UT phased array inspection of turbines

Transcription

1 UT phased array inspection of turbines components : experiments and simulation Bruno ISSENMANN Gilles ROUGERON Steve MAHAUT (CEA/LIST) Stéphane LABORDE (ALSTOM Power Service) 1

2 Industrial context (1) In order to develop new inspection techniques, it is necessary to run simulation to help to determine the fine parameters The CIVA platform allows to simulate complex setups in order to foresee the kind of NDT image that will be mesaured in the real configuration For many configuration CIVA allows to foresee the expected echoes and to understand the UT images in complex component. 2

3 Industrial context (2) Steam turbines are some of the most highly stressed components in a power plant Blade attachment are sensitive areas for which inspection decisive It is needed to inspect the blades attachement in circumferential grooves because of SCC risks 3

4 Industrial context (3) Goal : Detection and sizing of defects located in the bottom of serrations in the circumferential direction Access surface Access surface 45 ±5 general flaw orientation Possible initiation all along the fillet 4

5 Testing on ALSTOM mock-ups (1) Probe : Phased array probe from Imasonic Signal frequency 10MHz Sectorial scanning from -10 to 10 (1 step) transmitting L-waves EDM notches are semi-elliptical. (lengths are L=5mm ; heights H=1mm or H=2.5mm, 45 tilted). 5

6 Testing on ALSTOM mock-ups (2) displacement BScan (3 shot) 2 flaws Sectorial scan H=2.5mm -10 to 10 Multiple echoes are generated 6

7 Testing on ALSTOM mock-ups (3) Simulation (Civa 9.2) Diffraction echo Acquisition Backwall echo LTL corner echo Backwall corner echo indirect echo LLLL Backwall echo L Backwall corner echo L LTL corner echo L T L L Diffraction echo L Flaw Indirect echo LLLL (replicae) L 7

8 Civa model and its extensions(1) Semi-analytical models for UT beam propagation and flaw scattering Computable echoes in version 9.2 of CIVA for UT defect response Direct specular or diffraction echoes Corner echoes Indirect specular or indirect diffraction echoes Only one bounce maximum on the backwall surface between the probe and the defect New developments CIVA (now available in CIVA10) : account of echoes formation with "self" reflexion on defects) The indirect echo mode LLLL can be simulated by computing : and a reflexion on the defect followed by a reflexion on the backwall in the emited beam by coupling it with a direct received beam. 8

9 Civa model and its extensions(2) New «Computation parameters» of UT Defect Response module. Addition of a new control type in order to compute indirect specular echo with two bounces on the flaw. Other extensions to UT Defect Response Multiple bounces on any surface type of the specimen (surface, backwall, interface or lateral wall) Specimen can have 3D CAD type. Addition of tools Interactivity (positioning of probe and defects) Ray tracing has been improved List of echo modes A fast estimation tool of important echo modes Please refer to «Simulation of ultrasonic inspection involving multiple skips and realistic defects» S. Chatillon, N. Leymarie, G. Rougeron and S. Mahaut, (UT MODELING session) 9

10 Validation on a canonical specimen (1) Indirect specular echo amplitude to be validated Backwall surface Flaw Specimen : 5 slopes : 0, 5, 10, 15 and 20 Defect : planar (H=1cm x 2cm), vertical or 20 tilted Probe : 48 elements linear phased array. (first 16 elements are used) The probe emits a 5MHz ultrasonic wave Sectorial scanning where T wave is emitted from 20 to 60 every 5 10

11 Validation on a canonical specimen (2) T45 slope 0, flaw vertical T45 slope 5, flaw tilted 20 Corner echo acquisition Indirect specular echo simulation (Simulation/Acquisition)<2dB (Simulation/Acquisition)= dB Reference : side drilled hole response (for simulation and acquisition) Diffraction simulations and measurement of flaws echoes for each shot and backwall slope : overall good qualitative agreement (time of flight and echodynamic shapes) all observed echoes are simulated fair quantitative agreement except for some cases 11

12 Back to testing on Alstom mock-ups (1) Civa 9.2 simulation Acquisition Civa 10.0 simulation Diffraction echo Backwall echo Backwall corner echo LTL echo No indirect LLLL echo Indirect LLLL Echo (replicae) 12

13 Back to testing on Alstom mock-up (2) Comparison of the acquired and computed echodynamic curves of the indirect LLLL echo Black: Acquired echo Red: Computed echo 12dB gap Flaw positioned in accordance with specimen specification Flaw moved away of 0.6mm from the vertical side of the specimen. The maximum amplitude of acquired and computed echoes are in accordance. Echo calculation with Civa UT models are very dependant to the positioning and orientation of the flaw. 13

14 Back to testing on Alstom mock-up (3) The gap can be significant because with a slight variation of the angle or position of the flaw, the direction of the beam related to the interface is different. In this case, a variation of the notch orientation leads to an important loss of signal due to non optimal specular reflexion. 45 : the incident beam is reflected on the flaw but is not strictly perpendicular to the backwall 48 : the beam has the optimal orientation related to the flaw and the specular reflexion is going back to the probe. 14

15 Echo simulation on 3D CAD (new in CIVA 10.) Experiment Simulation diffraction replicae Backwall echoes Indirect echo (replicae) 3D CAD model > triangles 15

16 Conclusion Echo model in Civa UT has been extended bounce on defect in field computation computation on 3D CAD specimen multiple bounce on any surface during field computation Qualitatively reproducts observed echoes backwall and flaws echoes, shadowing effects, replicae (multiple bounces, with first reflexion applied on the flaw) Sensibility to positions and angular variations of the flaws Some further validation cases to be carried out 16

17 Thank you for your attention. Questions? 17