The Application of TOFD Technique on the Large Pressure Vessel

摘要

The TOFD technique (Time of flight diffraction) is an ultrasonic image-generating technique, which offers the capability of detection, location and sizing. To a certain extent characterization of discontinuity in the weld material as well as in the adjacent parent material is also possible. Compared with purely reflection-based techniques, the TOFD technique, which is based on diffraction, is less sensitive to the orientation of the discontinuity. Simultaneously, the determination of the defects relies on the time of flight diffraction rather than the amplitude of reflection wave as the conventional UT method. So, the detectable reliability of the discontinuity is much enhanced. Presently, the TOFD technique is widely used to the metal NDT on the nuclear industry, the power industry and the pressure equipments. This paper describes the using of the TOFD equipment which is made by the AIS company in America. In the field, we performed the three inspections on a large spherical vessel (3000M~3) using the TOFD and X-ray radiography and conventional UT independently. Compared the testing results, we can conclude that the TOFD technique not only has the higher detectable probability of defects, but also has the higher measuring precision on the height of defects than RT and UT.