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Simulation and experimental analysis of austenitic stainless steel weld joints using ultrasonic phased array

The phased array ultrasonic technique provides enormous advantages over the conventional ultrasound technique, mostly because of its ability to focus and steer the beam, and its electronic scanning capabilities. Phased array ultrasonic testing of austenitic stainless steel welds is very difficult, due to the presence of coarse or large grains, anisotropic grain structure in the welds and the acoustic impedance mismatch between the base metal and weld metal interface. Due to the influence of these phenomena, it is difficult to analyze the inspection results and to classify the ultrasonic indications. In this paper, two different types of phased array probes (linear array (LA) and dual matrix array (DMA)) are investigated to improve the reliability of ultrasonic testing for austenitic welds. Modelling is used to simulate the propagation of ultrasonic waves in welds using a combination of the approaches of the ray-based model and the semi-analytical model. The optimization of phased array probes (both LA and DMA) for better signal-to-noise ratio and defect detectability has been studied with the help of simulation. The modelling results are validated with experimental results carried out on weld samples. Experiments are carried out on stainless steel weld samples with artificial defects of side drill hole and notches. The experimental ultrasonic images are obtained with linear array probes and dual matrix array probes and were validated with radiographic images. The study reveals that the DMA probe is superior to the LA probe and this is confirmed through the signal-to-noise ratio calculation. The present work clearly indicates that the DMA probe is a promising candidate to evaluate austenitic stainless steel welds.