PSI - Issue 20

N.A. Makhutov et al. / Procedia Structural Integrity 20 (2019) 63–74 N. A. Makhutov and V. V. Zatsarinnyy / Structural Integrity Procedia 00 (2019) 000–000

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calculations based on stresses  according to (10) and (11) with the purpose of excluding brittle or ductile ruptures by way of introducing the margins [ t  ] according to critical temperatures t k . [ t  ] = t э - t k . (12) According to the experience of the leading branches of technology (including, in particular, the atomic industry) the value [ t  ] is accepted not lower than 30 o С. For extreme climatic temperatures in the regions of Siberia and the North ( t min = -55 o C and t mах = +50 o С) we consider critical temperatures t k : at -85 o C and +80 o С. Based on the data of Table 7 and formulas (10…12) the values of the  n safety factors are provided for the abovementioned calculation temperatures t (+20 o С, -85 o С) and fixed values σ э ( Р = 50%) and σ э ( Р = 1%). With the decrease of the t э temperatures the safety factors increase in connection with the growth σ т , σ в , k S However, for the technical equipment operated under the conditions of negative temperatures, an increase of operating stress levels is observed (due to the increase of dynamic, seismic, snow, ice loads and to the increase and the probabilistic dispersal of variation coefficients v э ). That having been said, the coefficient of temperature increase of σ э was accepted at 1 for t = +20 o C and t = -85 o C and at 0.95 for t = +80 o C; the variation coefficients v э were accepted at 0.1 for t = +20 o C, at 0.15 for t = -85 o C and at 0.08 for t = +80 o C. Refined values of the margins which change for these conditions are given in the Table 7. It is seen from this table that the increase of σ т , σ в , k S and coefficient of operation loading leads to reduction in safety factors with the decrease in temperature. 5. Conclusion Therefore, based on the available experimental and literature data the researches on effect of temperature factor on the probabilistic MMP characteristics and safety factors were performed. According to the proposed calculation procedure for 15H2NMFA and 3 steels the probabilistic characteristics of strength and plasticity were determined. Under the changing conditions of operating loading at negative temperatures (with the increase of strength characteristics and operation loading levels) the reduction in safety factors may occur. References Design code for the strength of equipment and pipelines of nuclear power installation (PNAE G-7-002-86), 1989, Energoatomizdat, Moscow, pp. 525 (in Russian). Makhutov, N., 1981. Deformation criteria for failure and calculation of structural elements for strength. Mechanical Engineering, Moscow, pp. 272 (in Russian). Makhutov, N., 2005. Structural integrity, lifetime and techogenic safety. In two parts. Part 1: Criteria of strength and resource pp. 494. Part 2: Justification of the resource and security. Nauka. Novosibirsk, pp. 610. (in Russian) Makhutov, N., 2008. Strength and safety: fundamental and applied research. Nauka, Novosibirsk, pp. 528. (in Russian) Makhutov, N., 2015. Safety of Russia. Legal, socio-economic and scientific and technical aspects. Scientific basis of technogenic safety. Scientific hands Makhutov, N.. MGOF "Znanie", Moscow, pp. 936. (in Russian) Table 7. The change in calculated safety factors t, 0 C Р = 50% Р = 1% n σ T n σ B n σ S n σ T n σ B n σ S +20 -85 1,5 1,5 2,6 2,6 4,8 4,8 1,11 1,03 1,99 1,81 3,25 2,96