The remaining life prediction of those is accomplished by accelerated degradation tests such as creep testing. However, creep testing is both time-consuming and expensive and hence impossible to apply under industrial conditions, where prompt management and analysis are necessary. While residual lifetime predictions and safety assessments of power plant facilities are made using standard mechanical testing methods such as uni-axial tensile and fracture mechanics tests. However, these tests cannot be applied to in-service structure components because of their destructive nature. A nondestructive instrumented indentation technique is thus attractive for investigating the mechanical properties of in-service systems. This technique can measure flow properties by analyzing indentation load-depth curves reflecting the deformation behavior of the material beneath the rigid spherical indenter. In this study, heat treatment was used to produce degraded samples of X20CrMo12.1V and SA-213 T23, materials widely used in power plant pipelines, and their mechanical properties versus degree of degradation were evaluated by instrumented indentation. We assess the degradation of mechanical properties by microstructural analysis and discuss the possibility of appraising the safety of power plant facilities by in-situ monitoring of mechanical properties using instrumented indentation testing. (C) 2008 Elsevier Ltd. All rights reserved.