Measuring incipient fatigue in reactor pressure vessel steels

The materials examined in this work are low alloyed steels, typically SA608, used in the pressure vessels and piping of LWR nuclear unites. Following evaluation of a number of candidate methods attention was focused on a specialized transmission electron microscope (TEM) method referred to as selected area diffraction or SAD. Based on testing of laboratory and service samples, it appears that technique meets the identified requirements for a successful inspection. Objectives of this report are to summarize the method for those that might be interested in applying it, to demonstrate that this fatigue measurement method is of potential benefit, and finally to propose an assumption that a microstructural conditioning must take place before a microscopic fatigue initiation and propagation. (author)