【2026 Control Systems】Basis and Key Points for Identifying Hidden Dangers in SIS Systems
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1. The inspection is based on GB/T 50770-2013: The verification of Safety Integrity Level (SIL) must comply with the target PFDavg as specified in IEC 61511-1:2016 / IEC 61508 series; the calculation of PFDavg should take into account sensors, logic controllers, and actuators, as well as common cause failures (beta factor). API RP 576-2020 “Inspection and Maintenance of Safety Valves” requires that the valve’s partial stroke test (PST) cover an opening degree of ≥15%, to be carried out once a month
2. Key inspection points – SIL verification: Check the calculation report to confirm that the data used comes from O-REDA or FMEDA, and that the results meet the target SIL. Bypass management: Bypass approvals require dual signatures, within a time limit of ≤8 hours, and compensation measures must be established. Functional testing: A full-circuit test is conducted annually, including sensor signal simulation and the actual operation of the actuators.
3. Case: A company failed to take the β factor into account during SIL2 verification, which resulted in an underestimation of PFDavg; it was ordered to conduct the verification again. In another incident, the prolonged activation of the interlock bypass eventually led to a high-pressure steam leak.
For reference: In the operation of hazardous chemicals and chemical processing plants, automation systems such as DCS, PLC, SIS, and GDS serve as both the \"brain\" for production control and the \"last line of defense\" for safety protection. During hazard identification, it is necessary to refer to **standards (GB), international standards (IEC/ISA/API), and industry regulations**, as well as documents such as the \"Guidelines for Identifying and Addressing Safety Risks and Hazards in Hazardous Chemical Enterprises\", to ensure that the entire process of design, operation, and maintenance remains compliant and under control.
Specific requirements: The \"Guidelines for the Identification and Rectification of Safety Risks and Hazards in Hazardous Chemical Enterprises\" specify mandatory items such as DCS/SIS independence, GDS coverage rate, and PLC emergency stop functions.
“Regulations on Safety Management of Instrumentation Systems in Chemical Enterprises”: Any modification to the interlock logic must go through the MOC process, along with a HAZOP analysis.
\"Guidelines for the Implementation of Process Safety Risk Management in Chemical Enterprises\": The SIS system must undergo full-circuit testing annually.
MOC scope expansion: In addition to logical modifications, it also includes hardware replacement, firmware upgrades, and network structure adjustments.
1. Industrial control network security: In accordance with GB/T 30976-2014 Guidelines for Security Protection of Industrial Control Systems, identify issues such as weak passwords, remote access, and patch management.
2. Emergency plan integration: Check whether GDS/SIS alarms are integrated with emergency broadcasting and the dispatch center to ensure timely information transmission.