Time-of-flight diffraction ultrasonics

About: Time-of-flight diffraction ultrasonics is a research topic. Over the lifetime, 544 publications have been published within this topic receiving 3189 citations.

SAFT and TOFD—A Comparative Study of Two Defect Sizing Techniques on a Reactor Pressure Vessel Mock-up

Abstract: 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.

Inspection robot for spherical storage tanks

Abstract: Osaka Gas Co. Ltd has utilized ultrasonic flaw detection systems (time of flight diffraction method) to externally inspect the inner and outer surfaces of weld seams on spherical storage tanks while the tanks are in use. In these systems, the vehicle mounted with an ultrasonic flaw detection probe is designed to travel in a straight line only. To improve the work efficiency, we developed an inspection robot that is propelled by four independently driven magnetic wheels. This robot has been in experimental operation on an actual spherical tank. The introduction of this robot has shorten inspection time by about one week from the conventional 23 days, and reduced the conventional number of inspectors required from 4 to 2.

Automatic detection and classification of weld flaws in TOFD data using wavelet transform and support vector machines

Abstract: Ultrasonic time-of-flight diffraction (TOFD) is known as a reliable non-destructive testing technique for the inspection of welds in steel structures, providing accurate positioning and sizing of flaws. The automation of data processing in TOFD is required towards building a comprehensive computer-aided TOFD inspection and interpretation tool. A number of signal and image processing tools have been specifically developed for use with TOFD data. These tools have been adapted to function autonomously, without the need for continuous intervention through automatic configuration of the critical parameters according to the nature of the data and the acquisition settings. This paper presents several multi-resolution approaches employing the wavelet transform and texture analysis for de-noising and enhancing the quality of data to help in the automatic detection and classification of defects. The automatic classification is implemented using a support vector machines classifier, which is considered faster and more accurate than artificial neural networks. The results achieved so far have been promising in terms of accuracy, consistency and reliability.