Heat treatment issues in heat exchangers
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For a fixed-tube-sheet heat exchanger, with chlorine in the tube side and water on the shell side, the strength of the heat exchange tube joints requires expansion joints; should only the tube box be heat-treated, or should the heat exchange tube joints also be heat-treated? Does GB150’s 10.4.1.3 require that the heat exchange tube joints be included in this process?
Based on the user’s requirements, we have manufactured two carbon steel heat exchangers, one smaller (with a diameter of 400 mm), and the pipe joints in both the tube box and the shell have been heat-treated. Only the lower tube bank of those with a large diameter (2000 mm) requires heat treatment. GB151 only specifies that heat treatment is required when the opening diameter exceeds a certain size, but no specific requirements seem to be given.
The medium in the pipe is chlorine; if I were to design it, I would choose heat-treated pipe ends, but the strength of the fusion joint decreases after heat treatment.
There is no issue with the heat treatment of the tube sheet; after welding the tube fittings on the tube sheet, local heating using electrodes can be employed for stress-relief heat treatment. I don’t understand why the heat exchange tubes and tube sheets still need to be accounted for separately Is the shell-side tube bundle vibrating too much? Is there still a suspicion of crevice corrosion? I think it is sufficient to conduct high-level leakage tests on the shell side of the heat exchanger (to ensure that chlorine does not enter the shell side).