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Technical Discussions
Nanaji
NDT Inspector, ASNT level 2
India, Joined Oct 2014, 1

Nanaji

NDT Inspector, ASNT level 2
India,
Joined Oct 2014
1
04:17 Mar-04-2018
What is Suitable Method for inspection of wind turbine blades

Hello,
I am new to composite UT.
What is the best Suitable Method for wind turbine blades ultrasonic testing

 
 Reply 
 
Simon Amallraja
Simon Amallraja
06:04 Mar-06-2018
Re: What is Suitable Method for inspection of wind turbine blades
In Reply to Nanaji at 04:17 Mar-04-2018 (Opening).

We recommend Shearography for WMB applications. Contact us for more info.

 
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Dan
Engineering,
SimpleNDT, Brazil, Joined Mar 2018, 5

Dan

Engineering,
SimpleNDT,
Brazil,
Joined Mar 2018
5
19:47 Mar-06-2018
Re: What is Suitable Method for inspection of wind turbine blades
In Reply to Nanaji at 04:17 Mar-04-2018 (Opening).

You will mainly use straight beam with composite specific probes, like m2008 from Panametrics. Other low frequence probes can be tested, usually within 0.5 to 1MHz

Angle beam inspection can only be performed on very specific cases and the probes are not the same as used for welds (as the composite is made of fiber layers, the velocity on the layer/fiber direction is much higher so critical angle is something like 8 degrees)

Equipment should have square wave function so the wave have more penetration power.

You will be limited to find bonding failures, delamination and other defects that are parallel to the surface (layer direction), which means that cracks will not be detected but you can always add visual inspection for this.

Signal is a little bit messy because of the interface between layers, specially if there are hand layup on the area, which many times make the inspection impossible to be done. Many times you will have some intermediate signal that will not mean anything, and usually to be considered something you will have an intermediate signal plus completely backwall loss but this need to be validated as depends on the manufacturing process and material quality. Dont expect to be able to precisely identify small defects (probably >25mm).

You can not inspect where there is core.

Best Regards,

Dan

 
 Reply 
 
Dan
Engineering,
SimpleNDT, Brazil, Joined Mar 2018, 5

Dan

Engineering,
SimpleNDT,
Brazil,
Joined Mar 2018
5
19:51 Mar-06-2018
Re: What is Suitable Method for inspection of wind turbine blades
In Reply to Dan at 19:47 Mar-06-2018 .

Just one thing. When I refer issues to crack detection is only when they are perpendicular to beam...you can obviously use UT to detect cracks that are perpendicular for example when it happens on the root or shear web bonding.

 
 Reply 
 
Joe Buckley
Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT, United Kingdom, Joined Oct 1999, 528

Joe Buckley

Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT,
United Kingdom,
Joined Oct 1999
528
21:54 Mar-06-2018
Re: What is Suitable Method for inspection of wind turbine blades
In Reply to Nanaji at 04:17 Mar-04-2018 (Opening).

As Simon says Shearography can be useful, or low frequency ultrasonics.

You might find the paper I gave at the last European conference interesting. I'm no longer with Sonatest, but I understand this technology is now fairly mature.

http://www.ndt.net/events/ECNDT2014/app/content/Paper/275_Buckley.pdf




 
 Reply 
 
J.B.
J.B.
18:48 Mar-14-2018
Re: What is Suitable Method for inspection of wind turbine blades
In Reply to Joe Buckley at 21:54 Mar-06-2018 .

zoom image

Sandia's table about suitable NDT-Methods

I personally would be careful to suggest Shearography (with a background of more than 25 years of R&D in this field since about 1990 for aerospace use) - the physics limit the defect detectability in thick FRP structures; especially in the rear half of the structure delaminations cannot be seen as the deformation after heat loading does not show on the front but on the back, as the stiffness is lower there in that case - so no chance to get them. Maybe vacuum loading or vibration loading (Refer to ISISYS - http://www.isi-sys.com/shearography-systems/ ) could deliver better results.
I would recommend PAUT.
SANDIA labs have conducted large POD studies even for wind turbine NDT (Their NDT POD Data collections for aerospace are already famous) – I recommend the following papers
• http://energy.sandia.gov/sandia-wind-turbine-blade-flaw-detection-experiments-in-denmark/
• http://energy.sandia.gov/wp-content/gallery/uploads/2A-C-4-Roach-SAND2012-5436C1.pdf
• https://www.osti.gov/servlets/purl/1327862
• https://www.osti.gov/servlets/purl/1242772
• https://www.osti.gov/servlets/purl/1244426
• http://windpower.sandia.gov/2010BladeWorkshop/PDFs/3-C-3-Roach.pdf
• http://energyworkshops.sandia.gov/wind-workshops/2016-wind-turbine-blade-workshop/
• http://energyworkshops.sandia.gov/wind-workshops/2014-wind-plant-reliability-workshop/
• Some more might be found on Slideshare:
2014 Sandia Wind Turbine Blade Workshop- Roach & Rice - https://www.slideshare.net/sandiaecis/2014-sandia-wind-turbine-blade-workshop-roach-rice
• Optimizing Quality Assurance Inspections to Improve the Probability of Damage Detection in Wind Turbine Blades - https://www.slideshare.net/sandiaecis/optimizing-quality-assurance-inspections-to-improve-the-probability-of-damage-detection-in-wind-turbine-blades
• Neidigk: 2013 Sandia Wind Plant Reliability Workshop - https://de.slideshare.net/sandiaecis/neidigk-sandia-2013-wind-plant-reliability-workshop
Important background on the POD exercises can be found in the following papers dealing with aircraft maintenance NDT:
• http://www.tc.faa.gov/its/worldpac/techrpt/tc15-63.pdf
• http://www.tc.faa.gov/its/worldpac/techrpt/tc15-4.pdf
Nevertheless I would not agree with some conclusions of Sandia's papers, especially in the field of sandwich structure SANDIA did not use the latest techniques with PAUT and RotoArrays to be found on newer aircraft NTMs which provide even astonishing results used on complex foam-FRP structures.
 
