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DNV GL © 2014 27 August 2014 SAFER, SMARTER, GREENER
27 August 2014
Matt Malkin and Dayton Griffin
ENERGY
Blade Reliability Trends
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A 4-year update to Lessons Learned from Recent Blade Failures
2014 Sandia Blade Workshop

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DNV GL © 2014 27 August 2014
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The 2014 Update: Motivation
Blade failures are rare, potentially high consequence events, and they
continue to occur.
We want to move blades to the distant background as a risk item for
turbine operations.
Site suitability analysis vs. failure investigation:
Are we missing something?
In short: Lessons learned in 2010 still generally hold true… with a few
specific updates.

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DNV GL © 2014 27 August 2014
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Lessons Learned: 2014 Updates
Cause of blade
failure
Manufacturing defect
Progressive damage
Distortion of blade
sections
Excessive loads due
to system dynamics
Excessive loads due
to environmental
conditions
Wrinkles
Bonds
Lots of touch labor
Ramps in production rates
Quality of quality systems
Pushing process-related limits
Ultrasonic NDT has been in use for >10 years
”Bulging/breathing” effect, mostly in root transition region, due to blade
loading
Lightning moves up in priority. Lightning damage continues, even with
updates to LPS designs and retrofits.
Low specific ratings and finely tuned turbine siting.
Resonant phenomena: analytical needs push the limits of current
capability to accurately capture effects of vortex-induced vibration
(parked or idling rotor)
Initiating from transport/handling damage, lightning strikes

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DNV GL © 2014 27 August 2014
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Lessons Learned: 2014 Updates
Cause of blade
failure
Examples of risk mitigants
Blades at existing wind
projects
New production blades
Near term Long term
Manufacturing defect
Inspection: Visual, NDI
Ground-based NDI
Preventive reinforcement
Access to turbine
controls
LPS retrofits
Re-assess site conditions
Manufacturing monitoring
Improved acceptance
criteria
Automation
Non-destructive
inspection
Wider use of
building-block
design/test
approach
Damage tolerant
design methods
Targeted
manufacturing
changes from
assessment of cost
of poor quality
Application of
IEC 61400-5
Progressive damage Condition monitoring
Distortion of blade
sections
Nonlinear FEA
Comprehensive structural
verification
Excessive loads due
to system dynamics
Improved controls
Improved analytical tools
Excessive loads due
to environmental
conditions
Improved site inflow data,
Improved LPS design and
increased testing

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DNV GL © 2014 27 August 2014
Conclusion: Challenges for this Community
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1. Eliminate the effect of manufacturing defects on blade failure rates.
• Assess cost of poor quality; make targeted improvements.
• “Gold in the mine” – dig in the right places. Avoidance of wrinkles
and avoidance of understrength bonds are key areas.
• New materials? New processes? Process compatibility? More
automation?
• All must be at the right costs, non-recurring and recurring.
2. Improve non-destructive inspection, particularly for adhesive bonds.
• Existing projects: Ground-based.
• New production: Proof testing or destructive testing.
3. Improve analytical tools
• For site suitability assessments.
• For resonant phenomena.
4. Improve lightning protection system design (standards), and testing.

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DNV GL © 2014 27 August 2014
SAFER, SMARTER, GREENER
www.dnvgl.com
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Matt Malkin
matthew.malkin@dnvgl.com
206-387-4296