Define superheated vapor

A vapor that is obtained by raising the temperature of a substance above the saturation temperature while maintaining a constant pressure. Superheated water vapor, which is the working substance in steam engines, is produced in the steam superheaters of boiler units. The thermal efficiency of steam engines increases as the temperature of the superheated water vapor is raised. Steel, which is the usual material from which boilers and pipes are made, permits superheating of water vapor up to a temperature of 570°C at pressures up to 25 meganewtons/m2, or 250 kilograms-force/cm2. Specially designed installations can operate at a superheated-vapor temperature of 650°C and a pressure of 30 MN/m2.