1、 The wear forms of ultrasonic probes
Several forms of wear and tear commonly encountered in work practice
Based on the above figure, it can be seen that the original characteristics of the ultrasonic probe will be changed after wear, mainly manifested in an increase or decrease in the refractive angle K value, a change in the sound beam incidence point (probe front), and a change in coupling (coupling will deteriorate after wear in flat plate testing, while coupling will improve with increasing contact surface during pipe or bar testing).
The depth and position of defects will change on the ultrasonic flaw detector as the angle of sound beam refraction and the incident point change. When the coupling compensation of the equipment remains unchanged, the deterioration of coupling will lead to a decrease in the sensitivity of the flaw detection, while conversely, it will lead to an increase in sensitivity.
If due to personal habits, frequent testing from one fixed side to the other can cause the ultrasonic probe to be worn off, resulting in beam deviation and positioning errors of defects.
After changing the characteristics, it is easy to cause missed detections or misjudgments, which brings uncertainty to the testing work.
If there is mild wear, this change can be corrected by adjusting the data of the ultrasonic flaw detector on the test block. If there is severe wear, it cannot be compensated by adjusting the data of the ultrasonic flaw detector. In this case, it is necessary to replace the ultrasonic probe or repair the ultrasonic probe to correct it.
3、 Repair of ultrasonic probes
After a period of testing work, in addition to routine debugging, the repair work of the ultrasonic probe should be based on the degree of wear of the probe.
If the ultrasonic probe is only slightly worn, it should be polished on coarse sandpaper to ensure that the contact surface between the ultrasonic probe and the workpiece is parallel to the upper plane. After rough processing, it should be finely ground with water sandpaper to ensure smoothness and coupling.
After repair, debugging should be carried out on the ultrasonic test block to determine its front edge and K value, and the DAC curve should be remade to ensure the accuracy of the flaw detection data.
If the ultrasonic probe is severely worn, the excess part should be ground on a grinder to ensure that the working surface is parallel to the upper plane (the chip should not be exposed), and then polished with coarse and fine sandpaper to ensure smoothness.
Due to the fact that the ultrasonic oblique probe wedge used nowadays is usually made of organic glass, an organic glass plate with a size slightly larger than the probe's repair surface and a thickness of about 3-5mm should be used for repair. The surface should be smooth and free of scratches. The ultrasonic probe head should be bonded to the organic glass plate using chloroform, and the bonding effect should be ensured by clamping it with a vise. After drying, the excess part of the organic glass plate should be removed to complete the repair.
The repaired ultrasonic probe should follow the procedure of the new probe to determine its front edge, K value, and remake the DAC curve.
The repair method for severe wear is also applicable to the manufacturing of special ultrasonic probes. For example, when testing seamless steel pipe welding seams, a curved surface that matches the tested material can be first made and bonded to the ultrasonic probe to ensure coupling and avoid missed detections.
4、 Calibration of ultrasonic probes
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