance: worn-out material.
4.4 Damage characterization
4.4.1 General

A damage characterization is a description of what has happened based on a detected typical

combination of damage appearances. Defined characteristics provide the basis for establishing the

cause of damage.

Damage characterizations are clearly different from each other, as specified in 4.4.2 to 4.4.11.

4.4.2 Static overload

Material is loaded above compressive yield strength corresponding to actual operation temperature.

4.4.3 Dynamic overload

Material is loaded above fatigue strength corresponding to actual operation temperature. Intensive

dynamic load also favours damage by weakening the fit.
4.4.4 Wear by friction

Wear by friction is confined to changes in microgeometry and to the loss of material as a result of

interaction between journal and bearing. Movement between backing and housing also favours wear

by friction.
4.4.5 Overheating

The heat balance in the lubricant, the bearing, the environment and the cooling system as required

at design stage is not realized resulting in a higher temperature than anticipated. The viscosity and,

therefore, the load capacity decrease with increasing temperature. This results again in temperature

increase. The bearing, therefore, cannot operate stably if cooling cannot stop further temperature

increase.
4.4.6 Insufficient lubrication (starvation)
This affects the tribological system.
4.4.7 Contamination

Contamination of lubricant with foreign particles or reaction products can result in damage to a

bearing. Foreign particles embedded between bearing backing and housing also favour damage.

4.4.8 Cavitation erosion

Decreased pressure in liquids leads to evaporation of liquids and formation of vapour bubbles, which,

when liquid pressure increases, implode, generating locally very high pressure, and cause erosion on

sliding surfaces.
4.4.9 Electroerosion

A potential difference between journal and bearing can lead to an electric arc with locally high current

flow which damages journal and bearing surface.
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ISO 7146-1:2019(E)
4.4.10 Hydrogen diffusion

Hydrogen can be incorporated in the steel backing or in an electroplated layer of the bearing. If

hydrogen diffusion is blocked by a layer, blisters occur.
4.4.11 Bond failure

Bond failure is delamination between lining and backing or between layers. A metallographic

examination is required to distinguish it from other damage characterizations.
4.5 Relationship between damage appearance and damage characterizations

Damage characterization and damage appearance alter with the progress of damage from a primary to

a secondary characteristic (see Figure 1).
Different damage characterizations can correspond to the same damage appearance.
One damage characterization can correspond to various damage appearances.
Multiple damage characteristics can be found in one failure event.

The damage characteristics provide the basis for analysing the cause (see Figure 2).

Typical relationships are shown in Table 1 for damage to sliding surface and to bearing back. In most

cases, Table 1 is the guideline for diagnosis of the final damage cause from the damage appearances via

the damage characteristics.

Figure 1 — Damage appearances altering with the progress from primary to secondary

characteristics
Key
Damage cause.
Damage characteristics.
Damage appearances.
Figure 2 — Damage characteristics provide the basis for analysing the cause
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ISO 7146-1:2019(E)
5 G
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