Ultrasonic flaw detectors, there are two main types of flaw detection using ultrasound, the penetration method and the reflection method. The penetration method uses two probes, one for transmitting ultrasound and one for receiving ultrasound. When testing, the two probes are placed on both sides of the workpiece, and the internal quality of the workpiece is discerned according to the change in energy after the ultrasonic waves have penetrated the workpiece.
Reflective method of flaw detection high frequency generator generated by the high frequency pulse excitation signal on the probe, the resulting wave to the workpiece internal propagation, such as the existence of defects inside the workpiece, part of the wave as a defect wave is reflected back, the rest of the emitted wave as the bottom wave will also be reflected back. The location of the defect can be determined from the position of the emitted wave, the defect wave and the bottom wave relative to the scan baseline; the size of the defect can be determined from the amplitude of the defect wave; the nature of the defect can be analysed from the shape of the defect wave; if there is no defect inside the workpiece, only the emitted wave and the bottom wave are present.
Ultrasonic Flaw Detector
During the inspection process, it is important to first understand the technical requirements of the drawings for the quality of the weld. Acceptance standards for steel structures are based on GB50205- 2001 "Code of Construction Quality Acceptance for Steel Structures" to implement. Standard provisions: for the drawings require weld welding quality level for a level when the rating level for Ⅱ specification requirements to do 100% ultrasonic flaw; for the drawings require weld welding quality level for the second level when the rating level for Ⅲ specification requirements to do 20% ultrasonic flaw; for the drawings require weld welding quality level for the third level when not to do ultrasonic internal defect inspection.
It is worth noting here that ultrasonic flaw detection is used for full penetration welds, and the proportion of flaw detection is calculated as a percentage of the length of each weld, and is not less than 200mm.
If an impermissible defect is found, the length of the flaw should be increased at both ends of the defect by not less than 10% of the length of the weld and not less than 200mm, and when there is still an impermissible defect, the weld should be subjected to a 100% flaw inspection. In addition, the thickness of the base material, joint type and bevel type of the workpiece to be tested should be known. Generally, the thickness of the base material is between 8-16mm, and the bevel type has several forms such as I type, single V type and X type. Only after the above has been clarified can preparatory work be carried out before the flaw detection.
Standard test blocks (CSK- IA, CSK- ⅢA) must be used to calibrate the overall performance of the instrument and the panel curve before each flaw detection operation to ensure the accuracy of the flaw detection results.
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