SIST ISO 7146-1:2009

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

This part of ISO 7146 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 may 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.

Gleitlager - Ölgeschmierte metallische Gleitlager - Terminologie und Schadenscharakterisierung - Teil 1: Allgemeines

Paliers lisses - Aspect et caractérisation de l'endommagement des paliers métalliques à couche lubrifiante fluide - Partie 1: Généralités

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

General Information

• Status: Withdrawn
• Public Enquiry End Date: 29-Jul-2008
• Publication Date: 06-Apr-2009
• Withdrawal Date: 23-Jun-2020
• ICS: 21.100.10 - Plain bearings
• Technical Committee: ISEL - Mechanical elements
• Current Stage: 9900 - Withdrawal (Adopted Project)
• Start Date: 24-Jun-2020
• Due Date: 17-Jul-2020
• Completion Date: 24-Jun-2020
• Ref Project: ISO 7146-1:2008 - Plain bearings — Appearance and characterization of damage to metallic hydrodynamic bearings — Part 1: General

Relations

• Replaces: SIST ISO 7146:2002 - Plain bearings -- Terms, characteristics and causes of damage and changes in appearance
• Effective Date: 01-May-2009
• Revised: SIST ISO 7146-1:2020 - Plain bearings - Appearance and characterization of damage to metallic hydrodynamic bearings - Part 1: General
• Effective Date: 23-Apr-2020

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 7146-1
First edition
2008-10-15

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 7146-1:2008(E)
©
ISO 2008

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ISO 7146-1:2008(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
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Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.


COPYRIGHT PROTECTED DOCUMENT


©  ISO 2008
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail [e-mail]
Web www.iso.org
Published in Switzerland

ii © ISO 2008 – All rights reserved

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ISO 7146-1:2008(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Descriptions, causes, and features of damage . 2
4.1 Damage . 2
4.2 Damage causes. 2
4.3 Damage appearances. 2
4.4 Damage characterization . 3
4.5 Relationship between damage appearance and damage characterizations . 3
5 Guidelines for damage analysis. 5
5.1 General. 6
5.2 Step 1 . 6
5.3 Step 2 . 6
5.4 Step 3 . 6
5.5 Step 4 . 6
5.6 Step 5 . 6
6 Damage to the bearing surface — damage characteristics, typical damage appearances
and possible damage causes . 7
6.1 General. 7
6.2 Static overload . 7
6.3 Dynamic overload. 8
6.4 Wear by friction. 15
6.5 Overheating . 18
6.6 Insufficient lubrication (starvation). 20
6.7 Contamination. 25
6.8 Cavitation erosion. 36
6.9 Electro-erosion. 38
6.10 Hydrogen diffusion. 39
6.11 Bond failure . 41
7 Damage to the bearing back. 42
7.1 General. 42
7.2 Dynamic overload on the bearing back.42
7.3 Wear by friction on the bearing back. 44
7.4 Contamination with particles on the bearing back . 46
8 Special position of damage appearances . 47
Annex A (informative) Example of use of Table 1. 50

© ISO 2008 – All rights reserved iii

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ISO 7146-1:2008(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 7146-1 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 first edition of ISO 7146-1, together with ISO 7146-2, cancels and replaces ISO 7146:1993 the technical
content of which has been technically revised and augmented.
ISO 7146 consists of the following parts, under the general title Plain bearings — Appearance and
characterization of damage to metallic hydrodynamic bearings:
⎯ Part 1: General
⎯ Part 2: Cavitation erosion and its countermeasures

iv © ISO 2008 – All rights reserved

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ISO 7146-1:2008(E)
Introduction
In practice, damage to a bearing may often be the result of several mechanisms operating simultaneously. 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, and it will then
be 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 part of ISO 7146 is based primarily upon the features
visible on the running surfaces and elsewhere, and consideration of each aspect is required for reliable
determination of the cause of bearing damage.
Since more than one process may 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 may give a helpful guide.
In Clauses 6 and 7, examples of all damage characteristics with typically associated damage appearance are
given.

