Failure analysis and life assessment of boiler tubes require precise knowledge of the real operating time. Coarseness of the microstructure is take-and temperature - dependent. Thus
a "mean" operating temperature may be estimated with study of the coarsening kinetics and measurement of carbide size. In this paper a carbide coarsening kinetics model of 12Cr1MoV steel is described and a model of the "critical size" analysis for life estimation is proposed.