When the temperature and pressure are high, and under the action of thermal deformation, thermal shock, hot corrosion and fluid pressure, the connection between the heat exchange tube and the tube sheet is easily destroyed, and it is difficult to ensure the joint strength and sealing by expansion or welding. Requirements.
At present, the method of expanding and using is widely used. The expansion joint and the welded structure can effectively dampen the damage of the tube bundle vibration to the weld seam, can effectively eliminate the stress corrosion and the gap corrosion, improve the fatigue resistance of the joint, thereby improving the service life of the heat exchanger, and simply expanding or Strength welding has higher strength and tightness.
For ordinary heat exchangers, the form of "expansion-intensity-strength welding" is usually adopted; and the use of the heat exchangers with severe conditions requires the form of "strength expansion-seal welding". Expansion joint and welding can be divided into two types: first expansion and post welding and first expansion after welding in the order of expansion and welding.
The lubricating oil used in the expansion joint penetrates into the joint gap, and they are highly sensitive to weld cracks, pores, etc., so that the phenomenon of defects during welding is more serious. These oils that penetrate into the gap are difficult to remove, so the first expansion and post-welding process is not suitable for mechanical expansion. Although the sticking is not resistant to pressure, the gap between the tube and the tube hole of the tube sheet can be eliminated, so that the tube bundle can be effectively damped to the welded portion of the tube mouth. However, the conventional manual or mechanically controlled expansion method cannot achieve uniform swelling requirements, and the liquid bag expansion method using the computer to control the expansion pressure can conveniently and uniformly achieve the swelling requirement. During welding, due to the influence of high-temperature molten metal, the gas in the gap is heated and rapidly expanded. These high-temperature and high-pressure gases may cause certain damage to the sealing performance of the strength expansion when leaking.
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