I. Eddy current testing. Eddy current testing includes conventional eddy current testing, far-field eddy current testing, multi-frequency eddy current testing and pulsed eddy current testing. Using eddy current sensors to sense metal, the type and shape of defects on the surface of square tubes will produce different types of signals. It has the advantages of high detection accuracy, high detection sensitivity and fast detection, and can detect the surface and the lower surface of the pipeline under test, not affected by the surface of the square pipe oil and other impurities. The disadvantage is that it is easy to judge the defect-free structure as defect, the error detection rate is high, and the detection resolution is not easy to adjust.
Second: ultrasonic detection
When ultrasonic waves enter an object and encounter a defect, some of the sound waves are reflected. The transceiver function analyzes the reflected wave, and can detect the defects abnormally and accurately. Ultrasonic testing is often used to detect forgings. The detection sensitivity is high, but the pipe with complex shape is difficult to detect. The surface of the tube is required to have a certain degree of smoothness, and the gap between the probe and the surface is filled with coupling agent.
Third: magnetic particle detection
The principle of magnetic particle method is to achieve a magnetic field in square tube material. According to the interaction between defect leakage field and magnetic powder, when there is discontinuity or defect on the surface or near the surface, the magnetic field line will be deformed locally at the discontinuity or defect, resulting in magnetic poles. Its advantages are less investment in equipment, high reliability and strong intuition. The disadvantages are high operation cost, inaccurate defect classification and slow detection speed.
Fourth: infrared detection
An induced current is generated on the surface of the square tube through a high-frequency induction coil. Induced current will cause the defect area to consume more power, resulting in local temperature rise. Infrared ray is used to detect local temperature and determine the depth of defects. Infrared detection is generally used for the detection of flat surface defects, not for the detection of irregular metal surface.
Fifth :magnetic leakage detection
Square tube magnetic flux leakage detection method is very similar to magnetic particle detection method, its scope of application, sensitivity and reliability are better than magnetic particle detection method.
