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Evaluation of the nature of internal defects, causes of defects and preventive measures ①

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The echo height of a single blowhole is low, and the waveform is a single slit, which is relatively stable. Detected from all directions, the reflected waves are roughly the same, but when the probe of the ultrasonic flaw detector is moved a little, it disappears, and a cluster of reflected waves will appear in the dense pores, and the wave height varies with the size of the pores. When the probe rotates at a fixed point, the phenomenon of ups and downs will appear.



The main reasons for such defects are that the welding material is not dried at the specified temperature, the coating of the electrode is deteriorated, the welding core is corroded, the welding wire is not cleaned, the current is too large during manual welding, and the arc is too long; the voltage during submerged arc welding is too high. Or the network voltage fluctuates too much; the purity of the shielding gas is low during gas shielded welding. If there are pores in the weld, it not only destroys the compactness of the weld metal, but also reduces the effective cross-sectional area of ​​the weld and reduces the mechanical properties. Especially when there are chain pores, the bending and impact toughness will be significantly reduced. .



The measures to prevent such defects are: do not use electrodes with cracked coating, peeling, deterioration and rusted cores, and rusted welding wires can only be used after rust removal. The welding materials used should be dried at the specified temperature, the groove and both sides should be cleaned, and the appropriate welding current, arc voltage and welding speed should be selected.