A New Model-Based Approach for Ultrasonic Testing of Dissimilar Welds

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1 A New Model-Based Approach for Ultrasonic Testing of Dissimilar Welds Dr. Frank Schubert Head of Department Computational Methods Fraunhofer Institute for Non-Destructive Testing Dresden, Germany NDT in Progress 2011 Prague October 11, 2011

2 Main Problem of Phased Array Weld Testing Isotropic material with straight ray paths and a single scalar wave speed Focal laws well understood Anisotropic weld with curved ray paths and different local group velocity vectors Focal laws unknown in general

3 Possible Solution: Compensation of Anisotropy Effects by Model- Based Approaches and Advanced Imaging Techniques Conventional Phased Array Sampling Phased Array (SPA) without Compensation SPA with Compensation Quantitative Ultraschallprüfungen an anisotropen Materialien mittels Sampling Phased Array Technik A. BULAVINOV, R. PINCHUK,S. PUDOVIKOV, S. V. RAMANAN

4 Typical Procedure: Detemination of Grain Orientations Combined with Published Values of Elastic Parameters Microstructural quantification, modelling and array ultrasonics to improve the inspection of austenitic welds C Nageswaran, C Carpentier and Y Y Tse, Insight Vol 51 No 12 December 2009

5 Determination of Time-of-Flight Information by Image-Based EFIT- Modelling Image based EFIT simulation for nondestructive ultrasonic testing of austenitic steel K Nakahata, S Hirose, F Schubert, B Koehler, ASMP 2009

6 Determination of Time-of-Flight Information by Image-Based EFIT- Modelling Image based EFIT simulation for nondestructive ultrasonic testing of austenitic steel K Nakahata, S Hirose, F Schubert, B Koehler, ASMP 2009

7 Determination of Time-of-Flight Information by Ray Tracing A 2D model of ultrasonic wave propagation in an anisotropic weld Q. Liu, H. Wirdelius NDT&E International

8 Drawbacks of the Present Model-Based Approaches Grain orientation alone does not provide elastic/acoustic parameters Published values are typically not very reliable Elastic parameters of real welds may differ significantly This leads to an inaccurate time-of-flight model for phased array testing Consequence: Perform measurement of wave propagation at the real weld microstructure and weld geometry followed by extraction of acoustic travel times from wave front snapshots

9 Typical Geometry of a Dissimilar Weld Micrograph (model weld) Elastic Model Fehlerabbildung in Mischschweißnähten mit einem angepassten SAFT-Algorithmus K.J. Langenberg, A. Shlivinski, R. Marklein, V. Schmitz, W. Müller, U. Mletzko, DGZfP 2005

10 The Test Mock-up

11 Surface After Conventional Chemical Etching Ferrite Austenite Figure 5: Small test sample after etching, showing positions a-g and 1-9, respectively.

12 Photo Micrographs of the Different Weld Regions Position a Position b Position c Figure 6: Microscopic photographs in the cladding at the positions a-c as shown in Fig. 5 (magnification 25x). Position d Position e Position f Figure 7: Microscopic photographs in the cladding at the positions d-f as shown in Fig. 5 (magnification 100x).

13 Scanning Laser Vibrometer System at IZFP Dresden Scanner Laser vibrometer Sample with UT probe Laser vib rometer - set up for wave propagation measurements.

14 Vibrometer Measurements at the Polished Surface Ultrasonic transducer. Untreated smooth surface of one of the small weld samples. Only the darker ferritic part can be seen on the left. The remaining part does not show any details of the grain structure. The modelling clay around the small outer surfaces is used to suppress ultrasonic reflections.

15 Vibrometer Results for 45 Shear Wave 2 MHz

16 Vibrometer Results for 45 Shear Wave 2 MHz Strong interaction of the shear wave with the weld

17 Vibrometer Results for 45 Pressure Wave 2 MHz Rather weak interaction of the pressure wave with the weld

18 Vibrometer Results after Hard- and Software Improvement Much better signal-to-noise ratio + shorter scan times

19 Vibrometer Results after Hard- and Software Improvement PA single element excitation from the ferritic side (outer pipe surface) Single element excitation from the cladding side (inner pipe surface)

20 Vibrometer Results after Hard- and Software Improvement From ferritic side Through the cladding

21 Dissimilar Weld Model for Automatic Phased Array Testing P1 P2 y P3 P4 P5 x P6 D: Cladding P7 B: Austenite C2 C1 A: Ferrite C: Weld E: Buffering P8 P9 P10 P11 P12 P13 P14 P15

22 Dissimilar Weld Model for Automatic Phased Array Testing Buttering

23 PCUSpro Array Hard- and Software of IZFP-D 2.25 MHz 5 MHz 10 MHz re 37: PCUSpro array prototype with 64 channels developed for weld inspection with the om-made phased array transducer described in chapter 9 (top). Prototype of phased array ware interface for conventional and sampling phased array testing (bottom picture). 1.5 MHz

24 Possible Imaging Modes of PCUSpro Array Platform Mode 1: Focused Sector Scan Mode 2: Dynamic Depth Focusing Mode 3: Full Focusing al phased array imaging. The focal depth is fixed and the focal point (red dot) Isotropic model with single scalar nter of the phased array transducer resulting in a traditional sector scan. wave speed Can be used if no or only little information about the weld is available Default setting for manual testing Material-dependent wave speed for automatic testing can be used Identical or even better performance than conventional PA systems Isotropic/anisotropic model with different weld regions Can be used if basic knowledge about the weld is available (weld geometry and typical wave speeds) Dynamic depth focusing to the most relevant regions/interfaces Much better performance than conventional PA systems Can only be used for automatic testing! Simultaneous optimal focusing to all pixels/voxels (software-based) Best possible performance (tomography) Needs full vibrometer scan for each weld type In dissimilar welds currently only usable for P wave testing Off-line reconstruction Challenge: Real-time capability

25 Results with PCUSpro Array for Manual Testing at 2.25 MHz = 3mm

26 Results with PCUSpro Array for Manual Testing at 2.25 MHz Focused Sector Scan

27 Typical Result with other PA System for Manual Testing at 2.25 MHz Conventional Sector Scan

28 Results with PCUSpro Array for Manual Testing at 2.25 MHz Final Result of Model-Based Approach

29 Automatic Testing with PCUSpro Array at Pipe Mock-Up Probe holder Scanning device

30 Results with PCUSpro Array for Automatic Testing at 2.25 MHz B-, C- and D-Scan representation

31 Summary Dissimilar welds still represent a big challenge for ultrasonic testing due to their heterogeneous and anisotropic microstructure Model-based approaches try to compensate the disturbing effects by using time-of-flight models of real weld geometries Previous approaches used image-based information of the grain orientation together with published values of elastic parameters Our new approach is based on the direct measurement of the relevant wave speeds of the real welds by using laser vibrometry It leads to a detailed time-of-flight model for the focal law calculator. With this knowledge a better beam steering and focusing can be obtained leading to better images and a more precise defect localisation This model-based approach was implemented into the PCUSpro Array platform and was successfully tested at small weld samples and a pipe mock-up