What state is steam at 100 psi and 400F?

At a pressure of 100 psi (which is approximately 6.9 bar), the temperature of steam can be analyzed using steam tables, which provide the relationship between pressure, temperature, and the state of water/steam. At this pressure, saturated steam—where the steam is in equilibrium with water—exists at approximately 329°F. Since the given temperature of 400°F is much higher than the saturation temperature at 100 psi, the steam is no longer in equilibrium with liquid water.

Therefore, at 100 psi and 400°F, the steam is classified as superheated. Superheated steam is steam that has been heated beyond its saturation point at a given pressure; it does not contain any liquid water and is used in various applications, including turbo machinery and heating processes, as it is more efficient in energy transfer. Thus, the characteristics of superheated steam—higher temperature and absence of moisture—apply clearly in this scenario.