1. Eddy's current flaw detection.
Eddy current flaw detection includes basic eddy current flaw detection, far-field eddy current flaw detection, multi-frequency eddy current flaw detection, and single pulse eddy current flaw detection. Using eddy current sensors to detect metal materials, the types and shapes of defects on the surface of square tubes will produce different types of signals. It has the advantages of high inspection accuracy, high inspection sensitivity, and faster inspection speed. It can inspect the surface and lower surface of the tested pipeline and is not affected by oil stains and other residues on the surface of the tested square steel pipe. The disadvantage is that it is easy to identify a defect-free structure as a defect, the false detection rate is high, and the inspection screen resolution is not easy to adjust.
2. Ultrasonic testing
When ultrasonic waves enter an object and hit a defect, part of the sound wave frequency creates a reflective surface. The multi-purpose receiving and transmitting functions can analyze reflected waves, detect abnormalities, and accurately detect defects. Ultrasonic testing is commonly used in the inspection of steel castings. The inspection sensitivity is high, but complex pipelines are not easy to inspect. It is required that the surface of the rectangular tube under inspection has a certain glossiness, and the gap between the camera and the surface under inspection is sealed with a silane coupling agent.
3. Magnetic particle inspection
The basic principle of the magnetic particle flaw detection method is to create an electromagnetic field in the raw material of the square steel pipe. According to the interaction between defect leakage electromagnetic field and magnetic particle inspection, when there is a discontinuity or defect on the surface or near the surface, the magnetic field lines will be partially deformed at the discontinuity or defect, resulting in a magnetic field. Its advantages are low investment in machinery and equipment projects, high stability, and a strong image. The shortcomings are increased actual operating costs, inaccurate classification of shortcomings, and slow inspection speed.
4. Infrared detection
Through the high-frequency magnetic induction coil, an induced electromotive force is generated on the surface of the square tube. The induced electromotive force will cause the defective area to consume a large amount of electromagnetic energy, causing the local temperature to rise. Use infrared induction to check the local temperature and determine the depth of the fault. Infrared sensors are generally used to detect surface defects, and discomfort is used to detect surface irregularities in metal materials.
5. Magnetic flux leakage inspection
The magnetic flux leakage inspection method for square and rectangular tubes is very similar to the magnetic particle inspection method. Its application field, sensitivity, and stability are stronger than the magnetic particle inspection method.

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