The understanding that SIS is a “static” system
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For example, in a safety instrumented system, when the liquid level is too high, an interlock shuts down the feed isolation valve; does this mean that this isolation valve cannot be manually operated within the SIS? In this way, the SIS operator station is just for display purposes only and lacks any operational functions, right?
There’s always an unlocking function, after all, things can’t stay intact forever. Without considering maintenance, this is unreliable
Generally, it is not recommended to consider such an operation; after all, the sequence of actions has already been established. You need to look at the original design, and if you feel it is necessary, you can communicate with the design institute to add a manual control condition
The design was intended for safety purposes; therefore, in theory, the SIS should not be touched while driving. However, it can be bypassed, and this requires consultation with the design team
The interlocks in the SIS system are all equipped with startup bypasses and maintenance bypasses (soft bypasses). As for which interlocks require bypasses, this must be determined through thorough discussion with the design institute.
The liquid level can be connected to the SIS, while the valves can be connected to the DCS; interlocks can be used to cut off the power or gas supply to the valves, but the valves must be of the FC type
The SIS system serves as a safety guarantee during the operation of the plant. However, many parameters are not in compliance with SIS requirements during the startup and shutdown phases of the plant. It’s impossible to allow the plant to fail to start up or for safety accidents to occur due to SIS interruptions during startup; therefore, it is necessary to provide displays, and in some cases, bypass systems as well
This problem is usually resolved by bypassing it; once the issue is dealt with, the system can be switched back to automatic mode. By \"static\" is meant that, during normal operation, the system does not operate at all.
That is, after abnormal process parameters trigger a chain reaction, the valves are actuated in response; the feedback comes from the SIS interlock system. Once the process parameters return to normal, the conditions can be reset and the interlock will disappear on its own
That is, after abnormal process parameters trigger a chain reaction, the valves are actuated in response; the feedback comes from the SIS interlock system. Once the process parameters return to normal, the conditions can be reset and the interlock will disappear on its own