The flexible start up stop, quick start have been considered as essential functional requirements in the development of new steam turbines. To develop a steam turbine with 566 °C live steam temperature, not only the flexible start up and stop, quick start function, but also the reasonable working life of units influenced by the transient thermal stress are going to be considered. The design of above factors faces challenge. On the other hand, benefited from improved computing technique and ability, it is possible to calculate history temperature field and thermal stress more accurate for each project-specific component. In this paper, certain supercritical unit inlet valve will be investigated. The valve has been operated for more than 6 years in certain power plant. Thermocouples are equipped in both stop valve chamber and control valve chamber at 100% wall depth to obtain actual operation data. According to the characteristics of different heat transfer stages, numerical analysis is performed to obtain accurate history temperature field and stress field using varied boundary conditions from the cold start at room temperature until the unit at full load.
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