PSI - Issue 36

Halyna Krechkovska et al. / Procedia Structural Integrity 36 (2022) 43–50 Halyna Krechkovska, Viktor Sylovanyuk, Oleksandra Student et al./ Structural Integrity Procedia 00 (2021) 000 – 000 7 49

possible to predict a possible decrease in the strength of steels after long-term operation due to their damage under the influence of a different number of shutdowns of TPP units with cooling of the pipeline system. To do this, it is enough to calculate the value of the fraction of resource exhaustion by the indicator (τ op ٠ N op ) / (τ N ٠ N N ) corresponding to the analysed steel and using the dependence in Fig. 5 to determine its ultimate strength after long term operation.

1,05

  UTS /  0 UTS

0,90

N op =501

0,75

N op =576

0,00

0,25

0,50

0,75

1,00

( op N op ) / (  N N N )

Fig. 5. The relationship between the loss of the ultimate strength  / 0 of 15Kh1M1F steel during operation and the fraction of its resource exhaustion by the indicator (τ op ٠ N op ) / (τ N ٠ N N ), which clearly demonstrates the influence of the shutdown numbers of units (501 and 576) on the reducing the ultimate strength of steel due to accumulation of bulk damage in it through block shutdowns and heat cycles associated with this. The dependence shown in Fig. 5 makes it possible to do predictive estimates for reducing the ultimate strength of operated steel on other blocks with the corresponding number of shutdowns of TPP units and the bulk damage caused by them. To do this, it is only necessary at first to calculate the value of the fraction of the resource exhaustion of this steel by the proposed indicator (τ op ٠ N op ) / (τ N ٠ N N ) and determine the corresponding ratio  / 0 from the graphical dependence in Fig. 5. 4. Conclusions For heat-resistant steel 15Kh1M1F, operated for  2  10 5 h on the main steam pipeline of the TPP, a relationship is built between the loss of its ultimate strength relative to the initial state  / 0 and the fraction of the exhaustion of the regulated resource both by the operation lifetime and by the number of shutdowns of the units (τ op ٠ N op ) / (τ N ٠ N N ). This dependence makes it possible to predict the change in the ultimate strength of steel due to its bulk microstructural damage caused by the effect of a different number of shutdowns of TPP units. References Andreikiv 1 , O., Ye., Skal’s’kyi, V. R., Opanasovych, V. К. , Dolins’ka, I. Ya., Shtoiko, I. P., 2017. Determination of the Period of Subcritical Growth of Creep-Fatigue Cracks Under Block Loading. Journal of Mathematical Sciences 2, 103 – 113. Andreikiv 2 , O. E., Sas, N. B., 2007. Strength of thin-walled structural elements with cracks under the conditions of creep. Materials Science 43(2). 174−182. Babii, L.O., Student, O.Z., Zagórski , A., Markov, A.D., 2007. Creep of degraded 2.25Cr – Mo steel in hydrogen. Materials Science 43(5), 701 – 707. Ваlitskii, А. І., Panasyuk, V. V. 2009, Workability assessment of structural steels of power plant units in hydrogen environm ent, Strength of Materials 41(1), 52 – 57. Baltušnikas 1 , A., Lukošiūtė, I., Levinskas, R., 2010 . Transformation kinetics of M 23 C 6 carbide lattice parame in low alloyed steelters. Materials Science (Medžiagotyra) 16(4), 320 – 323. Baltušnikas 2 , A., Levinskas, R., Lukoštūtė. I., 2007. Kinetics of Carbide Formation Duri ng Ageing of Pearlitic 12X1MФ Steel. Mater ials Science 13(4), 286 – 292. Dzioba, I.R., 2010. Properties of 13KhMF steel after operation and degradation under the laboratory conditions. Materials Science 46(3), 357 – 364. Gianfrancesco, A., Venditti, D., Allen, D. J., Morris, A., Caminada, S., Pillot, S., Rodriguez, M. M., Friedman, V., Hartrott, P., Siegele, D., Holmström, S., Juhani, R., Pekka, N, Kim, C., 2009. Applications of advanced low -alloy steels for new high-temperature components, Office for Official Publications of the European Communities.