Thermal and Mechanical Equipment Safety and Operational Reliability

Abstract—

The development of new, heat-resistant high-chromium martensitic steels and mastering their production and use at the end of the last century made it possible to construct thermal power equipment for a steam temperature of 600–620°C. The manufacture of equipment made of these steels is supported by the necessary regulatory documents, and there is a positive experience of its long-term operation. An analysis and generalization of the results obtained from tests of steel grades P91 and Di82 for long-term strength have shown that the obtained values are in compliance with the requirements of Russian and European standards for using them at elevated steam parameters. However, the heat resistance properties of these steels at temperatures below 550°C are somewhat lower than the level stipulated by the European standard. As a result of a regression analysis of an experimental data array, an approximation in the form of a fifth-degree polynomial is proposed, which establishes the material service life dependence on temperature and stress for P91 and Di82 steels. In the course of investigations carried out at the All-Russia Thermal Engineering Institute (VTI), the main regularities pertinent to the development of the deformation and destruction processes in these steels under creep conditions were established. Specific correlations between the accumulated creep deformation and the metal microdamage degree with linking them to the worked-out service life fraction were established. These results formed the basis of the developed scale for classifying the chromium steel microdamage during long-term operation. The practical application of this scale opens the possibility to assess the service life exhaustion stage based on the scheduled diagnostics results, thereby contributing to achieving better operational reliability of equipment made of martensitic chromium steels. In Russia and in other industrially developed countries, a scientific and technical base has been created for manufacturing advanced equipment made of new chromium steels that allow this equipment to operate at temperatures up to 640°С. It is necessary to continue studies of the service characteristics of these new steels for their further improvement and subsequent introduction into production.