Reliable operation of secondary equipment of PWR nuclear power plants is an integral part of nuclear and radiation safety of the entire NPP unit. The problem of stress strain state of steam turbine structural components under plastic deformation is considered. The theory of elastic-plastic deformations is used to solve the problem along with the finite element method. The paper presents the results of computer assessment of stress strain state of locking joint of working blades of the first stage of a intermediate-pressure cylinder (IPC) and high-pressure cylinder (HPC) body of a steam turbine, which makes it possible to characterize the degree of relaxation and stress redistribution in the structure in comparison with obtained earlier results. It is provided that the use of the presented calculation method in designing new structures of steam turbine components operating in the area of high thermal and power loads, taking into account the contact interaction of components, as well as different mechanical and physical properties of materials, and their changes depending on operating temperature, at this stage of software development allows one to identify problem areas in the design and prevent further breakdowns in the turbine. Based on the comparison of operational data of the developed design solutions and calculation assessment, it is proved that the chosen calculation method can significantly increase the operational reliability not only of the turbine unit but also the nuclear unit as a whole, as well as reduce economic costs caused by turbine unit downtime during maintenance.
An algorithm to confirm the seismic resistance of equipment by a calculation method is proposed, and the limits of its application are determined. A mathematical model of the equipment is developed, and an example of the determination of natural frequencies and stresses for a three-dimensional structure is given. Two main types of calculation were used – static and dynamic. In the static calculation, the stress-strain state of a structure was determined. The values of the obtained stresses were compared with the allowable ones for the materials used, on the basis of which conclusions were made about the strength of the structure under seismic effects. The dynamic calculation resulted in the determination of the rigidity of the structure. The comparison of the stress values obtained for this equipment allowed us to make a conclusion regarding its resistance to seismic effects. The seismic resistance of the equipment was estimated on the example of the K-1000-60 / 1500 steam turbine condenser, and calculated at a seismic intensity of 6 points on the MSK-64 seismic intensity scale. In the course of solving this problem, results of the stress distribution in the housing and other structural elements of the condenser due to the action of combined normal operation and design-basis seismic loads were obtained. The seismic resistance of the equipment was calculated using the finite element method. This allowed us to present a solid body in the form of a set of individual finite elements that interact with each other in a finite number of nodal points. To these points are applied some interaction forces that characterize the influence of the distributed internal stresses applied along the real boundaries of adjacent elements. To perform such a calculation in CAD modeling software, a three-dimensional model was created. The obtained geometric model was imported into the software package, which significantly reduced complexity. The use of the calculation method allows us to significantly reduce the amount of testing when confirming the seismic resistance of equipment. Results of the assessment of the spatial complex stress state of the steam turbine condenser design due to the action of combined normal operation and design-basis seismic loads are obtained.
A structure’s material plasticity influence on the pattern of contact interaction of its elements during operation is studied. The stress-strain state problem for the inner casing of a steam turbine high-pressure cylinder operating at supercritical steam parameters (over 240 atm and 565 °C) is solved. The problem is solved by using a finite-element software package. A model of thermoplasticity with kinematic and isotropic hardening is considered. In carrying out the study, experimental strain curves were used for the materials of the connection. The main dependencies used in solving the problem are given. The method of solving the thermal contact problem of interaction of flange connector elements in the conditions of plasticity is based on the application of a contact layer model. To be able to take into account changes in the load from the fastening in the process of combined strain of both the fastening and the casing, first proposed is a method of the three-dimensional modeling of the thermal tightening of the fastening of the horizontal casing connector by applying the linear coefficient of linear expansion of the material. The proposed approach allows modeling the stress of the initial tightening of studs by specifying a fictitious change (decrease) of the coefficient of linear expansion of a stud given as a separate body in the calculation scheme. The magnitude of the specified change in the coefficient of linear expansion is determined from the relationship between the stress of the initial tightening in the stud and the required, for its creation, elongation, which is implemented in the calculation scheme in the presence of different values of linear expansion of both the stud and the casing. To conduct the numerical experiment, an ordered finite-element grid of the casing design was constructed. A 20-node finite element was used in the construction of the casing grid and the fastening. The effect of force loads and the temperature field, in which the structural element under consideration is operated, is taken into account. An analysis of the results of distribution of equivalent stresses and contact pressure during operation is carried out. The difference between the obtained results and the results of solving the problem in the elastic formulation is noted.
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