The Research and Application of Wheeled Dry-Coupling Ultrasonic Technology in Steel Plate Thickness Measurement

When using the ultrasonic test (UT) technique for material evaluation and defect detection, applying a liquid coupling agent between the detection probe and the inspected workpiece surface is expected to ensure detection performance. In this article, we proposed a wheeled dry-coupling ultrasonic detection method that uses room-temperature vulcanized molded silicone rubber (RTV) instead of a liquid coupling agent to fabricate a wheeled dry-coupling ultrasonic probe. We investigated the acoustic propagation characteristics of the dry-coupled ultrasonic contact interface, derived the reflection coefficient, and developed a contact model for the rough interface. The doped filler experiments on dry-coupled materials improved the acoustic impedance of dry-coupled materials, and the reflection coefficient difference between dry-coupled (silicone rubber) and liquid-coupled (oil) was 0.014. For plates to be measured with different roughness, the reflection coefficient was 0.68 when a load of about 40 N was applied, and the dry-coupling effect was good. Finally, we conducted experiments on the thickness measurement of steel plates, and the experimental results showed that the maximum relative error of the wheeled dry-coupled ultrasonic method in detecting the plate thickness was only 2.86%. The study eliminates the step of applying liquid coupling agent on the probe, avoiding the contamination of the equipment surface, satisfying the thickness measurement accuracy and will improve the inspection efficiency, which provides some ideas for the automated wall thickness measurement of large petrochemical equipment.