Discussion on the qualitative analysis of welding seam ultrasonic testing Wang Yunchang Jiangbo (Jiangxi Electric Power Testing Research Institute Jiangxi Shangchang 330006) According to the field inspection experience, the method for qualitative analysis of ultrasonic testing defects was summarized, and Hengda ultrasonic plastic welding machine made this method Detailed introduction.
285: B Preface The three key contents of the evaluation of defects in ultrasonic testing technology are: the location, quantification and qualitativeness of defects. At present, the research on the location and quantitative evaluation of defects in ultrasonic testing technology is relatively mature, but the nature of defects is rarely evaluated (the ultrasonic testing standards require the location and quantitative evaluation of defects, but the qualitative evaluation of defects is relatively Difficult without request). This is because the reflection characteristics of the defect to the ultrasonic wave depend on the defect's orientation, geometry, length and thickness relative to the ultrasonic wave propagation direction. The roughness of the surface of the defect, the content of the defect, the nature and type of the defect, etc. In the actual inspection, because it is difficult to identify the nature of the defect, some products with non-hazardous defects are often repaired and unnecessary waste will be caused. At the same time, the dangerous defects (such as cracks) contained in some products will be ignored. There are hidden safety hazards in its use, which makes the qualitative analysis of defects in ultrasonic testing particularly important.

1 Qualitative analysis of defects According to the basic theoretical knowledge of ultrasonic, combined with the experience of qualitative analysis of defects in the actual ultrasonic inspection work, there are mainly the following qualitative evaluation methods for defects in ultrasonic inspection.

1.1 Waveform Judgment Method At present, the most widely used in ultrasonic testing is the A-type display pulse detector. Through long-term ultrasonic testing practice and a full understanding of materials and manufacturing processes, the defects found in ultrasonic testing are dissected, analyzed, and analyzed. Through the accumulation of rich experience, the static and dynamic waveforms of the defect echoes displayed on the display screen can be used for testing. The steepness of the front edge of the echo and the descending slope of the back edge of the echo, the peak shape, and the return Wave occupying competition, the amplitude, position, quantity and envelope shape of the defect echo when moving the probe, the number of multiple reflections of the bottom wave and the decreasing law of the amplitude, the loss of the height of the bottom wave, etc. and according to the defect in the inspection work The position, distribution status, equivalent size and extension of defects, combined with specific material characteristics, process and basic theoretical knowledge of ultrasound to make comprehensive judgments can achieve a more accurate assessment of the nature or type of defects. The following are the echo characteristics of common defects in welds.

1.1.1 The echo of the pores in the weld has a fast wave speed and a low amplitude. When the probe is used to detect the defect, it can be found that the echo has the characteristics of a point defect and has no extension length.

1.1.2 The echo position of the slag and slag inclusion in the weld is irregular and the waveform is disordered. When the probe is moved, the echo side is slow, and the starting degree is slow, the peak is relatively blunt, and the trailing edge slope is not large. , The echo accounted for a large amount. When the sound beam of the probe changes its perpendicularity to its extending direction, the amplitude change is not significant, and the cycle appears as an irregularly shaped long strip defect. 1.1.3 Insufficient penetration and incomplete penetration in welds include intermediate and root incomplete penetration, especially for incomplete root penetration, the echo has a faster wave speed and strong response, on both sides of the weld It can be found by exploration, and the reflected wave amplitude is approximately the same as shown in the phase diagram of the waveform of the crack and non-metallic inclusions: the wave screen of the defect waveform is first calibrated with time. This can be achieved by using a test block with a known sound velocity. During the test, the echo height of the defect should be 100% full scale, and then read the 90% full scale line, the k and f corresponding to the intersection of the 20% full scale line and the echo packet route. 3. For crack-like defects, the echo is small, and It is smaller than that of non-planar defects. For loose inclusion defects, due to the dispersion characteristics of the irregular interface around the defect, the echo is larger. The defect echo method and waveform judgment method determine the gas-containing crack defect (echo The front edge is steep, the echo is small, and the slope of the back edge of the echo is large) is corresponding, but the defect echo method can be used to determine the nature of the defect more accurately.

2 Conclusion There are some other methods for qualitative analysis of defects in ultrasonic testing. For example, according to the spectral envelope shape of the defect echo and the defect geometry and orientation, as well as the ratio of the defect size to the ultrasonic length, it is possible to transmit a narrow pulse wave in the competition band to the defect and analyze the spectrum of the received echo signal. Judging the type and nature of defects, as well as ultrasonic holographic technology and the use of computers to process defect echo signals, can effectively distinguish the nature of defects.

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