Abstract:

An amplitude weight frequency modulated coded excitation signal is designed by Hamming window weight method, and the novel excitation method is combined with time-of-flight diffraction(TOFD) inspection technique, which can make the time resolution, signal to noise ratio(SNR), defect positioning and sizing accuracy be enhanced comprehensively, and can effectively improve the problem of ultrasonic inspection for coarse-grained welds. In order to analyze the inspection ability of the amplitude weight frequency modulated coded excitation signal designed, the TOFD imaging inspection experiments excited by coded signal and conventional signal are carried out by using the 5 MHz transducers for the side-drilled holes in the austenitic stainless steel base metal and welds, the results show that in the same inspection conditions, amplitude weight frequency modulated coded excitation can enhance the quality of images and signals, and make the clutter and noise be suppressed, the diffracted waves of defect upper and lower tips be accurately distinguished, the duration of the waves be decreased 30%, the time resolution of TOFD testing be increased; the average relative error of defect positioning and sizing is 3.8%, which decreases 47% compared with conventional excitation. The excitation method can make the inspection SNR more than 16 dB, higher 7 dB than conventional excitation.

Key words: amplitude weight, austenitic stainless steel welds, coded excitation, ultrasonic time-of-flight diffraction imaging inspection