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Main Bearing Wear Model


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According to a report by Windpower Engineering & Development, the cost to repair main bearings is one of the highest compared to other turbine systems ranging from $150,000 to $300,000. As fielded turbines age, the aggregated downtime has increased to more than 20,000 hours.

The presentation features:

- New capabilities in the DigitalClone Live software that predict early wear initiation in the main bearing raceways and rollers.
- How to understand the current health of the main bearing in a particular asset to mitigate damage prior to failure.
- How to reduce the cost of repair, currently ranging from $150K - $300K for each occurrence, and reduce the amount of downtime.

View the Webinar Recording at:

Published in: Engineering
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Main Bearing Wear Model

  1. 1. Main Bearing Wear Model
  2. 2. SentientScienceCorp.-Proprietary/PrivateLevel1 Host Natalie Hils Director, of Revenue Marketing +1 716.807.8655 Main Bearing Wear Model
  3. 3. SentientScienceCorp.-Proprietary/PrivateLevel1 Webinar Instructions Main Bearing Wear Model
  4. 4. © 2016 Sentient Science Corporation – Confidential & Proprietary DigitalClone® Material Science Differentiation ☑ Extend Life☑ Root Causes☑ Long-Term Forecast Main Bearing Wear Model
  5. 5. SentientScienceCorp.-Proprietary/PrivateLevel1 Sentient Science Customers Main Bearing Wear Model
  6. 6. SentientScienceCorp.-Proprietary/PrivateLevel1 Main Bearing Wear Model Main Bearing Wear Model 01 Main Bearing Business Challenge Understanding the cost and risk associated with main bearing failure. 02 Why Main Bearings Fail Outlining premature failure and common failure modes. 03 The Main Bearing Wear Model A deep dive into Sentient’s DigitalClone Live main bearing wear model. 04 The DigitalClone Solution Deploying DigitalClone to provide life extension actions.
  7. 7. SentientScienceCorp.-Proprietary/PrivateLevel1 Main Bearing Wear Model 01 Main Bearing Business Challenge Understanding the cost and risk associated with main bearing failure.
  8. 8. SentientScienceCorp.-Proprietary/PrivateLevel1 Why Investigate Main Bearings? 9 High Risk: Main bearing failure often transfers thrust loads to the gearbox, which can lead to catastrophic damage in the gearbox. High Cost: Main Bearing Replacement ranges from $150K - $300K. In extreme cases can cause upwards of $500K. Uncertainty: Alerted of main bearing failure after SCADA temperature alarms are going off. Supply Chain Control: Lack of control in supply chain due to no lead time for main bearing failures, causing unexpected downtime. Main Bearing Wear Model
  9. 9. SentientScienceCorp.-Proprietary/PrivateLevel1 Average Cost of Main Bearing Replacement Main Bearing Wear Model Cost Breakdown: Challenge: 1. Limited understanding of how many failures and where 2. Unaware of why the main bearing has failed Solution: 1. Life extension actions to avoid unexpected downtime and mitigate replacement costs Category Cost Downtime $10 -$30K Labor $15K - $35K Bearing Replacement $38K - $50K Main Shaft Repair $50 - $120K Average High Cost to Repair: $335K Average Low Cost to Repair: $190K
  10. 10. SentientScienceCorp.-Proprietary/PrivateLevel1 Presenter Dr. Arnab Ghosh Computational Material Scientist +1.765.588.7126 Main Bearing Wear Model
  11. 11. SentientScienceCorp.-Proprietary/PrivateLevel1 Main Bearing Wear Model Why Main Bearings Fail Outlining premature failure and common failure modes. 02
  12. 12. SentientScienceCorp.-Proprietary/PrivateLevel1 Premature Failure in Main Bearings Main Bearing Wear Model Three Point Configuration Spherical Roller Bearing INNER RACE, OUTER RACE, ROLLER CAGE, GUIDE RINGS High Radial load capacity Accommodates misalignments Require relatively high ratio of radial to axial load Increased sliding due to Heathcote slip Thrust Load Bearing Design Low RPM Loss of Lubrication Uneven Load Distribution Surface Roughness Lubricant Viscosity High Pressure High Sliding Low Lambda Low Lambda
