Enhancing the reliability of ultrasonic testing by digital signal processing

The successful detection of defects in a structure using non-destructive testing (NDT) is very significant to maintain a reliable operation of the structure. Thus the reliability of the NDT method becomes a critical factor that influences the reliability evaluation of the structure. A brief review on the NDT reliability literature is presented in the first section of the paper. The reliability operating characteristic curve of ultrasonic contact testing and immersion testing of frictional bonded piping joints is plotted using the signal-to-noise ratio (SNR) as a criterion. It shows that ultrasonic testing of these specimens has a higher reliability in the detection of macro-defects than micro-defects. Immersion testing has a higher reliability than contact testing. Digital signal processing (DSP) technology has the potential to increase the SNR of the ultrasonic signal. A traditional DSP routine, band-pass filtering, and the most recent DSP method, wavelet transform, are utilised to enhance the SNR of signals, to increase the reliability of the ultrasonic testing. The results indicate that after the SNR of signals is enhanced by a suitable digital signal processing technique, the reliability of the ultrasonic testing increases.