Welding is one of the so-called special processes that require verification to ensure correct execution in sufficient quality. Low-quality weld is not satisfying the requirements for in-service operation, either due to presence of defects (e.g. cracks, lack of fusion, porosity), or due to undesirable microstructure changes in heat-affected zone, that causes degradation of the weld joint. Welds are the main topic of NDT that searches for defects. The main method for detection of internal defects is the ultrasonic testing, that recently saw many new applications. This article shows how to use Phased Array probes to detect microstructure changes due to failure to follow the welding procedure. It was experimentally confirmed that the technique is able to identify microstructure changes in heat-affected zone created by change of welding parameters or by poor restart. The technique may be in principle performed in parallel with ultrasonic testing for defects, so it is possible to be used one instrument to perform complex assessment of weld joint quality.Keywords: phased array, ultrasonic testing, welding, structural changes
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