In this paper, the application of heat treatment of metals in the production of thermal power plants is elaborated. The reason for carrying out heat treatment on steel products and the influence on mechanical properties are described. Due to the extreme working conditions in thermal power plants, the material for the construction of plant components should be carefully selected. The types of materials that will be used in the construction of the plant depend on the mode of operation and the fuel used by the thermal power plant. The main characteristics of these materials are good mechanical properties at elevated temperatures and corrosion resistance. In addition to the choice of material, it is necessary to carefully choose the appropriate heat treatment for that material. The required properties and structure of the material are achieved by heat treatment. The selected material for the production of the pipe bundle in one thermal power plant is described, properties and characteristics before the welding process. Groove fabrication and proof of TIG welding process are defined. After the welding process, the heat treatment of the welded joint was carried out and it was subjected to various tests, which required satisfaction before the start of operation.