Abstract: According to the TSG G0001-2012 Boiler Safety Technical Supervision Administration Regulation, the butt weld needed X-ray test. The test was generally carried out according to the NB/T 47013.2-2015 Nondestructive Testing of Pressure Equipment Section 2:X-ray test through X-ray elliptical imaging or vertical imaging to standards. Normally, such defect as the lack of inter-run fusion is difficult to detect as variation of in-coming directions of the X-ray. Through theoretical and testing study on different UT methods, a kind of clamping fixture for holding axial/circumferential phased array probes in combination with flexible wedges with curvature has been developed for detecting the defect of the lack of inter-run fusion, thus breaking through the limitation of X-ray test.