How is the discharge capacity of an ASME relief valve rated?

In setting the discharge capacity of an ASME relief valve, it is crucial to note that this capacity is rated based on the equivalent capacity of saturated steam at a specified pressure. This is because relief valves are designed to protect equipment from overpressure, and the performance is measured by the amount of steam or other fluids they can handle when operating at a certain pressure.

The equivalent capacity of saturated steam provides a standardized method to evaluate how much fluid the valve can safely discharge under emergency conditions. It assumes a specific set of conditions, allowing engineers to compare the effectiveness of different valves across various applications consistently.

Given this context, understanding the discharge capacity in relation to the equivalent capacity of saturated steam takes into account not only the valve's size but also the phase and properties of the fluid under the operating conditions. All this makes option B the most accurate choice regarding the rating of discharge capacity for ASME relief valves.