Study on Ultrasonic Phased Array Detection and CIVA Simulation of Placed Fillet Weld

Abstract Nozzle fillet welds are widely applied in large-scale industrial equipment such as power station boilers, differing significantly from butt welds in connection geometry. Influenced by welding configurations and post-service stress concentrations, these welds are prone to critical defects like cracks and lack of fusion, posing substantial safety risks to equipment operation. The unique geometry and structural complexity of nozzle fillet weld increase the challenges and procedural intricacies of conventional ultrasonic testing. While radiographic testing demonstrates higher sensitivity to volumetric defects, it risks missing planar defects (e.g, cracks, lack of fusion) with improper irradiation angles and introduces radiation hazards. Magnetic particle and penetrant testing are restricted to surface or near-surface defect detection. This study utilizes CIVA simulation software to conduct ultrasonic phased array detection simulations on nozzle fillet weld models, selecting 7.5 MHz and 5 MHz probes for comparison. Simulation results show that the 7.5 MHz probe provides high-definition imaging with distinct defect contours, minimal artifact interference, and enhanced quantitative accuracy. Although the 5 MHz probe offers deeper penetration, its inferior imaging quality and artifact interference justify the selection of the 7.5 MHz probe for experimental validation. To simulate defects in nozzle fillet welds, fabricated simulated test blocks contain lack of fusion, incomplete penetration, and root cracks. Phased array ultrasonic testing (PAUT) is performed on the simulated specimens, incorporating zoning inspection and segmented scanning strategies. Detection results indicate that PAUT can effectively identify prefabricated defects in nozzle fillet welds, with measured defect dimensions closely aligning with design specifications. This work establishes a technical foundation for advancing intelligent detection methodologies in nozzle fillet weld inspection.