© ISO 2008 – All rights reserved v

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INTERNATIONAL STANDARD ISO 7146-1:2008(E)

Plain bearings — Appearance and characterization of damage
to metallic hydrodynamic bearings —
Part 1:
General
1 Scope
This part of ISO 7146 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 may 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 referenced documents are indispensable for the application 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
ISO 7146-2, Plain bearings — Appearance and characterization of damage to metallic hydrodynamic
bearings — Part 2: Cavitation erosion and its countermeasures
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.
3.1
damage to plain bearings
bearing damage
all changes 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 7146-1:2008(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, 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 will be
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).
List of damage appearances:
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) blue, black colour;
l) corrosion, fluid erosion;
m) embedded particles, particle-migration tracks, formation of wire wool;
n) electric arc craters;
o) cavitation erosion appearance: worn-out material.
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ISO 7146-1:2008(E)
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): affecting the tribological system.
4.4.7 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.
4.4.10 Hydrogen diffusion: hydrogen may be incorporated in the steel backing or in an electroplated layer
of the bearing. If hydrogen diffusion is blocked by a layer, blisters will occur.
4.4.11 Bond failure: delamination between lining and backing or between layers. A metallographic
examination is required to distinguish 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.
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ISO 7146-1:2008(E)

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

a
Damage cause.
b
Damage characteristics.
c
Damage appearances.
Figure 2 — Damage characteristics provide the basis for analysing the cause
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ISO 7146-1:2008(E)
5 Guidelines for damage analysis
Table 1 — Interaction of damage appearances and damage characterizations
Damage appearance Damage characterizations Subclause

× × ×   ×    Static overload 6.2
a
  × ×      Dynamic overload 6.3
b
  × ×     Dynamic overload 7.2
a
    × ×    Wear by friction 6.4
b
    ×    Wear by friction 7.3
× × × ×   ×    Overheating 6.5

    × × ×   Insufficient lubrication (starvation) 6.6
a
×    × × × × ×  Contamination (particles, chemicals) 6.7
b
×    × × × ×  Contamination (particles, chemicals) 7.4
6.8 and
        × Cavitation erosion
ISO 7146-2
       × Electro-erosion 6.9
   ×      Hydrogen diffusion 6.10
   ×      Bond failure 6.11
a
Damage to the sliding surface.
b
Damage to the bearing back.

© ISO 2008 – All rights reserved 5
Depositions
Creep deformation
Deformations due to temperature cycles
Thermal cracks
Fatigue cracks
Material relief (loss of bond)
Frictional corrosion
Melting out, scoring
Polishing, scoring
Trace of mixed lubrication, worn material
Blue, black colour
Corrosion
Fluid erosion
Embedded particles, particle-migration tracks,
formation of wire wool
Electric arc craters
Cavitation erosion appearance: material worn out

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ISO 7146-1:2008(E)
5.1 General
Analysis should be undertaken only by experts experienced in bearing metallurgy, bearing technology and
bearing damage. Damage analyses based on photos alone are mostly unsuccessful.
The following steps are a guideline for damage analysis.
5.2 Step 1
Establish service life. There is significant difference between damage after a short service life and damage
after a long service life. With both cases similar damage appearances occur, but the cause is usually different.
Typical causes of damage after short service life: faults in geometry or assembling, dirt, effect from a previous
damage, modified service conditions since last start up.
Typical cause of damage after long service life: modified service conditions.
Typical cause of damage after very long service life: reduced dynamic material capability due to fatigue.
5.3 Step 2
Strict differentiation between damage characterization and damage appearance is important. For a thorough
analysis, all visible damage appearances shall be evaluated and combined in one or more damage
characterizations, based on Table 1.
5.4 Step 3
Take into consideration the total system: bearing — shaft — lubricant — housing.
It is helpful to make a chemical analysis of a sample from the bearing layer and to check its microstructure. If
necessary, lubricant and filter content should be analysed.
5.5 Step 4
All information in connection with the period before the detected damage and the period during the damage
should be brought together.
5.6 Step 5
Reviewing the initial list of damage characteristics together with the information from steps 3 and 4 usually
leads to a reduction of the number of damage characteristics under consideration. This will lead to the
possible damage cause.
See Annex A for an example of use of Table 1.
6 © ISO 2008 – All rights reserved

