Can SIS valves be used in normal operations by the process?
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There is an SIS valve at the tank outlet, which was originally designed for emergency shutdown. Since there is no dedicated backflow process available, the outlet pipeline has to be used during backflow; therefore, the SIS valve needs to be closed. Is this in compliance with the regulations? Are there any regulations on this aspect in national standards?
Emergency shut-off valves are designed to stop the flow of materials, and all that is required of the SIS system is to operate independently and reliably. As for the temporary shutdown itself being a safety interlock action, that certainly isn’t a problem. If it is in a chained closed state, you need to open the valve during special periods. In that case, the SIS system needs to be bypassed; at this time, it is necessary to carry out the necessary changes and obtain confirmation and signatures from the supervisors of relevant process safety equipment departments, and in cases where there is a high level of risk, the factory manager must also be informed. It is also fine to establish corresponding protective and monitoring measures (to ensure safety based on the actual situation).
Actions are possible, but if forced shutdown is required, proper mandatory approval procedures must be followed.
Of course not; take a look at the specifications’ definition of an SIS system
This requires a written document from the company, and it must be reported to the Safety Supervision Bureau
Normally, it is not allowed to share a DCS with an SIS system – it depends on whether SIL certification has been obtained; SIL1 level is permitted, while systems at SIL2 or higher require a separate setup. The relevant safety inspection agencies will check this aspect, and if it is temporary, you can handle it on your own; P – restoration after the incident
Let’s see how you have designed this. If your valve is a pure SIS valve, it is generally not used for normal operation in the process; if there is a need for such functionality in the process, then there must be a separate valve available for control by the DCS. However, in most cases, isolation valves are rarely pure SIS valves; instead, they often consist of one valve connected in series with two solenoid valves, one connected to the SIS and the other to the DCS. In such cases, it is possible to control the valve directly using the DCS
Based on the SIF circuit classification, per the specifications, isolation valves at SIL1 level can be shared with the DCS, while those at SIL2 or higher must be separated. But safety production is currently quite challenging; it seems that chemical companies are under inspection every day, and the scrutiny is likely to become even stricter in the future. Therefore, in the actual design process, even for SIL1 circuits, separate isolation valves are installed for the newly added equipment ； For the modification devices, add as many as possible; if installation conditions are limited, they can be shared. However, the valves must meet safety standards, and dual solenoid valves should be installed to receive signals from both the DCS and SIS systems, with the SIS system having priority.
We enter the SIS system after the DCS signal is generated; in this way, the DCS can control the switches, and the SIS emergency shutdown function can also be used for control