For tanks rated at SIL2, a 1oo2 dual-level interlock is used; do both level gauges meet the SIL2 certification requirements?
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For tanks rated at SIL2, a 1oo2 dual-level interlock is used; do both level gauges meet the SIL2 certification requirements?
It is sufficient for the instrument loop to meet SIL2; it does not mean that the field instruments must necessarily meet SIL2.
Are you referring to the protection circuit that ensures the storage tank meets SIL2 standards? Assuming your DCS is SIL3, then for a 1oo2 level gauge, it is generally not possible to achieve SIL2 using two SIL1 devices; 2oo3 is feasible. However, for storage tanks, using pressure alarms is more practical and cost-effective than using level sensors. The common practice is to use SIL2 for pressure circuits and SIL1 for level circuits.
To calculate the entire circuit, it’s not enough to look only at the sensors; one must consider the path from the sensors to the central controller and then to the actuator, in order to compute PFDavg
What needs to be considered is the SIL level of the entire system; the liquid level alone cannot be taken into account
The SIL level is determined based on the PFD. For circuits, SIL generally means that if any instrument in the circuit fails, the entire circuit fails as well. The SIL of a circuit is calculated comprehensively based on the PFDs of the various instruments within that circuit. Therefore, the circuit has SIL level requirements, and each individual instrument must also meet SIL requirements. The SIL classification is determined through safety analysis; currently, HAZOP analysis and the SIL classification of circuits in China are not very rigorous. If in doubt, refer to the regulations; the attachments contain national standards and petrochemical regulations. Those interested can take a look at IEC-61508\61511.
A rough approach is that if your SIS loop level is SIL2, it is recommended to increase the safety instrument level for that loop by one tier. The proper method involves calculating the PFD for each instrument in that loop; as long as the calculation results meet the required standards, that’s sufficient
First, you mentioned the tank with SIL2 rating; I assume you mean that the entire circuit is required to have a SIL2 rating. In that case, the sensing end of the transmitter must also have a SIL2 rating, which means that the detector assembly following the 1oo2 configuration must be of SIL2 level. Then, since 1oo2 can improve the PFD, it is possible for a single instrument to require only a SIL1 rating; however, as a precaution, it is recommended to choose a SIL2 rating when making the selection. In that case, 1oo2 will definitely be at SIL2 level, while also meeting the structural requirements.
It is recommended to refer to GB/T20438.6-2006, which explains this in detail. If the storage tank is designated as SIL2, then the protection system (loop) required for that tank should also be of SIL2 level. The SIF for SIL2 can be constituted by instruments and controllers of SIL1 level; this depends on the combination of sensors, controllers, and actuators used.
Radar madman. . . With radar involved, even the supposedly safest instrument systems can become unsafe; that’s what I think.