Strength expansion of heat exchanger tubes for heat exchangers

1, strength expansion joint

In order to ensure the sealing performance and the tensile strength of the heat exchange tube and tube plate, the expansion joint is adopted. The tube end is inserted into the pipe hole through the expansion tube, and the tube end is penetrated into the hole of the tube plate hole, so that the tube reaches the plastic deformation, and the hole of the tube plate is enlarged to generate elastic deformation. After the tube expander is pulled out, the tube plate is elastically restored, and the contact surface of the tube and the tube plate generates a large extrusion force, so that the pipe and the pipe plate are firmly combined together, and the two purposes of sealing and pulling force can be achieved. Tube plate on the tube hole, there are holes in the wall and the wall is not slotted 2, as shown in figure 1.

At present, there are 3 main methods of expanding tube, such as rolling, water pressure expansion and explosive expansion.

The expansion applies to the design pressure is less than 4 MPa, the design of temperature are less than 300, no vibration, no large temperature changes, no obvious stress corrosion. Because the pipe hole pipe and tightly, can make the pipe joint to reduce corrosion, and can withstand the pull-out force.

2, strength welding

There are two types of welding between the heat exchange tube and tube plate. The typical structure of the end face welding is shown in figure 2.

The application situation of tube bundle and tube plate welding:

(1) the tube spacing is too small or thin tube plate can not be used when expansion;

(2) when the thermal cycle is severe and the temperature difference is high;

(3) when the pressure is high or the connection tightness is strict. It can ensure the tensile strength of the welded joint;

(4) in the case of maintenance difficulties, such as atomic energy processes and heat exchangers in certain chemical processes.

The end face welding belongs to incomplete fusion welding, which is divided into two parts according to the different requirements:

(1) strength welding (to ensure the connection strength between the heat exchange tube and tube plate);

(2) seal welding (only to play a sealing role).

The end face welding joint has the advantages of welding, inspection and maintenance. However, there is a gap between the tube and the tube plate, which is not suitable for the occasions with large vibration and crevice corrosion.

3, expansion welding and use

When the sealing performance requirements are high, the vibration or fatigue load or crevice corrosion, the use of composite tube plate should be selected and used for expansion welding.

High temperature and pressure, and the thermal deformation, thermal shock, thermal corrosion and fluid pressure, heat exchange tube and tube plate joint is easy to be damaged, the expansion or welding are difficult to guarantee the connection strength and the sealing requirements. At present, the widely used method of expansion welding. The results show that the fatigue resistance of the welded joint can be effectively eliminated by expanding and welding, and the stress corrosion and crevice corrosion can be effectively eliminated, and the service life can be prolonged. In addition, the heat transfer area of the tube medium on the tube plate is much larger than that of the shell medium on the tube plate. This can reduce the temperature difference between the two sides of the tube plate, reduce the warpage of the tube plate, is conducive to the reliability of the tube plate seal.

Expansion welding connection according to the expansion and welding requirements are different, can be divided into the strength of welding + expansion, strength welding + strength expansion, strength expansion + sealing welding, strength expansion + sticking + sealing welding, strength welding + strength expansion + expansion, etc..