Non-destructive Testing Instrument: Estimation of Internal Defect Properties, Causes, and Preventive Measures

Ultrasonic flaw detectors typically emit ultrasound at the object being tested (such as industrial materials or the human body), then utilize its reflections, Doppler effect, and transmission to obtain internal information about the object, which is processed to form an image.

    The Doppler effect method in the flaw detector utilizes the Doppler frequency shift phenomenon that occurs when ultrasound encounters a moving object to determine its motion direction and velocity, among other characteristics. The transmission method, on the other hand, analyzes the changes in ultrasound after passing through the object to deduce its internal properties; its application is currently in the research and development stage.

    Internal Defect Assessment of Non-Destructive Testing Equipment: Causes and Preventive Measures

    Porous Areas: The echo height of a single pore is low, with a waveform resembling a single slit, which is relatively stable. Reflection waves from various directions are generally similar, but they disappear as soon as the probe is moved slightly. Dense pores produce a cluster of reflection waves, with wave height varying with the size of the pores. When the probe rotates at a fixed point, an alternating phenomenon occurs. The primary cause of such defects is that the welding material was not dried at the specified temperature, the flux coating of the welding rod has deteriorated and fallen off, the core wire has rusted, the wire was not cleaned thoroughly, the current was too high during manual welding, and the arc was too long.;Arc welding can result in excessive voltage during the process or significant fluctuations in the power grid voltage.;Low purity of protective gas during gas shielded welding. The presence of gas pores in the weld not only ruins the compactness of the weld metal but also reduces the effective cross-sectional area of the weld, lowering its mechanical properties. Particularly when chain-like gas pores are present, there will be a significant decrease in bending and impact toughness. Measures to prevent such defects include: not using electrodes with cracked, peeled, deteriorated flux coating or rusted core, and rusted welding wire must be de-rusted before use. The welding materials should be dried according to the specified temperature, the bevel and both sides cleaned, and appropriate welding current, arc voltage, and welding speed should be selected.