Determination of the heat treatment curve for machine components of power generation plants using finite element analysis

Resumo

Heat treatment cycles allow stress relieving of machine components of hydroelectric and thermoelectric
plants. Differences between the heating/cooling rate of surface and core of these components during the three heat
treatment stages (heating, holding and cooling) lead to thermal deformation and stresses that need to be controlled
to avoid failure. Finite element analysis is used in this work to determine the optimal heating/cooling rate to
guarantee that the components subjected to heat treatment in a radiant tubes furnace do not suffer damage at any
stage of the process. The results of this work are focused on a Francis turbine runner, which is a critical component
in this industry due to its size, geometrical complexity and maintenance costs. Transient thermo-structural analysis
is implemented in commercial software with non-linear properties. In addition, the proposed numerical approach
allows evaluating the maximum power requirement of the furnace to follow the heat treatment curve. The results
indicate that the lower the heating/cooling rate, the greater the thermal uniformity obtained within the turbine
runner; therefore, there is less risk of mechanical damage. However, the final decision on the heat treatment rate
depends on the duration constraints of the process.