A presentation from 2017 that has been updated with some new information on analysis techniques

1. New Sampling and Grease
Analysis Techniques to Diagnose
Blade Bearing Issues
Rich Wurzbach
MRG Labs
Presented June 18, 2017
Updated
March 5, 2021

2. Grease is Different
• Viscosity is the property of oil that sets the
lubricating film, and dictates how oil flows
• Grease is an oil (base + additives) with a
thickener
• Grease behavior is non-Newtonian; it is
designed to stay put in the machine
• Dynamically, grease will flow, but only very
close to the bearing/gear
• Sampling and analysis techniques for oil are
inadequate for grease

3. Blade Bearing Failures
• Blade bearing failures rank lower in
forced outage rate
• Blade bearing failure can be the
most catastrophic-failure to pitch
• $300,000-700,000 cost of repair
• Some operators experiencing high
failure rates (e.g., 8 failures in <50
turbines)
• Oil analysis techniques have lead to
undiagnosed failures

4. Undetected failures
• Root-Cause Failure Analysis showed
significant raceway and ball damage
• Routine grease analysis identified no
problem; latest sample was trending
down
• Sampling method was determined to be
inadequate; analysis technique limited to
small (<10micron) wear only

5. Danish Research
• Project initiated April 2015,with
DONG, Statkraft, COWI and GEUS
• Two Siemens 3.6MW, 107m rotor
bearings were recovered for testing

6. Project Drivers
• Sampling technique must adhere to
Theory of Sampling (TOS)
principles
• Samples must be readily obtainable
with tools carried uptower for
inservice sampling
• Analysis must be capable with small
sample lot size and be
representative of conditions
discovered upon disassembly

7. Sampling Development
• Access areas were limited to smaller holes
• Existing ASTM sampling standard device
too large
• “Grease Thief Slim” developed with
clearance of 8mm dia.
• Sample size of 1 gram consistent with TOS
principles in DS 3077 Denmark sampling
standard

8. 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.
Analysis Technique

9. Analysis Results
• FdM results did not correlate to
typical spectroscopy Fe ppm values
• Lab data from Denmark and US
correlated very well for FdM

10. Findings
• FdM (Ferrous Debris) effective on
larger wear, repeatable across labs
• Damage confined to two small areas
on raceway; representative samples
obtained independent of position
• Where used, grease cups give a
time-resolved picture of wear
• Both moisture content and wear
levels were repeatable and
representative

11. Other Research
• Main Bearing grease
sampling and analysis
project with DONG &
Vattenfall, published in
2013
• EPRI Report #1020247
“Effective Grease
Practices” for sampling
in gearbox enclosure
and FdM vs Elemental
Spectroscopy

12. Grease Standards
• ASTM D7718: Obtaining in-service
grease samples
• ASTM D7918: Die Extrusion and
integrated tester for inservice
grease analysis
• AWEA Recommended Practices RP
812-814 for sampling
• AWEA Recommended Practice 815
for grease analysis

13. Use of the Grease Thief

14. Use of Grease Thief
• Confirmed in two research projects
with DONG, Vattenfall and Statkraft
• Kits for sampling wind turbine
bearings, including “Slim” kit for
some blade bearings, utilized
worldwide, ASTM standard
compliant
• Thousands of samples analyzed
from main, blade, generator and
yaw

15. Analysis beyond Wear
• Reliable monitoring important in
detecting active abnormal wear
• Wear is lagging indicator; leading
indicators include oxidation,
consistency and contaminant
monitoring

16. Monitoring Consistency
• Grease leaking onto blades:
perception problem & degradation
• Most common causes: grease
breakdown & mixing

17. Leading indicators
• Moisture is accurate to ppm levels
using humidity sensor (Vapor Pro)
• Consistency by Die Extrusion can
predict loss of grease (blade
staining and future wear impact)
• Particulate contaminants initiate
fatigue and abrasion
• Anti-oxidant monitoring allows
optimal grease replenishment

18. Low-cost grease screening
• Fdm (wear), Colorimetry can be
applied to screen samples for
further analysis
• Statistical analysis and meta-data
used to identify action levels for
advanced analysis and further
inspections
• 2021 Update: FerroQ device
enhances capabilities of FdM+ to
better represent heterogenous
particulate distribution in samples

19. Wear Level (FdM) stats

20. Silicon Levels

21. Die Extrusion Index

22. Anti-Oxidant Levels

23. Grease Analysis Goals
• Find a reliable and representative way to
access grease from the critical components
in the wind turbine drivetrain
• Create cost-effective methods to screen
large numbers of samples with a very small
sample size
• Develop advanced analysis tools to apply to
outlier results to pinpoint failure causes and
provide lower-cost proactive options
• Utilize proven and standardized techniques
for sampling and analysis

24. Grease Monitoring Results
• Adding screening grease analysis to
uptower climbs <$30 bearing
• Screen samples for more advanced
analysis, include leading indicators
• Know about latent problems for
efficient scheduling of actions
• Lower cost uptower repairs
including grease flushing
• Extending blade bearing life