The RB-C test block is designed according to the requirements of ultrasonic testing of the toroidal butt joint of the curved surface of pressure equipment. The test block is suitable for ultrasonic testing of the toroidal butt joint with the radius of curvature of the test surface ranging from 80mm to 250mm.

Test method: Select the diagonal probe that has been verified and place it at the position a in the diagram. Move the probe back and forth so that the direct sound beam can get the maximum reflection echo on the φ2mm cross through hole. Adjust the echo amplitude to 80% of the height of the full screen, record the dB value at this time, which is the first point. The probe is placed at position b in the diagram, and the probe is moved forward and backward so that the direct sound beam can get the maximum reflection echo on the φ2mm cross through hole. Adjust the echo amplitude to 80% of the height of the full screen, record the dB value at this time, which is the second point. The probe is placed at position c in the diagram, and the probe is moved forward and backward so that the direct sound beam can get the maximum reflection echo on the φ2mm cross through hole. Adjust the echo amplitude to 80% of the height of the full screen, record the dB value at this time, which is the third point. The probe is placed at position d in the diagram, and the probe is moved back and forth so that the direct sound beam can get the maximum reflection echo on the φ2mm cross through hole. Adjust the echo amplitude to 80% of the height of the full screen, record the dB value at this time, which is the fourth point. Connecting the above points into a curve is the base line specified in the standard.