- - -

 

 

 

 

 

 

A national laboratory of the U.S. Department of Energy 

Office of Energy Efficiency & Renewable Energy 

National Renewable Energy Laboratory 

Innovation for Our Energy Future 

Subcontract Report Failure Atlas for Rolling Bearings NREL/SR-5000-52524 in Wind Turbines 

T. E. Tallian 

Global Energy Concepts LLC, Kirkland, Washington 

Published under sponsorship of the 

U.S. Department of Energy
 

2006
 

NREL is operated by Midwest Research Institute ● Battelle Contract No. DE AC36 99 GO10337 
National Renewable Energy Laboratory

1617 Cole Boulevard, Golden, Colorado 80401-3393

303-275-3000 • www.nrel.gov

Operated for the U.S. Department of Energy

Office of Energy Efficiency and Renewable Energy

by Midwest Research Institute • Battelle

Contract No. DE-AC36-99-GO10337

Subcontract Report

NREL/SR-5000-52524 Failure Atlas for Rolling Bearings 

in Wind Turbines

T.E. Tallian

Global Energy Concepts LLC, 

Kirkland, Washington

NREL Technical Monitor: Jim Johnson

Published under sponsorship of the

U.S. Department of Energy

2006
 

 

 

 

 

 

 

 

 

 

This publication was reproduced from the best available copy
 

Submitted by the subcontractor and received no editorial review at NREL
 

NOTICE 

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Tallian: Wind turbine bearing failure atlas

Introduction.doc 12/13/05 

INTRODUCTION. 

Rolling bearings are a critical component of the mainshaft system, gearbox and generator in the 

rapidly developing technology of power generating wind turbines. The demands for long service 

life are stringent; the design load, speed and temperature regimes are demanding and the 

environmental conditions including weather, contamination, impediments to monitoring and 

maintenance are often unfavorable. As a result, experience has shown that the rolling bearings are 

prone to a variety of failure modes that may prevent achievement of design lives. 

Morphological failure diagnosis is extensively used in the failure analysis and improvement of 

bearing operation. Accumulated experience shows that the failure appearance and mode of failure 

causation in wind turbine bearings has many distinguishing features. The present Atlas is a first 

effort to collect an interpreted database of specifically wind turbine related rolling bearing 

failures and make it widely available. 

This Atlas is structured as a supplement to the book: T. E. Tallian: Failure Atlas for Hertz Contact 

Machine Elements, 2d edition, ASME Press New York, (1999). The main body of that book is a 

comprehensive collection of self-contained pages called Plates, containing failure images, bearing 

and application data, and three descriptions: failure mode, image and suspected failure causes. 

The Plates are sorted by main failure mode into chapters. Each chapter is preceded by a general 

technical discussion of the failure mode, its appearance and causes. The Plates part is 

supplemented by an introductory part, describing the appearance classification and failure 

classification systems used, and by several indexes. 

The present Atlas is intended as a supplement to the book. It has the same structure but contains 

only Plate pages, arranged in chapters, each with a chapter heading page giving a short definition 

of the failure mode illustrated. Each Plate page is self contained, with images, bearing and 

application data, and descriptions of the failure mode, the images and the suspected causes. 

Images are provided in two resolutions: The text page includes 6 by 9 cm images. In addition, 

high resolution image files are attached, to be retrieved by clicking on their “push pin” icon. 

While the material in the present Atlas is self-contained, it is nonetheless a supplement to the 

book and the complete interpretation of the terse image descriptions and of the system underlying 

the failure code presupposes familiarity with the book. 

Since this Atlas is a supplement to the book, its chapter numbering follows that of the book. Not 

all failure modes covered in the book have been found among the observed wind turbines. For 

that reason, and because of the omission of introductory matter, the chapter numbers in this Atlas 

are not a continuous sequence. 

ACKNOWLEDGMENTS. 

The Atlas is prepared as part of a project sponsored by the U.S. Department of Energy under 

Phase II of the Low Wind Speed Turbine Project, in cooperation with Global Energy Concepts, 

LLC. Images were graciously released for use in the Atlas by several wind turbine manufacturers 

and operators, who do not wish to have their names published. The images were, with few 

exceptions, prepared in Northwest Laboratories of Seattle, WA, by and under the supervision of 

Mr. Rainer Eckert. Without his outstanding contributions, this atlas would not exist. 
Tallian: Wind turbine abearing failure atlas

Chapter 4. Nicks.
 

Failure code 00.01. 

Definition: Nicks are plastic depressions (short gashes; multiple, aligned or randomly oriented 

marks; or rounded depressions). They are caused by impressing (statically or by impact) a hard, 

possibly sharp object into the surface. Nicks are produced, by definition, prior to or after service. 

A similar appearing damage caused during service is a dent. 

Chapter 4.Nicks.doc 12/12/2005
 

 

 

Tallian: Wind turbine bearing failure atlas Chapter 4: Nicks

Plate_4.1.doc 12/3/2005 

Plate No. 4.1 Failure Code: 00.01.1.2 

Plate No. 4.1 

Archive No. DSCN3011.jpg 

Image type light macrograph 

Scalebar millimeter scale 

Component CRB, R 

Application gearbox 

Speed (Kndm) 49 

Load (P/C) 0.08 

Lubrication synthetic hydrocarbon oil 

Temperature,C ? 

Failure code 1 00.01.1.2: Scratch mark, tool 

mark. 

Failure code 2 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

On the end face of the roller, extending to the corner radius, a long rounded nick with raised edges. 

Image description. 

The corner radius of the roller runs E – W on the image, just N of the millimeter scale. The boundary of the roller end face, to 

the N of the radius, is marked by a dark contact band. A wedge-shaped depression, made by a blunt-edged tool, crosses from 

the corner radius into the side face. The dark contact mark follows the edges of the dent, suggesting a raised edge. 

Suspected causes. 

The most likely source of the dent is a blunt edged mounting tool (a “drift”), resting on the roller side face and given a hammer 

blow. Since the dark contact marks extend alongside the nick, it must have been made prior to service. 
 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 4: Nicks

Plate_4.2.doc 12/3/2005 

Plate No. 4.2 Failure Code: 00.01.2 A: B: 

Plate No. Plate 4.2 

A B 

Archive No. A: DSCN1727.jpg 

B::DSCN1578.jpg 

Image type A, B: light macrograph 

Scalebar millimeter ruler 

Component CRB IR 

Application gearbox 

Speed (Kndm) 49 

Load (P/C) 0.08 

Lubrication synthetic hydrocarbon oil 

Temperature,C ? 

Failure code 1 00.01.2: Scratch mark, toolmark, 

scuffmark 

Failure code 2 00.20.1.3: Contact corrosion 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

A, B: Toolmark at roller path edge. A: Contact corrosion streak 

Image description. 

A: The N half of the image is the (rough finish) lead-in surface to the IR roller path. The S half is the roller path. Beneath the 

yellow dye mark at the image top is a series of gray marks across the lead-in surface. At the roller path edge, is another darker 

mark, which distorts the finishing lines, suggesting mechanical nicking. A contact corrosion streak extends across the roller path 

along the line of the nick. 

B: Sharp, rough wedge-shaped toolmark starting from the roller path edge and continuing into the roller path. A sharp-edged 

tool (“drift”) has slipped off the ring face and scraped the roller path. 

Suspected causes. 

The mechanical damage on the rings is due to tool use, either in mounting or dismounting. The marks in A: are corroded and 

therefore probably occurred after service, whereas the mark in B: appears fresh (except for some varnish discoloration near the 

tip of the triangle) and may have occurred in dismounting. 
 

 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 4: Nicks.

Plate_4.3.doc 12/3/2005 

Plate No. 4.3 Failure Code: 00.01.2 

Plate No. 4.3 

Archive No. DSCN1786.jpg 

Image type view 

Scalebar millimeter ruler 

Component CRB, R 

Application gearbox 

Speed (Kndm) 49 

Load (P/C) 0.08 

Lubrication synthetic hydrocarbon oil? 

Temperature,C ? 

Failure code 1 00.01.2: Scratch mark, toolmark 

Failure code 2 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

On the end face of the cylindrical roller, a cross of many centered, arced, fine scratch marks forming bands. 

Image description. 

Two bands of light gray, fine, arced scratch marks crossing each other in the center of the roller sideface. 

Suspected causes. 

The source of the scratch marks is not determined. No intentional sliding contact occurs between the roller and any other part 

during service, which would create marks of the shape and location observed. The innerring flange does not extend to the 

maximum height of the marks. An object, extending beyond the innerring flange, rotating with the innerring against nonrotating rollers would produce marks of the observed shape. 
 

 

Tallian: Wind turbine bearing failure atlas. Chapter 4: Nicks.

Plate_4.4.doc 12/3/2005 

Plate No. 4.4 Failure Code: 00.01.1 

Plate No. 4.4 

Archive No. DSCN1790.jpg 

Image type light macrograph 

Scalebar millimeter ruler 

Component CRB, R 

Application gearbox 

Speed (Kndm) 49 

Load (P/C) 0.08 

Lubrication synthetic hydrocarbon oil 

Temperature,C ? 

Failure code 1 00.01.1: Local nick 

Failure code 2 00.12.3.2.1.4. Wear track at 

contact edge 

Failure code 3 . 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

On a cylindrical roller, a sharp cut (nick) across the corner radius, leading into the end face. Mild circumferential flange-contact 

wear. 

Image description. 

N image half shows roller end face, with corner running roughly W – E. A sharp, angled, wedge-shaped cut in corner radius. 

Circumferential wear bands of dark and light gray, along face edge. Barely visible millimeter ruler along S image edge. 

Suspected causes. 

The cut across the corner radius is an impact mark from a sharp-edged tool. The circumferential wear marks arise from normal roller to flange 

contact. 
 

 

Tallian: Wind turbine bearing failure atlas. Chapter 4: Nicks

Plate_4.5.doc 12/3/2005 

Plate No. 4.5 Failure Code: 00.01.1 

Plate No. 4.5 

Archive No. DSCN1879.jpg 

Image type light macrograph 

Scalebar millimeter ruler 

Component SRB, OR 

Application gearbox planetary gear 

Speed (Kndm) 10? 

Load (P/C) 0.15? 

Lubrication synthetic hydrocarbon oil 

Temperature,C 

Failure code 1 00.01.1: local nick 

Failure code 2 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

In the spherical roller path of the outerring is a long, deep, roughly circumferential depression. The distinction between a nick 

(outside service) and a dent (in service) is not unequivocal, but the irregular shape and depth suggest a toolmark in disassembly. 

The absence of a “halo” surrounding the mark makes subsequent rollover unlikely. 

Image description. 

Inside oval dye mark, an elongated deep local gouge, with both ends curved. 

Suspected causes. 

Gouge mark from a slipped tool in disassembly is likely. Roll-over of a malleable piece of metal debris cannot be excluded. 
 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 4: Nicks

Plate No. 4.6 Failure Code: 00.01.2 A: B: 

Plate No. 4.6 

Archive No. A: DSCN1896.jpg. 

B: DSCN 1897.jpg 

Image type A: view. 

B: light macrograph 

Scalebar A, B: millimeter ruler. 

Component SRB. R 

Application gearbox planetary gear 

Speed (Kndm) 10? 

Load (P/C) 0.15? 

Lubrication synthetic hydrocarbon oil 

Temperature,C ? 

Failure code 1 00.01.2: Scratch, tool mark, scuff 

mark. 

Failure code 2 

Failure code 3 

Failure code 4. 

A 

B 

DESCRIPTIONS 

Failure description. 

Patches of scratch marks on roller OD. 

Image description. 

A: In image center, several patches of fine, roughly axial, scratch marks. 

B: Magnified image of scratch marks. The marks consist of parallel straight lines, at a small angle to the axial direction, 

confined within patches 1 – 3 mm long. 

Suspected causes. 

If a spherical roller bearing, with fine solid contaminant on the rolling surfaces, is swiveled during dismounting, then scratches 

similar to those in the images can arise. The patches of marks appear too large to have been caused by axial vibratory motion of 

the non-rotating bearing, in service. 

Plate_4.6.doc 12/3/2005 
 

 

 

Tallian: Failure Atlas for Wind Turbine Bearings. 

Plate No. 4.7 Failure Code: 00.01.2 A B 

Plate No. 4.7 

Archive No. A: loc2 35x 

B: loc2 300x 

Image type A, B: SEM 

Scalebar A: 500 μm 

B: 50 μm 

Component CRB IR 

Application Gearbox, planet 

Speed (Kndm) 14 

Load (P/C) 0.15 

Lubrication synthetic polyglycol 

Temperature,C 70 

Failure code 1 00.01.2: scratch, toolmark 

Failure code 2 00.17.1.2: microspalling 

Failure code 3 

Failure code 4. 

A 

B 

DESCRIPTIONS 

Failure description. 

An axial scratch was produced across the roller path, probably in assembly. Upon roll-over, a raised edge of the scratch suffered 

surface distress microspalling. 

Image description. 

A: At image center, a thin dark N – S line is a scratch mark. 

B: At higher magnification, the W edge of the scratch is serrated, as the uneven raised edge was rolled down and subsequently 

microspalled. The bottom of the scratch is featureless in this image. The right edge of the scratch apparently had not been raised 

and was left smooth during roll-over. 

Suspected causes. 

The scratch is so long that it could only have been produced prior to or during assembly of the bearing. A scratch with raised 

edge, surface distress tends to produce local surface distress. 

Plate 4.7.doc 2/20/2006 
 

 

Tallian: Failure Atlas for Wind Turbine Bearings. 

Plate No. 4.8 Failure Code: 00.01.2 

Plate No. 4.8 

Archive No. DSCN3395.JPG 

Image type light macrograph 

Scalebar millimeter ruler 

Component CRB OR 

Application gearbox planet 

Speed (Kndm) 14 

Load (P/C) 0.15 

Lubrication Synthetic polyglycol 

Temperature,C 65 

Failure code 1 00.01.2: scratch, toolmark, 

scuffmark 

Failure code 2 00.17.2: localized surface distress 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

In outerring roller path, two 10 mm long, curved, branching scuffmarks, with surface distress halo at the edges. 

Image description. 

On outerring roller path, in the area surrounded by red line, two curved, brush-stroke shaped, branching scuffmarks extending 

NW from the undercut. The edges are surrounded by a dark margin representing a glazed, surface distress “halo.” 

Suspected causes. 

The length and angled direction of the marks excludes formation during service. The marks are assumed to be assembly 

damage which was subsequently over-roller, causing the surface distress halo. 

Plate 4.8.doc 2/21/2006 
Tallian: Wind turbine bearing failure atlas

Chapter 7.Mild wear.doc 12/13/2005 

Chapter 7. Mild wear. 

Failure code 00.12. 

