Does the safety valve operate after or before the safety instrument system?
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There are two approaches to safety measures in case of an increase in reaction pressure: 1. First, the DCS takes action when overpressure occurs; if the pressure continues to rise, the safety valve activates; and if the pressure keeps increasing, the SIS then takes action； 2. After overpressure occurs, the DCS takes action first; if the pressure continues to rise, the SIS activates; and if the pressure keeps rising, the safety valve finally operates ； From the perspective of what is permitted by regulations, which method is allowed? Or are both okay? Which method will everyone choose?
It should be the first option; if SIS production is stopped hastily, the losses will be substantial
Regarding the sequence of operation for safety valves, different options may exist depending on the design of various safety instrument systems and relevant regulatory requirements. According to the first method, when the pressure exceeds the set value, the DCS (Distributed Control System) takes action first; if the pressure continues to rise, the safety valve activates; and if the pressure keeps rising, the SIS (Safety Instrumented System) finally takes action. According to the second method, when the pressure exceeds the set value, the DCS takes action first; if the pressure continues to rise, the SIS takes action; and if the pressure keeps rising, the safety valve finally activates. From the perspective of what is permitted by regulations, there may be some standards or guidelines that provide specific requirements or recommendations. Therefore, relevant standards or guidelines should be carefully referred to to determine which approach meets the requirements. As for which method to choose, it may need to be evaluated based on the specific engineering design and actual conditions. This involves many factors, such as the system’s security requirements, the characteristics of the equipment, and its mode of operation. Normally, the safest and most feasible method is chosen to ensure the safe and stable operation of the system under overpressure conditions. .
According to the protective layer model, the safety instrument system takes precedence over physical protection (safety valves)
The safety relief device is the last line of defense.
I went out of my way to download a picture for you; tell me, how worrying is that! On such a professional forum, as someone in the instrumentation field, I’m not sure whether SIS should take action first or physical protection should do so first...:'(
I have a question – one without SIS. Call the police first; if that doesn’t work, activate the DCS ； Should we start with a DCS action first, and if that doesn’t work, then trigger an alarm? Here we have the former type, but seeing that it’s the latter type elsewhere, I’m a bit confused.
It’s clear from this diagram – the safety valve is the ultimate safety device, and it doesn’t open unless it’s really necessary: lol
I have a question: Is it necessary for the SIS to take precedence over the safety valve? For example, in a case of overpressure, the safety valve releases pressure; but if the SIS is activated, the exhaust pipe is opened directly and remains open without closing. With this setup, does SIS come before the safety valve?