On the deformation issue of the circumferential welds of stainless steel tube sheets
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For the circumferential welds of the tube sheet and shell sections, due to the thin thickness of the tube sheet and its composition of stainless steel, the plane of the tube sheet tends to bulge after the circumferential welds are completed. Do any of you have any solutions for this issue? There are a few more questions: 1. Is preheating not required for welding dissimilar steels, such as stainless steel and carbon steel? 2 If welding is forced to be completed without deformation by using special tools and fixtures, resulting in high stress, what potential problems might this pose in the future?
According to the poster’s description, this is a fixed-tube-sheet heat exchanger, and the deformation of the tube sheet is caused by the welding of the heat exchange tubes and the circumferential weld between the tube sheet and the shell. Therefore, first, it is necessary to control the welding deformation of the heat exchange tubes and the tube sheet, by controlling the welding line energy and welding sequence. Additionally, the circumferential weld at one end of the tube sheet is not welded first; rather, that weld is constructed after the welding of the heat exchange tubes is completed. And pay attention to wire energy control and welding sequence.
During the processing and shaping of tube sheets, it is important to analyze the amount of deformation; we have worked on equipment with a diameter of 4900 MM and a tube sheet thickness of only 50 mm
This idea has been considered, but I personally think that doing so would easily subject the heat exchange tubes to high stress, which could even lead to stress corrosion and reduce the service life of the heat exchanger
Hello, I would like to ask what the welding process is like when manufacturing this equipment. Since mechanical processing can already ensure that the surfaces are flat, there is also some machining allowance left at the sealing surfaces
In fact, the greater the deformation, the higher the welding residual stress. When welding pipes to tube sheets, it is advisable to use a low line energy, and the pipe joints should be welded starting from the center of the tube sheet in a cross pattern. A ring weld is reserved on the tube sheet as well, in order to minimize welding stress.
There are those with sealing surfaces. It is difficult to control when the tube sheet is too thin; a structure in which both the shell and the tube side cylinders are welded to the tube sheet is used, and the welding sequence and speed are carefully controlled along with certain measures to prevent deformation of the tube sheet, which generally makes it possible to achieve the desired result.
For the sealing surface, we usually leave 4 units of machining allowance, which is no problem
““The tube sheet is welded outward at the center in a cross shape” – is this based on experience?
It is best to machine the sealing surface after the tube-to-plate welding is completed.
This principle should be similar to the sequence of tightening the bolts. It must have been concluded from experience, but I remember that book on heat exchangers also mentioned it along with illustrations.