The fundamental principle and key technology of the ultrasonic phased array and the ultrasonic time of flight diffraction (TOFD) are presented in detail. The phased array pulsing and receiving method can inspect various kinds of defects with good precision whereas the TOFD method can enhance the precision of detection with a dead zone on the pipeline surface. However, if the two methods are used together, the system will not only gain the best precision but also boost the inspection efficiency, avoiding the dead zone of the TOFD method. It is found that the inspection results can be affected by the coupling liquid. The inspecting procedure may be influenced by the relative position of probes and coding machine. In general, the ultrasonic phased array and TOFD technology are professional in inspecting welds and will be put into service extensively in future.
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