Heat treatment issues in heat exchangers
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Is heat treatment required after welding the fillet welds at the tube-sheet joints of the heat exchanger tubes? Is heat treatment generally carried out before or after expansion joining? Thank you!
I’ve never heard of it; there aren’t many heat treatments for heat exchangers, I guess.
A brief analysis of the welding joints between heat exchanger tubes and tube sheets https://wenku.baidu.com/view/56208522af45b307e8719749.html
Heat treatment for heat exchangers is certainly good, but it increases investment costs.
Under normal circumstances, welding is done first and then expansion follows. The reason for this is that during the expansion process, ball expansion is usually used to a large extent, and machine oil is required; if expansion takes place before welding, it is difficult to clean the machine oil completely, which means the quality of the weld cannot be guaranteed. For fixed tube sheets, local heat treatment is usually applied to the two welds between the tube sheet and the shell, and local heat treatment is also applied to the tube ends. What do you all think?
This depends on the material; for some heat-resistant steels or containers prone to stress corrosion, heat treatment of the pipe end welds is required. If heat treatment is required, it is best to carry it out after the welding and expansion at the pipe ends are completed.
Currently, we are facing a situation where high-pressure hydrogen (12 MPa) flows in the shell side, with the temperature being below 200 degrees (180°), close to the critical temperature according to the Nelson curve. The heat exchange tubes and tube sheets are made of 10/16MnIII. After welding the heat exchanger, hydrogen removal treatment is required for the shell side (since the U-tube sections need heat treatment to restore their properties). The heat exchange tubes also need to be expanded. Our approach is to carry out overall tube bundle heat treatment after welding, followed by hydraulic expansion. I wonder if any of you have better methods, or if it’s possible to avoid heat treatment altogether.