3rd Class Stationary Steam Engineer License Practice Test 2026 – Complete Exam Prep

When dry saturated steam at a high pressure, such as 200 PSI, is reduced to a much lower pressure like 25 PSI, it often undergoes a cooling and expansion process. This process can produce various types of steam depending on the final conditions.

In this context, dry saturated steam is steam that is at its boiling point for a given pressure and contains no water droplets. When the steam is released to a lower pressure, it can no longer maintain its saturated state as it expands. If it remains in a gaseous state and its temperature is above the saturation temperature at 25 PSI, it is classified as superheated steam. Superheated steam is defined as steam that is heated beyond its saturation temperature without increasing pressure, which occurs when the steam expands and cools while maintaining a gas state.

This means that at 25 PSI, if the temperature of the steam drops below the saturation temperature for that pressure but remains above the temperature required for it to be classified as saturated, it becomes superheated steam. Thus, the correct designation for the steam in this scenario, after the reduction in pressure from 200 PSI to 25 PSI, is superheated steam, since the conditions allow it to avoid condensation and remain fully in the gaseous state.