The paper discusses the issue of the modelling of strains and stresses resulting from heating and cooling processes of components in power plants. The main purpose of the work is to determine the mechanical behavior of power plant components operating under mechanical and thermal loading. The finite element method (FEM) has been used to evaluate the temperature and stresses changes in components as a function of time. Temperature fields in the components of power plants are dependent, among parameters, on variable heat-transfer conditions between components and the fluid medium, that may change its condition, flowing inside them. For this reason, an evaluation of the temperature field and the consequent stress fields requires the use of heat-transfer coefficients as time-dependent variables and techniques for determining appropriate values for these coefficients should be used. The methodology that combines computer modelling of the temperature fields with its measurements performed at selected points of the pipelines may be used in this case. The graphs of stress changes as a function of time have been determined for the chosen plant components. The influence of the heat transfer conditions on the temperature fields and mechanical behavior of components in question have been discussed.

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