Nondestructive characterization of materials by ultrasonic and micromagnetic techniques for strength and toughness prediction and the detection of early creep damage

In recent year, MDT-techniques for MATERIALS CHARACTERIZATION have been developed under the sponsorship of the German Minister of Research and Development in the Reactor Safety Research Programme in order to provide techniques for PSI and ISI which are sensitive and reliable in particular with respect to the prediction of STRENGTH and TOUGHNESS. As ferritic steels (pressure vessels and pipes in the primary circuit) are of special interest,R&D was concentrated on MICROMAGNETIC TECHNIQUES which significantly sense the microstructure and its changes under service and/or repair conditions. In order to characterize microstructural states superimposed by residual stresses in an unambiguous way numerical modelling was applied using advanced tools of mathematical approximation theory, i.e., multiregression algorithms and neural networks. For the detection of early creep damage in fossil power plant applications, i.e. micropores and their subsequent development to linked pores and microcracks, beside the MICROMAGNETIC- also the ULTRASONIC TTECHNIQUE was applied and optimized for on-site applicaitons at components like pipe bends. Whereas the ultrasonic the ULTRASONIC TECHNIQUE is sensitive to pore concentrations as small as >0.2%, the parameters of the MICROMAGNETIC TECHNIQUES are mainly influenced by temperature- and load-induced microstructural changes during lifetime and depending on the steel quality. The techniques were applied during 7 inspection intervals (2048 h - 21000 h) at two pipe bends (steelgrades 14Mo V 6 3 and X 20 CrMoV 12 l) loaded under praxis near conditions.