The impact of ultrasonic transducer wear on ultrasonic flaw detection and repair methods

In ultrasonic flaw detection, the ultrasonic angle probe generates friction with the workpiece during use. Due to different personal habits, workpieces being inspected, and usage frequencies, the probe will experience varying degrees of wear. After wear, the original characteristics of the ultrasonic probe will be damaged.  

This article discusses the impact of this damage on the detection work and how to correct this impact by repairing the ultrasonic probe.。

The following figure shows several common forms of wear encountered in work practice:

As shown in the figure above, after wear, the original characteristics of the ultrasonic probe will change, mainly manifested in the changes of the refraction angle K value (increasing or decreasing), the sound beam incident point (probe leading edge), and coupling (coupling will deteriorate after wear in plate flaw detection, while in pipe or bar material flaw detection, the coupling will improve as the contact area increases).

Changes in the sound beam refraction angle and incident point will cause changes in the depth and position of the defect on the ultrasonic flaw detector. If the coupling deteriorates without equipment coupling compensation, it will reduce the detection sensitivity; conversely, it will increase the sensitivity.

If the detection is frequently performed from one side to the other due to personal habits, it will lead to probe wear and deflection of the ultrasonic beam, resulting in positioning errors in the defect.

Changes in characteristics can easily lead to missed or misjudged defects, introducing uncertainty to the flaw detection work.

For slight wear, this change can be corrected by adjusting the data of the ultrasonic flaw detector on the test block. For severe wear, this cannot be compensated for simply by adjusting the ultrasonic flaw detector data. In this case, it is necessary to replace the ultrasonic probe or perform ultrasonic probe repair to correct it.

After a period of operation, in addition to regular debugging, the probe should be repaired according to the degree of wear.

If the ultrasonic probe is only slightly worn, it should be polished on coarse sandpaper to keep the contact surface of the ultrasonic probe with the workpiece parallel to the upper plane. After coarse processing, fine grinding should be performed with water sandpaper to ensure smoothness and coupling.

After repair, the leading edge and K value should be checked on the ultrasonic test block, 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 off on a grinding wheel 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.

Since the oblique wedges of ultrasonic angle probes currently used are usually made of organic glass, an organic glass plate with a size slightly larger than the surface to be repaired and a thickness of about 3-5 mm should be used for repair. Its surface should be smooth and scratch-free. Use trichloromethane to bond the ultrasonic probe to the organic glass plate, clamp it with a vise to ensure bonding, and remove the excess organic glass plate after drying to complete the repair.

The repaired ultrasonic probe should follow the procedure for a new probe to determine its leading edge and K value and to remake the DAC curve.

The repair method for severe wear is also applicable to the manufacture of special ultrasonic probes. For example, for detecting the weld of seamless steel pipes, a curved surface that matches the material being inspected can be made and bonded to the ultrasonic probe to ensure coupling and avoid missed detection.

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