Definition: Wear is defined as the removal of component surface material in the form of loose 

particles by the application of high tractive forces in asperity dimensions during service. It is 

distinguished from surface distress (Chapter 11), galling (Chapter 8) and fretting wear 

(Chapter 9). 
 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 7: Mild Wear

Plate No. 7.1 Failure Code: 00.12.3.2.2. A: B: 

Plate No. 7.1 

Archive No. A: ball SEM overview.jpg 

B: ball 150x.jpg 

Image type A: light macrograph 

B: SEM 

Scalebar A: millimeter ruler 

B: 100 μm 

Component DGBB, B 

Application wind turbine generator 

Speed (Kndm) 450 

Load (P/C) 0.05? 

Lubrication grease 

Temperature,C 70 

Failure code 1 00.12.3.2.2: Scratch marks, 

kinematic wear marks. 

Failure code 2 

Failure code 3 

Failure code 4. 

A. 

B. 

DESCRIPTIONS 

Failure description. 

Balls show numerous small round patches of fine parallel wear marks. 

Image description. 

A: On the ball surface, circular patches of about 1 mm diameter are filled with parallel scratch marks of 50 - 70 μm length and a 

few micrometers width. The marks cross lapping lines indicating they were produced in service. 

Suspected causes. 

It is conjectured that fine abrasive particles were trapped between ball and track, and the balls were subjected to small amplitude 

(50 μm) vibratory displacement. Corresponding round patches on the rings were not found. 

Plate_7.1.doc 12/11/2005 
 

 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 7: Mild Wear

Plate_7.2.doc 12/9/2005 

Plate No. 7.2 Failure Code: 00.12.3.2.2 A: B: C: 

Plate No. 7.2 

Archive No. A: DSCN1621.jpg 

B: loc2 500x.jpg 

C: 041212_trace.jpg 

Image type A: light micrograph 

B: SEM 

C: profile trace 

Scalebar A: millimeter scale 

B: 50 μm 

C: as marked 

Component DGBB OR 

Application wind turbine generator 

Speed (Kndm) 450 

Load (P/C) 0.05? 

Lubrication grease 

Temperature,C 70 

Failure code 1 00.12.3.2.2: Scratch marks, 

kinematic wear marks. 

Failure code 2 00.17.1.3: Incipient surface 

distress (glazing). 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

A series of “fingernail marks” (kinematic wear marks) are in the ball path of the outerring, positioned at approx. 400 to the 

rolling direction. The marks are on a surface distressed (glazed) area of the track. Finishing lines are reduced in depth at the 

edge of the elliptic marks, but not at the center. The marks are depressed by about 3 μm from the surrounding surface, probably 

by plastic flow. 

Image description. 

A: narrow, angled, depressed oval marks in a band between the two red dye lines in the N half of the image. 

B: SEM of the lengthwise center of one oval mark, running SW to NE in the image. Edges are outlined by lighter gray, finishing 

marks obliterated at the edges. Inside the mark, finishing marks are more pronounced than outside the mark, possibly 

highlighted by deposits. 

C: profile tracing across the marks, showing depths of about 2 μm. 

Suspected causes. 

The mechanism of formation of the marks is not well understood. Fingernail marks are typically score marks from fine debris or 

asperities sliding over the surface. However, the microtopography of the marks, showing no lengthwise scratches but rather 

depressed finishing lines, indicates a plastic surface depression. Regardless of the damage mechanism, the narrow marks placed 

at a consistent, large angle to the rolling direction, suggest a vibratory displacement between (lightly loaded) balls and ring. 
 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 7: Mild Wear

Plate_7.3.doc 12/9/2005 

Plate No. 7.3 Failure Code: 00.12.3.2.4 

Plate No. 7.3 

Archive No. ADSCN2321.jpg 

Image type light macrograph 

Scalebar millimeter scale. 

Component CRB OR 

Application gearbox 

Speed (Kndm) 12 

Load (P/C) 0.17 

Lubrication synthetic mineral oil 

Temperature,C ? 

Failure code 1 00.12.3.2.4: Scoring wear 

Failure code 2 00.12.1: Fit surface wear 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

OD of CRB OR turning in housing has produced localized scuffmarks. Without SEM examination, galling signs are not 

discernible. 

Image description. 

Grinding lines on OR OD rolled over, and scuffed during rotation of ring in housing. Four bands of scuffmarks are about 5, 10 

15 and 20 mm S of millimeter ruler. Metal was displaced but not obviously transferred to distant locations. 

Suspected causes. 

Sporadic rotation of ring in housing has deformed the ring surface texture. The absence of fretting corrosion suggests the motion 

did not persist over prolonged periods. 
 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 7: Mild Wear

Plate_7.4.doc 12/11/2005 

Plate No. 7.4 Failure Code: 00.12.3.2.02 

Plate No. 7.4 

Archive No. A: DSCN8288.jpg 

Image type view 

Scalebar inch ruler 

Component CRB IR 

Application gearbox, planet 

Speed (Kndm) 14 

Load (P/C) 0.15 

Lubrication Synthetic glycol based oil 

Temperature,C ? 

Failure code 1 00.12.3.2.02: Wear track when 

load rotates over outerring 

Failure code 2 00.18.2.2: Stippled lines or bands 

from rolled-in debris. 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

End of load zone on innerring roller track of bearing with load stationary on innerring. Load zone shifted to one side. Rolled-in 

lines within load zone. Additional (sliding) wear marks at load zone entrance. 

Image description. 

Contour of one end of load zone marked by dye dots. The load zone is shifted asymmetrically toward E (flanged) side of roller 

path. Circumferential bands of varying brightness mark rolled-in lines in load zone. At the boundary of the load zone, finer, 

matte, wear marks. 

Suspected causes. 

Bands such as seen in the load zone are often found under SEM to be stippled bands of rolled-in dents (see Plate 12.1). More 

diffuse, fine wear marks at load zone entrance suggest sliding of rollers upon load zone entry. The load zone is axially 

asymmetrical, indicating load maldistribution, with the pressure concentrated toward the flanged side of the roller path. 
 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 7: Mild Wear

Plate_7.5.doc 12/11/2005 

Plate No. 7.5 Failure Code: 0.13.2.2 

Plate No. 7.5 

Archive No. DSCN2759.jpg 

Image type light macrograph 

Scalebar millimeter scale 

Component DGBB OR 

Application wind turbine generator 

Speed (Kndm) 400 

Load (P/C) 0.04 

Lubrication grease with synthetic oil and 

unidentified thickener 

Temperature,C 70 

Failure code 1 00.13.2.2: Kinematic wear marks 

on rolling surface 

Failure code 2 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Two sets of kinematic war marks are seen on outerring ball path: (1) evenly spaced circumferential scratch marks and (2) sets of 

angled marks at 400

 to the axial direction. 

Image description. 

In the W quarter of the image, two rows of 1.5 mm long axial scratch marks. Axial spacing between rows about 4 mm, marks 

circumferentially spaced about 5 mm. 

Further E, at red arrows, clusters of scratch marks angled about 400

 to the circumferential direction. 

Suspected causes. 

The circumferential and the angled marks each appear to have been made by vibratory motions of the balls over the ring, in 

different directions, in the presence of fine hard contaminant. Angular vibrations would produce the circumferential marks, 

whereas a combination of angular and axial vibration is needed to cause the angled marks. 
 

 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 7: Mild Wear

Plate_7.6.doc 12/9/2005 

Plate No. 7.6 Failure Code: 00.12.3.2.2 

Plate No. 7.6 

Archive No. DSCN9229.jpg 

Image type light macrograph 

Scalebar millimeter ruler 

Component DGBB OR 

Application wind turbine generator 

Speed (Kndm) 450 

Load (P/C) 0.05? 

Lubrication grease 

Temperature,C ? 

Failure code 1 00.12.3.2.2: Kinematic wear 

marks in rolling surface 

Failure code 2 00.18.01.2: Denting of rolling 

surface, minor sliding 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Multiple long, shallow axial scuffmarks across the ball path, interspersed with dents of 1 – 3 mm diameter. 

Image description. 

On the dark gray background of the ball path, multiple, diffuse axial white marks of varying length, as if a dark varnish had 

been rubbed off. The marks do not appear to have appreciable depth. Blue dye marks indicate barely discernible round dents. 

SE of the axial marks, some faint circumferential white marks are visible. 

Suspected causes. 

The denting is attributed to debris collected in the grease. The mechanism creating the axial marks is not well understood. Axial 

vibrations causing sliding between balls and ring are suspected. The circumferential white marks may arise from circumferential 

sliding of the balls. 
 

 

Tallian: Wind turbine bearing failure atlas. Chapter 7: Mild Wear

Plate No. 7.7 Failure Code: 00.12.3.2.2 A: B: 

Plate No. 7.7 

Archive No. A: DSCN1896.jpg. 

B: DSCN 1897.jpg 

Image type A: view 

B: light macrograph 

Scalebar A, B: millimeter ruler. 

Component SRB. R 

Application gearbox planet 

Speed (Kndm) 10? 

Load (P/C) 0.15? 

Lubrication synthetic hydrocarbon oil 

Temperature,C ? 

Failure code 1 00.12,3,2,2: Scratch marks, 

kinematic wear marks 

Failure code 2 

Failure code 3 

Failure code 4. 

A. 

B. 

DESCRIPTIONS 

Failure description. 

Patches of localized scratch marks on roller OD. 

Image description. 

A: In image center, several patches of fine, roughly axial, scratch marks. 

B: Magnified image of scratch marks. The marks consist of parallel straight lines, at a small angle to the axial direction, 

confined within 1 – 3 mm long patches. 

Suspected causes. 

In the presence of fine solid contaminant, near-axial scratch marks on the roller OD may occur if there is axial or swiveling 

motion in the bearing, at velocities considerably greater than the rolling velocity. The data do not suffice to determine whether 

the marks occurred in the mounted bearing as a result of axial or swiveling vibratory motions or whether they occurred when 

the outerring was swiveled in the dismounted bearing by hand. It is noted that the same bearing also shows considerable debris 

denting indicating the presence of contaminant in service. 

Plate_7.7.doc 12/11/2005 
Tallian: Wind turbine bearing failure atlas

Chapter 8. Galling, skid marking. 

Failure code 00.13: Galling. 

Failure code 00.14: Skid marking (microscopic severe wear). 

Definitions. 

Galling is defined as the transfer of component surface material in macroscopic patches from a 

location on one contacting surface to a location on the other contacting surface and possibly back 

onto the first surface, by the action of high traction forces. 

Skid marking is asperity-scale surface material transfer. 

Chapter 8.Galling.doc 12/13/2005
 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 8: Galling, Skid marking.

Plate No. 8.1 Failure Code: 00.13.1 A: B: 

Plate No. 8.1 

Archive No. Image A:DSCN0254.jpg, 

Image B: DSCN0256.jpg 

Image type view 

Scalebar millimeter ruler 

Component SRB IR 

Application turbine main shaft 

Speed (Kndm) 9.6 

Load (P/C) 0.16 

Lubrication grease 

Temperature,C ambient 

Failure code 1 00.13.1: Fit surface galling 

Failure code 2 

Failure code 3 

Failure code 4. 

A: 

B: 

DESCRIPTIONS 

Failure description. 

The innerring bore of this spherical roller bearing formed multi-point welded seizures with the shaft. 

Image description. 

A: Multiple weld points near bore corner radius. B: Galling mark with oval weld point at center. 

Suspected causes. 

The main shaft of a wind turbine flexes significantly, and transmits heavy and variable loads to the bearing. Rig tests have 

confirmed that, under these conditions, welded gall marks can form, presumably at roller spacing. 

Plate_8.1.doc 11/29/2005 
 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 8: Galling, Skid Marking

Plate No. 8.2 Failure Code: 00.13.2.1.1.1 A: B: C: 

Plate No. 8.2 

Archive No. A: DSCN9126.jpg 

B: loc3 35x.jpg 

C: loc31 650x.jpg 

Image type A: view. 

B: SEM 

C: SEM 

Scalebar A: millimeter ruler 

B: 500 μm 

C: 20 μm 

Component CRB IR 

Application gearbox 

Speed (Kndm) 49 

Load (P/C) 0.08 

Lubrication Synthetic hydrocarbon oil 

Temperature,C ? 

Failure code 1 00.13.2.1.1.1: Incipient galling 

Failure code 2 00.17.1.1: Glazing (incipient 

surface distress) 

Failure code 3 

Failure code 4. 

A B 

C 

DESCRIPTIONS 

Failure description. 

Faint circumferential galling streak on roller path 

Image description. 

A: Coupon from IR roller path. Location of galling streak marked with two short lines of blue dye within box. 

B: Low magnification SEM. Two circumferential bands, slightly darker than background, are the transferred, galled material. 

C: High magnification SEM shows disorganized surface at the end (or possibly the beginning) of a galling streak. Remnant of 

grinding line is to the N, surrounded by featureless, glazed surface. 

Suspected causes. 

Momentary sliding between roller and ring surface, under conditions of low film ratio produced incipient galling streak in 

otherwise glazed surface. The disorganized surface at the end point of the glazing suggests the participation of a small brittle 

debris particle. 

Plate_8.2.doc 12/2/2005 
Tallian: Wind turbine bearing failure atlas.

Chapter 9. Fretting wear. 

Failure code 00.15. 

Definition: Fretting wear is adhesive wear taking place in a nominally static contact under normal 

load and microscopic surface-parallel motion. The two types of fretting wear are (common) 

fretting and false brinnelling. 

Fretting (common fretting) is defined as fretting wear in a conforming contact (typically a fit 

interface). 

False brinnelling is defined as fretting wear in a Hertzian contact. 

Chapter 9: Fretting wear.doc 12/12/2005
 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 9: Fretting Wear.

Plate _9.1.doc 11/28/2005 

Plate No. 9.1 Failure Code: 00.12.1.2.0.8 

Plate No. 9.1 

Archive No. DSCN2446.jpg 

Image type view 

Scalebar inch ruler 

Component CRB IR 

Application gearbox 

Speed (Kndm) 49 

Load (P/C) 0.08 

Lubrication synthetic hydrocarbon oil 

Temperature,C ? 

Failure code 1 00.12.1.2.0.8 Fretting on chatter 

marked fit surface 

Failure code 2 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Axial ridges of fretting corrosion in innerring bore. 

Image description. 

Brownish axial ridges of fretting corrosion, evenly spaced circumferentially, at about 0.5 inch (13 mm). The three yellow die 

lines indicate fret marks. 

Suspected causes. 

The innerring was fitted on a shaft with high surface waviness from machining (chatter). Fretting corrosion marks have 

developed over the high-pressure ridges caused by the shaft weave peaks. 
 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 9: Fretting Wear.

Plate No.9.2 Failure Code: 00.15.2 A: B: 

Plate No. 9.2 

Archive No. A: DSCN0087.jpg 

B: DSCN0094.jpg 

Image type A: view 

B: light micrograph 

Scalebar A: 8 mm 

B: 1.2 mm 

Component DGBB IR 

Application wind turbine generator 

Speed (Kndm) 450 

Load (P/C) 0.05? 

Lubrication grease 

Temperature,C ? 

Failure code 1 00.15.2: False brinnelling on 

contact surface 

Failure code 2 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Blue/black false brinnell mark on ball path of innerring. 

