All About Relief Valves Flashcards
Vessels connected to one another can be protected by a common relief device, provided there is no isolation valve in the piping that connects the vessels which may accidentally render one or more vessels unprotected. True or false?
True
All pressure vessels require overpressure protection. True or false?
True
All low-pressure storage tanks require pressure and vacuum relief for normal operation. True or false?
True
Lines that are in continuous service and kept indoors require relief protection
False. Only lines not used in continuous service, and kept under the hot sun, require relief protection.
A vessel jacket of the reactor does not normally require relief protection
False. A vessel jacket requires its own overpressure protection.
How does a leak in cooling water coils cause an overpressurisation scenario?
If the water vaporises upon coming in contact with the hot reactor mixture, it can expand in volume rapidly.
If the water reacts with the reactor mixture and gives off vapour in the process.
Compressors and turbines require relief devices on the discharge side for deadhead protection. T or F?
True.
Positive displacement pumps require relief devices on both the discharge and suction side. T or F?
False. Discharge side only.
There should be no isolation valves on the relief line for single relief valves. T or F?
True
A isolation valve can be installed on the relief line in a CSO or CSC arrangement, if there is more than one relief line. T or F?
True
Why are flare lines usually marked with ‘No Pockets’?
To permit free draining and ensure no blockage from trapped liquid.
The required flow area for two-phase flow is often smaller than single-phase flow. T or F?
False. 2-phase flows require a larger relief area. The discharge piping also needs to be sized larger.
What is the purpose of a KO Drum?
Remove liquid from relieved gases
What is the purpose of a Seal Pot?
Prevent flash-back of flame from Flare Stack.
Explain how a Seal Pot works
In the event of negative pressure, a backfire from the flare may occur.
Water in seal pot helps to extinguish the potential back fire.
This prevents the fire from being carried to upstream process lines.
What is the purpose of a Flare Stack?
To safely burn off relieved gases
What are the 3 considerations when designing a flare stack?
The pilot flame must remain lit at all times.
Air should be injected to promote smokeless burning.
Steam should be injected to atomise the hydrocarbon into smaller sizes for more efficient burning.
The height of the flare must be determined based on amount of heat generated.
The diameter of the flare must be suitable to maintain a stable flame.
What is the purpose of a Cyclone Separator?
Remove entrained liquid before KO Drum
What is the purpose of a Condenser
Recover valuable components and reduce volume of relief material that require treatment
What is a Scrubber
Remove toxic components from relieved gases by contacting it with a lean solvent
In a scrubber, the lean solvent is sent for further treatment, while the rich vapour may be sent to a flare. True or false?
False. The vapour would be lean by the time it exists the scrubber, not rich.
The pressure at which the relief valve begins to activate is known as the __________
Set pressure
The pressure increase in the vessel over the set pressure is known as the ______
Overpressure
Relieving Pressure = ______ + _______
Set pressure + overpressure
The maximum operating pressure in a reactor is known as the _______
Set pressure
The maximum GAUGE pressure allowed at the top of the vessel at a specified temperature is known as the _________
Maximum Allowable Working Pressure (MAWP)
The design pressure is the maximum GAUGE pressure allowed at the top of the vessel at a specified temperature. T or F?
True. MAWP and design pressure are same thing.
The relieving pressure is the total pressure in the tank when the relief valve begins to activate. True or false?
True
