1/16 P. Belanger and P. CawleyUK Research Centre in NDE Guided Wave Diffraction Tomography within the Born Approximation P. Belanger and P. Cawley UK Research Centre in NDE Imperial College London SW7 2AZ UK

2/16 P. Belanger and P. CawleyUK Research Centre in NDE Motivation Diffraction Tomography –General –Guided waves Finite Element Reconstruction –1 defect –2 defects –3 defects Experimental Reconstruction –Experimental setup –Incident field prediction –Experimental results Outline

3/16 P. Belanger and P. CawleyUK Research Centre in NDE Motivation Objective: Evaluate the maximum depth of corrosion patches at pipe supports (~1m), especially long supports on eg slug catcher lines. Use low frequency guided waves (cannot use ray tomography) 2 rings of transducers on either side of the support Large diameter pipe  simulation and experiments on plates

4/16 P. Belanger and P. CawleyUK Research Centre in NDE Circular array of sensors Source Propagating incident field Defect Propagation of the incident field towards the defect Total field = incident + scattered fields Scattered field Diffraction Tomography (1)

5/16 P. Belanger and P. CawleyUK Research Centre in NDE Diffraction Tomography (2) V0V0 V1V1 V0V0 Total field = incident field + scattered field Input to the diffraction tomography algorithm

6/16 P. Belanger and P. CawleyUK Research Centre in NDE Diffraction Tomography (3) Dispersion curves in a plate (large diameter pipe assumption) Frequency.thickness (MHz.mm) Group velocity (m/s) S 0 around 1.75 MHz.mm A 0 around 0.50 MHz.mm Does not consider: Mode conversion Reduced stiffness Reduced mass

7/16 P. Belanger and P. CawleyUK Research Centre in NDE Finite Element Reconstruction (1) Monochromatic reconstruction at 50 kHz : Simulated incident and scattered fields

8/16 P. Belanger and P. CawleyUK Research Centre in NDE Finite Element Reconstruction (2) Monochromatic reconstruction at 50 kHz : Simulated incident and scattered fields Multiple scattering Undersampling

9/16 P. Belanger and P. CawleyUK Research Centre in NDE Finite Element Reconstruction (3) Polychromatic reconstruction between 45 to 55 kHz : Simulated incident and scattered fields Multiple scattering Reduced grating lobes

10/16 P. Belanger and P. CawleyUK Research Centre in NDE Finite Element Reconstruction (4) Polychromatic reconstruction between 45 to 55 kHz : Simulated incident and scattered fields

11/16 P. Belanger and P. CawleyUK Research Centre in NDE Experimental Reconstruction Experimental Setup 64 transducer array 50% deep tapered defect 10 mm aluminium plate

12/16 P. Belanger and P. CawleyUK Research Centre in NDE Experimental Reconstruction Incident field prediction Incident field required to obtain scattered field. Cannot use baseline measurement. Incident must be predicted : FRF of each transducer Location of each transducer Wavelength

13/16 P. Belanger and P. CawleyUK Research Centre in NDE Experimental Reconstruction Experimental polychromatic reconstruction between 45 to 55 kHz : Predicted incident field and reconstruction only with the phase of scattered field FE with phase only

14/16 P. Belanger and P. CawleyUK Research Centre in NDE Conclusion Diffraction Tomography –Guided waves can be used at dispersive frequencies for thickness reconstruction Finite Element Reconstruction –The algorithm is stable for 3 discrete defects –The reconstruction can be improved if multiple frequencies are taken into account Experimental Reconstruction –It was shown that a predicted incident field can be used in experimental reconstruction

15/16 P. Belanger and P. CawleyUK Research Centre in NDE Future work Assess the performance of the algorithm for multiple defects or general corrosion. Repeat experiments with more defects. Modify the tomography algorithm for pipe inspection (similar to well-to-well tomography in geophysics).

16/16 P. Belanger and P. CawleyUK Research Centre in NDE Questions? Pipe support FE results Experimental results