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 methodologies for residual life assessment of high temperature components operating in power plants, particularly in non destructive methods, a testing technique has been set up at ENEL/CRAM based on creep-rupture tests in argon on welded miniature specimens.

Five experimental systems for creep-rupture tests in an argon atmosphere have been set up which include high accuracy loading systems, vacuum chambers and extensometer devices.

With the aim of establishing and validating the suitability of the experimental methodology, creep-rupture and interrupted creep testing programmes have been performed on miniature specimens (2 mm diameter and 10 mm gauge length).

On the basis of experience gathered by various European research laboratories, a miniature specimen construction procedure has been developed using a laser welding technique for joining threaded heads to sample material. Moreover, a special device for removing material-reduced samples from in-service components is also in development.

Low alloy ferritic steels, such as virgin 2.25Cr1Mo, 0.5Cr 0.5Mo 0.25V, and IN 738 superalloy miniature specimens have been investigated and the results, compared with those from standard specimens, show a regular trend in deformation vs time.

Additional efforts to provide guidelines for material sampling from each plant component will be required in order to reduce uncertainties in residual life prediction.