Abstract: Improved method and apparatus for controlling thermal stress on component parts of a steam turbine while providing maximum loading and unloading rates during startup, shutdown, and other periods of load change. From monitored and derived quantities, a loading rate is calculated for each of a plurality of preselected turbine component parts and the lowest rate is selected for control. Simultaneously, and in concert with load change calculation and execution, the steam admission mode of the turbine is automatically directed to either the partial arc mode or the full arc mode as necessary to reduce stress as compared with a preselected and adaptive stress reference value.