Image description. 

A: Rectangularly shaped false brinnell mark within red dye circle. The mark is discolored by oxidation (corrosion). 

B: Similar mark, shown magnified. The grinding lines are partly destroyed by the fretting. 

Suspected causes. 

Exposure of stationary bearing to vibratory conditions can produce false brinnelling. Often these marks are the same color as the 

undamaged surface. In this case, corrosion has apparently attacked the freshly worn surface. 

Plate_9.2.doc 11/28/2005 
Tallian: Wind turbine bearing failure atlas

Chapter 10. Spalling. 

Failure code 00.16: Spalling (Hertzian contact fatigue). 

Failure code 00.16.02.1: Microplastic deformation indication. 

Failure code 00.16.02.2: Contact fatigue cracking. 

Definition: Spalling is defined as macroscopic Hertzian contact fatigue. It is failure by the 

formation of macroscopic craters in the contact surface as a result of fatigue crack propagation in 

the Hertzian stress field. When fully developed, the craters are of depth comparable to that of the 

maximum Hertz shear stress. 

Chapter 10.Spalling.doc 12/12/2005
 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 10: Spalling

Plate 10.1 Failure Code: 00.16.1.1.2 

Plate No. 10.1 

Archive No. picture003.jpg 

Image type view 

Scalebar 20 mm 

Component CRB IR 

Application gearbox 

Speed (Kndm) 120 

Load (P/C) 0.1 

Lubrication synthetic hydrocarbon oil 

Temperature,C 70 

Failure code 1 00.16.1.1.2: Spall from 

subsurface defect 

Failure code 2 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

 Very deep isolated spalls, possibly from two origination points. Subsurface defect likely. 

Image description. 

50 mm wide, seashell shaped spall in roller path. Steep entry wall at NE end. Possible subsurface defect at mid-spall, starting 

new propagation. 

Suspected causes. 

Extreme depth of spall and unusual shape suggests origin from one or two major subsurface defects. 

Plate_10.1.doc 12/5/2005 
 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 10: Spalling

Plate_10.2.doc 12/5/2005 

Plate No. 10.2 Failure Code: 00.16.1.2.2 

Plate No. 10.2 

Archive No. HS Bearing spall 2 

Image type view 

Scalebar 20 

Component DGBB IR, S, B 

Application gearbox 

Speed (Kndm) 250? 

Load (P/C) unknown 

Lubrication synthetic hydrocarbon oil 

Temperature,C ? 

Failure code 1 00.16.1.2.2: Shallow entry spall 

from surface line-defect 

Failure code 2 00.15.2: False brinnelling 

Failure code 3 00.22.01.1: Axial cross-section 

crack in ring 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

False brinnell marks at ball spacing. Radially inward propagating axial cracks are at false brinnell marks. Large spall at one of 

the marks. Apparent false brinnell mark on ball. 

Image description. 

Red arrows mark false brinnell marks, most or all with inward going axial cracks. One of the marks has formed a large circular 

spall. A matte horizontal mark on a ball, just S of the scale bar is probably a false brinnell mark. 

Suspected causes. 

Vibratory loading during standstill has caused multiple false brinnell marks at ball spacing, and on the mating ball surfaces. 

Tensile hoop stress, from interference fit and possibly shaft bending, initiated tensile cracks at the points weakened by the 

false brinnelling. Spalling started from these surface defects. 
 

 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 10: Spalling

Plate_10.3.doc 12/5/2005 

Plate No. 10.3 Failure Code: 00.16.1.2.2 

Plate No. 10.3 

Archive No. center of spall 65x.jpg 

Image type SEM 

Scalebar 200 μm 

Component CRB IR 

Application gearbox 

Speed (Kndm) 120 

Load (P/C) 0.1 

Lubrication synthetic hydrocarbon oil 

Temperature,C 70 

Failure code 1 00.16.1.2.2: Shallow entry spall 

from surface line defect 

Failure code 2 00.16.03.1: Spall propagating by 

cracking at the spall bottom 

Failure code 3 00.22.01.1: Axial cross section 

crack in ring 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

 Major spall extending axially along an axial surface defect. Inward-going axial cracks at spall bottom. 

Image description. 

Low magnification SEM of rolling surface with long, straight spall extending N – S through image. The spall image consists of 

three vertical bands: the left and right side bands are inward-sloping spall bottom. The center band contains two to three black 

inward-going axial crack mouths. The material between the cracks is fragmented. 

Suspected causes. 

The ring was mounted with an interference fit. Axial surface defects, (probably false brinnell marks) are known to have formed 

on the rolling surface. They subsequently spalled and eventually led to tensile cracking. 
 

 

 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 10: Spalling

Plate_10.4.doc 12/5/2005 

Plate No. 10.4 Failure Code: 00.16.1.2.2 

Plate No. 10.4 

Archive No. DSCN0001.jpg 

Image type view. 

Scalebar 18 mm 

Component CRB IR 

Application gearbox 

Speed (Kndm) 120 

Load (P/C) 0.1 

Lubrication synthetic hydrocarbon oil 

Temperature,C 70 

Failure code 1 00.16.1.2.2: Shallow entry spall 

from surface line defect. 

Failure code 2 00.16.02.5: Advanced spalling. 

Failure code 3 00.22.01.1: Axial cross section 

crack in ring. 

Failure code 4. 00.16.01.2: Spalling at contact 

edge, from misalignment. 

DESCRIPTIONS 

Failure description. 

CRB innerring with one flange is spalled around roller path up to the undercut at the flange. Fingers of spalling, at roller 

spacing, extend across the roller path. Axial hairline cracks follow the fingers. Some corrosion spots. 

Image description. 

At image N, the entire surface of the roller path near and up to the flange undercut is spalled away. Rectangular fingers of 

spalling spaced at roller distance extend S from this spalled band toward, but not up to the unflanged track edge. Red arrows 

point to axial hairline cracks in the spall fingers. The small round dark spots are corrosion. 

Suspected causes. 

The CRB is known to be heavily loaded. Shaft deflection causes maldistribution of the pressure toward the flange. Prior to 

spalling, roller-spaced surface damage, probably from false brinnelling, occurred, forming favored spall initiation sites. Heavy 

interference fit on the shaft promotes inward going axial cracking under the original false brinnell marks, as the spalling 

progresses. 
 

 

 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 10: Spalling

Plate No. Plate 10.5 Failure Code: 00.16.1.2 

Plate No. 10.5 

Archive No. MVC008S.jpg 

Image type view 

Scalebar 20 mm 

Component SRB OR 

Application Gearbox planet 

Speed (Kndm) 140 

Load (P/C) 0.2 

Lubrication PAG (glycol) oil 

Temperature,C 75 

Failure code 1 00.16.1.2: Surface origin spall. 

Failure code 2 00.16.03.2: Spalling propagating 

by re-initiation at the surface. 

Failure code 3 00.16.01.2: Centered spalling, 

wide track. 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Spalling over large areas of both roller paths in spherical outerring sphere. Spalling is heavier in one roller path, indicating an 

axial load component. In the axial load carrying roller path, spalling reaches the track edge, indicating edge loading. The 

spalling is of relatively uniform depth with no indication of individual subsurface defects. The sharp axial edges of the wide 

spall area suggest pre-existing axial surface defects. 

Image description. 

The sphere containing both roller paths is visible behind the side face. The inner edges of both roller paths are outlined by a 

change in hue. Spalls of moderate depth are in both roller paths. In the rear path (image N), spalls are mostly localized, slightly 

inboard of roller path center but do not reach the edge. In the front path (image S), a continuous line of spalls crosses the image, 

outboard of the roller path center, except that a wide, straight edged patch of spalling extends completely to the inner roller path 

edge. In some areas, spalls extend to both path edges. One roller path is more spalled than the other path. The relatively uniform 

spall bottom shows no indications of large subsurface defects. The sharp axial edges of the wide spall zone suggest that a 

surface line defect was present to initiate or terminate the spalling. 

Suspected causes. 

This spherical roller bearing operates in a planet pinion, with the outerring mounted in the rotating pinion and the innerring on 

the planet pin. Significant deflections exist both from pin support bending (misalignment) and shape distortion of the thin 

walled pinion. Unintended axial forces may arise as well as pressure maldistribution along the roller length due to profile 

distortion. Lubricant supply is difficult to control. This combination of adverse influences may make the outerring shorter lived 

than the innerring and has, in the present case, led to premature failure. 

Plate_10.5.doc 4/16/2005 
 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 10: Spalling

Plate_10.6.doc 12/5/2005 

Plate No. 10.6 Failure Code: 00.16.02.11 

Plate No. 10.6 

Archive No. DSCN1662.jpg 

Image type light metallogram 

Scalebar 70 μm 

Component DGBB 

Application wind turbine generator 

Speed (Kndm) 450 

Load (P/C) 0.05 

Lubrication Oil? 

Temperature,C 80 

Failure code 1 00.16.02.11: Microplastic 

deformation bands or “butterflies” 

Failure code 2 00.06.1: Micro inclusion 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

A globular subsurface micro-inclusion is flanked by a series of localized deformation bands. The two short bands emanating 

from the inclusion are designated “butterflies.” Larger bands, further W in image, have been triggered by the stress field 

disruption causing the butterfly. Such bands, consisting of structure modified by repeated stressing etch lighter than the 

background; they have different hardness and a carbide and matrix structure very different from the undisturbed background 

material. Most reported observations indicate that deformation bands rise toward the surface in the overrolling direction. 

Image description. 

The mottled background is the Nital etched cross section of the bearing ring. The contact surface (not shown) is toward image 

N. A large round black spot midway along the E image edge is a non-metallic inclusion. It is flanked on both sides by light 

etching “butterfly” deformation bands. Additional bands are stacked toward image W. All deformation bands slant NW, rising 

toward the contact surface. 

Suspected causes. 

The triggering defect for the butterflies is the inclusion, which is a stress concentrator. Deformation bands are caused by longterm cycling under high Hertz stress, therefore they form more readily at inclusions than in the undisturbed matrix. In this case, 

secondary deformation banding may have been produced by the stress redistribution caused by the butterfly. 
 

 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 10: Spalling

Plate_10.7.doc 12/5/2005 

Plate No. 10.7 Failure Code: 00.16.02.1 

Plate No. 10.7 

Archive No. DSCN9943.jpg 

Image type light metallogram 

Scalebar 70 μm 

Component DGBB IR 

Application wind turbine generator 

Speed (Kndm) 450 

Load (P/C) 0.05 

Lubrication Oil? 

Temperature,C 80 

Failure code 1 00.16.02.11 Microplastic 

deformation bands or “butterflies” 

Failure code 2 00.06.1: Micro inclusion 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Four globular micro-inclusions are in the image. Along two, light etching deformation bands have formed, rising toward the 

contact surface. The elongated bands are the cross sections of laminar formations of material that has undergone cyclical 

microplastic deformation under repeated high Hertzian stresses. The deformation produces changes in the microstructure of the 

material. The matrix develops a cellular structure. Carbides migrate out of the bands and often form into thin, laminar carbides 

at the band interfaces. Deformation bands are oriented so that they rise toward the contact surface in the direction of overrolling. 

Image description. 

The N edge of the image is the contact surface. The mottled gray area is the Nital etched cross section of the ring. Small black 

dots are non-metallic inclusions. Light bands running from image SW to NE are the cross sections of deformation bands. Fine 

dark lines within the deformation bands may be lenticular carbides in cross section but are not clearly distinguishable from 

microcracks. 

Suspected causes. 

Deformation banding is a sign of prolonged cycling under high Hertzian stresses. Frictional (traction) stresses in the interface 

influence deformation band formation. A component showing general deformation banding of the matrix material is thought to 

have consumed a major portion of its fatigue life. However, factors other than stress level have influence on their formation, 

such as the operating temperature and incompletely understood details of the material structure. Therefore, no quantitative 

relation between deformation banding and the remaining life to spalling has been established. 
 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 10: Spalling

Plate_10.8.doc 12/9/2005 

Plate No. 10.8 Failure Code: 00.16.1.1 

 Plate No. 10.8 

Archive No. MVC-020S.jpg 

Image type view 

Scalebar 6 mm 

Component SRB OR 

Application gearbox planet 

Speed (Kndm) 14 

Load (P/C) 0.2 

Lubrication synthetic hydrocarbon oil 

Temperature,C 70 

Failure code 1 00.16.1.1: Subsurface origin spall 

(high Hertz stress) 

Failure code 2 00.16.03.1: Spall propagating by 

cracking at spall bottom 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Large subsurface fatigue cracks have begun to spall out, forming a continuous lamina, partially connected to the bulk material 

and with surface-opening cracks at some of the edges. 

Image description. 

In the image center, a N – S crack has opened, giving access for a probe to the surface parallel crack separating the lamina of 

surface material from the underlying bulk material. A second, longer, N – S crack is about 8 mm to the right. The rest of the 

image is the rolling surface, with the curved grinding lines of the spherical outerring roller path running SW to NE. Various 

scuffmarks interrupt the grinding lines. 

Suspected causes. 

This spherical roller bearing operated in a planet pinion, with outerring rotation. Bending deflections of the pinion and the 

outerring modified the load distribution resulting in outerring failure before innerring failure. The material is bainite hardened 

and thus relatively ductile. This may have contributed to the formation of large surface-parallel cracks before the overlying 

lamina of material broke away. 
 

 

 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 10: Spalling

Plate_10.9.doc 12/9/2005 

Plate No. 10.9 Failure Code: 00.16.01.1.2 

Plate No. 10.9 

Archive No. DSCN0249.jpg 

Image type view 

Scalebar millimeter and inch ruler 

Component SRB IR 

Application turbine mainshaft bearing 

Speed (Kndm) 9 

Load (P/C) 0.16 

Lubrication grease 

Temperature,C ambient 

Failure code 1 00.16.01.1.2: Centered spalling, 

wide track 

Failure code 2 00.16.1.2 Surface origin spall 

Failure code 3 00.17.1: Generalized surface 

distress. 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Extensive spalling on innerring roller track. A band of relatively shallow spalls is centered in the contact. On both sides of this 

band, deeper, scattered, axially elongated spalls extend to the edges of the roller track. Surface distress exists in the center band. 

The appearance suggests two distinct origins for the two spall types: surface distress for the central spall band and localized 

surface damage, possible from contact corrosion, false or real brinnelling, towards both edges. 

Image description. 

The image shows the unspalled roller path in the N part, followed S by the guidering land and then the spalled roller path. Some 

matte surface distress is visible in the N path, and matte, dented surface interspersed with shallow spalls, in the center of the S 

roller path. There are deep spalls extending axially to both sides of the central spalled band, to the edge of the roller path. 

Suspected causes. 

This bearing is known to have suffered a surface distress and spalling in the outerring (See Plate 13.1). It operates as a main 

turbine shaft bearing, with heavy, variable loads and speeds, including standstill. Ingress of water into the grease is possible. 