  13. 13. SentientScienceCorp.-Proprietary/PrivateLevel1 Failure Modes in Main Bearings Main Bearing Wear Model Wear on Inner Race Micropitting Macropitting Spalling Abrasive Damage Roller, Cage Crack FAILURE PROGRESSION IN MAIN BEARINGS (manifests as early as 6 TO 10 YEARS) Sentient’s Main Bearing Failure model identifies early manifestation of damage in Main Bearings and provides recommendations to slow down damage progression, such that the Remaining Useful Life of the bearing can be extended Asperity Plastic Deformation Adhesive wear, Surface Fatigue Wear Bands on Inner Race Incubates in the vicinity of wear bands Cyclic shear stresses at shallow depths below the asperities Loss of geometry due to significant micropitting High contact stresses, edge loads Debris dents the race and rollers Rapidly evolves and accelerates damage Exceptions from the typical failure progression is also observed. White Structure Flaking (WSF) caused due to material impurities, hydrogen embrittlement, cage and guide ring wear leading to cage cracks, roller turning. The main bearings can fail as early as 4 to 5 years
  14. 14. SentientScienceCorp.-Proprietary/PrivateLevel1 Main Bearing Wear Model The Main Bearing Wear Model A deep dive into Sentient’s DigitalClone Live main bearing wear model. 03
  15. 15. SentientScienceCorp.-Proprietary/PrivateLevel1 Bearing Life Analysis – Conventional vs Prognostics 16 TRADITIONAL APPROACH – FEA/EMPIRICAL EQUATIONS SENTIENT APPROACH – MATERIAL BASED PROGNOSTICS Quick evaluations of design/material/lubricant change Cost effective and scalable solution Saves time and resources Large number of outputs generated in short time Assess effect of parameters which are experimentally difficult Deterministic Bearing Life Macroscale wear model (FEA) Wear Coefficient Conduct Experiments Probablistic Bearing Life (L10/L50) Wear Location/Dep th/Coefficient Contact Mechanics Lubrication Model Material/ Physics based Wear Model
  16. 16. SentientScienceCorp.-Proprietary/PrivateLevel1 Main Bearing Wear Model DCL Main Bearing Model Strategy WINDLOAD MODEL BEARING DYNAMICS MODEL WEAR MODEL SCADA data Turbulence Intensity Windspeed Wind Direction Loads on Main shaft Bearing Configuration Geometry Bearing Clearances Material Elastic modulus Main shaft RPM Contact Pressure Sliding Velocity Material : Hardness, Elastic Modulus, Ultimate Strength Surface topography : 𝑅 𝑞, 𝑅 𝑠𝑘, 𝑅 𝑘𝑢, 𝛽 𝑥, 𝛽 𝑦 Lubricant: Viscosity, PV Coeff Main Bearing Risk Ranking [MTOD] Critical locations Life Extension Action Wear Rate Wear Coefficient Inputs Outputs Local Contact Forces Sliding velocities Equivalent Radii Overturning Moments Thrust, Radial Load
  17. 17. SentientScienceCorp.-Proprietary/PrivateLevel1 Reverse Engineering – Geometry & Surface Topography Main Bearing Wear Model Sentient conducts an in-depth analysis of bearing samples received from the customer to enlist the input parameters required for physics-based models (Geometry, Surface topography, Hardness, Microstructure) Bearing Sample IR Roller OR 𝑹 𝒒 0.41 0.46 0.39 𝑹 𝒔𝒌 -0.93 -0.35 -1.32 𝑹 𝒌𝒖 4.28 3.25 5.23 𝜷 𝒙 23.93 25.54 12.43 𝜷 𝒚 533.51 136.45 9.60 Example of Surface Topography analysis Example of Geometry measurements on inner race of an asymmetrical SRB
  18. 18. SentientScienceCorp.-Proprietary/PrivateLevel1 Reverse Engineering – Micro-hardness, Microstructure Main Bearing Wear Model Microhardness comparison of five different bearing suppliers/designs Example of Microstructure Analysis (showing an inclusion and martensitic phase) A first hand comparison of different suppliers can be provided based on surface roughness, micro-hardness and material cleanliness. However, a more detailed assessment based on failure models is required to draw definitive conclusions.
