SIL classification and verification issues
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Discussion is welcome: 1. After HAZOP analysis, which deviations require further SIL classification (e.g., those with a high risk level, extremely severe deviations, or control points with interlocks)? 2. If the actuator is a control valve, it is equipped with a solenoid valve that enables interlock functionality by receiving signals from the SIS system. Which specific components of the control valve have their PFDs required to meet the SIL level (for example: solenoid valves, electrical valve positioners, actuators, valve bodies, etc.)?
1. Analysis should be conducted by combining the interlock logic diagram with the high-risk scenarios identified in the HAZOP analysis, using the interlock table as a basis and the high-risk scenarios from HAZOP as supplements. 2. In accordance with IEC requirements, it is not allowed for control valves and isolation valves to be shared (for SIL1 and above).
1. The procedural documents specify that LOPA analysis should be conducted further for scenarios with medium or higher risk levels. 2. SIL1 is suitable for shared use; in this case, the key actuating components of the control valve – namely the solenoid valve, actuator, and valve body – must be certified, while a valve positioner and feedback device are not required.
1. Which deviations of nodes require HAZOP analysis depends on the risk level of the scenario associated with that deviation. 2. The solenoid valve, actuator, and valve body of the on/off valve all require PFD value calculations. It is advisable to share control valves and isolation valves at SIL1 level; sharing is not allowed at SIL2 and above.
1. After a HAZOP analysis, it is usually necessary to assign a SIL rating to those deviations with a high or extremely high risk level, as well as to those critical control points that involve the control of safety interlock systems (SIS). 2. If the actuator is a control valve equipped with a solenoid valve to receive signals from the SIS system for interlock purposes, it is necessary to ensure that the solenoid valve, the electrical valve positioner, and the actuator’s PFD meet the corresponding SIL level requirements. The valve body itself is generally not directly involved in the SIL classification, but its overall performance and reliability affect the safe operation of the system. .
1. The quality of the HAZOP report is a key factor affecting the SIL classification; to ensure that no aspects are overlooked in the SIL classification, it is usually necessary to analyze it in conjunction with the interlock tables as well as the high- and low-risk scenarios identified in the HAZOP analysis. 2. According to GB50770, SIL1 is the appropriate level for shared use; in this case, the solenoid valve, actuator, and valve body of the control valve must be certified.
This post was last edited by locky83 on 2024-11-1 12:42. 1. After HAZOP analysis, which nodes show deviations that require further SIL classification (e.g., high risk levels, extremely severe deviations, control points with interlocks)? To answer question one, after a HAZOP analysis, a LOPA analysis is conducted to determine the risk reduction capability of other protective measures. If the risk level after applying these additional protective measures is still not at an acceptable level, then it is necessary to add more SIF loops. Whether such SIF loops can achieve the desired risk reduction level needs to be determined through SIL grading
For reference: IEC-61882-2016 – Guide to the Application of Hazard and Operability Study (HAZOP Study) (English).
1. Which deviations of nodes require HAZOP analysis? It is necessary to consider the risk level of the scenario associated with that deviation; for scenarios with a risk level of medium or higher, further LOPA analysis should be conducted to determine the SIL rating. 2. According to IEC requirements, it is not allowed to adjust and shut down jointly (for SIL1 and above).