Heat exchangers expansion joints

The PWS consists of six primary coolant loops that circulate moderator to cool the reactor. Each loop consists of a main coolant pump, two parallel heat exchangers, expansion joints, and valves. All branch lines connected to the primary water system up to the first normally closed isolation valve require seismic qualification to assure pressure boundary integrity. This qualification has been demonstrated by various dynamic analyses or by the previously mentioned interim verification program procedure. 

The foregoing designs were discussed as ring expansion joints by Kopp and Sayre, Expansion Joints for Heat Exchangers (ASME Misc. Pap., vol. 6, no. 211). All are statically indeterminate but are subjected to analysis by introducing various simplifying assumptions. Some joints in current industrial use are of lighter wall constniction than is indicated by the method of this paper. 

For fixed tubesheet design of shell and tube heat exchangers don t allow too high a temperature difference between tubeside and shellside without providing a shellside expansion joint. The author has seen 70 F (one company) and 100°F (another company) used as this limit. An easy way to calculate the maximum stress is as follows ... 

On initial start-up and shut-down the heat exchanger can be subjected to damaging thermal shock, overpressure or hydraulic hammer. This can lead to leaky tube-to-tubesheet joints, damaged expansion joints or packing glands because of excessive axial thermal, expansion of the tubes or shell. Excessive shell side flowrates during the "shake down can cause tube vibrations and catastrophic failure. 

E — Heat Exchanger, condenser, reboiler, etc. Ej — Jet Ejector Ex — Expansion Joint F — Fan... 

A heat-exchanger tube is expanded into the tubeplate to effect a joint. However, to avoid bulging the tube outside the confines of the tubeplate, expansion never takes place through the whole tubeplate thickness and a... 

A thermal expansion joint may be installed on the exchanger shell. As plant size increases, the shell-and-tube heat exchanger becomes more cost effective and will be the exchanger of choice. At intermediate sizes, both types must be evaluated for process and economic reasons. 

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