NDE of austenitic cladding by using low frequency eddy current and EMA-excited SH-Waves

The state of the art inspection the austenitic cladding is the EC-techniques for surface breaking cracks and UT for defects in the interface zone and the ferritic base material below it. A new approach covering the surface a swell as the subsurface zones including the interface is the Multifrequency-EC-technique with low frequency components in the range between 500Hz up to 5kHz. To achieve the necessary penetration depth the smaller current damping at low frequencies and some other aspects have to be considered. A new UT-technique based on Horizontally Polarized Shear waves (SH-waves) excited by electromagnetic acoustic (EMA) transducers will be presented. Due to their polarization SH-waves are only weakly reflected at the interface base metal/cladding and penetrate nearly completely into the austenitic cladding. Furthermore indications from the grain structure of the cladding are essentially smaller than using other wave modes. Due to their complete angle mirror effect Sh-waves are v ery sensitive for crack detection. In the report the EC-and the UT-inspection system are described. Results of applications of both techniques obtained on specimens with artificial defects as well as results from utility applications on cladded tubes in a power plant are presented.