Abstract: Because of unique structure and complex stress, the socket fillet weld of pipe usually has dangerous defects arising from incomplete penetration and fusion during welding process, and yields stress concentration in the operation process. According to the structural characteristics of socket fillet weld of small-diameter pipe, two different types of reference blocks (placement type and insertion type) were designed and manufactured, and they were used to adjust the detection sensitivity to improve the detection accuracy. Typical defect samples were made for experimental research.The unique phased array inspection technology for socket fillet weld of small-diameter pipe was summarized. The feasibility and accuracy of the inspection technology were confirmed by the application in the installation and maintenance of thermal power units. The development of this testing technology provides a reference for the popularization and application of phased array ultrasonic testing technology in socket fillet weld detection.