What is the function of a pressure relief device (PRD) and what criterion governs its setting?

• A. PRD acts as a primary pressure sensor.
• B. PRD protects equipment from overpressure by venting; setting must ensure relief capacity matches potential overpressure without causing unnecessary loss.
• C. PRD reduces process temperature.
• D. PRD stores energy for startup.

Answer: (B)

The key idea is that a pressure relief device protects equipment from overpressure by venting its contents when pressure rises to unsafe levels. The setting is chosen so the device will relieve fast enough to keep pressure from exceeding the system’s maximum allowable limit, while its relief capacity is adequate for the worst-case overpressure without venting more than is necessary. In other words, you want enough relief flow to handle the anticipated surge but not so sensitive that normal operation or startup causes excessive venting. This makes the option describing protective venting and appropriately sized relief capacity the best fit. The device is not intended as a primary sensor, nor does it reduce temperature or store energy.