  19. 19. SentientScienceCorp.-Proprietary/PrivateLevel1 Bearing Analysis Tool (BAT) Main Bearing Wear Model rotor side generator side • largely unloaded upwind rollers • intermittent contacts continuous loading of downwind rollers sliding velocity distribution load distribution Roller to Race contact details Input to Wear Model
  20. 20. SentientScienceCorp.-Proprietary/PrivateLevel1 Location of Wear/Micropitting Bands Main Bearing Wear Model 1 11 21 310 100 200 300 400 2 35 68 101 134 168 201 234 267 301 334 Wearmetric[N/s] 1 11 21 310 100 200 300 400 2 35 68 101 134 168 201 234 267 301 334 Wearmetric[N/s] Downwind Inner Race Downwind Outer Race Samples received by SentientKotzalas & Doll, 2010 UW UWDW DWDWEarly Stage Sentient’s main bearing model can predict the circumferential and axial location of wear on the main bearing. • The inner race is more likely to wear compared to the outer race • The upwind side is unworn while the downwind side is severely worn • Wear bands are seen as two distinct bands around the center of downwind side race or at the center depending on bearing design and the loads supported by the bearing Wear Peaks Wear Indicator = Pressure x Sliding Velocity
  21. 21. SentientScienceCorp.-Proprietary/PrivateLevel1 Outputs of Wear Model Main Bearing Wear Model Wear Rate (m/cycle) vs Pressure and misalignment Wear Coefficient vs Pressure and misalignment Example wear outputs from the analysis of a 230/600 SRB Main Bearing Wear evolution of interacting surfaces
  22. 22. SentientScienceCorp.-Proprietary/PrivateLevel1 Main Bearing Wear Model The DigitalClone Solution Deploying DigitalClone to provide life extension actions. 04
  23. 23. SentientScienceCorp.-Proprietary/PrivateLevel1 Effect of Surface Roughness Main Bearing Wear Model 𝑹 𝒒 = 𝟎. 𝟐 𝝁𝒎 𝑹 𝒒 = 𝟎. 𝟒 𝝁𝒎 Rq = 0.2 Rq = 0.4 5.39E-11 4.85E-09 4.66E-11 8.74E-09 0.00E+00 1.00E-09 2.00E-09 3.00E-09 4.00E-09 5.00E-09 6.00E-09 7.00E-09 8.00E-09 9.00E-09 1.00E-08 0.2 0.4 WEARRATE(M/CYCLE) ROUGHNESS Grease1 Grease2 Comparison of worn surfaces Contact Index (Red indicates asperity contact) Comparison of Roughness and Lubricant Contact Pressure Profiles 𝑹 𝒒 = 𝟎. 𝟒 𝝁𝒎 𝑹 𝒒 = 𝟎. 𝟐 𝝁𝒎 Surface Roughness has a major impact on the wear rate. Depending on lubricant viscosity and relative velocity, increased asperity contacts cause increase in wear rates
  24. 24. SentientScienceCorp.-Proprietary/PrivateLevel1 Effect of Hardness Main Bearing Wear Model H=2.5 GPa (24 HRC) WR = 2.26 x 10-6 m/cyc H=5 GPa (49 HRC) WR = 1.12 x 10-6 m/cyc H=7 GPa (60 HRC) WR = 8.16 x 10-7 m/cyc Hardness is an important property which affects wear rate. Wear Rate reduces with increasing hardness in agreement with experiments. y = 4E-10x2 - 7E-08x + 4E-06 R² = 0.9996 0.0E+00 5.0E-07 1.0E-06 1.5E-06 2.0E-06 2.5E-06 0 10 20 30 40 50 60 70 80 WearRate(m/cyc) Hardness (HRC) H=9 GPa (67 HRC) WR = 6.234 x 10-7 m/cyc
  25. 25. SentientScienceCorp.-Proprietary/PrivateLevel1 Effect of Temperature Main Bearing Wear Model 𝑇 = 70 𝑂 𝐶, 𝑊𝑅 = 6.971 𝑥 10−8 𝑚/𝑐𝑦𝑐 𝑇 = 50 𝑂 𝐶, 𝑊𝑅 = 3.791 𝑥 10−8 𝑚/𝑐𝑦𝑐 50 𝑂 𝐶 70 𝑂 𝐶 50 𝑂 𝐶 70 𝑂 𝐶 RPM = 20 RPM = 3 Temperature can increase due to dry contact and/or environmental conditions. A linear increase in temperature causes an exponential decrease in viscosity which can be detrimental to the two surfaces in contact. At higher RPMs, the contacts are more sensitive to temperature because the preexisting oil film is being degraded. At lower RPMs, the oil film is non- existent and therefore the contacts are less sensitive. Comparison of worn surfaces Contact index showing the interaction between RPM and temperature
  26. 26. SentientScienceCorp.-Proprietary/PrivateLevel1 Effect of Main Shaft RPM Main Bearing Wear Model RPM = 5 RPM = 15 FILM THICKNESS PROFILE ASPERITY CONTACTS ASPERITY CONTACTSFILM THICKNESS PROFILE 230/600 Bearing 𝜂 = 0.54,0.42,0.34,0.17 𝑃𝑎. 𝑠 𝜆 = ℎ (𝑅 𝑞1 2 +𝑅 𝑞2 2 ) 𝜆 < 1: Boundary Lubrication LAMBDA RATIO Lower main shaft RPMs (<5 RPM) can be very detrimental to raceway and rollers as the bearing operates in boundary lubrication regime.
