Wind turbine lubricant sampling, flushing, and analysis

Wind Turbine Lubricant Monitoring
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© 2014 Maintenance Reliability Group, LLC. All rights reserved. 1

Strategies for Wind Lubricant
Sampling and Analysis
• Experience with additive sludging in gearbox applications
• Flushing strategies for wind gearbox for lubricant
changeover
• Retrofit for improved gearbox sampling options
• Drivetrain grease sampling
– Main Bearings
– Pitch Bearings
– Generator and Yaw
• Danish wind industry research results
• Grease Analysis
• Case Studies

Variable moisture levels in traditional gearbox
oil

Moisture in Gearbox oil

Gearbox oil particulate-conclusions
• Sulfur is an element found commonly in EP additives, and
seen in this concentrations it is unlikely to be from an
environmental source.
• The additive package from the lubricant product used in
these gearboxes is contributing to the formation of small
crystal particles during exposure to the real operating
conditions seen in this application, including varying water
concentrations.
• Consider reevaluating the lubricant choice for this
application or improving control of the water concentration,
which may affect the stability of the additives in the current
product.

Flushing gearbox oil for changeover
• Location of gearbox uptower makes flushing difficult
• Importance of minimizing oil carryover during new product
changeover
• Specialized equipment and processes for maximum
flushing effectiveness.
Image from http://www.sageoilvac.com/

Proper Flushing
• Use of flushing agent
• Heating of oil to lower viscosity and improve
flush
• Removal of access covers and use of
extensions to direct flow and suction
• Flushing and jetting planetary and other
sections
• Sampling and analysis to confirm flushing
effectiveness

Sampling Fitting installation
• Angle of gearbox may require different placement
of sampling fitting
• Retrofit of drain with pitot tube to avoid “crud trap”
• Multiple samples to address main & planet gear
sections
Image from http://www.nrel.gov/

GGrreeaassee SSaammpplliinngg TToooollss
10

SSaammpplliinngg TTeecchhnniiqquueess
MOV Gearbox
1 2 3 4 5
Electric Motor Bearing
1 2 3 4 5
Pillow Block Bearing
1 2 3 4
11

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
12

Other Sampling Locations
• Pitch bearing grease
bellows
• Can be removed and
sampled in lab
• Grease Thief or spatula
used to sample drain
path behind bellows trap
13

Other Sample Locations
• Generator bearings for install of Grease Thief
• Use of T-handle to position for sample in active zone
14

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
15

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.
16

Grease Thief Analyzer To Measure Consistency
with 1 Gram

Grease Thief Die Extrusion and Anti-Oxidant
Testing

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

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

Linear Sweep Voltammetry and FTIR
•RULER test establishes anti-oxidant
levels in new grease
•Purged grease levels show residual
anti-oxidants; can be used to adjust
greasing frequencies, indicate
abnormal oxidation stressors
•FTIR can show oxidation, presence
of grease thickener type, organic
contaminants
22

Optical Spectroscopy
•Optical spectroscopy quantifies the appearance of grease
•Grease aging, contaminants, mixtures, chemometrics
23

AAnnaallyyttiiccaall FFeerrrrooggrraapphhyy
seen in white reflected and green
transmitted light, to show normal
presentation of entry deposit
particulate.
24
The 100x ferrogram is
The 100x ferrogram is taken in
crossed polarized light. Resulting
illuminated particles are crystalline
debris, typically indicative or dirt or
other abrasive contaminants.

Wear Levels Across a Fleet of
Wind Turbines-USA
25

Wind Turbine grease sampling and
analysis
• 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
• Rich Wurzbach, MRG Labs, inventor of Grease Thief
• 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

• Fundamental Sampling Principle
–Using the Grease Thief
• Representative sampling
–Thorough characterization of the heterogeneity of grease
in main bearings

Test parameters of Grease
• For the heterogeneity characterization of grease in main
bearings of wind turbines the following parameters were
used:
–Consistency and flow characteristics
–Ferromagnetic iron (Hall-effect sensor)
–Wear metals
–Particle characterization (size & distribution)
–Residual oil in grease
–Antioxidants

Heterogeneity characterization –
Ferromagnetic iron
• Sampling of grease while draining the main bearing
through the drain plug
• 27 increments collected (each sample approximately 20
grams)
20000
18000
16000
14000
12000
On site sampling
10000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
Sample no
Iron (FdM Plus)

3D-sampling, OEM repair shop

3-D Sampling, OEM repair shop

3-D sampling

Ferrous debris method comparison
• 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

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

Comparison of grease consistency (by Grease
Thief Index) of different sampling procedures

Conclusions from 3-D sampling
OEM repair shop
• Analysis of analytical results reveal no statistically significant
differences between the 3D sample arrays extracted
• The grease is thoroughly well mixed
• Standard SWP bearing samples falls fully within the span of the 3D
experimental results. This also apply to samples taken close to
inspection cover
• It is concluded that standard bearing sampling (for the bearing
investigated) results in valid characterization of the grease.

Phase 2 – Field trials
• Grease analysis parameter
–Iron using a ferro-magnetic debris Monitor (fdM, "Hall-monitor").
Measures all ferro-magnetic debris/particles in
the grease irrespective of size
–Iron (and other wear elements) using Rotating Disc
Electrode Atomic Emission Spectrometry (RDE). This
method only detects particle < 6-8 μm.
–Characterization of wear particles using optical
microscopy
–Moisture
–Consistency
–Anti-oxidants using RULER-technique

Trends for fdM-Fe, main bearings

Trends of moisture in wind turbine bearings
Grease type: Klüberplex BEM 41 141
•Thickener: complex Li
•Base oil: Mineral oil & PAO
•Viscosity @ 40C: 130 cSt
•NLGI-class: 2

Trends of moisture in bearings
Grease type: SKF LGWM1
•Thickener: Li
•Base oil: Mineral oil
•Viscosity @ 40C: 200 cSt
•NLGI-class: 1

Linear Sweep Voltammetry and FTIR
•RULER test establishes anti-oxidant
levels in new grease
•Purged grease levels show residual
anti-oxidants; can be used to adjust
greasing frequencies, indicate
abnormal oxidation stressors
•FTIR can show oxidation, presence of
grease thickener type, organic
contaminants
41

Other projects: US Wind turbines
Wear Levels in Comparison
42

Wear levels in Robot fleet-comparison

Conclusions
• Grease in the area accessed by the Grease Thief is thoroughly
well mixed and comparable to the samples taken in the shop
between the rollers
• Bearings removed from service following field sampling and
analysis trials corresponded precisely to the predicted condition
when disassembled and characterized
• In-service grease analysis complements condition monitoring
systems (vibration analysis) and is particularly useful in slow-speed
shafts where some vibration trends lag grease condition
and wear particle indications
• Grease sampling can be cost-effectively deployed during
periodic uptower maintenance visits with easily understood and
utilized sampling kits and tools
• Early detection of abnormal conditions can be sometimes
rectified uptower (grease flushing, relubrication, etc)
substantially reducing the event cost and risk of failure

Wind turbine lubricant sampling, flushing, and analysis

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