Application of LFM excitation on ultrasonic testing for austenitic stainless steel welds

摘要

Multi-pass welds of austenitic stainless steel are characterized by an anisotropic and heterogeneous structure with bulky columnar crystal that leads to serious attenuation, scattering, distortion and noise interference in the ultrasonic propagation and makes ultrasonic testing difficult. In order to improve both echo SNR and time resolution in ultrasound detection system, linear frequency modulated (LFM) pulses are used for exciting signal in ultrasonic testing of austenitic stainless steel welds. Experimental investigation on testing austenitic stainless steel welds with buried defects has been carried out with ultrasonic LFM-TOFD (Time of Flight Diffraction with LFM excitation) detection technique. The results from D-scan and A-scan image show that LFM excitation can reduce effectively beam distortion and noise interference, increase SNR by about 12 dB and reduce measuring error to 0.04μs, compared with traditional narrow pulse excitation. Hence, it will be beneficial for detection and evaluation of coarse grain materials.