A TECHNIQUE FOR THE RESIDUAL LIFE ASSESSMENT OF HIGH-TEMPERATURE COMPONENTS BASED ON CREEP-RUPTURE TESTING ON WELDED MINIATURE SPECIMENS

Following the present trend in the development of advanced methodologi es for residual life assessment of high temperature components operati ng in power plants, particularly in non destructive methods, a testing technique has been set up at ENEL/CRAM based on creep-rupture tests i n argon on welded miniature specimens. Five experimental systems for c reep-rupture tests in an argon atmosphere have been set up which inclu de high accuracy loading systems, vacuum chambers and extensometer dev ices. With the aim of establishing and validating the suitability of t he experimental methodology, creep-rupture and interrupted creep testi ng programmes have been performed on miniature specimens (2 mm diamete r and 10 mm gauge length). On the basis of experience gathered by vari ous European research laboratories, a miniature specimen construction procedure has been developed using a laser welding technique for joini ng threaded heads to sample material. Moreover, a special device for r emoving material-reduced samples from in-service components is also in development. Low alloy ferritic steels, such as virgin 2.25CrlMo, 0.5 Cr 0.5Mo 0.25V, and IN 738 superalloy miniature specimens have been in vestigated and the results, compared with those from standard specimen s, show a regular trend in deformation vs time. Additional efforts to provide guidelines for material sampling from each plant component wil l be required in order to reduce uncertainties in residual life predic tion.