Dr. Carsten Hein Westergaard: 2013 Sandia National Laboratoies Wind Plant Reliability Workshop

Together, we make your blades stronger

Bladena’s new simple retrofit for increased reliability and repair of the trailing edge bonds

Dr. Carsten Hein WestergaardPresident, NextraTEC Inc.Board member, Bladena ApsBladena [email protected]

Sandia National LaboratoriesWind Reliability workshop 2013 August 13 – 14, 2013, Albuquerque

Bladena US based service partners

mailto:[email protected]


Agenda

• Short introduction to Bladena• Trailing edge damages• Effect of D-string• Pilot projects• Installation• Recommendations• Future projects

©Bladena 2013


• Spin out from Danish Technical University, established 2011

• Seven patents making blades stronger and more durable developed at RISØ (DTU)

• Technology based on 10+ years of research & experience at DTU

• Based in Denmark

• Two Strong Service Partners in North America

.

©Bladena 2013

D-StringSimply effective!

Bladena – the company

Together, we make your blade stronger


Catastrophic trailing edge failures, starts small

• Repairs can be costly and does not eliminate the need for larger fleet repairs or replacement at a later stage

• Significant risk for catastrophic failure remains, when the small cracks propagate unnoticed

Unrepaired cracks lead to de-bonding Blade broken near max chord Trailing edge splitting

©Bladena 2013


Root causes of trailing edge cracks are many

• Design system, verification system and standards applied: – Non accommodating for critical errors; for example; lack of combined loads

verification during testing– Exclusion of important failure mode combinations; for example, breathing of panels

which leads to accelerated peeling

• Manufacturing deficiencies:– Tolerances, random and/or systematic; for example, incorrect application of fibers– Quality deviations; for example, application of glue or curing of glue bond deviations

• Unforeseen blade loading events:– Systematic; for example, by failure of sensors– Random occurrence; for example, induced by extreme weather events

• Service methods– It is very difficult to detect hairline cracks, service methods can influence the root

cause of failure mode development

• Almost always, failure is a sequence or combination of these root causes

©Bladena 2013


Blade panel deformations induced by edgewise gravity induced loads during any operation of any wind turbine makes the panels breath

©Bladena 2013

Panel breathing


Panel breathing and peel stress

• Peel stresses at the bond lines, peels the adhesive from the shells by stress concentration

• Until peeling occurs, the stresses will create surface tension right at the trailing edge bond line eventually developing into (hairline) cracks

• Trailing edge bonds are designed for shear stress, which occurs from blade bending during wind loading.

• Peel stress is added to the shear stress

©Bladena 2013


Panel breathing accelerates crack propagation through peeling and necessitates regular inspections and preventative repairs

Hairline crack found at inspection

Uptower repairs of trailing edge cracks

©Bladena 2013

It starts with hairline cracks


D-String reduces breathing(Deformation Limiting String)

Typically, ten strings spaced along the trailing edge limits the panel breathing, sufficiently

©Bladena 2013


The D-String limits the outward panels from breathing, hence reducing peel stresses in the bond lines

©Bladena 2013

Without D-Strings With D-Strings installed

Typical 10 D-Strings installed in max chord area

Typical 10 D-Strings per blade

Finite element model prepared for a specific blade sized by calibration with site measurements of the in-situ panel deformations


First demonstration project – rope access installation

Installed in Denmark in January 2013.

©Bladena 2013


First US Pilot Project

First pilot under installation in Texas

Platform access

Partners:

©Bladena 2013


First step: Size string by one time measurement of panel deformationCurrently three blades are documented with D-string implantation

For other blades:A. Blade Survey to establish key dimensions of

blade, and determine needs for step B&CB. Pilot, where loads and deformation levels are

measured and installation methods are testedC. If needed: panel testing to establish panel

strengthD. Feasibility study establishes:

Suitable strength and fatigue life of panel and D-String

FEM simulation Verify the effect of the D-String Variations from a standard installation

©Bladena 2013

Step B: Measurements with temporary installed sensor from rope access, typically there are three places used to qualify D-string installation


Estimating impact through measurements

Without D-Strings

With D-Strings installedTest on turbine, results from

temporarily installed sensors

Resulting analysis

©Bladena 2013


Easy Installation from platform or rope access

©Bladena 2013


Static safety against damage to blade skin from D-string

• A comprehensive test program of the D-String has been performed at DTU, demonstrating safety margins against damage to the supporting blade skin foam sandwich

• A string (fuse) is included for well defined protection at breaking point 1.5kN

• Field test has shown measured string loads are very low, with peaks up to 0.4kN during emergency stops

©Bladena 2013


Fatigue safety against damage to blade skin from D-string

Measured extreme event

Typical normal load situation

Fuse

©Bladena 2013


Increased reliability based on measured data• Based on the in-situ measured deformation and stress, the lifetime stress

reduction can be calculated. By using Palgren-Miners, rule the life extension can be calculated

• In the pilot projects, the measured improvement from the D-string is a 97% reduction in stress. This can be translated to: “If the blade was prone to cracks after 4 years, the life expectancy would be expanded to 40 years, i.e. a factor 10 in lifetime”

Without D-Strings

With D-Strings installed

Resulting analysis based on measurements

©Bladena 2013


Preventive or reactive use ?Age Frequency of

damageAction Result of D-string use

ReactiveA few damagedblade(s)

1 to 4 years

One time isolated event(s)

Add D-string to blade repair

• Avoid scrap• Additional safety in repair• “New” healthy blades in

inventory• Direct savings

ProactiveMultiple damaged blades

2 to 10 years

Multiple events, more than 1/200 rotors damagedper year

Install D-string fleet wide on turbine type, preferably combined with blade inspection

• Life extension through reduced stress in hairline cracks

• Life extension far beyond 20 years for un-cracked blades

• Preventive savings by reduced (eliminated) failure rate

Preventive N/A No damage documented

Install D-string fleet wide on turbine type

• Strongly reduced sensitivity to manufacturing deficiencies or any other potential weaknesses

• Statistical mean value moved far beyond 20 year life, so “no failures” will occur

• Stronger blades

Improved new built blades

N/A Statistical variance of design

Include D-string in new blade build

©Bladena 2013


Next project: Cross-sectional shear distortion was observed in the field

Measurements on a MW turbine showed cross-sectional shear distortion under normal operation

Cross section shear, adds loading to the leading edge bond, and possible additional failures

©Bladena 2013


Three new combined technologies making blades stronger in the field

1) D-String2) X-Stiffener3) Floor

1) Stronger trailing edges 2) Stronger leading edges3) Strong root panels less prone to buckling

©Bladena 2013

Together, we make your blades stronger ©Bladena 2013

Thank you

Dr. Carsten Hein Westergaard

President, NextraTEC Inc.

Board member, Bladena ApsBladena representative

[email protected]



mailto:[email protected]

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Dr. Carsten Hein Westergaard: 2013 Sandia National Laboratoies Wind Plant Reliability Workshop