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Non destructive testing of steel structure welding quality

In the process of steel structure welding, the angle error of welding and the imprecise process of welding will cause its quality defects. In the field of construction, the quality of steel structure welding is very important. Once the steel structure materials have problems, it will cause serious construction accidents. Therefore, attention should be paid to the quality inspection of steel structure welding. As for the shortcomings of steel structure welding, in most cases, ultrasonic nondestructive testing is adopted for steel structure welding materials to understand the welding quality of steel structure and optimize the production process of steel structure without damaging the overall performance of steel structure.

1. Slag inclusion detection

During welding, if the current is not properly controlled, too small current will cause slag inclusion in the welding materials. When using ultrasonic nondestructive testing to determine the slag inclusion defect, generally use the feature that the slag inclusion echo signal is not high and is serrated. When translating the probe, if the wave amplitude has significant changes, and the detection reflection amplitude of each direction is also different, judge the slag inclusion defect based on this situation.

2. Radiographic testing

Radiographic testing is to determine the defects of the structure by increasing or decreasing the intensity of the object γ The size, shape and quantity of defects can be evaluated according to the image information recorded on the film when the ray penetrates the sample. This testing method is the most basic and widely used non-destructive testing method, but its biggest disadvantage is that the radiation is large, causing harm to human health.

3. Fusion detection

In the process of welding, too many impurities will lead to poor fusion, and too fast welding speed and inappropriate welding current will make the welding materials biased in the process of fusion. In the process of ultrasonic detection to judge whether the internal welding of welding materials is fused, when the ultrasonic probe is used for translation, the waveform is relatively stable and the reflected wave amplitude is different, there is a problem of non fusion. If the welding materials are not fully fused, many subsequent application problems will arise, which will greatly reduce the overall construction efficiency.

4. Crack detection

The crack defect is very deadly for the welding material. It is different from other common defects and has a strong danger, sometimes even causing the entire weldment to break. When detecting crack defects, the echo height of ultrasonic wave is large, the amplitude is wide, and even there are multiple peaks. When the ultrasonic probe moves for detection, the reflected wave in the probe will continuously shake, and when the probe continues to turn, the wave crest in the probe will show significant stagger.

In steel structure engineering, it is very necessary to strictly control the quality of steel structure, so non-destructive testing of steel structure welding quality is particularly important. In order to ensure the safety of welding quality without damaging the internal construction of steel structure building materials, it can also effectively detect the welding quality problems of materials.

5. Visual inspection

Visual inspection is the main method for the first stage of non-destructive testing in the world. The steel structure shall be inspected with the naked eye and based on previous experience to investigate whether there are significant problems in the steel structure, so as to judge whether subsequent inspection is affected, and then four routine inspections shall be carried out. This method can only detect the external defects of the structure. It is generally used to detect the appearance of the welding parts to ensure that the appearance quality meets the requirements of the specification and avoid major defects. However, because it is more dependent on the experience of the detection personnel, its application scope is narrow.

6. Magnetic particle testing

It is applied to the detection of welding parts of steel structures, and can quickly and accurately detect whether there are cracks, lack of fusion and other defects in the weldments. However, it can only detect whether there are defects in the steel structure components with a thickness of 8 mm. Its detection principle is that after ferromagnetic workpieces and materials are magnetized, discontinuous and locally deformed magnetic lines of force will occur on the surface and near surface of the workpieces, thus magnetic leakage field will occur. Magnetic particles will be applied on the surface of the workpieces, and under appropriate light, magnetic marks will be formed, and visible discontinuous positions, shapes and sizes can be seen.

7. Eddy current testing

Eddy current testing places the coil with alternating current on the metal plate to be tested or sheaths it outside the metal tube to be tested. Alternating magnetic fields will occur inside and near the coil, so eddy induced alternating current will occur in practice, which is called eddy current. The distribution and size of vortices are not only related to the shape and size of coils and the size and frequency of AC current, but also depend on conductivity, magnetic permeability, shape and size, coil spacing, and whether there are cracks on the surface.

8. Ultrasonic testing

Ultrasonic testing is applicable to the detection of internal defects of metal and non-metallic composite materials. The defects are judged by the changes in amplitude and waveform of defects in the ultrasonic wave. It is sensitive for plane defect detection, and can quickly detect the defects of incomplete penetration and incomplete fusion. The corresponding ultrasonic detector is convenient to carry, low in price, harmless to human body and environment, and easy to use on site.