All vessels need reliefs, including reactors, storage tanks, towers, and drums.
Blocked-in sections of cool liquid-filled lines that are exposed to heat (such as the sun) or refrigeration
need reliefs.
Positive displacement pumps, compressors, and turbines need reliefs on the discharge side.
Storage vessels need pressure and vacuum reliefs to protect against pumping in or out of a blocked-in
vessel or against the generation of a vacuum by condensation.
Vessel steam jackets are often rated for low-pressure steam. Reliefs are installed in jackets to prevent
excessive steam pressures due to operator error or regulator failure.