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ISO 7146-1:2008(E)
6 Damage to the bearing surface — damage characteristics, typical damage
appearances and possible damage causes
6.1 General
A discussion of damage to the bearing surface follows. For each damage characterization given in 4.4, typical
damage appearances, possible damage causes and typical examples are given.
6.2 Static overload
6.2.1 Typical damage appearances
Creep deformation: shallow depressions of bearing material in the region of maximum load and temperature,
beginning smooth and ending in crack-free semicircular bulges in the direction of rotation, sometimes like
crests of waves (see Figure 3).
Traces of mixed lubrication (see Figure 4), depositions, thermal cracks.
6.2.2 Possible damage causes
Loading of the bearing was higher than that allowed for in the design and/or the bearing temperature was
higher than estimated for an extended period.
6.2.3 Typical examples (see Figures 3 and 4)

Figure 3 — Creep deformation, shown by crack-free semicircular bulges in the direction of rotation
(material: steel/tin-based white metal)
© ISO 2008 – All rights reserved 7

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ISO 7146-1:2008(E)

Figure 4 — Propeller shaft bearing, showing the effects of too slow a speed in relation to load capacity
(material: steel/tin-based white metal)
6.3 Dynamic overload
6.3.1 Typical damage appearances
Fatigue cracks: Cracks which extend from the sliding surface in the loaded zone propagating as a network.
The cracks change direction above the bonding area.
Lining material from the backing is the final result of the development of fatigue cracks (see Figure 5).
See also possible damage appearances such as frictional corrosion on the bearing back (7.1).
6.3.2 Possible damage causes
The cracks start when the fatigue limit of the bearing material is exceeded due to high dynamic load at the
operating temperature. The damage is not based on bond faults.
8 © ISO 2008 – All rights reserved

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ISO 7146-1:2008(E)
6.3.3 Typical examples (see Figures 5 to 12)

Key
1 lining material 5 eroded cracks
2 bonding area 6 cracks with perpendicular propagation
3 backing material 7 material relief
4 cracks
Figure 5 — Schematic diagram of progress of fatigue cracks

a)  under inertial load b)  under gas load
Figure 6 — Typical fatigue cracks of internal combustion engine bearing
(material: steel/aluminium alloy)
© ISO 2008 – All rights reserved 9

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ISO 7146-1:2008(E)
direction of shaft rotation →

a)
direction of shaft rotation →

b)  section from Figure 7 a) showing the lower half at increased magnification
Figure 7 — Cracks in the electroplated overlay (material: steel/lead bronze/electroplated overlay)
10 © ISO 2008 – All rights reserved

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ISO 7146-1:2008(E)

Figure 8 — Cracks in the overlay of a multilayer bearing in a narrow area of high loading
(material: steel/lead bronze/electroplated overlay)

NOTE The crack runs at a small distance from the bonding area.
Figure 9 — Section of spalled layer (material: steel/tin-based white metal)
© ISO 2008 – All rights reserved 11

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ISO 7146-1:2008(E)

a)

b)
Figure 10 — Fatigue cracks and material relief by dynamic overload
(material: steel/tin-based white metal)
12 © ISO 2008 – All rights reserved

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ISO 7146-1:2008(E)

Figure 11 — Material relief by dynamic overload because of insufficient fit on the bearing back
(see also 7.2)
© ISO 2008 – All rights reserved 13

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ISO 7146-1:2008(E)

a)

b)  section from Figure 12 a): clear illustration of the defect at increased magnification
Figure 12 — Detachment of the overlay leaving occasional residual islands relieved by a dark
background (material: steel/lead bronze/electroplated overlay)
14 © ISO 2008 – All rights reserved

