PSI - Issue 2_B

7

O. Yasniy et al. / Procedia Structural Integrity 2 (2016) 840–846 Author name / Structural Integrity Procedia 00 (2016) 000–000

846

The number of temperature fluctuations is equal to 87 times a day for Class 1 and 1 time per day for the Class 2 and they occur each 0.28 and 24 hours, accordingly. The number of cycles for a crack to grow from the current depth of 25 mm to a critical defect size of 35 mm is shown in Fig. 4. With the increase of temperature difference between the external and internal surfaces of header from 10 ° C to 50 ° C the number of loading cycles required for a crack to grow to a depth of 35 mm is reduced in 24.72 times from 2.2∙10 6 to 8.9∙10 4 , or from 251.17 thousand hours to 10.16 thousand hours. It was calculated, that the average magnitude of temperature fluctuations is 15 °C for Class 1 and is 46.2 °C for Class 2. For a crack to grow from the current depth of 25 mm to a critical defect size of 35 mm under temperature fluctuations of Class 1 (Class 2) there must be 112 thousand hours and 10.2 thousand hours of operation. It was assumed that the mechanism of crack growth is determined only by fatigue, which can be divided into Class 1 and Class 2 temperature fluctuations. The extension of header lifetime can be achieved by reducing the temperature fluctuations range and their frequency. Conclusions . The residual durability superheater header was investigated by analyzing the stresses calculated by the finite element method to determine the maximum allowable size of the defect and the time of its growth up to a critical depth along the center hole. The loading cycles due to thermal fluctuations were grouped into two classes. It was revealed that the steam temperature fluctuations under quasi-stable mode of operation greatly contribute to the growth of cracks. These loading cycles were identified and determined to be the most influential factor in the growth of cracks. The dependences of the residual life of superheater heater on temperature fluctuations under the quasi-stable mode of operation were obtained. Dmytrakh, I.M., Vainman, A.B., Stashchuk, M.H., Toth, L., 2005. Reliability and durability of structural elements for heat-and-power engineering equipment. Reference manual. Academperiodyka, Kyiv (in Ukrainian). Kwon, O., Myers, M., Karstensen, A.D., Knowles, D., 2006. The effect of the steam temperature fluctuations during steady state operation on the remnant life of the superheater header. International Journal of Pressure Vessels and Piping. 83 (5), 349−358. Yasniy, O.P., Pyndus, Yu. I, Iasnii, V.P., 2014. The assessment of stress intensity factors in semi-elliptical cracks of superheater header of thermal power plant. Inter-university journal «Scientific notes», 47, 211–220. ANSYS, 2013, SAS IP, Inc., Ansys Help System, Mechanical APDL, Theory reference. Paris, P., Erdogan, F., 1963. A critical analysis of crack propagation laws. Journal Basic Engineering, 528–534. Yasniy, O., Brevus, V., Nemchenko, V., 2012. The influence of temperature on cyclic crack resistance of superheater header. Scientific journal of Ternopil National Ivan Pul’uj Technical University, 68 (4), 35-41. References