In response to the single-sided accessibility issue caused by the weld structure and the significant positioning deviation caused by spherical detection surface in the surge nozzle to vessel weld of pressurizer in nuclear power plant,a phased array ultrasonic inspection(PAUT)technology and a defect positioning correction algorithm are developed,which are verified in a simulated body with natural defects and compared with the results of radiographic inspection.The results show that,combined with the defect positioning correction algorithm,the PAUT technology meets the requirements of the performance demonstration,and the detection capability is equivalent to that of radiographic inspection.