What are the common welding defects? What are the methods for detecting weld defects?

Date：2022-06-16 15:41:20Views：1135

There are many kinds of weld defects, which can be divided into internal defects and external defects according to their positions in the weld. External defects are located on the outer surface of the weld, which can be seen with the naked eye or a low magnification, for example, the weld size does not meet the requirements, undercut, overlap, crater, air hole, crack, slag inclusion, incomplete penetration, incomplete fusion, etc. Internal defects are located inside the weld. Such defects are found by destructive inspection or flaw detection methods, such as incomplete penetration, incomplete fusion, pores, cracks, slag inclusions, etc.

Common methods of welding defect inspection

1，Visual inspectionGenerally, the inspection depends on visual observation. With the help of some tools, the accuracy of inspection can be greatly improved. The commonly used tools include: weld inspection gauge, tape, steel ruler, low power magnifying glass, etc., which are generally used to inspect the defects outside the weld.

2，Air tightness testGenerally, it is necessary to inspect the air tightness of the melter and pipeline, and different inspections shall be conducted according to the requirements of the tested object. ① For the submerged test, place the container filled with a certain pressure in the water tank and press it down to a certain depth, then rotate it slowly to observe whether there are bubbles on the container to determine whether there is leakage. ② For soapy water inspection, use a brush dipped in soapy liquid on the container filled with a pressure gas to apply it to the weld successively, and it is qualified if there are no bubbles.

3，Kerosene testIt uses the strong permeability of kerosene to test the tightness of the weld. Apply lime water on one side of the weld (outside of the container), and then apply kerosene on the other side of the weld (inside of the container) after the lime water is dry to test whether there are oil spots on the white lime.

4，Pressure test, also known as pressure test, it includes hydraulic test and pneumatic test. Pressure test is an inspection method to check whether there is leakage and pressure holding by pressurizing the vessel (water pressure or air pressure) to the test pressure. The test pressure shall be higher than the working pressure, otherwise the safe operation of the vessel cannot be guaranteed. The pressure test is used to evaluate the overall strength performance, deformation and leakage of welded components such as boilers, pressure vessels and pressure pipelines.

On the one hand, the pressure test can test the compactness of the structure, on the other hand, it can also test the strength of the structure. For hydrostatic test, close the water valve when it is filled with water and the air is completely discharged, and then pressurize the vessel by stages with high-pressure water pump until it reaches the test pressure (generally 1.25 ~ 1.5 times the working pressure); Inspect the weld for water drops (leakage). If yes, it indicates that there is leakage;

Check the pressure maintaining condition. After stopping pressurization, maintain the pressure for 5 ~ 10min, and the pressure shall not drop significantly. For the air pressure test, the high-pressure air pump is used to step up the pressure of the container step by step and maintain the pressure for a certain period of time every liter until it reaches the specified test pressure. Check whether there is leakage with soap water and check the pressure maintaining condition.

5，Radiographic testingDuring the process of penetrating the material, the intensity of the ray is weakened and attenuated due to absorption and scattering. The attenuation degree depends on the attenuation coefficient of the penetrating material and the thickness of the penetrating material. If there is a defect inside the Transilluminated workpiece, and the defect medium and the inspected workpiece have different attenuation degrees to the ray, the intensity of the ray passing through the workpiece will be different, resulting in different photosensitivity of the film. After the darkroom treatment, the blackness of the defective part on the negative film is larger, The film evaluator can judge the defects based on this. Radiographic testing shall be conducted by personnel with full-time qualification certificates.

6，Ultrasonic testingIt is a method to detect the internal or surface defects of metal materials and their workpieces by using the acoustic characteristics of ultrasonic wave propagating in the medium. When ultrasonic wave propagates in the metal, it will be reflected at the interface. During detection, ultrasonic wave has reflected pulses on both surfaces of the workpiece. If there is a defect inside the workpiece, the third pulse will appear between the two boundary pulses. The defect position can be determined according to the position of this pulse. The ultrasonic flaw detection equipment is light and flexible with a wide detection range.

7，Magnetic particle testingThe permeability of ferromagnetic metal material is much greater than that of air. When it is magnetized in the magnetic field, the magnetic lines of force will be concentrated in the material. If there are defects such as pores, cracks and slag inclusions on the surface or near the surface of the material, it is difficult for the magnetic lines of force to pass through these defects. Therefore, a local magnetic leakage field will be formed at the defect. At this time, magnetic particles will be scattered on the material, and the magnetic particles will be attracted to the defect by the magnetic leakage field, And then show the macroscopic trace of defects. Demagnetization treatment shall be carried out for the workpiece that has undergone magnetic particle testing.

8，Other inspections: ① magnetic yoke inspection; ② Penetrant testing; ③ Eddy current testing; ④ Bending test; ⑤ Impact test; ⑥ Metallographic examination.

The above is the content related to welding defect detection compiled by the core detection team. I hope it can help you. Shenzhen Chuangxin Online Testing Technology Co., Ltd. is a well-known professional testing institution for electronic components in China, with 3 standardized laboratories covering an area of more than 1000 square meters. The scope of testing services covers: testing and verification of electronic components, IC authenticity identification, material selection for product design, failure analysis, function testing, factory incoming material inspection, X-ray testing of components and parts, tape braiding and other testing items.