Abstract: The working principle of TOFD technique was described. The testing effects were compared between radiographic testing and ultrasonic testing method for the detection of volute plate and seam weld. The actual weld section showed that the planar defects, which were difficult to detect by conventional ultrasonic testing and radiographic testing method, were easy to TOFD technique, but there was some error for the porosity, inclusions and such as volume-like defects between TOFD testing and actual section. Due to its high defect detection rate, sensitive to planar defects, less limits by direction, fast testing speed, intuitive scanning image and with no radiation and so on, TOFD technique had good prospect on the safety evaluation at petrochemical installations and so on special equipments.