What are the effects of maintaining a high temperature for an extended period after heat treatment on the pipe ends of heat exchangers?
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The tube ends of the heat exchanger undergo post-weld heat treatment; according to standard requirements, 30 minutes is sufficient, but what are the consequences if they are insulated for 2 hours?
I would like to ask whether the heat treatment of your tube ends is done locally, only on the tube ends themselves, or on the entire tube bundle including the heat exchange tubes. In our previous experiences with heat treatment, we carried out it on the whole bundle, and as a result the heat exchange tubes got twisted up.
We have encountered this situation before, so we carry out heat treatment separately; this is because there is a certain risk of physical damage to the tube bundle during installation, and also because the supporting capacity of the tubes changes after they are heated. Unless a special heat treatment fixture is used
Try not to keep it warm for too long!
This must meet the heat treatment requirements specified in the weld evaluation; if it exceeds those specifications, it is considered an unqualified process, and a new set of verification weld evaluations needs to be prepared.
The holding time specified in NB/T47015 is the minimum holding time; no upper limit for the time is specified. As mentioned above, it will involve issues related to weld evaluation.