Issues regarding the selection of valves for safety instrumented systems
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I was given a project for a company that uses chlorine; according to current regulations, it is required to install an SIS system. During the design phase, several shut-off valves were included, with pneumatic actuation. The problem is that this company doesn’t have any areas where compressed air is needed. It’s simply not worthwhile to install an air compressor station just for a few valves that are hardly used at all. Moreover, since it’s a private company, cost considerations also need to be taken into account. So I discussed with the design institute whether it would be possible to use valves with a different driving mechanism; the institute said that according to the regulations, cut-off valves must be able to close within 10 seconds and must have SIL certification. I asked several valve manufacturers; electric valves certainly cannot meet the requirements, but solenoid valves can be closed within %0s. So I would like to ask everyone how to make a choice in this situation; please, experienced experts, give some advice
Relatively speaking, solenoid valves are quite small, right? Are the pipes used in this process also not very large?
Hello. The pipe diameter of liquid chlorine entering the vaporizer is DN25; the main chlorine pipeline has a diameter of DN65, and no isolation valves are installed on the branch pipes
Is there nitrogen available? If so, nitrogen can be used even in non-enclosed spaces
In process pipelines, it is impossible to use solenoid valves without a gas supply. The closing and opening times of pneumatic valves depend ultimately on the cylinder, not on the solenoid valve. Solenoid valves act very quickly; their function is merely to cut off or restore the gas supply. I’ve only seen small air circuits; the water circuits are controlled by solenoid valves, so it’s impossible to use them in process pipelines. For safety reasons, it was designed in this way, and under the given conditions, it can be considered suitable for an air compression station.
Thank you for the explanation; I’ve learned a lot!
Consider pipeline solenoid valves. Consult ASCO and HERION.
Electric valves almost never achieve a SIL rating; SIS requires that equipment reach at least SIL1
If instrument air is not available, nitrogen can be used. If liquid nitrogen is not available, a small vaporization and pressure reduction device can be employed, using liquid nitrogen or high-pressure nitrogen from cylinders; a few shut-off valves are also needed, as the amount of gas required is not large
Also, your thinking is wrong – the device contains chlorine gas, and you still say it’s for a few pneumatic valves that are hardly ever used. Hopefully they won’t be needed, but when the time comes when they are required, not being able to use them will be the most dangerous situation.
Um… it seems that our SIS valves are pneumatic