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ISO 7146-1:2008(E)
6.4 Wear by friction
6.4.1 Typical damage appearances
Polishing happens during a short period of mixed lubrication on start and stop conditions. As long as this
polishing does not give rise to a detectable reduction in wall thickness, such running-in marks are normal. This
is not damage in the sense of the definitions of this part of ISO 7146 (see Figure 13).
Scoring occurs under continuous or recurrent mixed-film lubrication conditions for longer periods. Scoring
marks appear in the most highly loaded region of the bearing, across the whole width of the bearing. The
transition from unmarked to marked areas is quite gradual. The reduction in wall thickness is significant.
Segmented plain bearings experiencing appreciable wear at high rubbing surface temperatures often initially
show traces of mixed lubrication; later, worn material from one segment is deposited on the leading edge of
the next segment in the direction of rotation (see Figure 16).
For information on possible damage appearance on the bearing back, see 7.3.
6.4.2 Possible damage causes
Extreme operating conditions such as slow turning or starting under load, short and hard contact with the
counterface, inadequate clearance or other geometrical defects (misalignment or faulty mounting) lead to
wear by friction.
6.4.3 Typical examples (see Figures 13 to 17)

Figure 13 — Running-in polishing and burnishing in the main loaded area of a thin-walled bearing
(material: steel/AlSn)
© ISO 2008 – All rights reserved 15

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ISO 7146-1:2008(E)

Figure 14 — Abrasive wear of the overlay in the main loaded area on a thin-walled bearing
(material: steel/lead bronze/electroplated overlay)

Figure 15 — Abrasive wear near the ends of the bearing (joint face area) in a thick-walled journal
bearing, due to faulty mounting (material: steel/tin-based white metal)
16 © ISO 2008 – All rights reserved

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ISO 7146-1:2008(E)
direction of shaft rotation →

Figure 16 — Wear by friction due to segment assembling on different levels — worn material from one
segment deposited on the leading edge of the next segment in the direction of rotation —
the segment shown gets a reduction in oil supply (secondary damage characteristic: loss of lubricant)
(material: steel/tin-based white metal)

Figure 17 — Wear by misalignment between bearing backing and shaft
(material: steel/tin-based white metal)
© ISO 2008 – All rights reserved 17

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ISO 7146-1:2008(E)
6.5 Overheating
6.5.1 Typical damage appearances
Deposition: overheating leads to ageing of the lubricant, its thermal decomposition, and finally to depositions.
The phenomenon is concentrated in the minimum oil film region, or in other places in the oil circulatory system,
occurring more severely when oil additives have become depleted (see Figure 19).
Brown or black deposits appear on the bearing surface, but not as a result of chemical attack between the
bearing material and the lubricant. The discoloration is due to very thin lacquer-like oxidized layers in areas of
maximum temperature. It is relatively soft and can generally be removed using a solvent cleaning fluid or
scratched off using a pointed instrument (see Figure 20).
Creep deformation: shallow depressions of bearing material in the region of maximum load and temperature,
initially smooth and ending in crack-free semicircular bulges in the direction of rotation, sometimes like crests
of wave (see Figure 18).
Deformations due to temperature changes: as t
...

SLOVENSKI STANDARD
SIST ISO 7146-1:2009
01-maj-2009
1DGRPHãþD
SIST ISO 7146:2002
'UVQLOHåDML7HNRþLQVNLVORMNRYLQVNLKOHåDMHY,]UD]LLQ]QDþLOQRVWLSRãNRGE
GHO6SORãQR
Plain bearings - Appearance and characterization of damage to metallic hydrodynamic
bearings - Part 1: General
Gleitlager - Ölgeschmierte metallische Gleitlager - Terminologie und
Schadenscharakterisierung - Teil 1: Allgemeines
Paliers lisses - Aspect et caractérisation de l'endommagement des paliers métalliques à
couche lubrifiante fluide - Partie 1: Généralités
Ta slovenski standard je istoveten z: ISO 7146-1:2008
ICS:
21.100.10 Drsni ležaji Plain bearings
SIST ISO 7146-1:2009 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST ISO 7146-1:2009

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SIST ISO 7146-1:2009

INTERNATIONAL ISO
STANDARD 7146-1
First edition
2008-10-15

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 7146-1:2008(E)
©
ISO 2008

---------------------- Page: 3 ----------------------

SIST ISO 7146-1:2009
ISO 7146-1:2008(E)
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.