Apparently, surface distress and subsequent spalling took place in the center band of the roller path. A separate failure 

mechanism is likely for the scattered spalls extending edge to edge of the roller path. Localized surface damage, as from contact 

corrosion, false or true brinnelling is likely to initiate such spalling. 
 

 

 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 10: Spalling

Plate No. 10.10 Failure Code: 16.02.1.1 A: B: 

Plate No. 10.10 

Archive No. A: ADSCN2609.jpg 

B: ADSCN2613.jpg 

Image type metallogram 

Scalebar A: 100 μm 

B: 100 μm 

Component CRB IR 

Application gearbox 

Speed (Kndm) synthetic hydrocarbon oil 

Load (P/C) 12 

Lubrication 0.17 

Temperature,C 

Failure code 1 16.02.1.1 Microplastic 

deformation bands 

Failure code 2 

Failure code 3 

Failure code 4. 

A B 

DESCRIPTIONS 

Failure description. 

White etching microplastic deformation bands of irregular shape. A: Group of bands with four differently oriented elements. B: 

Band oriented at 450 to the rolling direction. None of the bands is oriented at the 25 – 300

 angle to the rolling direction usually 

found in heavily loaded, long-life bearing rings. 

Image description. 

A: In the horizontal center of the image, a C-shaped band, with vertical center part, extends from about 400 μm to 800 μm 

depth. Smaller white etching bands to the E and S. 

B: Straight, angled, 400 μm long band at image center. The orientation is about 450

 to the surface. 

Suspected causes. 

In wind turbine gearbox bearings, deformation bands of unusual shape and orientation are repeatedly found. The commonly 

accepted hypothesis is, that the commonly found shallow angle bands form, in the absence of macroscopic subsurface defects, 

along preferred planes oriented at 25 – 300

 angle to the overrolling direction. The cause for the abnormally oriented bands found 

here is not known, but unusual influences, such as (a) high contact tractions, possibly operating in reversing direction, (b) 

hydrogen weakening of the steel matrix, or (c) extremely high, short acting transient loads acting early in service, have been 

suggested. 

Plate_10.10.doc 12/9/2005 
 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 10: Spalling

Plate No. 10.11 Failure Code: 16.02.1.1 

Plate No. 10.11 

Archive No. ADSCN2610.jpg 

Image type metallogram 

Scalebar 100 μm 

Component CRB IR 

Application gearbox 

Speed (Kndm) 12 

Load (P/C) 0.17 

Lubrication synthetic hydrocarbon oil 

Temperature,C ? 

Failure code 1 16.02.1.1 Microplastic 

deformation bands 

Failure code 2 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Several short white etching microplastic deformation bands at an angle of about 300 to the overrolling direction, at widely 

varying depth. 

Image description. 

Five deformation bands, about 200 μm long, nearly in the same vertical plane, straight and angled about 300 to the rolling 

direction, except for thickened and bent W ends of some bands. No clearly visible inclusions. 

Suspected causes. 

Deformation bands are usually seen in heavily loaded long lived bearings, in the material volume exposed to high Hertz 

stresses. In wind turbine gearboxes, load, speed, sliding and lubrication conditions vary widely during the duty cycle. It is not 

known how these variations influence deformation bands. Unusual chemical stresses, such as hydrogen damage, have been 

proposed as a contributing cause. 

PLate_10.11.doc 12/7/2005 
 

 

 

 

Tallian: Wind turbine bearing failrue atlas. Chapter 10: Spalling

Plate_10.12.doc 12/10/2005 

Plate No. 10.12 Failure Code: 00.16.02.1.1 

Plate No. 10.12 

Archive No. ADSCN2710.jpg 

Image type metallogram 

Scalebar 100 μm 

Component CRB IR 

Application gearbox 

Speed 12 

Load (P/C) 0.17 

Lubrication synthetic hydrocarbon oil 

Temperature,C ? 

Failure code 1 00.16.02.1.1: Microplastic 

deformation bands or butterflies 

Failure code 2 00.16.02.2: Contact fatigue 

cracking 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

In two vertical planes, multiple short deformation bands, at steep (450) angle to the rolling surface. In one vertical plane, 

radially inward going crack from the surface through the deformation bands. Dark etching locations near the crack. 

Image description. 

At image W, two short (150 μm) deformation bands at 450 angle to the surface. At image E, radially inward going straight crack 

crossing the image. Three short, angled deformation bands cross the crack. (The crack does not follow the band outlines). 

In the SE image corner, the (apparent crack) is followed by diffuse, dark etching spots. 

Suspected causes. 

Deformation bands and the crack both indicate high loads operating over a long cycling time. The scattered depth of the bands 

suggest variable loading. The radially inward going crack suggests the presence of tensile hoop stress. 
Tallian: Wind turbine bearing failure atlas

Chapter 11. Surface distress. 

Failure code 00.17 

Definition: Surface distress is defined as microscale spalling failure fatigue of rolling contact 

surfaces resulting in asperity scale microspall craters. In ductile materials such as steel, the failure 

process proceeds by the formation of (a) glazed (burnished) surface areas; (b) asperity scale 

microcracks and (c) asperity scale microspall craters, in that sequence. 

Chapter 11.Surface distress.doc 12/12/2005
 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 11: Surface Distress

plate_11.1.doc 12/8/2005 

Plate No. 11.1 Failure Code: 00.17.1.2 

Plate No. 11.1 

Archive No. DSCN0232.jpg 

Image type view 

Scalebar inch and metric measuring tape 

Component SRB OR 

Application turbine main bearing 

Speed (Kndm) 9 

Load (P/C) 0.16 

Lubrication grease 

Temperature,C ambient 

Failure code 1 00.17.1.2:Microspalling 

(advanced surface distress) 

Failure code 2 00.16.1.2: Surface origin spall 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

In the outerring load zone of this spherical roller bearing, a broad band of severely microspalled surface distress has removed 

all signs of the original surface finish. The edges of the band abut on multiple, surface origin spalls, some of which extend far 

beyond the surface distressed band. 

Image description. 

The edges of the matte, surface distressed band are marked by red dye dots. In the center of the band, the surface is matte, but 

not grossly spalled. As the edges are approached, deeper and deeper spalls are seen, some of which extend axially far beyond 

the surface distress band boundaries. 

Suspected causes. 

This bearing is known to have suffered major spalling failure on the innerring as well as the spalling shown on the outerring. 

(See also Plate 10.9). The surface distress suggests that the lubrication was marginal. The deep spalls, especially those 

extending far beyond the surface distressed area may have originated from contact corrosion or false brinnell marks. The 

bearing operated under substantial vibratory loading, sometimes in standstill, and the grease may have become wet. 
 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 11: Surface Distress

Plate_11.2.doc 12/8/2005 

Plate No. 11.2 Failure Code: 00.17.01 A: B: C: D: 

Plate No. 11.2 

Archive No. A:DSCN7803x.jpg 

B: loc2 35x.jpg 

C: loc2 430x.jpg 

D:ADSCN3059.jpg 

Image type A: light macrograph 

B: SEM 

C: SEM 

D: metallogram. 

Scalebar A: millimeter ruler 

B: 500 μm 

C:50 μm 

D: 30 μm 

Component CRB IR 

Application gearbox planet 

Speed (Kndm) 12 

Load (P/C) 0.17 

Lubrication synthetic hydrocarbon oil 

Temperature,C 70 

Failure code 1 00.17.01: Surface distress with 

sliding 

Failure code 2 00.17.1.2. Surface distress 

microspalling. 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Series of surface distress microspalls showing 400 directionality with rolling direction, surrounded by “glazed” featureless 

plastically flown surface. 

Image description. 

A: N half of image shows circumferential damage bands, not further analyzed. To the S, several horizontal bands of angled 

marks, as if gouged by sliding at 400

 to rolling direction. B: Low magnification SEM image of marks, with angled start line to 

the NE of each mark, followed by microspalled areas to the W. C: High magnification SEM showing individual microspall. 

Featureless glazed surface surrounds the microspall. D: cross section showing 20 - 30 μm depth of exfoliated spalled lamina. 

Suspected causes. 

After creation of a glazed, surface distressed background surface, the rollers of this CRB suffered a series of short, sharp axial 

displacements at a speed comparable to the rolling velocity, scratching out a 400 start line for the microspalls, which then 

progressed in the overrolling direction. The cause of the axial displacement is not established. The shallow depth of the spalls 

shows that they did not form from dents. 
 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 11: Surface Distress

Plate_11.3.doc 12/11/2005 

Plate No. 11.3 Failure Code: 00.17.02 

Plate No. 11.3 

Archive No. flange undercut 150x.jpg 

Image type SEM 

Scalebar 100 μm 

Component CRB IR 

Application gearbox planet 

Speed (Kndm) 14 

Load (P/C) 0.15 

Lubrication glycol based synthetic oil 

Temperature,C 70 

Failure code 1 00.17.02: Surface distress with 

sliding 

Failure code 2 00.17.1.1: Glazing (incipient 

surface distress) 

Failure code 3 00.17.1.2: Microspalling 

(advanced surface distress) 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

On the load bearing surface of the flange, high Hertz pressure in combined rolling and sliding motion has produced surface 

distress up to the undercut edge, indicating that the undercut edge bears pressure. 

Image description. 

The light gray band at image N is the undercut. It is separated from the flange surface by an irregular edge, with material 

extruded into the undercut. S of the edge, the background surface is featureless, with the grinding lines completely obliterated. 

Interspersed in this background are circumferentially elongated microspalls up to 150 μm long. The black patches on the surface 

are probably rust deposits. 

Suspected causes. The slide/roll ratio in a flange contact is substantial. A lower slide/roll ratio is achieved by placing the 

contact near the undercut. In the present case, the placement was too close, resulting in edge load and edge deformation at the 

undercut. The existence of the surface distress indicates low EHD film thickness, from high temperature, thin or insufficient 

lubrication. 
 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 11: Surface Distress

Plate_11.4.doc 12/11/2005 

Plate No. 11.4 Failure Code: 00.17.1.2 

Plate No. 11.4 

Archive No. DSCN8007.jpg 

Image type view 

Scalebar 10 mm 

Component CRB IR 

Application gearbox planet 

Speed (Kndm) 12 

Load (P/C) 10.17 

Lubrication synthetic hydrocarbon oil 

Temperature,C ? 

Failure code 1 00.17.1.2: Microspalling (severe 

surface distress) 

Failure code 2 00.16.01.2: Spalling at contact 

edge 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

The roller path on the IR has suffered generalized surface distress microspalling along grinding lines. Near the flange, deep 

spalling has developed. 

Image description. 

Many grinding lines on the W half of the innerring roller path have microspalled due to surface distress. At the E side, 

surrounded by a blue dye mark, deep Hertzian spalling has followed, extending to the flange undercut. 

Suspected causes. 

The primary failure mode is believed to be surface distress microspalling, due to low film ratio, contamination and possibly 

sliding. At the flanged side of the innerring, where the load is concentrated, the surface distress has triggered deep Hertzian 

spalling. 
 

 

 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 11: Surface Distress

Plate No. 11.5. Failure Code: 00.17.2 A: B: 

Plate No. 11.5 

Archive No. A: DSCN7990.jpg 

B: DSCN7973.jpg 

Image type A: view 

B: light macrograph 

Scalebar A, B: millimeter ruler 

Component CRB IR 

Application gearbox planet 

Speed (Kndm) 12 

Load (P/C) 0.17 

Lubrication synthetic hydrocarbon oil 

Temperature,C ? 

Failure code 1 00.17.2: Localized surface 

distress 

Failure code 2 00.17.1.2: Surface distress 

microspalling 

Failure code 3 00.20.1 

Failure code 4. 

A B
 

DESCRIPTIONS 

Failure description. 

On the roller path of the CRM IR, many grinding lines are decorated with surface distress “halos,” modified surfaces resulting 

from plastic flow at asperity level. Microspalls have formed at some of the asperity ridges. 

Image description. 

A: Discolored circumferential bands in the roller path mark surface distressed ridges. Some of the ridges show microspalls. 

Brownish corrosion stain overlays both roller path and land. 

B: Higher magnification view of distressed surface, with microspalls lined up along asperity ridges. 

Suspected causes. 

Marginal lubricant film thickness combined with possible sliding produced asperity level plastic flow and eventually 

microspalls. 

The bearing was exposed to corrosive environment (moisture), before and during service and probably also after dismounting. 

Plate_11.5.doc 12/11/2005 
 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 11: Surface Distress

Plate_11.6.doc 12/8/2005 

Plate No 11.6. Failure Code: 00.17 .2 

Plate No. 11.6 

Archive No. DSCN7942.jpg 

Image type light macrograph 

Scalebar 1 mm 

Component CRB IR 

Application gearbox planet 

Speed (Kndm) 12 

Load (P/C) 9.17 

Lubrication synthetic hydrocarbon oil 

Temperature,C ? 

Failure code 1 00.17.2: Localized surface 

distress (halo at defect) 

Failure code 2 00.17.1.2 Surface distress 

microspalling 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

On a surface with visible grinding lines, a grinding furrow accompanied by a burnished “halo” on one side, with the furrow 

microspalled. 

Image description. 

Near image center, a black circumferential microspall with jagged edges. A burnished band N of the microspall is lighter than 

the background. The furrow has spalled out forming a black elongated, sharp-edged depression. The lighter colored band 

crossing the NE image corner is a dye mark. 

Suspected causes. 

Separation of a grinding grit particle can cause a deeper-than-normal furrow in a ground surface. These furrows are preferential 

sites for surface distress because the EHD lubricant film collapses into them. The furrow edges contact the mating contact 

surface without film protection and are plastically rolled down. On further cycling, the deformed material around the furrow 

edges may spall out. 
 

 

 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 11: Surface Distress

Plate No. 11.7 Failure Code: 00.17.1.2 A. B. C. 

Plate No. 11.7 

Archive No. A: cDSCN8391.jpg 

B: 0052087 NWL Location 1,

 100x.jpg 

C: 005287 NWL Location 11, 

 240x.jpg 

Image type A: light macrograph 

B, C: SEM 

Scalebar A: millimeter ruler 

B: 500 μm 

C: 200 μm 

Component CRB R 

Application gearbox 

Speed (Kndm) 40 

Load (P/C) 0.15 

Lubrication synthetic hydrocarbon oil 

Temperature,C ? 

Failure code 1 00.17.1.2: Microspalling 

(Advanced surface distress) 

Failure code 2 00.17.1,.1 Glazing (Incipient 

surface distress) 

Failure code 3 

Failure code 4. 

A 

B 

C 

DESCRIPTIONS 

Failure description. 

Generalized surface distress over the rolling surface of a cylindrical roller. Some areas are glazed, others have suffered 

extensive microspalling and subsequent overrolling. 

Image description. 

A: The axial direction on the roller is N – S. The first three millimeters on the E are glazed, followed W by a 0.5 mm band of 

shallower microspalling and then by a severely microspalled area showing axial banding. 

B: The edge of the microspalled zone at 100 x shows microspall craters lined up in circumferential rows. 

C: Higher magnification of a microspall propagating in a striated fashion circumferentially. 

Suspected causes. 

