Blade production evaluation through damage assessment experience

Request for partnership with Benchmarking Center (ICB) at Fraunhofer IPK Berlin was wrapped up in order to define strategies for best practices on a management level of this sector. Dr. Holstein explained the core structural blade characteristics of turbine market leaders, common production technologies and its history and name the most frequently identified production related blade failures. His contribution was peppered with numerous updated inspection findings. Main difficulty in walking through the 5 step benchmarking model is the acquisition of the right industrial partners to join an open minded process to learn. I hear you say: This is impossible in wind business! But what the hell, I like this basic approach option.

"Siemens blade falls off at Europe's largest wind farm" - a so called top story in WINDPOWER MONTHLY

Articles from Windpower Monthly, formerly known as WindAlert, claim to present breaking top news from windy business. So does James Quilter in his article released on 23 March 2010. "This type of incident is exceptionally rare and highly unusual" the head of the operating company stated.
This might be his experience and right for him and his view of the picture.
My perception differs from this. As far as I know 2.3 MW Bonus or Siemens blades are built in a "closed-mold-shot" - a rare production technique, where dry textile and core material is loaded into the mold first and in a second step the two semi-shells are closed. After this is done in a third step infusion of resin is executed. So practically you have the choice of interleaved stacking and wrinkling textile material over a well sized PE core and then close under-shells and over-shell with the risk of clamped and jammed fibers. The other choice is to manage a somehow complicated "blow-up" effect (vac.-suction) after mold segments are closed and interlocked. How often do you open molds again because of leaks?
Now here I spread my wisdom of a 35 years of experience of blow-up production processes not only in wind industry. "You face a lot of technological problems and the risk of fiber-disorientation in terms of wrinkles gives repeatability not really a big chance".
So I do not believe in exceptionally rare incidents in this case, sorry. I am not saying that Murphy's law is a dictum (Anything that can go wrong will go wrong) but I claim: given a sufficiently long time, an event which is possible (non-zero probability) will almost surely take place.

Non destructive testing of blades before installation

Again questions arise if there is a way to test blades before installation or even after mounting with ultrasonics and/or infrared technology in order to quantify quality level or invisible or masked failures.

NDT techniques like the mentioned (US and IR) today (and I think for a long time in future) are not made to be used as a method for inspection of blades before installation in farms under construction. Both techniques have to be selected and adapted for the case of inspection one intends to do. IR has good features if you search for defects close to the surface. US have better potential if you want to look into the deep layers of structure. But non of these techniques can be used from root section to tip without dramatic change of parameters and system devices and measuring methods like frequencies, coupling heads, calibration and software setup. In other words: if you already know what kind of local fixed defect you are searching for and you already have tested and evaluated all these parameters for this case of testing, you have a slightly chance to be successful to find what you search for.

NDT like US and IR is not an all-purpose inspection feature and are to be chosen for very special assessment of blade defects. A day to day holistic blade quality inspection (inside and outside) like we do in many cases before installation is based on knowledge of the specific production process of the series production, the experience of noticed problems with this type of blade and the intuition of an old fox in the field of polymer chemistry, structural principles of blade design, aerodynamics, mass-dynamics of lightweight structures and last but not least independent standing of experts reference.

If you believe NDT blade testing is ready and in place for an universal monitoring of blade quality you may have been trapped by pseudo-scientific stories about fantastic new imaging techniques which is fiction for sure.

You ask for more information about the book project: tell the story of a case

First of all I would like to thank you all for your openness to contribute in one or the other way. I would very much appreciate if you could manage to describe a case where your technique or the concept you promoted was successful. This might be, for example, NDT in detecting rotor blade defects. There is some fascinating experience I know of, where ultrasound specialists have scanned sandwich sections with balsa core material where glass fibre layers were partially cut in some inexpressible stupid production process steps. If you don’t mind and if you are able to tell this story without embarrassing the involved parties, this way of illumination of the manuscript has my preference. That long winding canticle your competitors offer talking of putative ingenious equipment is boring to me. My intention is to act on fact boiling down the stories of this book.

I have some other "stories", or let us say "cases" in mind:
-> the peril of what we call greased lightning or
-> the putative efficiency of the 24 hours production cycle or
-> total blade quality through cascading qualified subsystem elements like embedded inserts, pultruded or prelaminated and consolidated structural sections and others.

What about your "story"? No wrinkles, collapsed flanges, tumbling webs ...
How do you feel about active load controlled single pitched blades?
What is the first thing you blade-brained guys have in mind if you go for 10 Megawatt machines?

Anyway - deadline of this call for contribution is coming up soon and I will get back to you offering a conference call for authors of the short list.

Take care - we do.

airborne inspections available

Encounter of my debut flight apparatus and its derelict

My personal flight career started on the rear seat of a C 172 with tail index D ELSE. This aircraft was owned by the Technical University of Berlin, astronautics and aeronautics branch, institute guidance and control and me at that time in the main study period to graduate for my engineer degree.
Its last mission was to deliver sky divers at my club at EDVH, the place out of which I operate my Airborne Blade Inspections.
Ashes to ashes and dust to dust.

About Oysters and Blades

If you want to check (without risk of poisoning yourself) the quality of an oyster, go for a cat and let her taste it –

– if she eats the oyster, it was good.

If you want to check (without any risk of observation faults) the quality of a rotor blade, go for an overload case –

– if the blade fails above the safe load value, then and only then you are sure, it was a good blade.

(old man’ saying with long beard, probably Professor emeritus)

I had a dream last night

And it does not seem that everything is all right. Long and winding roads were leading to this land of change where the wind was driving huge blades onshore and even more gigantic ones way out on sea providing turbines at its best. One can believe it is well done for our children and we always knew we should do it in the right way and this means to invest as much as we can to get off this oil and gas consuming way of life. Our personal capacity to invest is restricted. We invested our heart and brain and the wisdom grown was swallowed by affiliated groups of global players. So my dream ended with an apparent suicidal drop off the nacelle of a wind turbine. What I found this morning is that b.a.s.e. jumping is more naive and narcissistic than suicidal. Watch them jump, click here

What is essential to improve blade lifetime?

What is your opinion? How can we have best influence to improve blade lifetime?

:1: improve design?

:2: improve production technologies/quality management?

:3: improve maintenance and overhaul?

:4: improve terms of storage and transportation?

:5: improve inspection and blade accessment/on-site NDT method?

:6: improve meteorological prognosis?

:7: improve or develop realtime load measuring/managing and condition monitoring systems?

How do you feel we can improve - what is your experience? Do not hesitate to comment.

Frequently asked question about automatic blade inspections

These days I receive numerous mails and phone calls pointing out there is a new automatic blade inspection device available.

“Do you know this robotic system?” they ask. Yes, but …

From time to time you may find breaking news about putative brilliant inventions to solve the necessary blade inspections without the needs of a human inspector. Fantastic ideas are presented and spread out full-bodied across mainstream media. I don’t mind if this information is precise and do not keep quiet about the fact that this is based on academic style pipe dreams, chimeras to win project sponoring and not worth to deal with it. I even don’t mind the fact originators have to suffer in their upcoming insomnia which may develop to a full-grown nightmare when the truth was made public. It is for sure that top-ranking scientific institutes may suffer the loss of their reputation playing around like this.

Sorry, I don’t care.