COPYRIGHT PROTECTED DOCUMENT


©  ISO 2008
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail [e-mail]
Web www.iso.org
Published in Switzerland

ii © ISO 2008 – All rights reserved

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

SIST ISO 7146-1:2009
ISO 7146-1:2008(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Descriptions, causes, and features of damage . 2
4.1 Damage . 2
4.2 Damage causes. 2
4.3 Damage appearances. 2
4.4 Damage characterization . 3
4.5 Relationship between damage appearance and damage characterizations . 3
5 Guidelines for damage analysis. 5
5.1 General. 6
5.2 Step 1 . 6
5.3 Step 2 . 6
5.4 Step 3 . 6
5.5 Step 4 . 6
5.6 Step 5 . 6
6 Damage to the bearing surface — damage characteristics, typical damage appearances
and possible damage causes . 7
6.1 General. 7
6.2 Static overload . 7
6.3 Dynamic overload. 8
6.4 Wear by friction. 15
6.5 Overheating . 18
6.6 Insufficient lubrication (starvation). 20
6.7 Contamination. 25
6.8 Cavitation erosion. 36
6.9 Electro-erosion. 38
6.10 Hydrogen diffusion. 39
6.11 Bond failure . 41
7 Damage to the bearing back. 42
7.1 General. 42
7.2 Dynamic overload on the bearing back.42
7.3 Wear by friction on the bearing back. 44
7.4 Contamination with particles on the bearing back . 46
8 Special position of damage appearances . 47
Annex A (informative) Example of use of Table 1. 50

© ISO 2008 – All rights reserved iii

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SIST ISO 7146-1:2009
ISO 7146-1:2008(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 7146-1 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 first edition of ISO 7146-1, together with ISO 7146-2, cancels and replaces ISO 7146:1993 the technical
content of which has been technically revised and augmented.
ISO 7146 consists of the following parts, under the general title Plain bearings — Appearance and
characterization of damage to metallic hydrodynamic bearings:
⎯ Part 1: General
⎯ Part 2: Cavitation erosion and its countermeasures

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Introduction
In practice, damage to a bearing may often be the result of several mechanisms operating simultaneously. 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, and it will then
be 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 part of ISO 7146 is based primarily upon the features
visible on the running surfaces and elsewhere, and consideration of each aspect is required for reliable
determination of the cause of bearing damage.
Since more than one process may 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 may give a helpful guide.
In Clauses 6 and 7, examples of all damage characteristics with typically associated damage appearance are
given.

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SIST ISO 7146-1:2009
INTERNATIONAL STANDARD ISO 7146-1:2008(E)

Plain bearings — Appearance and characterization of damage
to metallic hydrodynamic bearings —
Part 1:
General
1 Scope
This part of ISO 7146 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 may 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 referenced documents are indispensable for the application 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
ISO 7146-2, Plain bearings — Appearance and characterization of damage to metallic hydrodynamic
bearings — Part 2: Cavitation erosion and its countermeasures
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.
3.1
damage to plain bearings
bearing damage
all changes 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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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, 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 will be
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).
List of damage appearances:
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) blue, black colour;
l) corrosion, fluid erosion;
m) embedded particles, particle-migration tracks, formation of wire wool;
n) electric arc craters;
o) cavitation erosion appearance: worn-out material.
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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): affecting the tribological system.
4.4.7 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.
4.4.10 Hydrogen diffusion: hydrogen may be incorporated in the steel backing or in an electroplated layer
of the bearing. If hydrogen diffusion is blocked by a layer, blisters will occur.
4.4.11 Bond failure: delamination between lining and backing or between layers. A metallographic
examination is required to distinguish 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.
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Figure 1 — Damage appearances alter with the progress from primary to secondary characteristics