The overall appearance of the bearing indicates insufficient elastohydrodynamic film ratio. The operational causes have not 

been identified. In this separator-less bearing, rollers also slide against each other, which may produce excess heating and 

impaired lubricant coverage on the rolling contacts. 

Plate_11.7.doc 12/11/2005 
 

 

 

 

Tallian: Failure Atlas for Wind Turbine Bearings. 

Plate No. 11.8 Failure Code: 00.17.2 A B 

Plate No. 11.8 

A B 

Archive No. A: DSCN0675.JPG 

B: IR 35x.JPG 

Image type A: light micrograph 

B: SEM 

Scalebar A: millimeter ruler 

B: 500 μm 

Component CRB IR 

Application gearbox planetary gear 

Speed (Kndm) 14 

Load (P/C) 0.15 

Lubrication Synthetic polyglycol 

Temperature,C 70 

Failure code 1 00.17.2: localized surface distress 

Failure code 2 00.17.1.3: microspalling 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Circumferential band of surface distress along grinding lines, with localized microspalling. 

Image description. 

A: Just S of the tips of both red arrows, a band of more prominent E - W lines is a band of surface distressed grinding lines. 

B: Over discontinuous stretches of the surface distressed band, the surface has microspalled, forming a “chipped” appearing 

surface. 

Suspected causes. 

In roller bearings, surface distress of the rolling surfaces often forms in discrete circumferential bands, as a result of minor 

differences in roughness, EHD film thickness or contamination. The bands are not uniform in severity around the 

circumference. Where the damage is more advanced, microspalls form. 

Plate 11.9.doc 2/20/2006 
Tallian: WInd turbine bearing atlas.

Chapter 12. Denting. 

Failure code 00.18. 

Definition: A dent is a plastic depression (short gash, rounded-edged hollow, sharp-edged single 

or multifaceted impression, depressed solid or stippled line caused in a working surface by a 

relatively incompressible object pressed into it by the passage of a contacting rolling element. 

Denting is the process by which dents form. Denting occurs in service, in contrast to handling 

damage, designated as a nick. 

Chapter 122.Denting.doc 12/12/2005
 

 

 

 

Tallian: Wind turbine bearing failure atlas Chapter 12: Denting.

Plate No. 12.1 Failure Code: 00.18.2.2.2 A: B: 

Plate No. 12.1 

Archive No. A: DSCN9896.jpg 

B: loc 1.2 700x.jpg 

Image type A: light micrograph 

B: SEM 

Scalebar A: millimeter ruler 

B: 20 μm 

Component CRB OR 

Application gearbox 

Speed (Kndm) 14 

Load (P/C) 0.15 

Lubrication synthetic hydrocarbon oil 

Temperature,C 75 

Failure code 1 00.18.2.2.2: Stippled bands from 

rolled-in debris 

Failure code 2 00.20.2: Corrosion pitting 

Failure code 3 00.20.1.3: Contact corrosion 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Circumferential damage marks on roller path, consisting of stippled bands from rolled-in fine debris. Incidental corrosion 

pitting. Two edges of a contact corrosion mark left by a roller. 

Image description. 

A: In E – W direction, bands of light gray, between numeral “1” and letter “A”. The red dots mark the outlines of a contact 

corrosion mark. 

B: S half of SEM image shows a profusion of about 5 μm size angled dents in rows along rolling direction. Many dents in each 

row are geometrically similar. At image center N are three rounded corrosion pits. 

Suspected causes. 

The stippled bands are produced by hard debris embedded in the roller and copied onto the ring surface during repeated 

rollovers. The bearing has suffered contact corrosion during standstill. The generalized corrosion pitting is incidental. 

Plate_12.1.doc 11/25/2005 
 

 

 

 

 

 

Tallian: Wind turbine bearing failure atlas Chapter 12: Denting.

Plate No. 12.2 Failure Code: 00.18 .1.3 A: B: C: 

Plate No. 12.2 

Archive No. A: DSCN0783.jpg 

B: DSCN9165.jpg 

C: outerring 23d axial mark 

 1000x.jpg 

Image type A: view 

B: light micrograph 

C:SEM 

Scalebar A, B: millimeter ruler 

C: 10 μm 

Component DGBB OR 

Application wind turbine generator 

Speed (Kndm) 450 

Load (P/C) 0.05? 

Lubrication grease 

Temperature,C 70 

Failure code 1 00.18.1.3: Multiple irregular 

denting from loose hard debris 

Failure code 2 00.18.01.2: Denting of rolling 

surface, minor sliding 

Failure code 3 00.18.1.2: Sharp individual dents 

from metal debris, asperities 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Multiple dents of varying shape and severity in outerring ball path. 

Image description. 

A: Outerring ball path with (1) parallel shallow axial lines within blue dye mark, and (2) individual dents from metallic 

particles. 

B: Dents from malleable metal particles, 1 – 3 mm size. 

C: Detail of one of the axial marks at high magnification shows irregular fine gouge marks, as from fine hard particles in the 

presence of small-scale random sliding motion. 

Suspected causes. 

The bearing operated in the presence of solid contaminant. Some of the particles formed rounded dents, as from malleable metal 

debris. Much finer, hard debris caused highly irregular fine scratch marks in the presence of small scale sliding in random 

directions. 

Plate_12.2.doc 11/25/2005 
 

 

 

Tallian: Wind turbine bearing failure atlas Chapter 12: Denting.

Plate_12.3.doc 11/22/2005 

Plate No. 12.3 Failure Code: 00.18.3 

Plate No. 12.3 

Archive No. ADSCN3455 

Image type view 

Scalebar inch tape 

Component BB (4-pt contact slewing ring) 

OR 

Application blade pitch control 

Speed (Kndm) non-rotating 

Load (P/C0) 0.35 

Lubrication grease 

Temperature,C ambient 

Failure code 1 00.18.3: Brinnelling 

Failure code 2 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Ball-paced brinnell marks in ball track of 4-point contact ball bearing slewing ring. 

Image description. 

Along the E – W centerline of the image, shiny brinnell marks in the groove are highlighted by horseshoe-shaped red lines. The 

brinnell marks have the same spacing as the balls in the bearing. See stack of balls with interposed nylon spacers, and 

superimposed yellow measuring tape, S of the ring. 

Suspected causes. 

The slewing ring participated in a turbine failure in which blades were broken and the tower collapsed. During this event, high 

overturning impact torques were imposed on the slewing ring. It is unknown whether some brinnell marks existed prior to the 

turbine failure. 
 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 12: Denting.

Plate_12.4.doc 11/22/2005 

Plate No. 12.4 Failure Code: 00.18.3 

Plate No. 12.4 

Archive No. ADSCN3505.jpg 

Image type view 

Scalebar inch and metric ruler 

Component BB (slewing ring) OR 

Application blade pitch control 

Speed (Kndm) non-rotating 

Load (P/C0) 0.35 

Lubrication grease 

Temperature,C ambient 

Failure code 1 00.18.3: Brinnelling 

Failure code 2 00.16.1.2.2: Shallow entry spall 

from surface line defect 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Multiple brinnell marks in ball track. Two spalls. 

Image description. 

Within horseshoe shaped orange pen lines, barely discernible brinnell marks. E and W of one pen line, two spalls. The axially 

extended oblong shape of the larger spall is compatible with origin from another brinnell mark, but the originating mark is not 

discernible. 

Suspected causes. 

This slewing ring has undergone a turbine failure accident during which blades broke and the tower collapsed. At that time, 

extensive brinnelling is likely to have occurred. Brinnelling (or false brinnelling) during service, prior to the accident is a likely 

damage occurrence in a blade pitch control slewing ring but is no longer identifiable. The spalls must have been initiated some 

time before the accident and developed gradually. It is conjectured but not proven that the spall originating damage was a 

brinnell or false brinnell mark. 
 

 

 

 

Tallian: Wind turbine bearing failure atlas Chapte 12: Denting.

Plate No. 12.5 Failure Code: 00.15.2 A: B: 

Plate No. 12.5 

Archive No. A: DSCN0087.jpg 

B: DSCN0094.jpg 

Image type A: view 

B: light micrograph 

Scalebar A: 8 mm 

B: 1.2 mm 

Component DGBB IR 

Application wind turbine generator 

Speed (Kndm) 450 

Load (P/C) 0.05? 

Lubrication grease 

Temperature,C ? 

Failure code 1 00.15.2: False brinnelling on 

contact surface 

Failure code 2 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Blue/black false brinnell mark on ball path of innerring. 

Image description. 

A: Rectangle-shaped false brinnell mark within red dye circle. The mark is discolored by oxidation (corrosion). 

B: Similar mark, shown magnified. The grinding lines are partly destroyed by the fretting. 

Suspected causes. 

Exposure of stationary bearing to vibratory conditions can produce false brinnelling. Often these marks are the same color as the 

undamaged surface. In this case, corrosion has apparently attacked the freshly worn surface. 

Plate_12.5.doc 11/22/2005 
 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 12: Denting.

Plate_12.6.doc 11/28/2005 

Plate No. 12.6 Failure Code: 00.18.1.2 

Plate No. 12.6 

Archive No. DSCN9165.jpg 

Image type light macrograph 

Scalebar millimeter ruler 

Component DGBB IR 

Application wind turbine generator 

Speed (Kndm) 450 

Load (P/C) 0.05? 

Lubrication grease 

Temperature,C 70 

Failure code 1 00.18.1.2: Sharp individual dents 

from metal particles 

Failure code 2 00.18.01.1.1: Denting on rolling 

surfaces, no sliding. 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Cluster of dents from rolled-over metal particles. 

Image description. 

In N image half, cluster of rounded dents, about 1.5 mm long. In S half, 3 mm long individual dent 

Suspected causes. 

The contact surface was dented by malleable, rounded metal particles, that were rolled over without significant sliding 
 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 12: Denting.

Plate_12.7.doc 11/26/2005 

Plate No. 12.7 Failure Code: 00.18.1.3 

Plate No. 12.7 

Archive No. IR 500x.jpg 

Image type SEM 

Scalebar 50 μm 

Component DGBB IR 

Application wind turbine generator 

Speed (Kndm) 450 

Load (P/C) 0.05? 

Lubrication grease 

Temperature,C 70 

Failure code 1 00.18.1.3: Multi-fragment dent 

Failure code 2 00.17.1.1 Glazing (incipient 

surface distress) 

Failure code 3 00.17.1.2 Microspalling 

(advanced surface distress) 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Multiple, fine, angular indentations in glazed surface. Some of the dents have formed microspalls. 

Image description. 

The background surface is featureless, “glazed”, with the grinding lines rolled down. Running E-W at image center is a grinding 

furrow. In the N half of the image are numerous jagged indentations, up to 50 μm long. On some of these, the edges have 

spalled out. Other spalled-out dents are in the S image half. 

Suspected causes. 

The bearing has operated with marginal lubrication, causing surface distress glazing. Fine, hard, brittle contaminant particles 

were present and made the jagged multi-fragment dents. The surface distress process has operated on the dent edges, causing 

microspalling. 
 

 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 12: Denting.

PLate_12.8.doc 11/26/2005 

Plate No. 12.8 Failure Code: 00.18.1.4 

Plate No. 12.8 

Archive No. DSCN1096.jpg 

Image type light macrograph 

Scalebar millimeter ruler 

Component DGBB OR 

Application wind turbine generator 

Speed (Kndm) 450 

Load (P/C) 0.05? 

Lubrication grease 

Temperature,C 70 

Failure code 1 00.18.1.4: Multiple irregular 

denting from fine, loose debris 

Failure code 2 00.`20.1.3: Contact corrosion 

Failure code 3 00.20.1: Corrosion stains 

Failure code 4. 00.13.2.2: Kinematic wear marks 

DESCRIPTIONS 

Failure description. 

The entire rolling surface shown is covered with randomly distributed, fine light-colored spots. Some are debris dents or 

kinematic wear marks, others are part of a corrosion stain. A strong and a weak axial band of contact corrosion cross the 

surface. 

Image description. 

The image shows a generalized grayish brown stain, darker on the E and N than in the SW image side. In the otherwise 

undisturbed areas, lighter gray spots of rounded and oblong shape, generally less than 1 mm wide and 1 – 4 mm long, are seen. 

Some of these, oriented E – W, show an appearance of depth and are debris dents (kinematic wear marks). Others may be local 

variations in the rust stain. Between the two rows of blue marker dots is a strong light gray band, attributed to contact 

corrosion. A fainter band of similar color is further W. 

Suspected causes. 

The bearing is known to have operated in a corrosive and debris contaminated environment. The rust stain and its local spotty 

variations are attributed to the corrosive environment. Fine debris, in the presence of minor circumferential sliding, creates the 

circumferential dents / wear marks. A contact corrosion event took place in standstill, leaving behind the axial marks. 
 

 

 

 

 

 

 

Tallian: Failure Atlas for Wind Turbine Bearings. 

Plate No. 12.9 Failure Code: 00.18.1 A B 

Plate No. 12.9 

A B 

Archive No. A: DSCN0614.jpg. 

B: dent1 50x.jpg 

Image type A: Light macrograph 

B: SEM 

Scalebar A: millimeter ruler 

B: 500 μm 

Component CRB IR 

Application gearbox planetary gear 

Speed (Kndm) 14 

Load (P/C) 0.15 

Lubrication Synthetic polyglycol 

Temperature,C 70 

Failure code 1 00.18.1: local dent 

Failure code 2 00.17.2: localized surface distress 

Failure code 3 00.17.1.2: microspalling 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

On the innerring roller path, a local dent, made by a ductile debris particle. The elliptical edge surrounding the dent has suffered 

surface distress microspalling. 

Image description. 

A: An area on the rolling surface is marked by an orange ring. In image center, the rolling surface is visible, with grinding lines 

running E – W. A 1.5 mm long oval dent is visible in the center of the marked area. It is surrounded by a wide, darker-appearing 

mottled band. 

B: The dark band framing the dent is resolved into an unbroken band of surface distress microspall craters. 

Suspected causes. 

The dent was caused by the over-rolling of a ductile debris particle. When formed, it was surrounded by a raised edge of 

material. Continued over-rolling caused surface distress along this edge, where the lubricant film is thinner. 

Plate 11.8.doc 2/20/2006 
 

Tallian: Failure Atlas for Wind Turbine Bearings. 

Plate No. 12.10 Failure Code: 00.18.1.2.2 

 Plate No. 12.10 

Archive No. DSCN3631.JPG 

Image type Light micrograph 

Scalebar millimeter ruler 

Component CRB OR 

Application gearbox planet 

Speed (Kndm) 14 

Load (P/C) 0.15 

Lubrication synthetic polyglycol 

Temperature,C 65 

Failure code 1 00.18.2.2: stippled band from 

rolled-in debris. 

Failure code 2 00.18.1.3: local dent. 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

A band of repeated indentations at a small angle to circumferential. An isolated dent is seen away from the band. 

Image description. 

Running roughly W to E across the image is a band of depressions made by a few different shapes of indenting particle. Some 

shapes are repeated several times along the band, while others are sporadic. An isolated dent is in the N central part of the 

image. 

