What does "saturation temperature" refer to in steam engineering?

Saturation temperature is a critical concept in steam engineering that specifically relates to the relationship between temperature and pressure in liquid-vapor systems. This term represents the temperature at which water will boil and turn into steam at a given pressure. As the pressure increases, the saturation temperature also rises, meaning that water will reach its boiling point at a higher temperature. This effect is essential for understanding boiler operations and steam generation, as it informs operators what temperature to expect steam to form based on the pressure within the system.

In contrast, the other options do not accurately define saturation temperature. The first choice suggests a temperature at which steam condenses into water, which refers to the condensation point rather than a boiling point under pressure. The third option about the maximum temperature a boiler can reach is not tied specifically to the boiling process defined by saturation. Lastly, the fourth choice implies a relation to steam expansion, which, while it can be influenced by temperature and pressure, does not define the concept of saturation temperature. Therefore, the correct choice emphasizes the boiling point phenomenon that is fundamental to steam engineering practices.