AbstractSignificant changes in microstructure occur in many fossil plant components that operate for long times at elevated temperatures. Some examples include hydrogen damage in steam-generating boiler tubes, carbide coarsening in superheater tubes, creep cavitation in the heat-affected zones of thick-section weldments, and temper embrittlement in turbine rotors and disks. Quantitative estimates of the remaining useful lives of components affected by these damage mechanisms require that the degree of damage be determined and related to the life-limiting mechanisms.The paper discusses recent progress in the development and field demonstration of nondestructive techniques for characterizing the damage types listed above. This research has produced several products that have achieved or are close to commercial status. The research has also helped to define some of the limitations related to access, sensitivity, and signal interpretation of the nondestructive techniques. The paper discusses how these limitations can often be mitigated by using several nondestructive techniques in concert to obtain a more complete picture of material condition or by removing small specimens for detailed laboratory analysis.