A ranking of the complex of mechanical characteristics of heat-resistant steels operated in various structural elements according to their sensitivity to degradation will allow us to justify the feasibility of using the most sensitive mechanical indicator for evaluation of steel degradation. Basing on the results obtained in the work it is planned to develop and substantiate the legitimacy of the scientific and methodic approach to assessing the change in stress-strain state of heat-resistant steels after their long-term operation in real technological processes, using quantitative metallographic indicators and signs of a change in fracture mechanisms during long-term operation under influence of technological temperature-force and corrosion-hydrogenating factors. Finally, conditions for achievement of the critical technical state by steels of power engineering elements well be substantiated on the basis of performed estimations.