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

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ISO 7146-1:2019(E)

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Published in Switzerland
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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
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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
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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.
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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.
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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
a
Damage cause.
b
Damage characteristics.
c
Damage appearances.
Figure 2 — Damage characteristics provide the basis for analysing the cause
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