Abstract
The echo height from the defect is the important factor in ultrasonic testing. But the echo height is influenced by conditions of the contact of the probe with the test surface. In this paper, the influence of the surface roughness of the test material and the effect of many kinds of couplants are reported. The surface roughness has the same effect as the membrane thickness of the couplant. The heigher the test frequency and the lower the acoustic impedance of the couplant, the more the echo height is influenced by the surface roughness. Generally glycerin should be used for the couplant of ultrasonic testing for steel welds.
