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Chemical and Process Engineering Resources

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Category: Safety
Question: What is the procedure for considering a relief valve on the tubeside of a shell and tube heat exchanger?
Keywords: relief,valve,tube,tubeside,shell,heat,exchanger,rupture
Answer: BACKGROUNDFor a heat exchanger with the following characteristics:shell side: hydrocarbon stream 35000 Lb/hr @ 350 psitube side: steam flow 37000 Lb/hr @ 70psig. A relief valve should be installed in case of tube rupture and guidance is required.ANSWERYou must first find out what the design pressure of the two sides are. You should be able to determine this from the name plate on the heat exchanger. Assuming that the equipment has been hydrotested for at least 150% of design pressure, then if the design pressure of the high pressure side (your shell) is more than 2/3 of the design pressure of your low pressure side (your tubes), then you must consider tube rupture as a credible relief scenario. If the design pressures are within 2/3, then you do not. Note that I am talking about design pressures and not operating pressures.The assumption by API RP521 is that tubes seldom fail or rupture catastrophically but spring small leaks. These leaks seldom overpressure the low pressure side of the exchanger during operation.Recommended practices (API) stipulates that you do not only look at the design pressure of the heat exchanger but also of the attached upstream and downstream equipment. I would assume that downstream of the exchanger tube side is some condensate collection tank. For you to NOT consider a tube rupture scenario, the condensate collection tank must also have a design pressure that is within 2/3 of the shell side design pressure. If not, then at the time it's relief valve was sized, the tube rupture scenario must have been taken into account. If it wasn't, then it is in violation (assuming it has a relief valve of course).Source: Philip Leckner, First Content Manager