09-02-26 Topic - Connection form of heat exchanger tube plate and tube (prizes for participation)

Reprint 1 Introduction Steel shell and tube heat exchangers are widely used in chemical production. Whether it is a fixed tube sheet, a floating head tube sheet, or a U-shaped shell and tube heat exchanger, the connection between the tube and the tube sheet is a very important structure and link in the heat exchanger. Since the heat exchange tubes and tube plates are the only barriers between the tube side and the shell side of the heat exchanger, the quality of the joints between the heat exchange tubes and the tube plate is the most important factor in the failure of shell and tube heat exchangers, and has therefore become a common concern for users and manufacturing units. 2. Types of connection joints between tube plates and tubes. The types of connection joints between tube plates and tubes in heat exchangers are divided into expansion joints, welding joints, and expansion joints and welding joints according to different usage conditions of the heat exchanger. 2.1 The quality of the expansion joint mainly depends on the radial residual compressive stress on the pipe end. Its value is related to the materials and dimensions of the pipe and tube sheet, whether they are grooved, the expansion rate, the radial gap between the pipe and the tube sheet, surface roughness and other factors. In order to obtain good and stable expansion performance, in addition to strictly controlling the processing accuracy of the tube sheet and ensuring the appropriate hardness difference between the tube sheet material and the pipe material, it is also necessary to correctly select the tube expander, tube expansion power and control means to ensure appropriate expansion and adopt a reasonable expansion sequence. 2.2 The main problem in welding pipes and tube sheets is welding defects. Preventive measures include grinding the pipe ends to prevent node contamination and controlling the welding process to prevent burn-through or incomplete penetration. For some materials that are prone to cracks, pre-expansion before welding can also be used to reduce the gap between the pipe and the pipe hole. In order to prevent welding deformation and reduce residual stress during welding, it is divided into several areas according to the diameter. During welding, welding is performed radially from the center and sequentially in the diagonal areas. 2.3 Welding and expansion joints According to the processing conditions, welding and expansion joints can be divided into welding first and then expansion, and first expansion and then welding. Its advantages and disadvantages are as follows: 　　⑴ The first expansion and then welding manufacturing process requires a high degree of cleanliness of the tubes and tube sheets, otherwise manufacturing defects will easily occur. However, welding first and then expanding does not have high requirements on the cleanliness of the tube sheet and tubes. 　　⑵ In the process of expansion first and then welding, the welding has an adverse effect on the expansion joint and can easily cause the expansion joint to loosen. The gas generated during welding is difficult to eliminate, and weld defects are prone to occur. However, welding first and then expanding can fundamentally avoid this situation. 　　⑶ From the perspective of weld quality and use effect, the first welding and then expansion process is also * * It is better than the first expansion and then welding process. 3. Control links and control methods. In the manufacturing process of shell and tube heat exchangers, fully automatic argon arc welding of tubes and tube sheets should be adopted, and the manufacturing process of welding first and then expansion should be adopted. Specifically, the following links should be firmly grasped.: 　　(1) Strictly control the entry of raw materials into the factory and order higher-grade cold-drawn tubes as much as possible. For each batch of heat exchange tubes, the inspection department will send personnel to the heat exchange tube production plant to supervise the pressure test and spot check the outer diameter and wall thickness of the tubes. 　　(2) Strictly control the processing quality of the tube sheet. The processing of the tube hole of the tube plate uses secondary drilling and enlarging to ensure the dimensional accuracy and surface roughness requirements of the tube hole. When processing the tube holes to improve the dimensional accuracy, they must be processed according to the size requirements of the I-level heat exchanger tube holes. There should be no blisters, pit marks, edge burrs, or longitudinal scratches on the pipe hole wall. When the pattern structure is for strength expansion without welding, a reaming process is added to ensure that the joints are securely drilled. When inspecting the tube sheet, the inspector requires each hole to be measured, and the size range of the tube holes in each area is known and recorded. For pipe holes with a size at the upper limit, select a pipe with a deviation in the outer diameter to make up for the gap between the pipe and the pipe hole, and mark it carefully. Pay special attention when expanding the joint, and set the upper limit for the expansion rate to ensure the quality of the joint. 　　(3) Control the hardness difference between tube sheets and tubes. When the expansion joint process is used to connect the tube sheets and pipes, the hardness of the pipe end should be lower than the tube sheet hardness. The hardness difference should be controlled above HB 20-30, otherwise both ends of the pipe should be annealed. The annealing length is generally 200-250mm, and charcoal or coke should be used as heating fuel. The heating temperature for carbon steel pipes is 600-650°C, and the heating temperature for alloy steel pipes is 650-700°C. The other end of the pipe must be blocked during heating to avoid affecting heating due to air convection. The pipe should be rotated frequently during heating to ensure uniform heating throughout the pipe wall and avoid local overheating. The insulation time is 10-15 minutes. After taking it out, bury it in warm and dry sand or wrap it with insulation material (asbestos) and cool it slowly. When using the expansion joint process, the pipe ends must be inspected. If there are longitudinal scars, they cannot be used. 　　