Eddy current testing is one of the nondestructive testing methods for square rectangular hollow section.

　　Eddy current inspection is one of the most important processes in the production of high frequency welded square rectangular hollow section. High frequency welded square rectangular hollow section is widely used in the fields of fluid transportation, building components and container manufacturing. According to the technical requirements of welded pipe, the weld shall be free of cracks, cracks, incomplete fusion and other defects, and the surface shall be free of excessive scratches, crushing and other defects.

　　From the principle of eddy current generation, it can be seen that eddy current detection has the following six advantages:

　　1. Eddy current testing can realize fast and automatic testing;

　　2. Eddy current testing is also applicable to the testing of special-shaped materials, as long as the coil is made of various shapes, it can be tested;

　　3. Eddy current testing is especially suitable for surface and near surface testing of conductive materials;

　　4. Eddy current testing can be applied to the detection of high-temperature metal, because the metal has conductivity at high temperature;

　　5. Eddy current testing is only applicable to conductive materials. If it is non-conductive materials, eddy current can not be induced, nor can eddy current be used for testing;

　　6. Coupling agent is not required for eddy current testing. The electromagnetic field excited in eddy current testing is only a kind of electromagnetic wave, which has the characteristics of fluctuation and particle. Therefore, the probe and workpiece can propagate without coupling, so it can be used for non-contact testing. This is better than ultrasonic testing. Because ultrasound is a mechanical wave, it can only spread in matter. Therefore, coupling agent should be added between probe and workpiece in ultrasonic testing.

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