a
Damage cause.
b
Damage characteristics.
c
Damage appearances.
Figure 2 — Damage characteristics provide the basis for analysing the cause
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5 Guidelines for damage analysis
Table 1 — Interaction of damage appearances and damage characterizations
Damage appearance Damage characterizations Subclause

× × ×   ×    Static overload 6.2
a
  × ×      Dynamic overload 6.3
b
  × ×     Dynamic overload 7.2
a
    × ×    Wear by friction 6.4
b
    ×    Wear by friction 7.3
× × × ×   ×    Overheating 6.5

    × × ×   Insufficient lubrication (starvation) 6.6
a
×    × × × × ×  Contamination (particles, chemicals) 6.7
b
×    × × × ×  Contamination (particles, chemicals) 7.4
6.8 and
        × Cavitation erosion
ISO 7146-2
       × Electro-erosion 6.9
   ×      Hydrogen diffusion 6.10
   ×      Bond failure 6.11
a
Damage to the sliding surface.
b
Damage to the bearing back.

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Depositions
Creep deformation
Deformations due to temperature cycles
Thermal cracks
Fatigue cracks
Material relief (loss of bond)
Frictional corrosion
Melting out, scoring
Polishing, scoring
Trace of mixed lubrication, worn material
Blue, black colour
Corrosion
Fluid erosion
Embedded particles, particle-migration tracks,
formation of wire wool
Electric arc craters
Cavitation erosion appearance: material worn out

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5.1 General
Analysis should be undertaken only by experts experienced in bearing metallurgy, bearing technology and
bearing damage. Damage analyses based on photos alone are mostly unsuccessful.
The following steps are a guideline for damage analysis.
5.2 Step 1
Establish service life. There is significant difference between damage after a short service life and damage
after a long service life. With both cases similar damage appearances occur, but the cause is usually different.
Typical causes of damage after short service life: faults in geometry or assembling, dirt, effect from a previous
damage, modified service conditions since last start up.
Typical cause of damage after long service life: modified service conditions.
Typical cause of damage after very long service life: reduced dynamic material capability due to fatigue.
5.3 Step 2
Strict differentiation between damage characterization and damage appearance is important. For a thorough
analysis, all visible damage appearances shall be evaluated and combined in one or more damage
characterizations, based on Table 1.
5.4 Step 3
Take into consideration the total system: bearing — shaft — lubricant — housing.
It is helpful to make a chemical analysis of a sample from the bearing layer and to check its microstructure. If
necessary, lubricant and filter content should be analysed.
5.5 Step 4
All information in connection with the period before the detected damage and the period during the damage
should be brought together.
5.6 Step 5
Reviewing the initial list of damage characteristics together with the information from steps 3 and 4 usually
leads to a reduction of the number of damage characteristics under consideration. This will lead to the
possible damage cause.
See Annex A for an example of use of Table 1.
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6 Damage to the bearing surface — damage characteristics, typical damage
appearances and possible damage causes
6.1 General
A discussion of damage to the bearing surface follows. For each damage characterization given in 4.4, typical
damage appearances, possible damage causes and typical examples are given.
6.2 Static overload
6.2.1 Typical damage appearances
Creep deformation: shallow depressions of bearing material in the region of maximum load and temperature,
beginning smooth and ending in crack-free semicircular bulges in the direction of rotation, sometimes like
crests of waves (see Figure 3).
Traces of mixed lubrication (see Figure 4), depositions, thermal cracks.
6.2.2 Possible damage causes
Loading of the bearing was higher than that allowed for in the design and/or the bearing temperature was
higher than estimated for an extended period.
6.2.3 Typical examples (see Figures 3 and 4)

