Several issues in heat exchanger design
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In this shell-and-tube heat exchanger, the fluid on the tube side is seawater at a pressure of 5 MPa, while the fluid on the shell side is fresh water at a lower pressure. Question: (1) Should the tubes be joined to the tube sheet by expansion bonding or welding? (2) If white copper tubes are used for the pipes, what material would be suitable for the tube sheet? (3) Since the end cover is also exposed to seawater, can cast steel be used for it? The pressure is so high – is it okay? I’m asking for everyone’s advice!
1. Currently, the main methods for connecting the tube sheet to the heat exchange tubes are strength welding combined with expansion fitting; for applications under high pressure, strength welding is used along with enhanced expansion fitting. The design pressure of this heat exchanger is 5 MPa, so using the former should be no problem. 2. If copper pipes are used, and if economic conditions permit, it is advisable to use copper forgings for the tube sheet as well. 3. Since the tube sheet is in contact with seawater, it is recommended that the material of the tube sheet be the same; copper or a copper-lined structure is preferred. This post was last edited by c_m_1979 on 2008-1-22 at 17:41.]
The design pressure exceeds the range applicable to strength expansion joining; therefore, strength welding or a combination of strength welding and expansion gasketing can be used. However, the method of using strength welding to enhance strength expansion joining is not specified in any standard codes, so it is not recommended. The material for the end caps can be determined in accordance with the provisions of the Regulatory Guidelines. These guidelines state that cast steel should not be used for the cylinders and heads of pressure vessels, unless the manufacturer of such vessels has relevant experience in using this material and has received approval from a provincial or relevant safety inspection agency. Therefore, it is recommended to use lining or apply anti-corrosion paint.
May I ask if by \"experts upstairs\" you mean that the end caps should be made of copper-lined material? Thanks for the advice!
If the welding manufacturing process permits, it is feasible to use copper-lined materials for the end caps.
Those upstairs, stop misleading people. “Strength expansion + seal welding” – strength expansion can only be used for pressures below 4.0 MPa; it certainly won’t work in this case. The current design pressure is 5.0 MPa, so only strength welding can be used, usually in combination with expansion sealing
Reply to the post on floor 6: What I’m referring to is the requirements outlined in the code. Moreover, ordinary stainless steel corrodes more rapidly than carbon steel when exposed to seawater, which is a major issue in design. Dual-phase stainless steel or titanium can be used, though the cost is quite high.
Thank you to all the experts for their advice. My heat exchanger is used for simulating ship-related tests; given that titanium tubes are too expensive, beryllium copper tubes have been chosen. For welding purposes, a copper-steel composite plate is to be used as the tube sheet – is that a good choice? Is a copper alloy suitable for the end cover? This post was last edited by lijingfen23 on 2008-1-23 17:15.]
I really learned something from this; I understand now! :lol