Detection of surface defects of square and rectangular tubes

There are five main methods for detecting surface defects of square and rectangular tubes:
 

1. Eddy current inspection

Eddy current testing includes basic eddy current testing, far-field eddy current testing, multi-frequency eddy current testing, and single-pulse eddy current testing. Using the eddy current sensor to magnetically induce metal materials, the type and shape of the surface defects of the rectangular tube will cause different types of data signals. It has the advantages of high inspection accuracy, high inspection sensitivity, and faster inspection speed. It can inspect the surface and lower layers of the tested pipe, and is not harmed by residues such as oil stains on the surface of the tested square steel pipe. The disadvantage is that it is very easy to distinguish flawless structures as flaws, the false detection rate is high, and the inspection screen resolution is not easy to adjust.

2. Ultrasonic testing

When ultrasound enters an object and hits a flaw, a portion of the sound frequency creates a reflective surface. The multi-purpose function of receiving and sending can analyze the reflected surface wave, and can detect the faults accurately and accurately. Ultrasonic testing is commonly used in the inspection of steel castings. The inspection sensitivity is high, but the complicated pipeline is not easy to inspect. It is stipulated that the surface of the rectangular tube to be inspected has a certain degree of gloss, and the gap between the camera and the inspected surface is blocked with a silane coupling agent.

3. Magnetic particle inspection method

The basic principle of the magnetic particle inspection method is to complete the electromagnetic field in the raw material of the square steel pipe. According to the interaction between the defect leakage electromagnetic field and the magnetic particle inspection, when there is discontinuity or defect in the surface layer or near-surface layer, the magnetic field line will be partially deformed where there is no continuity or defect, resulting in a magnetic field. Its advantages are less investment in machinery and equipment projects, high stability and strong image. The defect is that the actual operation cost increases, the defect classification is inaccurate, and the inspection speed is relatively slow.

4. Infrared detection

According to the high-frequency magnetic induction electromagnetic coil, induced electromotive force is caused on the surface of the square tube. The induced electromotive force will cause the disadvantaged area to consume a lot of electromagnetic energy, causing the temperature of some parts to rise. Use infrared induction to check the temperature of some parts to identify the depth of the defect. Infrared sensors are generally used for the inspection of surface defects, and the discomfort is used for the inspection of irregular metal materials on the surface.

5. Magnetic flux leakage inspection

The magnetic flux leakage inspection method is very similar to the magnetic particle inspection method, and its application field, sensitivity and stability are stronger than the magnetic particle inspection method.

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