A Mechanistic Approach to Remanent Creep Life Assessment of Low Alloy Ferritic Components Based on Hardness Measurements

Abstract

Creep damage leading to failure in low alloy ferritic steels at service operating conditions results from: (i) structural coarsening leading to a continuous reduction in creep strength during exposure, and (ii) intergranular creep cavitation. A mechanistic model is presented for describing tertiary creep which accounts for both of these factors. By assuming a limiting creep ductility corresponding to a maximum cavitation potential a lower bound life predictive approach is given. The significant structural parameters are then the background solid solution strength, the interparticle spacing (λ) and the rate of increase of λ, although the long-term, creep-rupture strength is shown to be dictated largely by the latter. Consideration is given to the determination of these kinetics by means of hardness change measurements: good correlations are found with experimental data. A methodology for characterizing the remanent creep life of component material using hardness measurements and post-exposure aging is developed on this basis.