Abstract: Due to the special weld structure of orifice plate flowmeter shell, the short joint shape of flowmeter pipeline and the change of thickness and size, etc., the application of non-destructive testing technology is affected. In order to solve the problems of defect detection and thickness measurement of shell weld, and to meet the requirements of inspection, the application of time difference diffraction method, full focus phased array ultrasonic testing and conventional ultrasonic testing technology is studied. In order to ensure reliable and accurate detection, we should optimize the selection of ultrasonic detection methods. Through the analysis of test data, the structural display of different ultrasonic testing methods and the display characteristics of related weld defects are collected and summarized, which can provide reference for similar testing activities in the future.