The Process Of Connecting Heat Exchanger Tubes And Tube Sheets in Shell And Tube Heat Exchangers

Heat exchanger as a heat transfer equipment to transfer part of the heat of the hot fluid between materials to the cold fluid, has a wide range of applications in people's daily life and petroleum, chemical, power, pharmaceutical, atomic energy and nuclear industries. It can be used as independent equipment, such as heaters, condensers, coolers, etc.; it can also be used as a part of some process equipment, such as heat exchangers in some chemical equipment.
Especially in the chemical industry with a large amount of energy consumption, heat exchanger in the chemical production of heat exchange and transfer process is indispensable equipment in the entire chemical production equipment also occupies a considerable proportion.
Heat exchanger from its function, on the one hand, to ensure that the industrial process of the medium required by the specific temperature, on the other hand, is also to improve the energy utilization rate of the main equipment. According to its structural form of plate heat exchanger, floating head type heat exchanger, fixed tube plate heat exchanger and U-shaped tube heat exchanger and so on. In addition to the plate heat exchanger, the remaining types are shell and tube heat exchanger.
Due to the shell and tube heat exchanger has a larger heat transfer area per unit volume, and heat transfer effect is good, at the same time has a solid structure, adaptability, mature manufacturing process and other advantages, has become the most common use of a typical heat exchanger.
Shell and tube heat exchanger in the heat exchanger tube and tube plate connection
In the shell and tube heat exchanger heat exchanger tube and tube plate is the only barrier between the heat exchanger tube course and shell course, heat exchanger tube and tube plate connection between the structure and quality of the connection determines the quality of the heat exchanger and service life, is the heat exchanger manufacturing process is a critical link.
Most of the heat exchanger damage and failure occurs in the heat exchanger tube and tube plate connection parts, the quality of its connection joints also directly affects the safety and reliability of chemical equipment and installations, so for the shell and tube heat exchanger heat exchanger tube and tube plate connection process has become a heat exchanger manufacturing quality assurance system in the most critical control link. At present, in the heat exchanger manufacturing process, the heat exchanger tube and tube plate connections are mainly: welding, expansion, expansion and welding and gluing and expansion and other methods.

1. Welding
Heat exchanger tube and tube plate welding connection, due to the lower processing requirements for the tube plate, manufacturing process is simple, there is a better sealing, and welding, appearance inspection, maintenance is very convenient, is currently the shell and tube heat exchanger heat exchanger tube and tube plate connection of the most widely used connection method. In the use of welded connections, there is to ensure the sealing of the welded joints and tensile strength of the strength of the weld and to ensure the sealing of the heat exchanger tube and tube plate connection sealing weld. For the strength of the weld performance limitations, only for the vibration of the smaller and no clearance corrosion occasions.
Welded connection, the distance between the heat exchanger tube can not be too close, otherwise affected by the heat, weld quality is not easy to ensure, while the pipe end should be left a certain distance, in order to help reduce the welding stress between each other. The length of the heat exchanger tube extending out of the tube plate should meet the specified requirements to ensure its effective bearing capacity. In the welding method, according to the material of the heat exchanger pipe and tube plate can be welded by welding rod arc welding, TIG welding, CO2 welding and other methods. For heat exchanger pipe and tube plate connection between the high requirements of the heat exchanger, such as design pressure, high design temperature, temperature changes, as well as subject to alternating load heat exchanger, thin tube and plate heat exchanger, etc. should be used TIG welding.
Conventional welding connection methods, due to the existence of a gap between the tube and tube plate holes, prone to interstitial corrosion and overheating, and the thermal stresses generated at the welded joints may also cause stress corrosion and damage, all of which will make the heat exchanger failure. At present, in the domestic nuclear industry, electric power industry and other industries use heat exchanger, heat exchanger tube and tube plate connection has begun to use the bore welding technology, this connection method will heat exchanger tube and tube plate end of the weld to the tube bundle bore welding, the use of the full penetration form, the elimination of the end of the weld gap, improve the resistance to corrosion of the clearance corrosion and resistance to stress corrosion ability. Its anti-vibration fatigue strength is high, can withstand high temperature and high pressure, and the mechanical properties of the welded joints are better; the joints can be internal non-destructive flaw detection, and the internal quality of the weld can be controlled, which improves the reliability of the weld. However, the inner hole welding technology assembly is more difficult, high requirements for welding technology, manufacturing and inspection complexity, and relatively high manufacturing costs. With the heat exchanger to high temperature, high pressure and large-scale development, its manufacturing quality requirements are higher and higher, bore welding technology will be more widely used.

