Overpressure protection heat exchangers

Brown, P. M. M. and D. W. Prance, How to Protect Air-Cooled Heat Exchangers Against Overpressure, Hydrocarbon Processing, Aug. (1975) p. 103. 

Heat exchangers and similar vessels shall be protected with a relieving device of sufficient capacity to avoid overpressure in the case of an internal failure. 

We all need to understand thermal expansion of liquids. I have often heard that heating a completely liquid-full container, such as piping, a vessel, or a heat exchanger, will result in tremendous pressures. I always try to ensure that the situation not arise by encouraging procedures to avoid the situation or providing overpressure protection, but until now I had not taken the time to calculate the ultimate pressures that could develop. 

In the event of HX tube rupture, a blow-down of secondary CO2 (initially at 20 MPa) into the lead occurs. Molten lead and CO2 do not react chemically. Protection against overpressurization of the primary coolant vessel must be provided and activity that is entrained from the lead coolant into the CO2 must be contained. Thus, a pressure relief system is provided for the primary coolant system. The S-CO2 secondary circuit incorporates valves to isolate the failed heat exchanger and limit the mass of CO2 that can enter the primary coolant system. 

Overpressure and thermal protection of heat exchangers Continuous monitoring of pressure and temperature on this equipment Provkion of safety interlocks in fault tolerant mode S1L3 interlock system for flare load mitigation... 

The system consists of two blowdown trains, one for each steam generator. The blowdown water is extracted just above the tube sheet of a steam generator. Flow control valves adjust the blowdown flow rate from each steam generator and depressurise it. The blowdown flow is cooled by means of a regenerative heat exchanger, which uses the heat to warm the condensate. It then enters an ion-exchange purification unit, which removes impurities. Downstream of the purification unit, both trains combine into a common header, which contains a relief valve for providing overpressure protection for the low-pressure portion of the system. 

When protecting a column that has a reboiler, condenser, and overhead reflux drum, a single relief valve is frequently used, as long as there are no block valves or other means of creating flow restrictions between the equipment items. (The heat exchangers may need their own relief valve on the utility side if a hazards analysis shows that a leak from the process into the utility stream could cause unacceptable overpressure.)... 

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