Welding sequence for fixed tube sheet heat exchangers
Thread Content
During the fabrication of a fixed-tube-sheet heat exchanger, the tube sheet must be welded to both the heat exchange tubes and the shell. Regarding this welding sequence, it is better to weld certain welds first; this ensures the quality of the tube ends while also preventing deformation of the tube sheet’s sealing surface
My understanding: After the heat exchange tubes are installed, another tube sheet is added → the two tube sheets are aligned → the joints between the tube sheets and the cylinder body are fixed using spot welding (remember not to use full welding); at the same time, the length of the tubes that protrude from the tube sheets is checked. Then, the heat exchange tubes are fixed to the tube sheets via spot welding → the heat exchange tubes are welded to the tube sheets → and finally, the joints between the cylinder body and the tube sheets are welded. Precautions: 1. After the welds between the cylinder body and the tube sheet are spot-welded in place, do not proceed with welding, as doing so may cause the welds to contract, resulting in uneven lengths of the tube ends. Similarly, if there are larger nozzles, the same principle applies; moreover, welding the larger nozzles in advance may cause deformation of the cylinder, thereby increasing difficulties during the assembly of the tube bundle. So it’s sufficient to complete the base layer first; welding can be continued after the outer welds and other pipe ends have been welded. 2. During welding, it is best to carry out the root welding and the cover welding separately for the pipe ends. Additionally, pay attention to the order of welding: perform it in a symmetrical and even manner, rather than welding from top to bottom in sequence. . . I’m not sure if what I said is correct. . .
The welding sequence described upstairs is detailed and thorough, with sound reason analysis. However, one thing worth noting is that it’s better to complete the welding of one side of the tube sheet to the cylinder before inserting the tubes.
The tube sheet and the cylinder are welded together first; this causes the sealing surface of the tube sheet to deform, which makes it difficult to achieve proper sealing during subsequent pressure testing. How do you control this deformation?
When pulling the tube bundle as a whole, both tube sheets are spot-welded or tack-welded; once all the heat exchange tubes are in place, it has little impact, and it is possible to weld the cylinder ring seams and tube ends simultaneously
Indeed, the greatest challenge in manufacturing fixed-tube-sheet heat exchangers lies in controlling the deformation of the tube-sheet sealing surface. Different manufacturers adopt various approaches, depending on their overall manufacturing capabilities and the effectiveness of their process control. We have also encountered situations where pressure testing resulted in leaks due to welding deformation of the tube sheet sealing surface; we believe that this welding sequence is more effective for us.
To correct the distance between the two tube sheets, weld the tube sheets to the cylinder first; fixing the head flange and the tube sheets during the welding of the cylinder and tube sheets can reduce deformation.
This post was last edited by zjq1962 on 2020-5-28 at 12:58. “Do not weld, as if welding is done, the weld may shrink, resulting in uneven lengths of the pipe ends.” ” Following this approach on the second floor also has problems. If the pipe fittings are welded first and then the cylinder body is welded, what could have moved freely is now restricted; wouldn’t this result in high internal stresses in the welds of the pipe fittings?