A presentation made at the STLE Wind II session in Dallas Texas, USA, May 20, 2015

1. Grease Sampling and Analysis of
Wind Blade and Main Bearings
Rich Wurzbach
MRG Labs
York, Pennsylvania, USA

2. Bearing Failure Impact
• Main/Blade bearings are large, slow
• Unusual and unpredictable loading
patterns
• Slow speeds make vibration analysis
diagnosis difficult for early signs of
bearing wear, root-causes
• Single bearing failure can cost
~$200,000 for crane, downtime,
replacment

3. Grease Sampling
• Grease sampling historically difficult
• Capturing live-zone samples presents challenge
• Typical large sample sizes required difficult to
obtain
• ASTM D7718 presents new tools, methods
• Research projects at Electric Power Research
Institute (EPRI) and Danish Offshore Wind
Research Team establish strategies and tools

4. Grease Sampling Tools

5. Sampler Development
• EPRI project established need for
active and passive sampling devices
• Capture purged samples using
machine threads
• Insert sampling device into machine
to core sample at select depth
• Test stands used to validate efficiency
of capturing live zone samples

6. New Challenges in Grease Sampling
• Blade bearing access limited
• Access opening often smaller than sampler diameter
• Blade bearing research leads to slim version, dia. drops
from 0.50in (13mm) to 0.28in (7mm)

7. Main Bearing Sampling
• Grease flow dependent
on temperature, bearing
movement
• Grease Thief & T-handle
used to capture flowing
grease
• Revised T-handle
developed for Denmark
Off-shore Wind Research
Project

8. Blade Bearing Sampling
• Three Blade Bearings per wind turbine
• Can be double-row ball or tapered roller bearings
• Grease is typically delivered through autoluber lines
• Expelled grease captured in bellows or containers
• Containers can be harvested for sampling
• Slim sampler may be used to obtain live zone sampler
through drain line

9. Other Sampling Locations
• Generator bearings for
install of Grease Thief
• Use of T-handle to
position for sample in
active zone
• Sampling generator
bearings has discovered
inoperable auto-lubers
and winding insulation
damage captured in
grease

10. Types of Grease Analysis
• Performance
– Tribological, oxidation resistance, etc.
• Quality Control
– Batch conformation, Penetration value
• Failure Analysis
• In-service testing
– Equipment wear condition
– Contamination of grease
– Consistency changes
– Oxidation condition
10

11. Analysis Techniques
Sample is received. fdM+ is run Die extrusion is performed and substrate is made
Two strips are used to make
a dilution to run RDE/ICP.
One Strip is used
for FT-IR.
One Strip is Dissolved in Green
RULER solution to run RULER.

12. Grease Thief Analyzer To Measure
Consistency with 1 Gram

13. Die extrusion and sample preparation
•Extrusion of the grease at varying
rates
•Load cell response used to
measure flow and shear
characteristics of grease
•Compared to new fresh grease
13

14. Grease Consistency – Back Bearings in a USA
Wind Farm: Outliers in Yellow

15. Grease Consistency – Front Bearings in a USA
Wind Farm: Outliers in Yellow

16. Optical Spectroscopy
•Optical spectroscopy quantifies the appearance of grease
•Grease aging, contaminants, mixtures, chemometrics
16

17. 17
The 100x ferrogram is
seen in white reflected and green
transmitted light, to show normal
presentation of entry deposit
particulate.
The 100x ferrogram is taken in
crossed polarized light. Resulting
illuminated particles are crystalline
debris, typically indicative or dirt or
other abrasive contaminants.
Analytical Ferrography

18. • Fundamental Sampling Principle
–Using the Grease Thief
• Representative sampling
–Thorough characterization of the heterogeneity of grease in main
bearings
Wind Turbine grease sampling & analysis

19. Wind Main Bearing grease sampling
• 2-year project conducted with DONG Energy and Vattenfall,
two largest offshore wind operators in the world
• Dr. Kim Esbensen, internationally recognized expert in Theory
of Sampling (TOS), Denmark
• Systematic evaluation of grease heterogeneity, sampling
methodology, and analysis validity and repeatability for wind
turbine main bearings in on-shore and off-shore applications
• Results published at OilDoc, LUBMAT, and AWEA
• Findings: Samples cored by T-handle from drain access equally
representative to disassembly and extraction

20. 3-D sampling

21. • Analysis of iron (Fe) using a
analytical method which only
detects particles < 6 µm
• Note, this method gives iron
concentration from 50 to 170 ppm
› Analysis of ALL ferrous
magnetic particles irrespective
of size (Hall-technique).
› Note, this method gives iron
concentration from 30.000 to
40.000 ppm
Ferrous debris method comparison

22. Comparison of ferrous levels from different sampling
procedures
“SWP” is Siemens Work Practice: standard method for grease
sampling of disassembled bearing in the shop

23. Trends of moisture in bearings
0
100
200
300
400
500
600
700
800
900
Moisture,ppm
314 Front
314 Rear
319 Front
319 Rear
Grease type: SKF LGWM1
• Thickener: Li
• Base oil: Mineral oil
• Viscosity @ 40C: 200 cSt
• NLGI-class: 1

24. Wear Levels Across a Fleet of Turbines
24

25. Blade Bearing Sampling Research
• Current project underway with DONG Energy
and Statkraft, offshore wind operators in
northern Europe
• Development of specialized sampling tools to
access grease through drain holes
• Samples taken sequentially from catch drains
to asses time-resolved trends in grease/wear
condition

26. Blade Bearing Wear
• Ferrous debris levels typically higher than main bearings
• Different installations have higher or lower typical values
• May be due to environment, load or maintenance practices

27. Outlier Wear Image

28. Blade Bearing Consistency
• Hardening or softening a function of working, environment,
contaminants
• Criteria is enveloped around new grease values
• Most samples are satisfactory, some clear outliers

29. Outlier Colorimetry and Die Extrusion

30. Blade Bearing Cu Levels
• Cu primarily cage material, but could be a contaminant
• Levels normally very low, low trigger criteria for further test
• Analytical ferrography can determine type, size and source

31. Outlier Cu and Al with mixing
• Cu levels typically <10ppm, this sample >100ppm
• Very high Al values related to grease thickener
• RULER additives and FTIR confirm grease mixing, possible low
viscosity protection for cage sliding, or additive corrosion

32. Conclusions
• Grease sampling methods well established for wind applications
• ASTM D7718 and AWEA Recommended Practices outline tools
and techniques for representative samples
• Research in main bearing and pitch bearing grease analysis
support methodology
• Total cost per sample <$200, unexpected loss of single bearing
across fleet cost $200,000
• Early detection of abnormal conditions can be sometimes
rectified uptower (grease flushing, relubrication, etc)
substantially reducing the event cost and risk of failure

33. Grease Thief Technology Labs
SGS Herguth, Vallejo, CA, USA
Tekniker, Bilbao, Spain
Runningland, Shanghai, China
York College of Pennsylvania, USA
MRG Labs, York, PA, USA