The commonly used radiation for flaw detection includes magnetic particle flaw detectors and gamma rays emitted by isotopes, respectively referred to as magnetic particle flaw detectors and gamma ray flaw detectors. When these rays pass through (irradiate) a substance, the higher the density of the substance, the more the intensity of the rays decreases, that is, the intensity at which the rays can pass through the substance decreases. At this point, if photographic film is used for reception, the sensitivity of the film will be low; If instruments are used to receive, the signal obtained will be weak. Therefore, when using radiation to irradiate the damaged parts of the ultrasonic flaw detector, if there are defects such as pores and slag inclusions inside, the density of the material transmitted through the path with defects is much smaller than that of the path without defects, and the intensity of the radiation is reduced less. That is, the transmitted intensity is greater. If a film is used for reception, the light sensitivity is greater, and the plane projection of the defect perpendicular to the direction of the radiation can be reflected on the film; If other receivers are used, instruments can also be used to reflect the plane projection of defects perpendicular to the direction of the radiation and the transmittance of the radiation.

Ultrasonic waves with high frequency have strong linearity in propagation, are easy to propagate in solids, and are prone to reflection when encountering interfaces formed by two different media. Therefore, they can be used for flaw detection. Usually, an ultrasonic probe is used to have good contact with the surface of the workpiece to be tested. The probe can effectively emit ultrasonic waves to the workpiece and receive the ultrasonic waves reflected from the (defect) interface. At the same time, they are converted into electrical signals and transmitted to the instrument for processing. Ultrasonic flaw detector. The location of defects can be determined based on the speed (often referred to as sound velocity) and propagation time of ultrasound waves in the medium.

There are various methods for displaying defects in flaw detectors, including those that use magnetic particle display and those that do not. Magnetic particle inspection is called magnetic particle testing, which is one of the commonly used methods due to its intuitive display, simple operation, and people's willingness to use it. Without magnetic particle display, it is commonly referred to as magnetic leakage testing. It often uses induction coils, magnetic tubes, Hall elements, etc. to reflect defects. The flaw detector is more hygienic than magnetic particle testing, but not as intuitive as the former.