Krechkovska H. Assessment of heatcycling effect in high temperature hydrogenated environment on degradation of steam pipeline steels of thermal power plants

Effect of heatcycling on the mechanical characteristics of heat-resistant steels after high temperature hydrogen degradation. To investigate the changes of structure, mechanical properties and fracture mechanisms of heat-resistant steels of the main steam pipelines of thermal power plants (TPP) after its degradation in both service and laboratory conditions, to estimate the state of degraded steels and to propose a method for taking into account of heatcycling in the intensification of steels degradation. Among the test methods were modelling of steels degradation, metallography, fractography, micro X-ray spectral analyzes; estimation of mechanical characteristics, namely hardness, strength and plasticity, impact toughness, crack growth resistance under both static and cyclic loading. It was proved that: the structural changes in heat-resistant steels under the effect of heatcycling caused by shut-downs of technological process are intecified; an appearance of the fragments of intergranular fracture on the fracture surfaces of specimens after tensile, impact, fracture toughness and fatigue crack growth resistance tests is attributed to the attainment of the critical level of degradation of the 15H1MF steel. The method for estimation of current technical state of steam pipeline steels is proposed, which take into account a combined effect of service time and the number of shut-downs of technological process on the degradation level of metal. The normative document СОУ40.3-0013044-20:2010 of Minpalyvenergo of Ukraine was developed on the base of proposed method of assessment of the current technical state of operated metal. The test results were used by Private Joint-Stock company "Zahidenergo" and at the Ladyzhyn TPP for estimation of degradation level of steel caused by shut-downs of technological process. The field of application is power engineering.