The joint between the tube and the tube sheet is a vulnerable area on the tube bundle, and the failure of many tube bundles is due to local corrosion at the beginning of the joint. The heat exchanger joints are mostly welded, and there is a gap between the pipe and the tube sheet, and the shell-side medium enters into the dead space of the gap, which causes crevice corrosion. For the joints in the expanded form, due to the residual stress during the expansion process, there is a tensile stress zone on the inner and outer walls of the transition zone between the expanded and unexpanded sections, which is very sensitive to stress corrosion.
Once the temperature and medium conditions for stress corrosion occur, the heat exchanger is quickly destroyed by stress corrosion. Many alloy steel and stainless steel heat exchanger tubes are often cracked quickly due to localized corrosion and stress corrosion.
In the operation of the heat exchanger, the inner and outer walls of the tube bundle may be fouled, and the thermal resistance of the dirt layer is much larger than that of the metal tube, resulting in a rapid decrease in heat exchange capacity, and in severe cases, the flow path of the heat exchange medium will be blocked. .
In order to enhance heat transfer and reduce the fouling layer, a method of increasing the flow rate of the shell side fluid is generally employed. As the shell-side fluid flow rate increases, the likelihood of induced vibrations is also greatly increased, resulting in vibration of the tubes in the tube bundle, which ultimately causes the tube bundle to break.
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