What are the different functions of internal inspection and surface inspection?
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Internal rays and ultrasonic waves, external magnetic particle inspection – I’ve never seen any of these either; I’m not sure what purpose each one serves
Refer to the standard NB/T47013; you can also search forums for discussions related to non-destructive testing
Magnetic particle inspection can detect surface defects, while ultrasonic and radiographic inspection can detect deep defects.
Thank you. I know that. What I don’t understand is what kind of defects can exist on the surface; cracks on the surface are visible to the naked eye
Tiny cracks on the surface are often difficult to detect with the naked eye, but can be easily identified using magnetic particle or penetrant testing.
Tiny surface cracks are difficult to detect with the naked eye; for example, at the weld joints of tube sheets and heat exchange tubes, surface inspection is necessary
Penetrant testing is used to detect surface open defects, while magnetic particle testing is used to detect surface and near-surface defects. These surface defects, which are mainly linear in nature, are often invisible to the naked eye or make it impossible to determine their severity; therefore, appropriate non-destructive testing methods must be used for detection.
One is for detecting defects deep within, and the other is for detecting surface or near-surface defects. The cost difference is significant.