Should the cut-off valve on the SIS be represented with on/off buttons on the screen?
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This post was last edited by liu530014416 on 2021-10-22 at 21:23. For Honeywell’s SM system, there are no on/off buttons on the screen; when switching between storage tanks, DCS operators can only force the valves to open or close through the logic diagram. Question: Can a turn on/off button be added to the screen? If the security screening team detects our forced valves, will that cause any problems?
The valves of the SIS cannot be turned on or off arbitrarily; procedures must be followed and records kept for such actions. DCS operators are not allowed to turn the valves on or off on their own; if a DCS operator wants to do so
I’m afraid there might be some misunderstanding on your part regarding SIS; its purpose is to ensure safety, and it takes action to shut things down when safety conditions are met. Under normal operating conditions, the SIS does not participate in control; attempting to force the valves controlled by the SIS is considered illegal. Normally, these valves are not allowed to be operated, and forcing them to move will render their safety functions ineffective. So, if your operators need to force this valve to operate frequently, the best thing to do is to check the logic of the SIS to see if there’s an error somewhere – perhaps a valve that should be operated normally has been included in the SIS. The solution is to remove it from the SIS; adding switches on the screen isn’t a proper solution
The SIS system is a static safety interlock protection system; it is not possible to operate valves through the SIS system. Was the site in question modified after the installation of the SIS system, with the protection functions being provided by the valves that were originally used for process control? If so, it is recommended to add another solenoid valve at the valve location, connected in series with the solenoid valve controlled by the process control system. This solenoid valve is controlled by the SIS system; under normal conditions, the SIS system is powered, and the solenoid valve functions as an open path, not participating in any control processes. It is separate from the DCS-based process control. When it is necessary to switch tanks, simply operate the relay of the process control system to activate the valve. When interlock protection conditions are triggered, the solenoid valve controlled by the SIS system loses power, and the valve returns to a safe state (the valve is single-acting, and the fault position corresponds to the safe position defined by the SIS system’s actions)
Please take a look at clauses 5.0.8/9/10 of 50770: SIS does not participate in DCS operations, and DCS cannot operate SIS-related functions either
First of all, since it’s a storage tank, cut-off valves are generally installed at the inlet and outlet ports; they are used in conjunction with the SIS system. For storage tanks, fail-closed (FC) type valves are typically used, and such valves should remain in an open state. They only activate in response to high or low liquid levels. If you need to close these valves in order to stop the flow of liquid, that means there is a flaw in the design of your process system – another valve should be available to perform this function of stopping the flow of liquid. In other words, to solve this problem, you need to add a pneumatic cut-off valve to the DCS system
The SIS valve cannot be used as an operating valve; a separate valve dedicated to DCS operation is required.