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As an important heat transfer equipment, heat exchanger is widely used in many industries such as chemical, petroleum, and power. In the structural design of heat exchanger, the connection method between tube sheet and tube has an important influence on the performance and service life of the equipment. Reasonable selection and design of the connection method between tube sheet and tube can effectively improve the pressure resistance, corrosion resistance and heat transfer efficiency of heat exchanger. This article will analyze the common connection methods between tube sheet and tube of heat exchanger.
 

1. Overview of connection methods between tube sheet and tube of heat exchanger

The tube sheet of heat exchanger is a key component for supporting tubes. The tubes are fixed on the tube sheet by different connection methods to ensure that the fluid can effectively transfer heat between the tube and the shell. Common connection methods include expansion, welding, expansion welding and mechanical connection. These methods have their own advantages and disadvantages and are suitable for different process requirements and working environments.

2. Common connection methods

2.1 Expansion

Expansion is to make the tube plastically deform in the tube sheet hole through mechanical or hydraulic methods, so as to achieve a close fit between the tube and the tube sheet. Usually, a tube expander is used to expand the tube so that it can be firmly embedded in the tube sheet hole. This method mainly relies on the interference fit between the outer diameter of the tube and the hole diameter of the tube sheet.

Process characteristics:

The expansion operation is relatively simple, the cost is low, and it is suitable for large-scale production.

The expansion connection method can withstand a certain working pressure, but it performs poorly under high-pressure environments and may have leakage risks.

Expansion has certain requirements on the plasticity of the tube material, and is particularly suitable for materials with good plasticity such as copper tubes and aluminum tubes.

The corrosion resistance of expansion is poor, and gap corrosion is prone to occur in corrosive media.

Application scenarios:

The expansion method is mainly used in medium and low pressure heat exchangers, especially in environments where the heat exchange medium is relatively pure and less corrosive, such as air conditioning and refrigeration equipment, low-pressure steam boilers, etc.

2.2 Welding

Welding is to melt the tube and the tube sheet by heating or pressurizing to form a metallurgical bond. Welding mainly includes arc welding, TIG welding, laser welding and other methods. The appropriate welding process is selected according to the different materials.

Process characteristics:

The strength of the welded connection is high and can withstand high working pressure and high temperature environment.

The sealing after welding is good and there is basically no leakage problem.

The welding process is relatively complicated and requires operators with welding technology, and the cost is high. Some companies will use orbital welding machine for tube to tubesheet welding to replace manual operation to save labor costs.

The welding performance requirements for tube and tube sheet materials are high, and the welding of different materials requires special treatment to avoid cracks and deformation during welding.

The welded joint is prone to heat-affected zone corrosion, especially in corrosive media, and protective measures need to be taken.

Application scenarios:

The welding method is suitable for high temperature, high pressure and highly corrosive working environments, such as high-pressure heat exchangers in refineries and chemical plants, seawater desalination equipment, etc.

2.3 Expansion welding combination

The expansion welding combination is a combination of expansion and welding. First, the tube and the tube sheet are preliminarily connected by expansion, and then welded at both ends of the tube to ensure higher strength and sealing.

Process characteristics:

Expansion welding has the dual advantages of expansion and welding. It can not only take advantage of the fast and simple operation of expansion, but also improve the strength and sealing performance of the connection through welding.

This method can effectively reduce welding stress and prevent the generation of thermal cracks. It is suitable for heat exchangers under high pressure and high temperature conditions.

Expansion welding can reduce the thermal deformation generated during welding, especially suitable for the connection of thin-walled tubes and thick tube sheets.

Application scenarios:

Expansion welding is widely used in heat exchangers under high pressure vessels and high temperature conditions, such as high pressure heat exchangers in nuclear power plants and chemical plants.

2.4 Mechanical connection

Mechanical connection is to fix the tube to the tube sheet by threads, flanges or other mechanical means. This method is relatively rarely used under high pressure and high temperature conditions, and is mainly used for some special maintenance needs or occasions with special requirements for disassembly.

Process characteristics:

The mechanical connection is detachable, which is convenient for inspection and maintenance.

The connection strength and sealing are low, and it is not suitable for high pressure and high temperature environments.

The structure is relatively complex and the cost is high.

Application scenarios:

Mechanical connection methods are usually used in equipment that needs to be frequently disassembled and repaired, such as laboratory heat exchange equipment, movable heat exchangers, etc.

3. How to choose the right connection method

To choose the right connection method between the heat exchanger tube sheet and the tube, it is necessary to comprehensively consider factors such as working pressure, temperature, medium corrosiveness and economy.

Working pressure and temperature: For high pressure and high temperature environments, welding or expansion welding is a more reliable choice. For medium and low pressure conditions, expansion can meet the requirements.

Corrosive media: In highly corrosive media, welding or expansion welding should be preferred, and anti-corrosion measures should be taken. Expansion is prone to gap corrosion in corrosive media, so it should be used with caution.

Economy: The cost of expansion is relatively low and suitable for mass production; the cost of welding is higher, but its advantages are more obvious under high-demand conditions. Enterprises should balance cost and performance requirements according to actual conditions.

Conclusion

The connection method between the heat exchanger tube sheet and the tube plays a decisive role in the performance and service life of the heat exchanger. Various methods such as expansion joint, welding, expansion welding and mechanical connection have their own characteristics and are suitable for different working conditions. In actual applications, enterprises should reasonably select the appropriate connection method according to the use environment and process requirements of the equipment to ensure the efficient and safe operation of the heat exchanger.