Towards optimised inspection parameters for ultrasonic testing of austenitic welds through backscattered noise analysis


Austenitic steel welds are known to prove difficult for ultrasonic inspection, as their coarse grains attenuate, deviate and scatter the incident sound beam. This not only reduces the intensity of the ultrasound, but also results in increased backscattered noise levels, which may mask signals from defects. Efforts to characterise and mitigate these effects are impeded by the anisotropy of the austenitic grain structure across the weld, which arises from directional cooling of the weld metal. Low-frequency, longitudinal sound waves are therefore typically chosen to sufficiently penetrate the weld metal and minimise beam distortion. More specific guidelines are however difficult to ascertain due to the complexity of the material and the many inspection variables present. The purpose of this pilot study was to characterise backscattered noise comprehensively in both the time and frequency domains. The objective was not only to determine optimum inspection parameters for the component examined, but also to generate a robust methodology for the identification of optimised inspection parameters.