  27. 27. SentientScienceCorp.-Proprietary/PrivateLevel1 Wear Modeling - Elastic Plastic Effects Main Bearing Wear Model 𝜎 𝜖 𝑆 𝑦 𝐸 𝑀 Although the maco-scale/theoretical contact pressure observed in bearings is maximum of 1.5 GPa, asperity interactions due to surface roughness cause contact pressure to reach as high as 3 to 5 GPa. To accommodate for such higher pressures, an elastic-plastic constituent model is required. Comparison of contact pressures observed for an elastic-plastic model vs purely elastic model ELASTIC 𝑆 𝑦 = 1.5 𝐺𝑃𝑎 (Unhardened Steel) 𝑆 𝑦 = 7𝐺𝑃𝑎 (Hardened Steel, 60 HRC) 𝑆 𝑦 = 9𝐺𝑃𝑎 (Hardened Steel, 65 HRC)
  28. 28. SentientScienceCorp.-Proprietary/PrivateLevel1 Wear Modeling – Variable Coefficient of Friction Main Bearing Wear Model 𝑅 𝑞 = 0.17𝜇𝑚, 𝜇 = 0.3571 – 0.408 𝑅 𝑞 = 0.0017𝜇𝑚, 𝜇 = 0.3571 – 0.3573 𝑅 𝑞 = 0.017𝜇𝑚, 𝜇 = 0.3571 – 0.3626 𝑅 𝑞 = 0.5𝜇𝑚, 𝜇 = 0.3571 – 0.559 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0 0.1 0.2 0.3 0.4 0.5 0.6 COF RMS Roughness COFmin COFmax DMT Coefficient of friction is not assumed to be a constant but changes according to the geometry of the contacting asperities and surface energy of the material based on the DMT model of adhesion Depiction of variable coefficient of friction at asperity contacts
  29. 29. SentientScienceCorp.-Proprietary/PrivateLevel1 Wear Modeling Considering the Effects of Microstructure Main Bearing Wear Model Frictional Stress on the surface (topography and adhesion) Sub-surface stress (microstructure) Crack Initiation Crack Propagation +
  30. 30. SentientScienceCorp.-Proprietary/PrivateLevel1 Main Bearing Deployed in DigitalClone Live FOOTER 32
  31. 31. SentientScienceCorp.-Proprietary/PrivateLevel1 Actions Provide Life Extension & Value Across All Health States Hot Oil Flush, Re-grease Major Component Exchange Axially Realign the Bearing Races Monitor & Manage Main Bearing Loads Recommendations to improve reliability and minimize downtime: 1. Perform grease sampling, flush (Hot Oil) and re-grease on an annual basis 1. Measure for changes in axial displacement on an annual basis and consider methods to axially re-align the bearing races. (The available methods to re-align the races of the mainshaft bearing include re-shimming the bearing and/or the housing and warrant further discussion) 2. Consider blade pitch and rotor thrust measurements and optimization methods to assure blade pitch consistency and rotor thrust values are not in excess of OEM specification (to minimize axial displacement forces)
  32. 32. SentientScienceCorp.-Proprietary/PrivateLevel1 Average Cost of Main Bearing Replacement/Savings Main Bearing Wear Model Cost Breakdown: Life Extension Actions: 1. Planning replacement during low wind season 2. Ensuring MB availability 3. Reducing MB repair costs 4. Ensuring replacement component has optimal life 5. Supplier trade-off and impact on asset life Category Cost % Savings Downtime $10 -$30K 0 - 75% Labor $15K - $35K 10 - 25% Bearing Replacement $38K - $50K 10 - 25% Main Shaft Repair $50 - $120K 5 - 15% Average High Cost to Repair: $335K Up to ~$62K Average Low Cost to Repair: $190K
  33. 33. SentientScienceCorp.-Proprietary/PrivateLevel1 Questions? Main Bearing Wear Model Natalie Hils Director, Revenue Marketing +1 716.807.8655 Dr. Arnab Ghosh Computational Material Scientist +1.765.588.7126