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The inspection of the sealing weld is an important phase for the evaluation of the acceptability of final disposal canister, but the weld is only a part of the 3D shielding of copper shell. The main tasks for reliable NDT evaluation requires an extensive evaluation of the parameters which contains typical inspection related items like repeatability, S/N ratio, POD, setting up the equipment for inspection, and all practices for inspections. The other parameters are material parameters, their variation must be taken into account in the evaluation of NDT reliability. Further parameters include human factors, i. e. human inspectors and their interaction with technical systems; their effects were studied on an example of the evaluation of eddy current data. Final parameters are related to evaluation of detected defects, which means sizing and base for acceptance and this can be done in different ways. Some examples are given and results are compared with different methods for instance between radiographic testing and ultrasonic testing by raw data analysis and PA-SAFT results. Also, preliminary curves for the evaluation of metallographic results of 55 defects will be shown by EB weld measurements. Some practical items concerning copper inspections will be also discussed related to acceptability.
Defect sizing is required for a quantitative assessment of the quality and reliability of safety relevant components and materials using ultrasonic non-destructive testing. The SAFT (Synthetic Aperture Focussing Technique) and the TOFD technique (Time Of Flight Diffraction) are such promising sizing candidates, extracting more information from the raw ultrasound echo data and the corresponding crack tip response. In this work the phased array technique is used to inspect a clad mock-up model of a pressure vessel section. The full scale model contains artificial test reflectors which are located in the weld and in the cladding region as well. The defects—representing typical flaws at a very early stage—are analysed with different frequencies, beam angles and directions of incidence.
For the reconstruction of reflector indications a SAFT algorithm is applied to the phased array measurement results. Additionally the reflectors are analysed by means of the TOFD technique, using different beam angles at the same time. Both analysis methods are performed using different directions of incidence considering the complex cladding structure underneath the inner surface of the mock-up model. A direct comparison of the SAFT and TOFD techniques shows that, besides the clarity of the results, the detection and sizing capabilities of SAFT are far better.
The extremely low acoustic impedance of polypropylene ferroelectret combined with its piezoelectric properties makes this material suitable for construction of aircoupled ultrasonic transducers for non-destructive testing. For the fabrication of transducers with a stable quality, the reproducibility of their key parameters is of interest.
The reproducibility was evaluated by means of (i) impedance spectroscopy and (ii) pulse-echo measurements. (i) Impedance spectroscopy was applied to identify the resonance frequency, the coupling factor and the acoustic impedance of several nominally identical transducers. (ii) Pulse-echo measurements yielded the signal form of these transducers.
The variation of the signal amplitude measured with pulseecho technique was about 10 dB. A part of this variation Comes from the deposition of transducer electrodes and another part from local variations of ferroelectret properties. The variation of the signal amplitude was caused by the observed variation of the coupling factor, which was also about 10 dB. The variation of the acoustic impedance was only about 1 dB, thus having no effect on the variation of the signal amplitude.
These results indicate that the variability can be reduced by improving the control of electrode deposition and by optimizing the production technology affecting the reproducibility of material properties.
A time domain spectrometer in the range of 0.5–2 THz was used for time of flight (ToF) measurements of THz pulses for imperfection detection in non metallic materials. The measurements were performed in comparison to the established ultra sound pulse echo (PE) and time of flight diffraction (ToFD) technique. No coupling agent and no contact to the surface is required for THz ToFD measurements. Plastic test specimen with notches, voids and drilled side holes were used to study reflected and diffracted response signals. No major differences were observed between the UT and THz ToFD records for the first surface of the notches, voids and holes. Additionally to the UT records also signals were obtained from its back side and a second raw of holes. The THz measurement is fast and has the potential to substitute UT applications in some industrial areas. Within the German project 'Handheld' the potential for miniaturization of the time domain equipment is explored for efficient application.
Im Gegensatz zur Impuls-Echo-Technik, die im Wesentlichen auf der
Anton Erhard, Berlin Reflexion am Fehler basiert, wird bei der Time-Of-Flight Diffraction Technique (TOFD-Technik) die Beugung der Schallwellen am Fehler zum Nachweis genutzt. Zwei Winkelprüfköpfe für Longitudinalwellen sind in V-Durchschallung angeordnet. Die Prüfköpfe befinden sich jeweils auf einer Seite der Schweißnaht und werden bei der Messung parallel zur Schweißnaht verschoben. Das ausgesandte Schallbündel trifft auf Fehlerränder, an denen gebeugte Wellenanteile entstehen, die je nach Entstehungsort mit unterschiedlichen Schalllaufzeiten empfangen, in hochfrequenten A-Bildern abgespeichert und für die Auswertung in B-Bildern dargestellt werden.
Die Untersuchungen zeigen, dass die TOFD-Technik Beiträge zur Fehlergrößenabschätzung liefert, aber keinesfalls die Impuls-Echo-
Technik mit nachgeschalteter Röntgenprüfung ersetzen kann.