(4) Correctly select the pipe expander and control the appropriate expansion ratio. The appropriate degree of expansion must be maintained during expansion. Under-expansion cannot ensure the sealing of the expansion port. Over-expansion will cause pipe breakage and tube plate deformation due to excessive thinning of the pipe wall. The degree of expansion can be expressed by the pipe expansion rate. According to the pot regulations, when the inner diameter control method is used, the strength expansion rate should be controlled within the range of 1 to 2.1%. The pipe expansion rate can be calculated according to the following formula: H={（d1＋2t）／d－1}×100% where: 　　d1 The actual measured inner diameter of the pipe after expansion ； 　　t measured wall thickness of the pipe before expansion ； 　　d The measured diameter of the tube hole before expansion. 　　The converted formula: △d=（1＋H）d－d3 where: 　　△d Increase in inner diameter of heat exchange tube before and after expansion ； 　　d Actual measured diameter of tube hole before expansion ； 　　d3 is the outer diameter of the pipe before expansion. 　　Through years of practice, our company has, in principle, controlled the pipe expansion rate at about 1.8% during strength expansion and 0.9% during stick expansion. The specific control method is to calculate the inner diameter value of the heat exchange pipe after expansion according to the controlled expansion rate based on the diameter and wall thickness of the heat exchange pipe, and control the expansion rate by controlling the inner diameter of the pipe after expansion. According to the structural form of the tube plate and heat exchange tube joint, select the type of tube expansion ratio, roller length, position and other structural dimensions to ensure that there is a sufficient distance (in principle 15mm) between the starting position of the expansion joint (outside of the tube plate) and the weld to prevent expansion and cracking of the joint weld. At the same time, ensure that the expansion joint does not exceed the inside of the tube plate, and there is a 3mm distance from the inner end surface of the tube plate to prevent stress concentration on the pipes in the expansion transition zone. Test expansion is carried out before formal expansion. The thickness of the test expansion tube plate should be 5mm smaller than the thickness of the product tube plate to check the quality of the tube expander and the expansion performance of the pipe. At the same time, according to the test expansion results, it is determined where the expansion column of the pipe expander is. When the pipe expansion rate reaches the control value, the final position of the expansion rod should be marked for operation during actual expansion. Strength expansion is generally divided into two expansions, and the order of expansion should be paid attention to. The central area is expanded first, and then the peripheral area is expanded radially to reduce the deformation of the tube sheet and reduce the residual stress of the joint. 　　(5) The manufacturing process of welding first and then expansion is used. The cleanliness of the tube sheet tube holes and the heat exchange tube ends has a great influence on the welding quality of the joints. When the tube sheet is drilled, the oil and water left around the tube holes by lubricating oil and coolant are rinsed with high-temperature steam, and then dried with compressed air. The tube end length of the heat exchange tube is twice the thickness of the tube plate and polished with a cloth grinding wheel to remove rust and dirt on the tube end and outer surface. After the heat exchange tubes and tube plates are assembled, the welding must be completed within the specified time to prevent the welding quality from being corroded again over time. 　　(6) Full-automatic argon-arc welding of tube-tube sheets is used for the welding of tube-sheet and heat-exchange pipe joints. Full-time argon-arc welding of tube-tube sheets is performed by full-time welders. Advanced equipment, skilled technology, and a high sense of work responsibility ensure the welding quality. When welding, each joint is welded in two passes, and the arc closing point of the second pass covers the arc starting point of the first pass by 15°, so that the relatively weak parts of the arc starting point and the arc closing point do not overlap. These measures not only improve the intrinsic quality of the weld, but also ensure the welding height and sufficient pull-off force. 　　(7) Adopt practical and effective testing methods. Our company adopts the method of secondary pressure test on the shell side before expansion and after expansion to inspect the quality of welding and expansion. After welding and before expansion, the shell side is tested for air tightness with 0.6MPa gauge pressure compressed air to check the quality of the joints. Then the joints are expanded as required. After expansion, a pressure test is performed according to the test pressure required by the drawing. 4 Conclusion In summary, as long as the processing and manufacturing of steel shell-and-tube heat exchangers is strictly managed, the welding quality is ensured, the appropriate tube expansion rate is ensured, the appropriate expansion sequence is adopted, and practical and effective detection methods are adopted, it is completely possible to produce high-quality products for users.

