Abstract: Trail thin-walled pipes are the most vulnerable parts and locations to defects and leaks in the operation of nuclear power plants. The thin walled pipe seam of the trail was generally inspected by ray method, but the ray detection had some obvious limitations. There is a radiation risk in the detection, the detection area needs to be isolated, and the length of the test period makes it impossible for radiation detection to be used on a large scale during the overhaul of the nuclear power plant. In this paper, based on the natural defect test block, the ultrasonic inspection technology and the test ability of the thin walled tube socket weld phase control array are studied. On the basis of this, practical application of the technology was successfully carried out in the field of nuclear power overhaul and some defects were actually found.