Possibilities of Reliable Ultrasonic Detection of Subwavelength Pipework Cracks

Abstract

An occurrence of cracks in pipework could lead to potentially very dangerous malfunction in some critical engineering systems such as power plants. There is a clear trend of replacing traditional manual testing with non-invasive in-situ methods that should detect crack formation in its early stage. Such as approach would enable replacing of unhealthy pipe components during the regular periodic outages. Ultrasonic testing is known to be a rather mature and reliable technology. However, it suffers from serious problems in detection of the cracks of subwavelength size. This paper attempts to soften aforementioned problems by investigating the influence of a duration of the unipolar excitation signal on the achieved resolution. In addition, the transducer input electricalimpedance of NDT transmitter was measured by using different excitation pulses and their levels and the results are compared with those obtained using traditional frequency sweeping method at low excitation levels. Finally, use of some advanced signal processing algorithms that might lead to the automatic detection of subwavelength voids, in scenarios with low signal-to-noise ratio, is discussed.