2. Expansion
Expansion is a traditional heat exchanger tube and tube plate connection method, the use of expansion instruments to make the tube plate and tube elastic-plastic deformation and close fit, forming a solid connection, to achieve both sealing and resistance to pull off the purpose. In the manufacturing process of heat exchanger, expansion is suitable for no severe vibration, no excessive temperature changes, no serious stress corrosion occasions.
Currently used expansion process is mainly mechanical rolling expansion and hydraulic expansion. Mechanical rolling expansion expansion is not uniform, once the tube and tube plate connection failure and then use the expansion tube to repair is very difficult; the use of liquid bag hydraulic expansion by the computer-controlled operation, high precision, and can ensure that the expansion of the tightness of the uniform degree of uniformity, connectivity and reliability than the mechanical expansion of good. However, the processing precision requirements are strict, to ensure the success of the expansion of dense joints also have some difficulty, if the failure of the expansion repair is also more difficult.
3. Expansion and welding
When the temperature and pressure is high, and in the thermal deformation, thermal shock, thermal corrosion and fluid pressure, the heat exchanger tube and tube plate connection is very easy to be damaged, using expansion or welding are difficult to ensure that the connection strength and sealing requirements. Currently widely used is the expansion and welding method. Expansion and welding structure can effectively dampen the beam vibration damage to the weld, can effectively eliminate stress corrosion and crevice corrosion, improve the fatigue resistance of the joint. This improves the service life of the heat exchanger, and has higher strength and sealing than simple expansion or strength welding. For ordinary heat exchangers are usually used in the form of "sticking expansion % strength welding"; while the use of harsh conditions of the heat exchanger requires the use of "strength expansion % sealing welding" form. Expansion and welding according to the expansion and welding in the process order can be divided into the first expansion after welding and welding after the first expansion of two kinds.
(1) first expansion after welding expansion of lubricating oil used will penetrate into the joint gap, and they have a strong sensitivity to weld cracks, porosity, etc., thus making the phenomenon of defects in welding more serious. These penetration into the gap of the oil is difficult to remove clean, so the first expansion after welding process, should not be used in the way of mechanical expansion. The use of paste expansion is not pressure-resistant, but can eliminate the gap between the tube and the tube plate tube holes, so it can effectively dampen the tube bundle vibration to the welded part of the tube mouth.
However, the use of conventional manual or mechanical control of the expansion method can not achieve uniform expansion requirements, and the use of computer-controlled expansion pressure by the liquid bag expansion method can be convenient and uniform to achieve the expansion requirements. In welding, due to the influence of high-temperature molten metal, the gap gas is heated and rapid expansion, these gases with high temperature and high pressure in the leakage of the strength of the expansion of the sealing performance will cause some damage.
(2) first weld and then expand for the first weld and then expand the process, the primary problem is to control the accuracy of the tube and tube plate hole and its coordination. When the gap between the tube and the tube plate hole is small to a certain value, the expansion process will not damage the quality of the welded joint. But the ability of the weld opening to withstand shear force is relatively poor, so the strength welding, if the control is not up to the requirements, it may result in over-expansion failure or expansion damage to the welded joint.
In the manufacturing process, there is a large gap between the outer diameter of the heat exchanger tube and the tube plate tube hole, and the outer diameter of each heat exchanger tube and the tube plate tube hole gap along the axial direction is not uniform. When the weld is completed expansion, the tube centerline must coincide with the centerline of the tube plate hole to ensure the quality of the joint, if the gap is large, due to the rigidity of the tube, excessive expansion deformation will produce damage to the welded joints, or even cause the weld joints to be desoldered.
4. Glue plus expansion joint
Gluing and expansion process to help solve the heat exchanger tube and tube plate in the heat exchanger connection often leakage and leakage problems, it is important to be glued according to the working conditions of the correct choice of gluing agent. In the process of implementing the process should be combined with the structure and size of the heat exchanger to choose a good process parameters, including curing pressure, curing temperature, expansion force, and so on, and in the production process is strictly controlled. This process is simple, easy to implement, reliable, in the actual use of the enterprise has been recognized, has the value of promotion.
(1) in the shell and tube heat exchanger heat exchanger tube and tube plate connection method, alone using conventional welding or expansion are difficult to ensure that the connection strength and the requirements of the sealing.
(2) Expansion and welding method is conducive to ensure the strength and sealing of the connection between the heat exchanger tube and tube plate, and improve the service life of the heat exchanger.
(3) The method of gluing and expanding helps to solve the problem of leakage and seepage when connecting the heat exchanger tube and tube plate, and the process is simple, easy and reliable.
(4) As a full penetration welding method, the internal hole welding technology has good resistance to interstitial corrosion and stress corrosion, vibration fatigue strength and mechanical properties of welded joints; the internal quality of welded joints can be controlled, which improves the reliability of welded joints, and it is more suitable for popularization and application in high-end products in the first place.