The HZAOP analysis is rated as SIL2.
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The HZAOP analysis is rated as SIL2. Is SIL3 required for the SIL level of the entire SIS system? Or is it okay to use the SIS system with SIL2?
The HAZOP report constitutes a separate document; the SIL classification report (LOPA analysis report) involves analyzing each logical layer item by item, based on the HAZOP report, in order to determine its respective level. If none of them exceed SIL2, then SIL2 is fine. Why upgrade to SIL3? ?
According to the requirements of the “Design Code for Safety Instrumented Systems in Petrochemical Industry”, safety instrumented systems should correspond to a certain safety integrity level. Therefore, I believe that using SIL2 for safety instrumented systems is sufficient.
It is recommended to use SIL3 for the logic controller.
The entire loop only needs to meet SIL2. As for the sensing elements, logic controllers, and actuators, you can select any one of them as SIL3. However, it is still necessary to ensure that the entire loop meets SIL2
Basically, when it comes to purchasing control systems, the products by default meet the SIL 3 certification. Other sensors and actuators only need to meet SIL 2.
OK, I noticed that in the specification documents for the SIS system at the plant, SIL3 is selected. However, the actual safety integrity level assigned is SIL2, and all the instruments selected are rated for SIL2 as well. Hence, I have this confusion.
The key point isn’t which SIL level you choose; you must ensure that the SIL verification of your circuit meets the requirements and is successful. Additionally, nowadays it’s quite difficult to find an SIS control system with SIL2 certification on the market; one has to search high and low to find one
In principle, if all loops are SIL2, then the SIS system can also be rated as SIL2. However, the design institute will certainly take into account future modifications, capacity expansions, and the costs associated with brand selection. For example, opting for a domestic SIS with a SIL2 rating may result in lower costs, but its performance is rather mediocre. Meanwhile, choosing an imported SIL2-rated SIS is actually more expensive than going with a domestic SIS that has a SIL3 rating.