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Chemical and Process Engineering Resources

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Submitted Chris Haslego, Nov 21 2011 11:21 AM | Last updated Nov 21 2011 01:29 PM




Category: Safety
Question: When do relief valves have to be rating for simultaneous fire situations?
Keywords: relief,valve,fire,scenario,rating,simultaneous
Answer: BACKGROUNDWe have two relief valves from two pressure vessels connected to a piping system. Do any of the codes (API 520/521, ASME) say that one must rate the relief valves under a simultaneous fire situation? If so, different back pressures in the piping network would have an impact on the performance of both relief valves? ANSWERIf the vessels are withing 50 feet of each other, then consider them to be in the same fire zone. Therefore, you would calculate a simultaneous fire relief. And yes, the resulting built-up back pressure from each valve would have an affect on the other if they are connected to a common header. However, whether the built-up back pressure from one has an adverse affect on the other needs to be determined. That is why one always should use a balanced bellows valve when connected to a header system. A balanced bellows valve has significantly less of a chance to be adversely affected by the header pressure than do conventional valves.


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