The welded joint between tube and tube sheet shall be uniform in weld formation, well fused at the root, and the weld thickness shall meet the design requirements. The internal shrinkage of tube hole after welding shall not exceed 10% of the inner diameter of tube hole. For the welded joint of thin-walled heat exchanger tube and tube sheet, the volume of weld pool is allowed to be small, otherwise, the shrinkage in the tube hole will exceed the standard, which will affect the further tube expansion process and the heat exchange efficiency at work. Therefore, the heat input and the shape of the weld pool must be strictly controlled during welding, so that the weld joint can form a complete weld pool without too large internal shrinkage of the nozzle. For the tube to tubesheet joint with a wall thickness of less than 1mm, the tube end is easy to be turned inward during the welding process, so it is impossible to weld the tube to the tubesheet together.
The main reason is that there is always a certain gap between the tube and the tube sheet after assembly. The tube sheet is thick while the tube sheet is thin. During welding, the edge of the tube sheet hole has not melted yet and the tube has melted, so that the tube is turned inward and the weld pool cannot be formed. As the heat conductivity of austenitic stainless steel is only about 1 / 2 of that of carbon steel, it is more likely to produce tube end inward flanging. In order to adapt to the welding of stainless steel thin-walled tube and tube sheet, the pulse TIG welding method must be adopted, the welding parameters shall be adjusted properly through the test, and the special tooling and positioning mode shall be used at the same time to ensure the internal quality of the weld and the satisfactory weld formation.