cGMP double tube sheet heat exchanger

Our cGMP double tube sheet heat exchanger is a relatively new structure. There is a tube sheet at the end of the heat exchange tube, called the outer tube sheet, which also serves as the equipment flange and is connected to the heat exchange tube and the tube box flange respectively. There is another tube sheet at a position closer to the end of the heat exchange tube, called the inner tube sheet, which is connected to the heat exchange tube and the shell side respectively. There is a certain distance between the outer tube sheet and the inner tube sheet, which are connected with a Harvest short section to form an isolation chamber that does not bear pressure.

(1) The isolation cavity of the double tube sheet spacing is not connected to the tube side and shell side, and does not bear the medium pressure, but bears the mechanical load and thermal load of the equipment. The bearing capacity of the isolation cavity mainly depends on the double tube sheet spacing. When the fixed double tube sheet is subjected to the shell side water pressure test, there may be leakage at the connection between the inner tube sheet and the heat exchange tube. Therefore, when determining the double tube sheet spacing, the small space required for observation and leak detection must be considered. The double tube sheet spacing in the drawing is 13mm, and it is adjusted to 50mm based on manufacturing experience.

(2) The size of the expansion groove of the inner tube sheet tube hole The connection quality of the inner tube sheet and the heat exchange tube is the key to the manufacturing of the double tube sheet structure heat exchanger, and the pull-off force and sealing performance are the main indicators to measure the quality of the joint connection. In GB151-1999 "Shell and Tube Heat Exchanger", the width of the expansion groove is specified as 3mm, but it is also pointed out that it can be appropriately modified according to different expansion methods. In the drawing, the width of the expansion groove of the inner tube sheet tube hole is 3mm, the depth is 0.5mm, the first expansion groove is 8mm from the tube sheet end face, and the size chain of the second expansion groove is 8mm 3mm 6mm 3mm. According to the experience of hydraulic expansion and tube expansion test, the depth of the expansion groove is still set at 0.5mm, but the width of the expansion groove is adjusted to 5mm. The size chain of the second expansion groove is adjusted to 13mm 5mm 10mm 5mm.

(3) The length of the tube protruding from the tube sheet surface In the drawing, the length of the tube protruding from the tube sheet surface is 1mm, which meets the requirements of GB151-1999. However, in the heat exchangers imported from abroad for high temperature, high pressure, flammable, toxic or highly corrosive media, the length of the tube protruding from the tube sheet surface is generally 4-5mm. Combined with the experience of manufacturing urea unit heat exchangers and the characteristics of heat exchange tubes, the length of the tube protruding from the tube sheet surface is adjusted to 3-4mm. Use argon arc welding to weld two layers. The tube wall is not allowed to be overburned or welded through, and the tube head cannot have undercuts. Keep the tube end round and intact.

(4) Hardness difference between tube sheet and tube Hydraulic expansion will cause plastic deformation of the heat exchange tube and elastic deformation of the tube sheet. The purpose of expansion is to obtain sufficient residual contact stress between the heat exchange tube and the tube sheet. Therefore, the yield strength and hardness of the tube sheet material must be greater than the yield strength and hardness of the heat exchange tube material. Maintaining a certain hardness difference between the tube sheet and the tube is one of the important ways to improve the quality of expansion. Usually, the hardness difference is controlled at around HB30.