NONDESTRUCTIVE EVALUATION OF CREEP DAMAGE IN POWER-PLANT STEAM-GENERATORS AND PIPING BY MAGNETIC MEASUREMENTS

Magnetic hysteresis measurements have been used to evaluate creep dama ge in power plant weldments. This method relies on the sensitivity of the magnetic properties of steels, such as coercivity, remanence and h ysteresis loss, to microstructural changes occurring during creep. Dur ing high temperature creep there is a significant change in microstruc ture such as the formation of voids, dislocation networks and grain bo undary cavities. The evolution of these defects during creep affects t he magnetic properties by changing the impedance to magnetic domain wa ll motion and also by introducing internal demagnetizing fields associ ated with cavities. The present paper discusses results obtained from on-site inspection of creep damaged Cr-Mo steel welds at two thermal p ower plants. One of the objectives of this research was to establish w hether there were any trends in the magnetic properties as a result of creep damage which could be used later as part of a more comprehensiv e screening procedure for monitoring the progress of creep damage. (C) 1997 Elsevier Science Ltd.