Flexible PCB-Based Eddy Current Array Probes for the Inspection of Turbine Components

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2 Flexible PCB-Based Eddy Current Array Probes for the Inspection of Turbine Components Andre Lamarre - OlympusNDT-Quebec City Canada Benoit Lepage - OlympusNDT-Quebec City-Canada Tommy Bourgelas - OlympusNDT-Quebec City-Canada 4th International CANDU In-service Inspection Workshop and NDT in Canada 2012, June 2012, Toronto

3 Background Eddy current is a reliable non-destructive inspection method for turbine components. The use of eddy current arrays (ECA) is already known to increase the inspection speed and the reliability of the inspection process. One practical limitation of the ECA technology is each ECA probes have to conform to the shape of the inspected components making its use expensive and limited. Recently, Olympus NDT has overcome these limitations by introducing the flexible PCB-based ECA probe technology. This paper will present an overview of this technology and its applicability to turbine components.

4 Presentation Plan Eddy Current Array (ECA) principles Flexible ECA probe for general purpose Active shielded flexible ECA probe

5 What is Eddy Current Array Eddy current array technology is the ability to electronically drive several eddy current sensors placed side-by-side in the same probe assembly. Data acquisition is performed by multiplexing the eddy current sensors in a special pattern that will avoid mutual inductance between the individual sensors. Most eddy current probes and techniques for flaw detection can be used with eddy current array probes.

6 Eddy Current Array Advantages Allows larger coverage in a single probe pass while maintaining a high resolution. Improves flaw detection and sizing with C-scan imaging. Inspect complex shape with a probe made with to the profile of the parts

7 Advantages of ECA Testing

8 Eddy Current Array Advantages Allows larger coverage in a single probe pass while maintaining a high resolution. Improves flaw detection and sizing with C-scan imaging. Inspect complex shape with a probe made with to the profile of the parts

9 Inside an ECA probe Traditionally with hard coil sensors Brand New: Flexible Array on PCB film

10 General OmniScan ECA Features OMNI-P-ECA4-32 Conventional and Array ECT 4 input channels 43 channels Frequency range from 20Hz to 6MHz Dual Frequency operation 2 Encoder input 3 Alarm output 1 Analog output

11 ECA Advantages Fast Large Coverage Easy Imagery Data Recording Encoded Capability Olympus OmniScan ECA

12 Multi-purpose ECA Flex Probe

13 Flexible ECA Probe: FBB Coils 51mm of Coverage Very Flexible Two rows of coils to improve resolution Detachable cable Can be configured to be used in absolute or reflection modes

14 FBB Probe nb channel : 30 Coil type: Reflexion (transmit-receive) with each channel being build using an exciter coil and two receiver coils connected in series. Total coverage: 48mm Resolution: 1.6 mm Frequency range: 100KHz to 4000KHz Coil design: 32 X Circular coil, 3.1mm diameter Probe design: 2row of staggered coils

15 Blade Root Inspection Gas turbine generator blade Notches at different location Inspection in one pass Flexible ECA mounted on a shaped holder

16 Blade Root Inspection Cscan representation of the results

17 Turbine blade Inspection

18 Active shielded flexible ECA probe

19 Detecting defects near edges; problem Eddy current field spread in area wider than coils footprint Eddy current sensors detection capabilities limited near inspected component edges Edge signals very important compared to small defects.. Difficult to extract defect information

20 Detecting defects near edges; conventional approach Use of ferromagnetic and/or conductive cup around the coil limit the spread the magnetic field Improved detection near parts edges Applicable to coil array, but expensive to design and build

21 Detecting defects near edges; conventional approach Use of finite element simulation tools to illustrate the induced currents

22 Unique challenges pertaining to the use of flexible printed circuit board for building eddy current sensor array Thin copper layer ; typically less than 18 um Integrated eddy current shield offer limited potential (dop in copper is around 2MHz) Limited use of ferromagnetic material Compact array structure require compact shielding

23 Solution Active shielding of coils Magnetic field extending outside coil s is proportional to k*n*i/r^3 for unshielded coils. Concentric coils with adequate N 1* I 1 /N 2* I 2 ratio can generate the same far field but different inner field. Opposite field provide shielding out of coil footprint Inner coil Outer coil Eddy Current density Inner coil - Outer coil Inner coil Radius Outer Coil Radius k/r^3 0 0,5 1 1,5 2 2,5 3 Radial position (mm)

24 First evaluation of the solution with hand wound coils Raster scan on 0.8mm long X 0.4mm deep EDM, at the center and edge of a titanium plate. Best performance on edge notch obtained with actively shielded coil

25 Extending the concept to PCB Made coils Concept not limited by coil thickness Single layer actively shielded coil made by predefined number of turn ratio. Use of simulation tools to define details of coil structure. Easily adapt to non-round shapes

26 Probe description Qty of channel : 64 Coil type : Absolute, bridge (with reference coils on the probe) Total coverage : 76.8mm Resolution : 1.2 mm Coil design : Rectangular shaped (3mm large X 2.2mm long) with active shielding) Probe design : 3 rows of coil for optimized coverage (approx 1.3dB variation between coils vs. at coil center). 26

27 Sample in in in in in in in in. 27

28 Results 64 channels 3.15 in. of coverage 0.05 in. of resolution Notches size: Length: in. Depth: in. Width: in. 28

29 Summary ECA is used in different industries for surface inspection ECA is a quick and reliable way to inspect surface Flexible ECA probes are suitable for the inspection of turbine components like blades Active shielded ECA flexible probe improve the detection near the edge of components, creating a lot of possibilities

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