A dedicated shut-off valve is installed downstream of the throttle valve; this shut-off valve is closed during interlock operation. Is it also necessary to interlock and close the control valve as well?
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A dedicated shut-off valve is installed behind the control valve; this shut-off valve is closed during interlock operations. Is it necessary to also interlock the control valve to close it as well?
It depends on your security level requirements. Refer to SH/T-3018 Specification for the Design of Safety Instrumented Systems in Petrochemical Industries. 5.2 Principles for the independent installation of valves 5.2.1 For Level 1 safety instrumented systems, the valves can be shared with the process control system; it must be ensured that the safety instrumented system operates prior to the process control system. 5.2.2 For Class 2 safety instrumented systems, the valves should be separated from the process system. 5.2.3 For Class 3 safety instrumented systems, the valves should be separated from the process system. 5.3 Principles for redundant valve configuration 5.3.1 For Level 1 safety instrumented systems, a single valve can be used. 5.3.2 For Class 2 safety instrumented systems, redundant valves are recommended; if a single valve is used, the associated solenoid valves should also be arranged redundantly. 5.3.3 For Class 3 safety instrumented systems, redundant valves should be used, and the associated solenoid valves should also be provided in a redundant configuration. 5.3.4 For valves with redundant configuration, one control valve and one shut-off valve can be used.
This project does not have a safety instrumented system; it is controlled only by DCS. Which option should be chosen?
Without a safety instrumented system, does that mean the project has very low requirements regarding SIL levels? If that’s the case, then it shouldn’t be necessary to install interlocks on the control valve
This situation should not be necessary.
To ensure process stability, it is recommended to switch the control valve from automatic mode to manual mode after the isolation valve shuts down automatically, and set the output to zero. This prevents the control valve from opening too much after interlock reset, thereby avoiding impacts on subsequent process loads
Thank you for the advice. It is indeed a bit complicated; I’m not sure how to draw the logical interlock diagram
When the cut-off valve is closed, setting the output of the control valve to 0mA will do