Issues regarding instruments in the SIS system
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As the title suggests, in a SIS system, if it is of SIL2 level, can DCS instruments and SIS instruments share one another? Which standard is this type of? I couldn’t find it after searching for ages, so I have to turn to the experts for help! ! !
The requirements of this standard are very clear; refer to GB/T 50770
It can be seen that the documents require that safety instruments be independent of the process control system, but this concept is general in nature; therefore, subsequent documents provide further clarification on the relationship between \"preferred\" and \"required\" usage – indicating in what situations it is preferred to share them with a DCS, and in what situations it is required to do so. Since it is a SIL2 system, the HAZOP analysis must already have provided clear guidance on this matter, and information can be obtained by consulting relevant design firms. The points that require communication are connected to the DCS; SIS is primarily used for interlock protection, while DCS is mainly used for monitoring and control – this is also the mainstream approach in modern control system design. If there is anything you don’t know, feel free to contact me at 15169070869
Theoretically, they can be shared, but usually they are kept separate. Most of the current control devices are of SIL2 level. A single loop composed of SIL2 devices should also be able to achieve SIL2 status. Since the SIS and DCS share the same signal sources, as long as those signal sources meet the SIL2 standard, they can satisfy the safety requirements of both systems. However, it's hard to say what effects sharing a single signal source might have, so it's better to keep them separate (to avoid external interference for each one). Large companies like CNPC and Sinopec have explicit rules prohibiting shared use. Clause 6.2 of GBT 50770-2013 \"Code for Design of Safety Instrumented Systems in Petrochemical Industries\" stipulates that SIL1 level measuring instruments can be shared with the basic control system ； SIL2 level measuring instruments should be separated from the basic process control system ； SIL3 level measuring instruments should be separated from the basic control system.
Ultimately, it’s still a budget issue
The instruments of the SIS should be installed independently
GB/T 50892-2013 Code for Design of Instrumentation and Control Systems in Oil and Gas Fields and Pipeline Projects stipulates that: 4.4.2 The configuration of sensors in safety instrumented circuits shall meet the following requirements: 1 The independence of sensors shall comply with the following requirements: 1) In SIL1-level safety instrumented function circuits, sensors may be shared with the process control system； 2) For SIL2-level safety instrumented function loops, the sensors should be separated from the process control system ； 3) For SIL3 safety instrumented function circuits, the sensors should be separated from the process control system. 2 The redundant configuration of sensors shall meet the following requirements: 1) For SIL1-level safety function circuits, a single sensor can be used ； 2) For SIL2-level safety function circuits, redundant sensors are recommended ； 3) For SIL3 safety function circuits, redundant sensors should be used. The wording used is appropriate, that is, it is a recommendation rather than a requirement. :):):):):):):):)
The standards give a vague impression; currently it may relate to corporate investment issues, and small businesses will consider sharing them. In the long run, it’s better to be separated; who knows if these regulations will once again require separation in two years (if an accident occurs, it’s not advisable to remain ambiguous :()