: Dobmann, G.; Koble, T.D.; Kröning, M.; Willems, H.

Abstract
The contribution refers results for the development and application of nondestructive testing techniques for the early detection of creep damage on the box of the development of creep cavitation, porosity and micro cracking. Beside ultrasonic phase velocity measurements electromagnetic techniques have been investigated at creep test specimen of different steels as well as at pipe bends. Whereas the electromagnetic techniques and derived quantities for materials state characterization (Barkhausen noies, coercivity, magnetic distortion factor, electrical resistivity) follow very sensitive the temperature and load induced microstructure changes in the steels the ultrasonic phase velocity changes are strongly affected by creep cavitation, i.e. creep damage. The detectability starts when oriented creep pores occur in the component near surface zones. Ultrasonic surface waves are the relevant tool, excited by piezoelectric and received by EMAT - transducers.