Steam turbine plant

A steam turbine plant comprising:

• a steam generator;
• a steam turbine;
• a condenser;
• a main steam piping connecting the steam generator and the steam turbine;
• a bypass piping branched from the main steam piping and bypassing the steam turbine;
• a bypass valve provided in the bypass piping;
• a warming piping branched from a portion of the bypass piping upstream of the bypass valve or from a main body of the bypass valve and joining the main steam piping;
• a warming valve provided in the warming piping;
• and
• a control system that controls the warming valve,
• wherein the control system is configured to output a signal for controlling the warming valve in such a manner as to control a metal temperature of the bypass valve to within predetermined temperature ranges as follows:
• (1) being equal to or higher than a saturated temperature of steam flowing into the bypass valve, the saturated temperature being a saturated temperature of the flowing-in steam at a steam pressure during a normal operating;
• (2) having a temperature difference from the flowing-in steam of equal to or less than a first allowable value set in advance as an allowable value for thermal shock or thermal deformation produced on a material of the bypass valve;
• and
• (3) being equal to or lower than a second allowable value set in advance based on a relationship between the material of the bypass valve, the metal temperature of the bypass valve, and a formation rate of steam oxidation scale.