Grease Sampling and Analysis of Wind Blade and Main Bearings

Rich Wurzbach

MRG Labs

York, Pennsylvania, USA

Bearing Failure Impact

• Main/Blade bearings are large, slow

• Unusual and unpredictable loading patterns

• Slow speeds make vibration analysisdiagnosis difficult for early signs of bearing wear, root-causes

• Single bearing failure can cost~$200,000 for crane, downtime, replacment

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 ResearchInstitute (EPRI) and Danish Offshore Wind Research Team establish strategies and tools

Grease Sampling Tools

Sampler Development• EPRI project established need for

active and passive sampling devices

• Capture purged samples usingmachine threads

• Insert sampling device into machine to core sample at select depth

• Test stands used to validate efficiencyof capturing live zone samples

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)

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

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

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-lubersand winding insulation damage captured in grease

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

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Analysis Techniques

Sample is received. fdM+ is runDie 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.

Grease Thief Analyzer To Measure Consistency with 1 Gram

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

Optical Spectroscopy

•Optical spectroscopy quantifies the appearance of grease

•Grease aging, contaminants, mixtures, chemometrics

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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

• Fundamental Sampling Principle–Using the Grease Thief

• Representative sampling–Thorough characterization of the heterogeneity of grease in main

bearings

Wind Turbine grease sampling & analysis

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

3-D sampling

• 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

Comparison of ferrous levels from different sampling procedures

“SWP” is Siemens Work Practice: standard method for grease

sampling of disassembled bearing in the shop

Trends of moisture in bearings

0

100

200

300

400

500

600

700

800

900

Mo

istu

re, p

pm

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

Wear Levels Across a Fleet of Turbines

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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

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

Outlier Wear Image

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

Outlier Colorimetry and Die Extrusion

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

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 lowviscosity protection for cage sliding, or additive corrosion

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

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