A Review: The Dilemma With Premature White Etching Crack (WEC) Bearing Failures

Stadler, Kenred; Lai, Junbiao; Vegter, R. H.

doi:10.1520/stp158020140046

Cited by 26 publications

(36 citation statements)

References 28 publications

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“…Several theories on the root cause of WECs can be found in literature [36,37]. A short introduction of several popular root cause hypotheses will be given in order to illustrate the need for a deeper investigation of crack systems in failed components.…”

Section: Wec Theoriesmentioning

confidence: 99%

“…Several authors [11,[16][17][18]20,23,36,37,[39][40][41][42][43][44][45] have proposed that cyclic stresses due to normal over-rolling and local tensile stresses (e.g. caused by structural deformations) lead to the accumulation of strain energy around inhomogeneities (e.g.…”

Section: Fig 3 a Simplified Overview Of The External Or Environmentamentioning

confidence: 99%

“…3), water contamination, [52], stray current [53,54], severe contact conditions (low lambda, high sliding) and certain oil formulations (e.g. containing anti-corrosion sulphonates) [37,55] are seen as root causes for the onset of premature failures and WEC. Most authors believe that these conditions promote atomic hydrogen generation and subsequent penetration into the bearing steel, resulting in the acceleration of rolling contact fatigue mechanisms.…”

Section: Fig 3 a Simplified Overview Of The External Or Environmentamentioning

confidence: 99%

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An analysis of premature cracking associated with microstructural alterations in an AISI 52100 failed wind turbine bearing using X-ray tomography

et al. 2017

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Crack surrounded by local areas of microstructural alteration deemed "White etching cracks" (WECs) lead to unpredictable and premature failures within a multitude of applications including wind turbine gearbox bearings. While the exact cause of these failures remains unknown, a large number of hypotheses exist as to how and why these cracks form. The aim of the current work is to elucidate some of these hypotheses by mapping WEC networks within failed wind turbine bearings using high energy X-ray tomography, in an attempt to determine the location of WEC initiation, and the role of defects within the steel, such as inclusions or carbide clusters. Four completely subsurface WECs were found throughout the presented analysis, thereby confirming subsurface initiation as method of WEC formation. Additionally, a multitude of small butterfly like cracks were found around inclusions in the steel, however further analysis is needed to verify if these inclusions are initiation sites for WECs.

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Section: Wec Theoriesmentioning

confidence: 99%

Section: Fig 3 a Simplified Overview Of The External Or Environmentamentioning

confidence: 99%

Section: Fig 3 a Simplified Overview Of The External Or Environmentamentioning

confidence: 99%

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An analysis of premature cracking associated with microstructural alterations in an AISI 52100 failed wind turbine bearing using X-ray tomography

et al. 2017

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“…Different morphologies for White Etching Cracks in bearings have been observed, which are possibly linked with properties of different bearing steels, different bearing configurations and different service exposure. In many cases WEC propagate parallel to the bearing surface (should not be considered as butterflies) and then branch out in an irregular fashion, forming crack networks which are sometimes known as irregular WEC [7] and cause failure through spallation (WSF). Tensile circumferential hoop stresses will cause WEC to propagate radially through the inner ring, causing axial cracks at the surface, also known as hairline cracks.…”

Section: Introductionmentioning

confidence: 99%

3D X-ray computerized tomography of White Etching Cracks (WEC)

Danielsen

Carrasco

Fæster

et al. 2019

Materials Characterization

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“…Theories about the root causes of WECs include corrosion, hydrogen‐induced embrittlement from lubricant decomposition or water contamination, high‐stress and slip conditions, mechanical impact loading, tensile hoop stress from bearing seat form deviation, stray electrical current, or a combination of these influencing factors. Despite the variety of theories about WEC formation, there is general agreement in the industry that operating conditions prevalent in wind turbines—such as unsteady wind and gusts, idling, braking, misalignment, torque reversals, and grid faults—can lead to disturbed bearing kinematics, loading, and lubrication . Many of these conditions can also cause sliding of the rolling elements in the bearings.…”

Section: Introductionmentioning

confidence: 99%

Investigation of high‐speed shaft bearing loads in wind turbine gearboxes through dynamometer testing

Guo

Keller

2017

Wind Energy

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Many wind turbine gearboxes require repair or replacement well before reaching the end of their design life. The most common failure is bearing axial cracks, commonly called white etching cracks (WECs), which typically occur in the inner raceways of the high-speed parallel-stage rolling element bearings. Although the root causes of WECs are debated, one theory is that they are related to routine dynamic operating conditions and occasional transient events prevalent in wind turbines that can result in high bearing stress and sliding of the rolling elements. This paper examined wind turbine gearbox high-speed shaft bearing loads and stresses through modeling and full-scale dynamometer testing. Bearing outer race loads were directly measured and predicted using a variety of modeling tools in normal operations, misaligned conditions, and transient events particularly prone to bearing sliding. Test data and models of bearing loads were well correlated. Neither operational misalignment due to rotor moments nor static generator misalignment affected the bearing loads when compared with pure-torque conditions. Thus, it is not likely that generator misalignment is a causal factor of WECs. In contrast, during transient events, the bearings experienced alternating periods of high stress, torque reversals, and loads under the minimum requisite at high rotating speeds while showing indications of sliding, all of which could be related to the formation of WECs. KEYWORDS axial crack, bearing load, gearbox, reliability, white etching crack 1 | INTRODUCTIONThe cost of energy from wind has declined tremendously over the past 2 decades 1 owing to a combination of lower capital costs, higher availability and production, and more efficient operation 2,3 ; however, wind power plant operation and maintenance costs are frequently higher than anticipated, 4 and a significant portion of these costs is related to drivetrain reliability. 5 In 2007, the US Department of Energy established the Gearbox Reliability Collaborative (GRC) with the goal of understanding the root causes of premature gearbox failures and improving gearbox reliability. 6 To date, the GRC has focused on testing and modeling a 750-kW drivetrain, including the dedicated design and testing of 2 gearboxes. The GRC has led to major insights relating to the detrimental effect of rotor moments on planetary load sharing, the predicted fatigue life in high-torque conditions, and the risk of planetary bearing sliding in low-torque conditions. 7Although planetary gear and bearing failures attract much attention because of their high repair costs, the most commonly damaged components in wind turbine gearboxes are the rolling element bearings in the high-speed parallel stages. 8 The damage is dominated by axial cracks, also commonly called white etching cracks (WECs), rather than classic rolling contact fatigue. 9 The term white etching refers to the appearance of the steel microstructure when the bearing cross sections are polished, etched with chemicals, and examined under reflect...

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A Review: The Dilemma With Premature White Etching Crack (WEC) Bearing Failures

Cited by 26 publications

References 28 publications

An analysis of premature cracking associated with microstructural alterations in an AISI 52100 failed wind turbine bearing using X-ray tomography

An analysis of premature cracking associated with microstructural alterations in an AISI 52100 failed wind turbine bearing using X-ray tomography

3D X-ray computerized tomography of White Etching Cracks (WEC)

Investigation of high‐speed shaft bearing loads in wind turbine gearboxes through dynamometer testing

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