 Reply 
 
Johann Hinken
,
fitm Hinken Consult, Germany, Joined May 2014, 20

Johann Hinken

,
fitm Hinken Consult,
Germany,
Joined May 2014
20
10:40 Mar-22-2018
Re: What is Suitable Method for inspection of wind turbine blades
In Reply to Nanaji at 04:17 Mar-04-2018 (Opening).

Hello Nanaji,

I recommed Microwave testing. This is a rather new method, especially for insulating material and also for large inspection depths. For more details please look at the following links and contact me for additional information.

- Wikipedia, section microwave testing in: https://en.wikipedia.org/wiki/Microwave_imaging
- Introduction/overview on microwave testing: http://fitm.de/wp-content/uploads/2017/07/N38e-Microwave-Testing_An-Overview.pdf
- Wind turbine blades tested with the NIDIT procedure (a special microwave procedure): http://fitm.de/wp-content/uploads/2018/03/N39e-Wind-turbine-blade-edge-NIDIT-short.pdf
- Further application notes on microwave testing: http://fitm.de/index.php/applications/

Regards, Johann

 
 Reply 
 
Ash
Ash
02:53 May-20-2018
Re: What is Suitable Method for inspection of wind turbine blades
In Reply to J.B. at 18:48 Mar-14-2018 .

Hello JB

I have seen a lot about shearography, but how applicable is it in the field for a high rope technician? I have seen some bulky equipment that would be hard to carry.

Thanks

Ash

 
 Reply 
 
J.B.
J.B.
18:12 May-22-2018
Re: What is Suitable Method for inspection of wind turbine blades
In Reply to Ash at 02:53 May-20-2018 .

Shearography - is a difficult topic.
I know that in Airbus it never made it into production or maintenance except for niche applications - for reasons see e.g. http://www.ndt.net/article/atandt2010/papers/18.pdf, page 5 - table: Comparison of Test Methods .
Also at Boeing I know no application in the NTM, which really calls mandatory shearography for inspection. in the Boeing NTM it is somewhere mentioned in the General Part, but as far as I know nobody wants to use it because of the efford, e.g. the special qualification for NDT People (another Level II and Level III for nearly no benefit), costly Equipment, and the evaluation of shearographic images is not reliable - misinterpreation is common even by scientiffic personal end developers. So shearography usually lacks the unambiguity you are used with traditional NDT methods, e.g. UT, where TOF can be easily correlated with defect depth etc.
In aerospace the topic qualification (POD etc.) is hot, so as PAUT, UT, ET etc. can easily cover what shearography might promize to do, there was no reason to step into it. Check, which nation offers NANDTB approved Shearography Courses (NAS410/EN4179) and you will see, there is not much need.

And now think you have to deal with rather complex equipment while hanging on a rope down the blades....
I don't know if one of the few companies in the market already thought about an automatic crawler, which could help to do the Job...
By the way: usually the wall thickness of wind tourbine blades is rather thick - shearography measures the loss of stiffness.... so you would only recognize defects at the Surface!
I could imagine that you may have success with Vibration loading like offered by ISISYS (http://www.isi-sys.com/isi-sys-homepage/) or the Golden Eye (http://www.vew-gmbh.de/en/optical-metrology/golden-eye-shearography-system.html), but even here the image processing is tricky.

Shearography is still an exotic method and the data processing has still large deficites to offer easy and unambiguous signal interpretation. That is my personal opinion - I have done development work with this method since about 1990, but it could never compete with the traditional methods: especially after the Omniscan showed up the fortune of shearography went down.





 
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