Suspected causes. 

The bearing ingested a particle or group of friable particles, which temporarily embedded in the roller, and were copied 

repeatedly onto the outerring roller track. In the process of rollover, the embedded material was worn away. Some particles 

disappeared from the contact, while others made shallower indentations. An unrelated particle made the isolated dent. 

Plate 12.10.doc 2/21/2006 
Tallian: Wind turbine bearing failure atlas.

Chapter 13. Heat imbalance failure. 

Failure code 00.19 

Definition: Heat imbalance failure is a complex sequence of failure events precipitated by a 

(macroscopic) temperature excursion in the Hertzian contact machine element due to heat 

generated in excess of the heat simultaneously removed. 

Chapter 13.Heat imbalance failure.doc 12/12/2005
 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 13: Heat Imbalance Failure

Plate_13.1.doc 12/5/2005 

Plate No. 13.1 Failure Code: 00.19.2.1 

Plate No. 13.1 

Archive No. DSCN0024.jpg 

Image type view 

Scalebar millimeter ruler 

Component DGBB IR 

Application wind turbine generator 

Speed (Kndm) 400 

Load (P/C) 0.04 

Lubrication grease with synthetic oil, 

bentonite thickener 

Temperature,C 80 

Failure code 1 00.19.2.1: Hot plastic flow, 

without welding. 

Failure code 2 00.19.4.1 Friction polymer on 

rolling track 

Failure code 3 00.20.1: Corrosion 

Failure code 4. 00.21: Electric erosion. 

DESCRIPTIONS 

Failure description. 

Overheated, plastically rolled-out ball path with rolled-in debris. Entire ring discolored, possibly rusted after dismounting. 

Image description. 

Severely deformed ball path with multiple indentations. Entire ring brownish discolored, including lands. Discoloration from 

overheating not clearly distinguishable from possible rust after dismounting. Any signs of electric current passage have been 

obliterated by the plastic rollout. 

Suspected causes. 

The bearing is known to have operated with failing, severely dried-out grease lubrication in the presence of electric current 

passage. After destruction of the grease, the bearing overheated, resulting in hot plastic rollout of the ball groove. After 

dismounting, the bearing was stored and may have rusted. 
 

 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 13: Heat Imbalance Failure

Plate_13.2.doc 11/30/2005 

Plate No. 13.2 Failure Code: 00.19.2.1 

Plate No. 13.2 

Archive No. DSCN0032.jpg 

Image type view 

Scalebar millimeter and inch ruler 

Component DGBB, B 

Application wind turbine generator 

Speed (KdN) 400 

Load (P/C) 0.04 

Lubrication grease with synthetic oil, 

bentonite thickener 

Temperature,C 80 

Failure code 1 00.19.2.1:Hot plastic flow, 

without welding. 

Failure code 2 00.19.3: Scale formation 

Failure code 3 0-0.21: Electric erosion 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Overheated, plastically deformed balls, with multiple local surface indentation and dark discoloration (probably scale). 

Image description. 

Balls are battered, indented, original surface destroyed. Dark blackish-brown surface coating appears to be scale from 

overheating, with grease burned on. See also Plate 13.3. Any sign of electric erosion is obliterated by the plastic flow. 

Suspected causes. 

The bearing is known to have operated with failing, severely dried-out grease lubrication in the presence of electric current 

passage. After destruction of the grease, the bearing overheated, resulting in hot plastic deformation of the ball surface. Debris 

caused localized indentations. 
 

 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 13: Heat Imbalance Failure

Plate_13.3.doc 11/30/2005 

Plate No. 13.3 Failure Code: 00.19.2.1 

Plate No. 13.3 

Archive No. DSCN0036.jpg 

Image type view 

Scalebar 8 mm 

Component DGBB, B 

Application wind turbine generator 

Speed (KdN) 400 

Load (P/C) 0.04 

Lubrication grease with synthetic. oil, 

bentonite thickener 

Temperature,C 80 

Failure code 1 00.19.2.1: Hot plastic flow, 

without welding. 

Failure code 2 00.19.3: Scale formation 

Failure code 3 0-0.21: Electric erosion 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Overheated, plastically deformed ball, with multiple local surface indentations and dark discoloration (probably scale). 

Image description. 

This is one ball of the group shown in Plate 13.2, at higher magnification. It is battered, indented, and the original surface is 

destroyed. Dark blackish-brown surface coating appears to be scale from overheating, with grease burned on. Any sign of 

electric erosion is obliterated by the plastic flow. 

Suspected causes. 

The bearing is known to have operated with failing, severely dried-out grease lubrication in the presence of electric current 

passage. After destruction of the grease, the bearing overheated, resulting in hot plastic deformation of the ball surface. Debris 

caused localized indentations. 
 

 

 

 

Tallian: Wind turbine bearing failrue atlas. Chapter 13: Heat Imbalance Failure

Plate_13.4.doc 12/2/2005 

Plate No. 13.4 Failure Code: 00.19.1.4 

Plate No. 13.4 

Archive No. DSCN0862.jpg 

Image type view 

Scalebar 10 mm 

Component DGBB IR 

Application wind turbine generator 

Speed (Kndm) 400 

Load (P/C) 0.04 

Lubrication grease with synthetic oil, 

bentonite thickener 

Temperature,C 80 

Failure code 1 00.19.1.4; Heat discoloration 

from friction polymer 

Failure code 2 00.13.2: Wear in rolling surface 

Failure code 3 00.21: Electric erosion. 

Failure code 4. 12:7 Electric current damage to 

grease 

DESCRIPTIONS 

Failure description. 

Pronounced ball track, off center as from combined load. Lubricant deposit. Matte surface in track, as from electric erosion 

and/or wear. 

Image description. 

Lubricant varnish on rolling track and stains (possibly from decomposed lubricant) on lands. Ball track is shifted somewhat offcenter to the W of the image, as under combined load. On the track, the discoloration is more orange-colored. The discoloration 

is largely absent on the SW quadrant of the ball track. A matte gray surface is present. Near the E edge of the ball track, several 

circumferential wear bands. 

Suspected causes. 

This bearing is known to have operated in the presence of grease pack damage. Among the causes, electric current passage is 

suspected. The current directly damages the grease and also erodes the rolling surfaces. Overheating may have contributed to 

grease failure or may have been its result. 
 

Tallian: Wind turbine bearing failure atlas

Chapter 14.Corrosion, electric erosion.doc 12/13/2005 

Chapter 14. Corrosion, electric erosion. 

Failure code 00.20: Corrosion. 

Failure code 00.21: Electric erosion. 

Definitions. 

Corrosion of a contact component is defined broadly as including all failure by chemical (and 

electrochemical) attacks on surfaces. 

Electric erosion is damage to contact surfaces caused by the passage of electric current. 
 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 14: Corrosion, Electric Erosion.

Plate_14.1.doc 11/25/2005 

Plate No. 14.1 Failure Code:00.21.2 

Plate No. 14.1 

Archive No. DSCN0248.jpg 

Image type view 

Scalebar millimeter ruler 

Component DGBB OR 

Application wind turbine generator 

Speed (Kndm) 400 

Load (P/C) 0.04? 

Lubrication oil? 

Temperature,C 80 

Failure code 1 0.21.2: Electric erosion fluting 

Failure code 2 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

 Severe electric erosion fluting of the rolling track. 

Image description. 

The section of the outerring shown in the image comprises the innerring ball path with lands on both sides. The ball track is 

centered. A series of periodic troughs (boat shaped depressions) oriented axially, covers the ball track. These represent the 

electric current damage. 

Suspected causes. 

This bearing was equipped with an outerring coated with aluminum oxide on the OD and side faces, to prevent the passage of 

ohmic current. The coating was intact. The severe current damage is attributed to capacitive current, coupled into the bearing 

through the high capacitance of the thin insulating layer. Some designs of wind turbine generators operate with electronic 

controls entailing high frequency switching. It is theorized that the resulting high frequency voltage peaks drive capacitive 

currents through the bearing. The well documented phenomenon of periodic flutes arising from electric current passage 

(apparently irrespective of frequency), has not been satisfactorily explained. 
 

 

 

 

Tallian: Wind turbine bearing failure atlas Chapter 14: Corrosion, Electric Erosion.

Plate_14.2.doc 11/25/2005 

Plate No. 14.2 Failure Code: 00.21 A: B: 

Plate No. 14.2. 

A 

B 

Archive No. A: DSCN0005.jpg 

B:DSCN0009.jpg 

Image type A: view.; B: light macro 

Scalebar A: millimeter ruler 

B: 2 mm 

Component DGBB, OR; 

Application wind turbine generator 

Speed (Kndm) 400 

Load (P/C) 0.05? 

Lubrication Oil? 

Temperature,C 80 

Failure code 1 00.21: Electric erosion 

Failure code 2 00.15.1.3: Fit sideface fretting 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

 Fit surface fretting in aluminum-oxide insulating coating with possible electric spark damage. 

Image description. 

Image A: the outerring sideface is covered with a gray aluminum oxide coating. Two adjacent bright oblong patches with dark 

edges show an area where the coating has worn through. 

Image B: The surface of the worn oblong is pitted. 

Suspected causes. 

Through mounting damage and/or small interface motion, the insulating coating was worn through. The bearing operates in a 

generator where electric current passage is possible. Ohmic current can pass through the patch of damaged coating, probably as 

sparks, creating the pitted surface. It is then conducted through the contact interfaces into the innerring, and is likely to cause 

current erosion in the contact surfaces. 
 

 

 

 

 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 14: Corrosion, Electric Erosion.

Plate_14.3.doc 11/25/2005 

Plate No. 14.3 Failure Code: 00.21.2 A: B: 

Plate No. 14.3 

A. 

B. 

Archive No. A: area between flutes 750x.jpg. 

B: flute #1 center 750x.jpg 

Image type A, B: SEM 

Scalebar A, B: 20 μm 

Component DGBB, OR 

Application generator 

Speed (Kndm) 400 

Load (P/C) 0.05 

Lubrication oil? 

Temperature,C 80 

Failure code 1 00.21.2: Electric erosion fluting 

Failure code 2 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

 Typical electrically eroded surfaces. A: between flutes and B: within flutes. An overview of the damage is in Plate 14.1 

Image description. 

The two images are of the same magnification. 

Between flutes (image A) the grinding lines are obliterated and fine (~5 μm) pits cover much of the surface. Occasional larger 

pits are visible. 

Within a flute (image B) a similar surface additionally shows larger (10 – 15 μm) pits with melted and subsequently rolleddown edges. 

Suspected causes. 

Substantial electric current passing through the Hertz contact ablates the surface, obliterating the grinding lines and leaving fine 

pits outside the flutes and both fine and large pits within the flutes. 

A periodic occurrence of unidentified nature selects for the concentration of severe pitting in flutes. Note from Plate 14.1 that 

the flutes have considerable depth. Therefore, their surface has been ablated to a much greater degree than the surface between 

the flutes. 
 

 

 

Wind turbine bearing failure atlas Chapter 14: Corrosion, Electric Erosion

Plate_14.4.doc 11/30/2005 

Plate No. 14.4 Failure Code: 00.21.1 A: B: 

A: B: 

Plate No. 14.4 

Archive No. A: DSCN1092.jpg 

B: DSCN1096.jpg 

Image type A, B: light macrograph 

Scalebar A: millimeter ruler 

B:10 mm 

Component DGBB IR 

Application wind turbine generator 

Speed (Kndm) 400 

Load (P/C) 0.04 

Lubrication grease with synthetic oil, 

unknown thickener 

Temperature,C 80 

Failure code 1 00.21.1: Electric erosion 

pitting 

Failure code 2 00.17.1.1: Glazing (incipient 

surface distress) 

Failure code 3 00.17.1.2: Microspalling 

(advanced surface distress) 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

The ball track exhibits varying degrees of surface damage, including glazing, micropitting and some microspalling. Three 

macroscopically matted, “frosted” bands appear brownish (see Plate 14.5). Grinding lines are extensively obliterated. 

Image description. 

A: Finely “frosted” bands N of “1”, at “2” and S of “3”. Larger pits at “2”. 

B: Enlarged view of micropitted band, with a microspall in the red circle. 

Suspected causes. 

The bearing is known to have operated under failing lubrication due to a dried-out, carbonized grease pack. This condition can 

explain surface distress from severe asperity interactions. In addition, it is suspected that electric current passed through the 

bearing, explaining the premature grease failure and detailed features of the surface appearance, such as pits, which are not 

characteristic of asperity contact surface distress. 
 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 14: Corrosion, Electric Erosion

Plate_14.5.doc 12/11/2005 

Plate No. 14.5 Failure Code: 00.21.2 

Plate No. 14.5 

Archive No. 1600x within band BSE.jpg 

Image type SEM backscatter 

Scalebar 10 μm 

Component DGBB IR 

Application generator 

Speed (Kndm) 400 

Load (P/C) 0.04 

Lubrication grease with synthetic oil, 

unidentified thickener 

Temperature,C 80 

Failure code 1 00.21.2: Electric erosion 

Failure code 2 00.17.1.1 Incipient surface 

distress 

Failure code 3 12.3 Friction polymer, grease 

lubrication 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Micropitted, glazed surface. Partially covered with friction polymer where not etched. In direct visual examination, the surface 

shows an orange varnish and a “frosted” matte texture. 

Image description. 

W half of image is unetched surface. The E half is lightly etched. A thin varnish layer partially obscures some pits in the W half 

In the E half, a dense population of pits, slightly elongated in the E – W rolling direction is clearly shown on a featureless 

background surface. No grinding lines. 

Suspected causes. 

This bearing is known to have operated under failing grease lubrication (dried out, carbonized grease). Low amperage electric 

current is believed to have passed through the bearing, creating the fine pitting and probably contributing to the uniform 

material removal resulting in the featureless background surface. 
 

 

Wind turbine bearing failure atlas Chapter 14: Corrosion, Electric Erosion

Plate No. 14.6 Failure Code: 00.21.1 

Plate No. 14.6 

Archive No. 2000xloc1.jpg 

Image type SEM. 

Scalebar 10 μm 

Component DGBB IR 

Application wind turbine generator 

Speed (Kndm) 400 

Load (P/C) 0.04 

Lubrication grease with synthetic oil, 

unidentified thickener 

Temperature,C 80 

Failure code 1 00.21.1: Electric erosion pitting 

Failure code 2 00.17.1.1 Glazing (surface 

distress) 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Electric erosion micropit formed on featureless background surface. The pit bottom is rough, as if eroded, the pit edges are 

rolled down. 

Image description. 

On a topographically featureless background surface without grinding lines, showing some variation in electron emissivity 

(grayscale), a circular pit with rough bottom, as from erosion, and rolled-down edges. In contrast with severe electric erosion 

under high amperage current, the surface shows no clear evidence of having been remelted. 

Suspected causes. 

