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Ultrasonic testing is primarily used to detect hidden defects within butt welds and cracks on the inner surface of pressure vessel welds. It is also employed to identify potential cracks in pressure vessel forgings and high-pressure bolts. Ultrasonic testing can be divided into ultrasonic inspection, ultrasonic thickness measurement, as well as the use of ultrasound to determine grain size and stress levels. There is also the pulse reflection method, which relies on the echoes from defects and those from the bottom surface for making judgments ； There is a penetration method that determines the presence of defects based on defective shadows, as well as a resonance method that determines defects or plate thickness by using standing waves generated by the object under inspection. The most commonly used method at present is pulse reflection. Characteristics of ultrasonic testing: (1) It has a higher detection rate for surface-type defects, but a lower detection rate for volume-type defects. ⑵ Suitable for inspecting workpieces with thicker thicknesses. ⑶ Applicable to various test pieces, including butt welds, fillet welds, T-joints, plates, pipes, bars, forgings, composites, etc. ⑷ The testing cost is low and the speed is fast; the testing instruments are small in size and light in weight, making them convenient for use on-site. ⑸ It is impossible to obtain intuitive images of defects, positioning is difficult, and the quantitative accuracy is low. ⑹ There are no direct witness records for the test results.