Corner weld between heat exchange tube and tube sheet
Thread Content
Is it required that a fixed-tube-sheet heat exchanger undergo overall stress-relief heat treatment on the shell side? That’s what everyone does; once, our approach was as follows: restrain the cylinder – weld the tube sheet to the cylinder – weld one side of the heat exchange tubes to the tube sheet – perform overall heat treatment on the shell side – weld the other side of the heat exchange tubes to the tube sheet – and carry out local heat treatment on the welds between those heat exchange tubes and the tube sheet that were not subjected to overall heat treatment. Some people say that due to the temperature difference, performing local heat treatment on the heat exchange tubes and tube sheets is actually not a good idea. Seeking advice from experts
I think it depends on the circumstances: 1. If the shell side undergoes full stress-relief heat treatment due to the properties of the medium, then the tube sheet should be made of stainless steel through cladding; after the overall heat treatment of the shell side, the tube sheet and the heat exchange tubes are welded together, and the use of appropriate welding materials can eliminate the need for further heat treatment. 2. If it is due to the thickness of the shell side, the shell can be heat-treated before being welded to the tube sheet; ultimately, it should be possible to perform local heat treatment on the welds between the tube sheet and the shell. 3. If it is due to the material, you can follow the steps in point 1. These are my personal opinions, meant only for discussion.
First, it is necessary to understand the purpose of heat treatment before formulating a heat treatment plan. You didn’t explain clearly, so it’s hard to give advice.
Actually, the meaning is quite simple: is it necessary to perform heat treatment on the welds between the heat exchange tubes and the tube sheet, given the high level of hazard posed by the medium?
Since the medium in the shell side is highly hazardous, butt welding is not used for the tube sheet; overall heat treatment of the equipment’s shell side is required. Is heat treatment necessary for the fillet welds between the heat exchange tubes and the tube sheet?
It is best to complete all welding and non-destructive testing tasks first and then carry out overall heat treatment. If the heat exchanger is too large to be placed entirely inside the heat treatment furnace, electric heating strips can be used to apply heat treatment in sections, with each section overlapping the adjacent one by 400–500 mm.
During overall heat treatment, the temperature difference between the housing and the tubes during heating can cause deformation, resulting in significant residual stresses
All joints in contact with the medium should be heat-treated. The joint between the heat exchange tube and the tube sheet seems not to be in contact with the medium; generally, a combination of strength welding plus expansion fitting, or strength expansion plus sealing welding is used in design. However, this does not guarantee that there is no gap at all in all the expansion joints, and it is entirely possible for the medium to come into contact with the welded joints. Therefore, I believe it is necessary.
Agree with what was said on the 9th floor and by the moderator (who is the same person). It should be that way.
Even if the materials of the housing and the tubes are different and their linear expansion coefficients vary, segmental heat treatment will not pose any problems.