This article focuses on the life assessment methods for elevated-temperature failure mechanisms and metallurgical instabilities that reduce life or cause loss of function or operating time of high-temperature components, namely, gas turbine blade, and power plant piping and tubing. The article discusses metallurgical instabilities of steel-based alloys and nickel-base superalloys. It provides information on several life assessment methods, namely, the life fraction rule, parameter-based assessments, the thermal-mechanical fatigue, coating evaluations, hardness testing, microstructural evaluations, the creep cavitation damage assessment, the oxide-scale-based life prediction, and high-temperature crack growth methods.

Predicting the service life of structural components involves creep-fatigue crack growth (CFCG) testing under pure creep conditions. This article provides a discussion on the loading condition and the type of ductile and brittle material showing creep behavior. It focuses on a description of the experimental method that should be followed in conducting tests of CFCG with various hold times. The article describes the testing conditions, definitions, and the necessary calculations of various crack-tip parameters considered during static and cyclic loading in time-dependent fracture mechanics. The parameters considered for static loading are C*, C(t), C*(t), C*h, Ct, and Cst(t). For cyclic loading, the parameters are delta Jc and (Ct)avg. An overview of life-prediction models is also provided.

This article describes the concepts for characterizing and predicting elevated-temperature crack growth in structural materials. It discusses both creep and creep-fatigue crack growth and focuses mainly on creep crack growth tests that are carried out in accordance with ASTM E 1457. The article provides information on typical test procedures and equipment used for these tests. It concludes with information on crack growth correlations.