Figure 3 — Creep deformation, shown by crack-free semicircular bulges in the direction of rotation
(material: steel/tin-based white metal)
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Figure 4 — Propeller shaft bearing, showing the effects of too slow a speed in relation to load capacity
(material: steel/tin-based white metal)
6.3 Dynamic overload
6.3.1 Typical damage appearances
Fatigue cracks: Cracks which extend from the sliding surface in the loaded zone propagating as a network.
The cracks change direction above the bonding area.
Lining material from the backing is the final result of the development of fatigue cracks (see Figure 5).
See also possible damage appearances such as frictional corrosion on the bearing back (7.1).
6.3.2 Possible damage causes
The cracks start when the fatigue limit of the bearing material is exceeded due to high dynamic load at the
operating temperature. The damage is not based on bond faults.
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6.3.3 Typical examples (see Figures 5 to 12)

Key
1 lining material 5 eroded cracks
2 bonding area 6 cracks with perpendicular propagation
3 backing material 7 material relief
4 cracks
Figure 5 — Schematic diagram of progress of fatigue cracks

a)  under inertial load b)  under gas load
Figure 6 — Typical fatigue cracks of internal combustion engine bearing
(material: steel/aluminium alloy)
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direction of shaft rotation →

a)
direction of shaft rotation →

b)  section from Figure 7 a) showing the lower half at increased magnification
Figure 7 — Cracks in the electroplated overlay (material: steel/lead bronze/electroplated overlay)
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Figure 8 — Cracks in the overlay of a multilayer bearing in a narrow area of high loading
(material: steel/lead bronze/electroplated overlay)

NOTE The crack runs at a small distance from the bonding area.
Figure 9 — Section of spalled layer (material: steel/tin-based white metal)
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a)

b)
Figure 10 — Fatigue cracks and material relief by dynamic overload
(material: steel/tin-based white metal)
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Figure 11 — Material relief by dynamic overload because of insufficient fit on the bearing back
(see also 7.2)
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a)

b)  section from Figure 12 a): clear illustration of the defect at increased magnification
Figure 12 — Detachment of the overlay leaving occasional residual islands relieved by a dark
background (material: steel/lead bronze/electroplated overlay)
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6.4 Wear by friction
6.4.1 Typical damage appearances
Polishing happens during a short period of mixed lubrication on start and stop conditions. As long as this
polishing does not give rise to a detectable reduction in wall thickness, such running-in marks are normal. This
is not damage in the sense of the definitions of this part of ISO 7146 (see Figure 13).
Scoring occurs under continuous or recurrent mixed-film lubrication conditions for longer periods. Scoring
marks appear in the most highly loaded region of the bearing, across the whole width of the bearing. The
transition from unmarked to marked areas is quite gradual. The reduction in wall thickness is significant.
Segmented plain bearings experiencing appreciable wear at high rubbing surface temperatures often initially
show traces of mixed lubrication; later, worn material from one segment is deposited on the leading edge of
the next segment in the direction of rotation (see Figure 16).
For information on possible damage appearance on the bearing back, see 7.3.
6.4.2 Possible damage causes
Extreme operating conditions such as slow turning or starting under load, short and hard contact with the
counterface, inadequate clearance or other geometrical defects (misalignment or faulty mounting) lead to
wear by friction.
6.4.3 Typical examples (see Figures 13 to 17)

Figure 13 — Running-in polishing and burnishing in the main loaded area of a thin-walled bearing
(material: steel/AlSn)
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Figure 14 — Abrasive wear of the overlay in the main loaded area on a thin-walled bearing
(material: steel/lead bronze/electroplated overlay)

Figure 15 — Abrasive wear near the ends of the bearing (joint face area) in a thick-walled journal
bearing, due to faulty mounting (material: steel/tin-based white metal)
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direction of shaft rotation →

Figure 16 — Wear by friction due to segment assembling on different levels — worn material fro
...