Reasons for crack closure and possibilities for detection and sizing by NDE

Abstract On a cladded test specimen with 2 mm cylindric holes in different depths measurements with SH-waves, longitudinal waves (creeping waves), Rayleigh-waves as well from the clad as from the ferritic side were performed. Also investigations with the multifrequency eddy current prototype were carried out. The sensitivity of longitudinal waves of near grazing incidence is higher than that of SH-waves in depth between 7–11 mm. Comparable sensitivities are reached with SH- and longitudinal waves for crack-like defects in the interface austenitic cladding/ferritic base material. Surface defect can only be detected with SH-waves and Rayleigh-waves. From the ferritic side all test reflectors are detected by SH-waves. With the multifrequency equipment after suppressing disturbing influences the cylindric holes between 3 and 5 mm depth beyond the surface can be detected. There are no detection problems for surface breaking defects. Lower frequencies will enable to increase the penetration depth.