This bearing is known to have operated under failing grease lubrication (dried out, carbonized grease). Passage of low amperage 

electric current is suspected. Current passage creates micropits and may have contributed to the removal of grinding lines on the 

background surface, “glazed” by surface distress from inadequate lubrication. 

Plate_14.6.doc 11/25/2005 
 

 

 

Tallian: Wind turbine bearing failure atlas Chapter 14, Corrosion, Electric Erosion.

Plate_14.7.doc 11/30/2005 

Plate No. Plate 14.7 Failure Code: 00.21.1 

Plate No. 14.7 

Archive No. loc1 2000x.jpg 

Image type SEM 

Scalebar 10 μm 

Component DGBB IR 

Application wind turbine generator 

Speed (Kndm) 400 

Load (P/C) 0.04 

Lubrication grease with synthetic oil, 

unidentified thickener 

Temperature,C 80 

Failure code 1 00.21.1: Electric erosion pitting 

Failure code 2 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

 Surface electrically eroded to a very fine isotropic topography. 

Image description. 

Entire surface topography consists of very fine (1- 2 μm) rounded “pebbles,” as if locally melted. 

Suspected causes. 

The bearing is known to have operated under conditions where low amperage electric currents may have passed. It is 

conjectured that the currents result from switching transients in the circuit. The surface appearance is unlike that seen in 

mechanical surface distress. No source of chemical attack has been identified. Accordingly the ablation of the original ground 

finish and creation of the eroded ”pebbly” topography is attributed to the electric current. 
 

 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 14: Corrosion, Electric Erosion

Plate_14.8.doc 12/2/2005 

Plate No. Plate 14.8 Failure Code: 00.21.1 

Plate No. 14.8 

Archive No. loc3 1000x etched.jpg 

Image type SEM 

Scalebar 10 μm 

Component DGBB IR 

Application wind turbine generator 

Speed (Kndm) 400 

Load (P/C) 0.04 

Lubrication grease with synthetic oil, 

unidentified thickener 

Temperature,C 80 

Failure code 1 00.21.1: Electric erosion pitting 

Failure code 2 00.18.01.1.2: Denting of rolling 

surface, minor sliding 

Failure code 3 00.12.3.2 Wear in rolling surface 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Electric erosion, denting and possibly surface distress contributed to the topography at the edge of a “frosted” band. The 

surface was lightly etched to remove lubricant varnish. 

Image description. 

A few straight lines run from NW to SE corner of image. Other, fainter lines run SW to NE. One NW to SE line separates a 

lightly dented, smooth “glazed” area from a mottled, micropitted, lightly dented area (macroscopically a “frosted” band). Dents 

tend to be elongated in the E – W rolling direction. No grinding lines are visible. 

Suspected causes. 

This bearing is known to have operated under failing lubrication as a result of dried out and carbonized grease. Low amperage 

electric current passage is hypothesized. Frosted surface appearance with pits is associated with electric erosion. The elongated 

sharp dents are likely due to fine particulates. Inadequate lubrication may have contributed to removal of the grinding lines. The 

source of the few crossed straight lines is unclear: they may possibly be honing furrows. 
 

 

 

 

 

 

Tallian: Wind turbine bearing failure atlas Chapter 14: Corrosion, Electric Erosion

Plate_14.9.doc 11/25/2005 

Plate No. 14.9 Failure Code: 00.20.13 A: B: C: D: 

Plate No. 14.9 

Archive No. A: DSCN9892.jpg 

B: DSCN2037.jpg 

C: IR within corrosion 1000x.jpg 

D: loc3 850x.jpg 

Image type A: view 

B: light macrograph 

C: SEM 

D: SEM 

 Scalebar A: millimeter ruler 

B: millimeter ruler 

C: 10 μm 

D: 20 μm 

Component CRB IR 

Application gearbox 

Speed (Kndm) 14 

Load (P/C) 0.15 

Lubrication glycol based oil 

Temperature,C 80 

Failure code 1 00.20.13: Contact corrosion 

Failure code 2 00.20. 00.20.2: Corrosion pitting 

Failure code 3 00.20.1: Corrosion stain 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Contact corrosion mark on innerring roller path, from contact with roller under maldistributed loading. Additional, diffuse 

corrosion pitting. 

Image description. 

A: Overview of wedge-shaped contact corrosion mark across innerring roller path. The tip of the wedge points to the unflanged 

side. The mark consists of a stained outline. 

B: Part of the stained outline of the corrosion mark. 

C: Multiple, fine corrosion pits within the stained outline of the mark. 

D: Randomly distributed corrosion pits and stains away from the contact corrosion mark. 

Suspected causes. 

The bearing was exposed to corrosive environment (probably water in the lubricant) while standing still. Corrosion 

preferentially occurs within the lubricant meniscus forming at the edges of roller/ring contacts. However, random corrosion 

pitting also occurred away from the contact areas. 
 

 

 

 

 

 

Tallian: Wind turbine bearing failure atlas Chapter 14: Corrosion, Electric Erosion

Plate_14.10.doc 11/25/2005 

Plate No. 14.10 Failure Code: 00.20.1 

Plate No. 14.10 

Archive No. DSCN7851.jpg 

Image type view 

Scalebar millimeter scale 

Component CRB OR 

Application gearbox 

Speed (Kndm) 12 

Load (P/C) 0.17 

Lubrication synthetic hydrocarbon oil 

Temperature,C unknown 

Failure code 1 00.20.1: Corrosion stain 

Failure code 2 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Uniform corrosion stain in roller path. 

Image description. 

On OR roller path, W of “light rust” text, transparent tan to brown stain over grinding lines. 

Suspected causes. 

The bearing was exposed to a mild corrosive environment (moisture?) which created a uniform corrosion stain on the rolling 

surface. It is not known whether the stain arose late during the service life, or after dismounting. Stain formed before, or early 

during operation would have worn off. 
 

 

 

Tallian: Wind turbine bearing failure atlas Chapter 14: Corrosion, Electric Erosion

Plate_14.11.doc 11/25/2005 

Plate No. 14.11 Failure Code: 00.20.1.3 

 Plate No. 14.11 

Archive No. DSCN7776.jpg 

Image type view 

Scalebar 30 mm 

Component CRB OR 

Application gearbox 

Speed (Kndm) 12 

Load (P/C) 0.17 

Lubrication synthetic hydrocarbon oil 

Temperature,C unknown 

Failure code 1 00.20.1.3: Contact corrosion 

Failure code 2 00.20.1.2: Corrosion stain 

Failure code 3 00.15.2: False brinnelling 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

On the OR roller path and flange, streaks of corrosion, with possible false brinnell marks under the roller contacts. 

Image description. 

Numerous axial brown streaks across roller path and flange. The roller path streaks have an uncorroded center band where the 

roller contact prevented moisture access. That band may show false brinnell fretting. Next to the uncorroded band, the corrosion 

is densest under the lubricant meniscus, but extends outside the contact zones. 

Suspected causes. 

The bearing was subjected to corrosive environment (moisture?) during standstill. Vibratory effects may have produced some 

false brinnell fretting at the roller contacts. 
Tallian: Wind turbine bearing failure atlas

Chapter 15.Bulk cracking, fracture, permanent deformation..doc 

Chapter 15. Bulk cracking, fracture, permanent deformation. 

Failure code 00.22: Bulk cracking or fracture. 

Failure code 00.23: Permanent deformation. 

Definitions. 

Bulk cracking or fracture. In a contact component, bulk cracking designates cracks extending 

beyond the stress field of the Hertz contact. Bulk fracture is fracture leading to separation of a 

volume of material by a bulk crack. 

Permanent bulk deformation. A contact component suffers permanent bulk deformation if any of 

its macroscopic dimensions are permanently altered from the as-installed condition. Elastic 

deflection or thermal expansion is not permanent deformation. Nicks, dents and rolled-in marks 

are permanent deformation, but not bulk deformation. 

12/13/05 
 

 

 

Tallian: Wind turbine bearing failure atlas Chapter 15: Bulk Cracking, Fracture, Permanent Deformation

PLate_15.1.doc 11/24/2005 

Plate No. 15.1 Failure Code: 00.22.1 

Plate No. 15.1 

Archive No. ADSCN0056.jpg 

Image type view 

Scalebar millimeter tape 

Component BB (slewing ring) OR 

Application turbine blade pitch control 

Speed (Kndm) oscillatory 

Load (P/C0) 0.35 

Lubrication grease 

Temperature,C ambient 

Failure code 1 00.22.1: Overstress crack 

Failure code 2 00.23.1.1: Contact path rolldown 

in bearing 

Failure code 3 00.18.02.2: Severe or advanced 

denting. 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Extensive plastic rolldown of ball track with multiple debris dents. Case crack from ball path edge to land. 

Image description. 

The N half of the image shows the ball track. It appears plastically rolled down, with multiple debris dents. The tip of the arrow 

marked “crack” marks a crack extending across the land and down on the ring face. 

Suspected causes. 

Rollover in the presence of spall debris has plastically deformed and dented the ball path. Subsequently, the bearing participated 

in a turbine failure, with broken blades and tower collapse. Very large overturning torques were apparently imposed on the 

bearing. The accumulated stresses were sufficient to form a crack through the hardened case, which traveled across the land and 

down the ring face. 
 

 

 

 

 

Tallain: Wind turbine bearing failure atlas. Chapter 15: Bulk Cracking, Fracture, Permanent Deformation

Plate_15.2.doc 12/7/2005 

Plate No. 15.2 Failure Code: 00.22.2 A: B: 

Plate No. Plate15.2 

A: B: 

Archive No. A: DSCN0374.jpg 

B: Fig37.jpg 

Image type A: view 

B: metallogram. 

Scalebar A: 10 mm 

B: 500 μm 

Component CRB IR 

Application gearbox 

Speed (KNdm) 12? 

Load (P/C) 0.17? 

Lubrication synthetic hydrocarbon oil 

Temperature,C 60 

Failure code 1 00.22.2: bulk fatigue crack 

Failure code 2 0.22.01.1: axial cross section 

crack in ring 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Axial cracks on IR roller path, penetrating radially. One reaches a depth of approx. 3 mm. 

Image description. 

A: Family of fine axial; cracks penetrating radially inward into the innerring from the roller path 

B: Fine black crack line penetrating from surface at N edge of image, in approximate radial direction (N – S) with multiple 

branches in the region marked by red arrow. 

Suspected causes. 

Bearings in this position may suffer vibratory loads in near-stationary condition. False brinnell marks have been seen similar 

cases, at one or several sets of roller positions. The IR is a press fit on the shaft. The shaft may be subject to bending deflection, 

causing cyclic tensile stressing of the IR. The combination of bending and Hertzian stress cycles may cause cracking along the 

false brinnell marks. Under tensile hoop stress, the crack tends to propagate radially inward, even beyond the high Hertzian 

stress field and can eventually fracture the ring. 
 

Tallain: Wind turbine bearing failure atlas. Chapter 15: Bulk Cracking, Fracture, Permanent Deformation

Plate_15.2.doc 12/7/2005 
 

 

 

 

 

Tallian: Wind turbine bearing failure atlas Chapter 15: Bulk Cracking, Fracture, Permanent Deformation

Plate_15.3.doc 11/25/2005 

Plate No. 15.3 Failure Code: 00.22.2 

Plate No. 15.3 

Archive No. DSCN1552.jpg 

Image type view 

Scalebar 2o mm 

Component CRB, shrink ring 

Application gearbox 

Speed (Kndm) 49 

Load (P/C) 0.08 

Lubrication synthetic hydrocarbon oil 

Temperature,C 50 

Failure code 1 00.22.2:Axial cross section crack 

in ring 

Failure code 2 20.01:Mounting part damage 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Shrink ring holding split outerring together, fractured in two locations. 

Image description. 

Outerring OD with shrink ring groove. Fractured shrink ring loose on OD. 

Suspected causes. 

Assumed to be dismounting damage of shrink ring with possible manufacturing defect. 
 

 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 15. Bulk Cracking, Fracture, Permanent Deformation

Plate No. 15.4 Failure Code: 00.22.01.1 

Plate No. 15.4 

Archive No. HS Bearing Spall2.jpg 

Image type view 

Scalebar 10 mm 

Component DGBB IR, B, S 

Application gearbox 

Speed (Kndm) 250 

Load (P/C) ? 

Lubrication synthetic hydrocarbon oil 

Temperature,C 60 

Failure code 1 00.33.01.1: Axial cross section 

crack in ring. 

Failure code 2 00.16.1.1,2: Spall from 

subsurface defect. 

Failure code 3 00.15.2: False brinnelling at 

contact surface. 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Radially ingoing axial cracks in innerring ball path, at ball spacing. One crack has spalled out. 

Image description. 

The disassembled innerring is placed on top of the separator, which contains the balls in their pockets. White arrows show axial 

cracks in the ball path, at a spacing similar to that of ball contacts. One of the cracks has spalled out to form a circular spall. 

Suspected causes. 

Innerring surface damage suffered by the bearing while standing still (false brinnelling from oscillating motions, possibly 

contact corrosion or true brinnelling) has created weak zones in the ball path. Load cycling in the presence of high hoop stresses 

has originated radially ingoing cracks from these weak zones. Further cycling caused one crack to spall out. 

Plate_15.4.doc 11/25/2005 
 

Tallian: Wind turbine bearing failure atlas

Chapter 16. Guiding component failure. 

Failure code 16.1. Separator failure. 

Failure code 16.2. Guidering failure. 

Separator failure. Definition: This failure code encompasses all failure modes of rolling bearing 

separators. Separators (cages) are elements for the maintenance of specified spacing of rolling 

elements and (often) their retention in the bearing during disassembly. 

Guidering failure. Definition: This failure code encompasses all failure modes of guiderings in 

rolling bearings. Guiderings are separate rings, fitted to one of the Hertz contact rings. They may 

be separator guiderings used to center separators, or roller guiderings, holding rollers axially in 

place. 

Chapter 16.Guiding component failure.doc 12/12/2005
 

 

 

Tallian: Wind turbine bearing failure atlas CHapter 16: Guiding Component Failure

PLate_16.1.doc 12/3/2005 

Plate No. 16.1 Failure Code: 01.12 

Plate No. 13.4 

Archive No. DSCN0046.jpg 

Image type view 

Scalebar mm ruler 

Component DGBB, S 

Application Wind turbine generator 

Speed (KdN) 400 

Load (P/C) 0.04 

Lubrication grease with synthetic oil, 

bentonite thickener 

Temperature,C 80 

Failure code 1 01.12:Separator plastic 

deformation 

Failure code 2 12.2: Carbonized grease 

Failure code 3 01.13:Separator wear 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

The machined bronze separator pocket is battered by ball forces. The pocket surface shows wear. Carbonized grease adheres to 

the surfaces. 

Image description. 

The OD of the separator is at the NW image corner. One side face, including a ball pocket fills the image. At “a,” a carbonized 

piece of grease adheres to the surface. Smudges of carbonized grease are elsewhere. At ”b,” the edge of the pocket is hammered 

out. Traces of wear and the intersection line between two oppositely tapered pocket surfaces are seen on the rear pocket wall. 

