Analysis of the Static Strength of the Emergency-Cooldown Heat Exchanger with the Use of the Design Tightness Value of Flange-Joint Pins
Keywords:
emergency cooldown heat exchanger, extension of service life, design substantiation of safe operation, assessment of technical condition, thermal stress state of the ECHE, FE methodAbstract
Analysis of the design calculation of the 08.8111.335 SB emergency-cooldown heat exchanger (ECHE) strength revealed a number of deviations from the requirements of current regulations of Ukraine in nuclear energy, which, in particular, include the lack of information on the calculation of the static strength of heat-exchanger flange elements and the excess of allowable stresses in their pins. This article describes a mathematical model for calculating the ECHE thermal stress state, which is used to simulate the ECHE operation under conditions of normal use. A number of computer calculations of ECHE deformation processes were performed using the described equations of the three-dimensional theory of elasticity. Such calculations were performed, using the finite element (FE) method, to analyze the strength of the ECHE and, in particular, elements of its flange joints. Results of ECHE static strength calculations are given. The calculations were performed using the general FE model of the ECHE, the model including all its basic elements. In addition, individual FE models of ECHE flange joint elements DN2130 and DN2080 were developed, on whose basis their static strength calculations were performed. As a result of calculations of the strength of the main ECHE elements, it is concluded that the operating stresses for the considered groups of categories of design stresses in the design zones of the ECHE design do not exceed the allowable values, and, accordingly, the static strength conditions are met. Given the symmetry of ECHE flange joints, FE models of the half-period of one bolted joint were used to calculate their static joint strength. The main boundary conditions for all calculations were: the tightening force of pins, as well as the pressure and temperature of the operating environment. The calculation of the static strength of the flange joint elements DN2130 and DN2080, using the design value of the pre-tightening force of the pins, showed that the conditions of static strength are not met for the considered groups of categories of design stressesReferences
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