不锈钢薄壁管与管板的焊接有其明显的特点

     管与管板的焊接接头焊缝成形均匀，根部熔合良好，焊缝厚度符合设计要求。焊后管孔内缩不得超过管孔内径的10%。对于常州不锈钢薄壁管换热器管与管板的焊接接头，允许熔池体积小，否则管孔收缩会超标，影响管的进一步膨胀过程和工作时的换热效率。因此，在焊接过程中必须严格控制焊接热输入和熔池形状，使焊接接头能形成一个完整的熔池，而不会使喷嘴产生过大的内部收缩。对于壁厚小于1mm的管与管板的连接，在焊接过程中，管端容易向内翻转，不可能将管与管板焊接一起。主要原因是装配后管子和管板之间总是有一定的间隙。

    管板厚而管板薄。在焊接过程中，管板孔的边缘尚未熔化，管已熔化，使管向内转动，不能形成熔池。由于奥氏体不锈钢的导热系数仅为碳钢的1/2左右，更容易产生管端向内翻边。为适应常州不锈钢薄壁管与管板的焊接，必须采用脉冲TIG焊方法，通过试验适当调整焊接参数，同时采用专用工装和定位方式，保证焊缝内部质量和良好的焊缝成形。

   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.