Suspected causes. 

The bearing suffered a heat imbalance failure after the grease pack became unserviceable. When the lubrication failed and the 

bearing overheated, plastic deformation took place, the contact geometry was lost, friction between balls and separator 

increased, ball orbiting speeds became erratic and the balls applied large forces to the separator pockets, causing wear and 

plastic flow. 
 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 16: Guiding Component Failure

Plate No. 16.2 Failure Code: 01.12 

Plate No. 16.2 

Archive No. DSCN0048.jpg 

Image type view 

Scalebar millimeter ruler 

Component DGBB, S 

Application wind turbine generator 

Speed (Kndm) 400 

Load (P/C) 0.04 

Lubrication grease with synthetic oil, 

bentonite thickener 

Temperature,C 80 

Failure code 1 01.12: Separator plastic 

deformation 

Failure code 2 12.2: Carbonized grease 

Failure code 3 01.13: Separator wear 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

The machined bronze separator pocket is battered by ball forces. The pocket surface shows wear. Carbonized grease adheres to 

the surfaces. See also Plate 16.1. 

Image description. 

This is a view into the ball pocket of the separator shown in Plate 13.4. Both top and bottom edges are battered. About middeep into the pocket, an edge shows the intersection between the two oppositely tapered pocket parts. The area appears worn. 

Smudges of carbonized grease cover the surfaces. 

Suspected causes. 

The bearing suffered a heat imbalance failure after the grease pack became unserviceable. When the lubrication failed and the 

bearing overheated, plastic deformation took place, the contact geometry was lost, friction between balls and separator 

increased, ball orbiting speeds became erratic and the balls applied large forces to the separator pockets, causing wear and 

plastic flow. 

Plate_16.2.doc 12/2/2005 
 

 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 16: Guiding Component Failure.

Plate_16.3.doc 12/3/2005 

Plate No. 16.3 Failure Code: 01.16 

Plate No. 16.3 

Archive No. DSCN0559.jpg 

Image type view 

Scalebar millimeter ruler 

Component DGBB, S 

Application wind turbine generator 

Speed (Kndm) 400 

Load (P/C) 0.04 

Lubrication grease with synthetic. oil, 

bentonite thickener 

Temperature,C 80 

Failure code 1 01.16: Separator heat imbalance 

failure 

Failure code 2 01.13.1: Separator pocket worn 

Failure code 3 12.3: Friction polymer, grease 

lubrication 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Wear and heavy lubricant varnish in ball pocket of machined bronze two-piece separator, as a result of heat imbalance 

following grease pack failure. 

Image description. 

The separator ball pocket fills the image. The outside diameter is at the SE corner of the image. At the arrow, wide wear band. 

Elsewhere, brown lubricant varnish. 

Suspected causes. 

The bearing is known to have suffered failure of the grease pack, possibly as a result of electric current passage. As the grease 

failed, the temperature of the bearing and the friction between balls and separator increased, causing significant pocket wear. 

The high temperature caused deposition of a brown grease residue on the surfaces, including those not undergoing contact. 
 

 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 16: Guiding Component Failure

Plate_16.4.doc 12/4/2005 

Plate No. 16.4 Failure Code: 01.13.1 

Plate No. 16.4 

Archive No. DSCN0620.jpg 

Image type light macrograph 

Scalebar millimeter ruler 

Component DGBB S 

Application wind turbine generator 

Speed (Kndm) 400 

Load (P/C) 0.04 

Lubrication grease with synthetic oil and 

unidentified thickener 

Temperature,C 70 

Failure code 1 01.13.1: Separator pocket worn. 

Failure code 2 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Two deep, smooth wear marks in separator pocket. 

Image description. 

At arrows, two shiny, depressed, lozenge shaped wear marks in separator pocket, at diametrally opposite positions, where the 

driving or driven ball contacts the pocket. The wear is smooth; without galling. 

Suspected causes. 

The machined bronze separator was subjected at various times, to high ball contact forces, with the ball alternatively in the 

driving and driven positions. The lubrication was insufficient to prevent wear of significant depth. 
 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 16: Guiding Component Failure

Plate_16.5.doc 12/4/2005 

Plate No. 16.5 Failure Code: 01.13 

Plate No. 16.5 

Archive No. DSCN 2908.jpg 

Image type light macrograph 

Scalebar millimeter ruler 

Component CRB S 

Application gearbox 

Speed (Kndm) 49 

Load (P/C) 0.08 

Lubrication synthetic hydrocarbon oil 

Temperature,C ? 

Failure code 1 01.13: Separator wear 

Failure code 2 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

The disk-shaped separator rides in an outerring groove between the ring halves. Wear occurred in the roller pockets and on the 

guided sideface. 

Image description. 

A circumferential wear scar is visible near the OD of the side face of the separator, where it contacted the edge of the outerring 

groove. Moderate axial wear marks appear near the tip of the pocket. 

Suspected causes. 

Some wear in the pockets is normal. The rather deep and sharp wear scar on the sideface may have resulted from hard 

contaminant particles wedged between separator and ring groove. 
 

 

Tallian: Wind turbine bearing failure atlas. Chapter 16: Guiding Component Failure

Plate_16.6.doc 12/4/2005 

Plate No. 16.6 Failure Code: 01.13.1 

Plate No. 16.6 

Archive No. DSCN1825.jpg 

Image type light macrograph 

Scalebar millimeter ruler 

Component CRB, S 

Application gearbox 

Speed (Kndm) 14 

Load (P/C) 0.15 

Lubrication synthetic hydrocarbon oil 

Temperature,C ? 

Failure code 1 01.13.1: Separator pocket worn. 

Failure code 2 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Heavy wear on one corner of separator pocket, extending over part of one bar. 

Image description. 

Steel separator with yellow lubricant deposit (varnish) on surfaces. At NW pocket corner and extending about 4 mm into W bar, 

deep wear has produced a 450

 chamfer with a sharp receding edge in the corner. The wear ends abruptly at the S end. The worn 

surfaces are the color of steel with a few brown stain spots. 

Suspected causes. 

Roller skewing due to heavy axial load or misalignment can produce localized wear in the pocket corners. The abrupt end of the 

wear mark at its S end is unusual, since the roller corner cannot reach that location. 
 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 16: Guiding Component Failure

Plate No. 16.7 Failure Code: 01.13.1 

Plate No. 16.7 

Archive No. DSCN9176.jpg 

Image type view 

Scalebar millimeter ruler 

Component DGBB S 

Application wind turbine generator 

Speed (Kndm) 450 

Load (P/C) 0.05 

Lubrication grease with synthetic oil and 

unknown thickener 

Temperature,C ? 

Failure code 1 01.13.1: Separator pocket wear 

Failure code 2 01.13: Separator wear 

Failure code 3 01.13.3. Separator wear from 

unintended contact 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

The two-part machined bronze separator shows wear tracks in the ball pocket, in random directions, from embedded 

and subsequently released hard particles. Heavy circumferential gouge. Possible damage from unintended contact in free 

surfaces. Some of the damage may have been done during bearing dismounting. 

Image description. 

The separator consists of two rings riveted together, with the split near the center of the ball pocket. It is shown disassembled. 

The pocket halves face in, free surfaces face out. All surfaces have a battered appearance as if exposed to wear from loose 

debris. In the W image half, a deep circumferential gouge runs midway through the pocket half, with a debris particle 

apparently embedded near image center. In right half, “worm track” shaped random gouges. 

Suspected causes. 

The separator operated in a heavily contaminated environment. Debris became entrapped between pocket and ball, and was 

randomly dragged in a variety of directions. Some larger particles became temporarily embedded. Unusual directions of relative 

motion between ball and separator are required to explain the wear tracks of the debris, suggesting severe vibratory 

displacements. 

Plate_16.7.doc 12/5/2005 
 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 16: Guiding Component Failure

Plate_16.8.doc 12/9/2005 

Plate No. 16.8 Failure Code: 01.2 

Plate No. 16.8 

Archive No. DSCN1834.jpg 

Image type light macrograph 

Scalebar millimeter ruler 

Component SRB G (guidering) 

Application gearbox planet 

Speed (Kndm) 10? 

Load (P/C) 0.15? 

Lubrication synthetic hydrocarbon oil 

Temperature,C ? 

Failure code 1 01.2: Guidering failure 

Failure code 2 01.23: Guidering wear 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

On the side face of a cast iron guidering contacted by the roller ends, circular dents, fine debris denting and numerous epicyclic 

wear marks are seen. 

Image description. 

The side face of the guidering is shown. The edge of the guidering inner diameter, which rides on the innerring center land, is 

seen next to the E image edge. 2 mm diameter circular dents are in the center of the red dye mark. Fine debris dents of a few 

hundred micrometers size are dispersed on the surface. From the vicinity of the guidering edge, epicyclic wear marks extend to 

the W. Most wear marks begin about 1⁄2 mm from the guidering edge. A deep mark in the SE image corner extends to the edge. 

Wear marks cross each other in some areas. 

Suspected causes. 

Wear marks on the roller-contact surface of a guidering suggest thrust loading, but are not necessarily failure indications. Deep 

scratches, such as that in the SE image corner are likely to arise from debris entrainment. Crossed marks curving in similar 

directions arise from variations in roller skew. Relatively large circular dents can arise in service from axial impact loading of a 

stationary bearing, but in the location found (far inboard) are more likely to represent mounting or dismounting damage. Fine 

debris dents may have been produced by contaminant in a stationary bearing. 
 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 16: Guiding Component Failure

PLate_16.9.doc 12/5/2005 

Plate No. 16.9 Failure Code: 01.13.1 

Plate No. 16.9 

Archive No. DSCN1902.jpg 

Image type view 

Scalebar millimeter ruler 

Component SRB G (separator) 

Application gearbox planet bearing 

Speed (Kndm) 14 

Load (P/C) 0.15 

Lubrication synthetic hydrocarbon oil 

Temperature,C ? 

Failure code 1 01.13.1: Separator pocket wear 

Failure code 2 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

In the stamped steel separator of this spherical roller bearing, pronounced, but not severe separator pocket wear on the pocket 

end oriented toward the large-diameter separator end. 

Image description. 

The separator is a stamped, surface treated steel component. The pocket end face is a relatively rough cut surface. Near the ID 

edge, polishing wear across the entire pocket width has produced a shiny, smooth ledge. 

Suspected causes. 

Separator wear of some magnitude is expected in stamped cage pockets. The wear is even across the pocket width. No 

imminent failure is indicated. 
Tallian: Wind turbine bearing failure atlas

Chapter 18. Lubricant failure. 

Failure code 11: Oil failure. 

Failure code 12: Grease failure. 

Definition: Any failure of the (oil or grease) lubricant contained in the bearing. 

Chapter 18.Lubricant failure.doc 12/12/2005
 

 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 18: Lubricant Failure

Plate_18.1.doc 12/3/2005 

Plate No. 18.1 Failure Code: 12.6 

Plate No. 18.1 

Archive No. DSCN1082.jpg 

Image type light macrograph 

Scalebar 5 mm 

Component grease 

Application wind turbine generator 

Speed (Kndm) 400 

Load (P/C) 0.04 

Lubrication grease with synthetic oil, 

bentonite thickener 

Temperature,C 10 - 80 

Failure code 1 12.6: Grease dried out, discolored 

Failure code 2 12.7: Electric current damage to 

grease 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

The grease was removed from inside a DGBB. It is dry, brittle and discolored. Laboratory tests have shown loss of oil and 

depletion of antioxidant. 

Image description. 

Grease removed from inside the bearing is in a vial. It consists of friable chunks of dry-appearing material. Brown to dark 

brown color. 

Suspected causes. 

The bearing containing this grease is known to have operated in an environment where electric current passage is suspected. 

Vibration and wide temperature excursions also occur. It is suspected that current passage causes damage to the grease, drying it 

out so that it subsequently does not purge from within the bearing and continues to deteriorate. It no longer provides adequate 

lubrication; the bearing overheats, further compounding grease failure. 
 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 18: Lubricant Failure

Plate_18.2.doc 12/3/2005 

Plate No. 18.2 Failure Code: 1 A: B: 

Plate No. 18.2 

A 

B 

Archive No. A: DSCN0046.jpg 

B: DSCN1068.jpg 

Image type view 

Scalebar A: millimeter scale 

B: 30 mm 

Component grease 

Application wind turbine generator 

Speed (Kndm) 400 

Load (P/C) 0.04 

Lubrication grease with synthetic oil, 

bentonite thickener 

Temperature,C 10 - 80 

Failure code 1 12.6: Grease dried out, discolored 

Failure code 2 12.7: Electric current damage to 

grease 

Failure code 3 

Failure code 4. 

DESCRIPTIONS 

Failure description. 

Grease has suffered extensive oil loss. Chemical analysis shows its oxidation inhibitor is depleted. 

Image description. 

The grease consists of brittle, discolored friable blocks. When fresh, it was bright red. 

Probable failure cause. 

This bearing operated at high temperature, subject to vibration and possibly the passage of electric current. The mechanism of 

deterioration under this combination of damaging conditions has not been established. 
Tallian: Wind turbine bearing failure atlas

Chapter 19. Mounting component failure. 

Failure code 22: Shaft failure. 

Definition: Any failure of the shaft on which the bearing innerring is mounted. 

Chapter 19.Mounting component failure.doc 12/12/2005
 

 

 

 

 

 

Tallian: Wind turbine bearing failure atlas. Chapter 19: Mounting Component Failure

Plate No. 19.1 Failure Code: 22.3 A: B: 

Plate No. 8.3 

Archive No. A: shaft No. 6. Silicone replicas 

B: shaft No 6 cleaned.jpg 

Image type A: view 

B: light macrograph 

Scalebar A: unknown 

B: unknown, low magnification 

Component O (bearing seat on shaft) 

Application wind turbine gearbox - planet 

Speed (Kndm) 10? 

Load (P/C) 0.2? 

Lubrication none 

Temperature,C ? 

Failure code 1 22.3: Shaft galled. 

Failure code 2 22.2: Shaft fretted. 

Failure code 3 

Failure code 4. 

A: 

B: 

DESCRIPTIONS 

Failure description. 

Rough turned bearing seat shows wear along turning ridges. A circumferential band of regularly spaced axial gall marks suggests local 

welding to bearing bore with subsequent tearing of welds 

Image description. 

A: Overview of bearing seat. Cleaned area shows fretting wear bands and galling marks. 

B: In the W image half, circumferential lines of lighter gray are the worn crests of turning ridges. The wear marks are interrupted, suggesting 

chatter in the turning. In a N – S band running down image center, axial galling marks are visible, probably over the crests of the chatter. 

Suspected causes. 

Microscopic motion between shaft and bearing bore caused fretting wear (but no discoloration by fretting corrosion) over the high points of 

the shaft surface. In one band, the fretting progressed to galling. Dismounting may have modified galling marks. 

Planet bearing shafts are known to undergo considerable deflection under high load and often with asymmetrical support at the two ends. 

These conditions increase the risk of fretting. 

Plate_19.1.doc 11/30/2005