Improved Inspection of Composite Wind Turbine Blades with Accessible Advanced Ultrasonic Phased Array Technology

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1 Improved Inspection of Composite Wind Turbine Blades with Accessible Advanced Ultrasonic Phased Array Technology André Lamarre Olympus Scientific Solutions Americas, Canada NDT of Composites an ASNT Topical Conference, 9-10 May 2017, Seattle, WA

2 Content Description of wind turbine blades How ultrasonic phased array inspection works The detection capabilities of ultrasonic phased array technology The productivity of ultrasonic phased array technology Conclusions

3 Main Components of a Wind Turbine Wind blade Wind turbine blades Generates aerodynamic torque from the wind Nacelle Nacelle Converts the torque into electrical power Tower Holds the nacelle and rotor blades Provides access to the nacelle Tower Foundation Ensures that the turbine stays upright Foundation All these components require nondestructive testing to help ensure their integrity during manufacturing, construction, and maintenance. In this presentation, we focus on the use of ultrasonic phased array for inspecting wind turbine blades during manufacturing.

4 Basically, what is a wind turbine blade? A turbine blade is composed of an outer shell that is re-enforced by one or many internal structural beams, also called spar The number of spars depends on the size of the blade The interior of the blade is hollow Depending on the manufacturer, the spar could be an I-beam or a box

5 Basically, what is a wind turbine blade? The I-beam spar is composed of 2 spar caps and one shear web The box spar is composed of the 2 spar caps and 2 shear webs The spar caps are attached to the the skin with adhesive Materials Glass-reinforced fiber, carbon-reinforced fiber, balsam/wood, adhesive, resins, honeycomb structures, and coatings Most materials are not acoustic friendly

6 Manufacturing Flaws Flaws can be the result of the blade s design or during manufacturing Types of flaws include: Porosity Disbonds Delamination Inclusions The width of the adhesive and its position between the beam and shell Wrinkles (out-of-plane waviness)

7 Principles of Ultrasonic Phased Array

8 Blade inspection using ultrasonic phased-array Phased array probes are composed of multiple piezoelectric elements. Pulsing and receiving of the elements is electronically controlled to generate beams. 4 element aperture 1 mm (0.039 in.) Blade inspection is performed using linear scan beams

9 Data Point Density Low Density High Density Missed Detected Higher density Greater probability of detection

10 Large Effective Beam Conventional UT probe Phased array 64 elements Larger coverage in one pass Finer resolution

11 Analysis views Amplitude C-scan D-scan A-scan B-scan

12 Olympus Phased Array Instruments for Wind Blade Inspection OmniScan SX Flaw Detector OmniScan MX2 Flaw Detector FOCUS PX Acquisition Instrument Portable One PA probe Portable Multiple PA probes PC-based Multiple PA probes Scalable Manual and semi-automated inspection Semi and fully-automated inspection

13 Low-Frequency Linear Phased Array Probes Frequencies: 0.5 and 1 MHz Number of elements: 64 Length: 96 mm Elevation: 22 mm Pitch: 1.5 mm Plastic housing to reduce the weight

14 Low-Frequency Linear Phased Array Probes Mounted on 4 different wedges/probe holders One with a semi-contact probe holder for deep penetration One with the an Aqualene delay line for improved near-surface resolution Both probe holders are available as either curved or flat All wedges/probe holders have water irrigation and an encoder attachment

15 The Detection Capabilities of Ultrasonic Phased Array

16 Example of a Spar Cap Inspection Uses an automated scanner OmniScan MX2 flaw detector Olympus wind blade PA probe and wedge Results presented as an amplitude C-scan Superimposed image for illustration purposes

17 Example of a Spar Cap Inspection The C-scan below represents the ultrasonic mapping of the spar cap Bonded zones between the spar cap and shell Cross section Flanges Not to scale. For illustration purposes Length Cross section At CRP or GRP flanges, the ultrasound reflects off the inner side of the skin, resulting in a strong echo (represented in red on the C-scan) At bonded zones, if the bond is good, the ultrasound travels through the adhesive and disperses into the web, resulting in no or weak echo at the bonded interface (represented in blue or yellow on the C-scan)

18 Example of a Spar Cap Inspection Using the amplitude C-san image we can: Bonded zones between the spar cap and shell Flanges Cross section Length Measure the width of the adhesive zones Evaluate the quality of the bonds Locate deficiencies in a bonded area Cross section With the low-frequency phased array probe, the sizing resolution is 1.5 mm Not to scale. For illustration purposes.

19 Bonding Evaluation In this example, the bonded zone is deficient The width of the bonded zone is getting narrow An 80 mm long section is totally disbonded Localized unbonded areas are also present in the good area Approximate size: mm

20 Adhesive Thickness Measurement Depending on the adhesive material, echos from the interface shell s glue and the web s glue are visible The distance between these 2 echos characterizes the adhesive thickness Using the right velocity, the adhesive thickness can be evaluated In this case, the adhesive thickness is estimated as 14 mm

21 Delaminations Delaminations between different GRP or CRP layers can be located Delaminations Good reflector of ultrasound Delaminations A time-of-flight C-scan is useful to discriminate between a geometry echo and delamination

22 Detecting and Sizing Wrinkles Wrinkles are an out-of-plane alignment of layers They reduce the blade s tensile strength Can create out-of-plane delaminations Deviation in the vertical plane: 4 mm Length of the wrinkle: 17 mm

23 The Productivity of Ultrasonic Phased Array

24 Using Automated Ultrasonic Phased Array to Inspect a Spar Cap Girder OmniScan MX2 unit Scanner length: 5 m; scanner width: 0.5 m Scanning direction: length of the blade Indexing direction: cross-section of the blade 100 mm indexing Acquisition resolution: 1.5 mm in both axes 2 m 2 inspected in 40 seconds The C-scan and A-scan are both recorded The scanner is not an Olympus product.

25 Using Automated Ultrasonic Phased Array to Inspect a Spar Cap Girder (continued) OmniScan MX2 unit Scanner length: 5 m; scanner width: 0.5 m Scanning direction: crosssection of the blade Indexing direction: length of the blade Acquisition resolution: 1.5 mm in both axes C-scan and A-scan are recorded The scanner is not an Olympus product

26 C-scan Representation OmniScan MX2 unit Scanning direction: crosssection of the blade Indexing direction: length of the blade; 100 mm indexing Live mapping on the screen Bonded zones and flanges are clearly visible

27 Conclusions Ultrasonic phased array can be used to inspect wind blades with low-frequency probes (0.5, 1 MHz) The 1.5 mm resolution enables small flaws to be detected and accurate flaw sizing Flaws such as wrinkles, delamination, and disbonds can be detected and sized The linear scan capability enables fast inspection while maintaining 100% coverage of the part

28 Conclusions Off-the-shelf phased array units can be used as a standalone or integrated with automated scanners C-scan imaging enables analysis at a glance Use of A-B-C-D scans permit a more detailed interpretation Data is archived The use ultrasonic phased array can also be considered in the maintenance program of wind turbine blades