1. Applicable scope of strength expansion joint: The design pressure is less than or equal to 4MPa, the design temperature is less than or equal to 300 degrees, and there is no strong vibration, no excessive temperature change and no obvious stress corrosion during operation. 2. Applicable scope of strength welding: The design pressure is less than or equal to 35MPa, but it is not suitable for occasions with large vibration and crevice corrosion. 3. Applicable scope of combined use of expansion welding: Occasions with high sealing performance requirements ； Where subjected to vibration or fatigue loads ； Where there is crevice corrosion ； Where composite tube sheets are used. It can be seen that expansion welding has the widest scope of application.

GB151 1. Scope of application of strength expansion joints: The design pressure is less than or equal to 4MPa, the design temperature is less than or equal to 300 degrees, and there is no strong vibration, no excessive temperature change and no obvious stress corrosion during operation. 2. Applicable scope of strength welding: The design pressure is less than or equal to 35MPa, but it is not suitable for occasions with large vibration and crevice corrosion. 3. Applicable scope of combined use of expansion welding: Occasions with high sealing performance requirements ； Where subjected to vibration or fatigue loads ； Where there is crevice corrosion ； Where composite tube sheets are used.

Oh what is expansion joint? ? ? ? Don't know how to learn * middle

1Expansion joint: It is divided into strength expansion joint and sticking expansion joint. The expansion joint is mainly a slight expansion joint to eliminate the gap between the heat exchange tube and the tube hole. ； The strength expansion joint means that the sealing and pull-off strength of the connection between the tube plate and the heat exchange tube are ensured by the expansion joint. It is suitable for situations where medium penetration between pipe shells will not cause adverse consequences. The expansion joint structure is simple and the pipe repair is easy. Due to plastic deformation at the expansion joint end, residual stress exists. As the temperature rises, the residual stress gradually disappears, which reduces the sealing and bonding force at the pipe end. Therefore, this expansion joint structure is subject to certain limits on pressure and temperature. For heat exchange tubes whose tube sheets and heat exchange tubes are made of carbon steel, low alloy steel, or stainless steel respectively, if expansion joints are used to connect the tube sheets and heat exchange tubes, the following requirements must be met.: The linear expansion coefficient of the tube sheet and the heat exchange tube differs by 10%-30%, and the difference between the operating temperature and room temperature (21 degrees Celsius) shall not exceed 155 degrees Celsius. ； The linear expansion coefficient differs by 30%-50%, and the difference between its operating temperature and room temperature (21 degrees Celsius) shall not exceed 128 degrees Celsius. ； The coefficient of linear expansion differs by 50%, and its operating temperature must not exceed 72 degrees Celsius. 2 welding: Divided into strength welding and sealing welding. Sealing welding is a welding to ensure the sealing performance of the connection between the heat exchange tube and the tube sheet. Strength welding is to ensure the sealing and pull-off strength of the heat exchange tube and tube sheet. The strength welding of tubes and tube plates is suitable for heat exchangers used under various pressures and temperatures where the tube plates and heat exchange tubes are made of carbon steel, low alloy steel, stainless steel, and stainless steel is cladded on carbon steel or low alloy steel tube plates. This kind of connection, due to the gap between the heat exchange tube and the tube hole, should not be used in heat exchangers that corrode the shell side materials and vibrate greatly during operation. 3 Expansion welding combined use: It is mainly suitable for occasions with high pressure, strong permeability, or corrosive media on one side, and high requirements on the sealing surface to ensure that leakage does not contaminate the material on the other side. ； Or in order to avoid the impact of vibration on the weld during shipping and operation, and where it is subject to vibration or fatigue load ； Or where there is crevice corrosion and where composite steel plates are used.

1. Applicable scope of strength expansion joint: The design pressure is less than or equal to 4MPa, the design temperature is less than or equal to 300 degrees, and there is no strong vibration, no excessive temperature change and no obvious stress corrosion during operation. So obviously not resistant to temperature and corrosion. 2. Applicable scope of strength welding: The design pressure is less than or equal to 35MPa, but it is not suitable for occasions with large vibration and crevice corrosion. 3. Applicable scope of combined use of expansion welding: Occasions with high sealing performance requirements ； Where subjected to vibration or fatigue loads ； Where there is crevice corrosion ； Where composite tube sheets are used.

Turn 1 (Author Cheng Yanhai) The welded joint between the tube sheet and the tube The connection between the tube and the tube sheet is a relatively important structural part in the design of the shell and tube heat exchanger. It not only has a large processing capacity, but also must ensure that every connection is in operation of the equipment to ensure no leakage of the medium and the ability to withstand the pressure of the medium. The connection forms between the tube sheet and the pipe can include (1) expansion joint, (2) welding, and (3) expansion welding combination. (1) Expansion joint form: expansion joint is mainly used to eliminate the gap between the heat exchange tube and the tube hole. ； Strength expansion refers to the connection where the sealing and tensile strength of the connection between the tube plate and the heat exchange tube are guaranteed by expansion joints. It is suitable for situations where medium penetration between pipe shells will not cause adverse consequences. The expansion joint structure is simple and the pipe repair is easy. (2) The welded structure of the welded pipe and the tube plate, because the pipe hole does not need to be grooved, the roughness of the pipe hole is not required, it is easy to process and manufacture, has strong pull-off strength, high structural strength, repair welding and disassembly are more convenient than expanded pipes, and is widely used. It is usually called strength welding. If the height of the pipe is only 1mm above the tube plate, it is called sealing welding. Sealing welding only ensures the sealing performance of the connection between the pipe and the tubesheet, but cannot guarantee its pull-off strength. (3) Under high temperature and high pressure combined with expansion welding, the pipe end joint faces an extremely harsh working environment. Whether it is welding or expansion joint, it is difficult to ensure that it meets the requirements. Although the expansion joint method can withstand higher pressure, when the temperature rises above 300-400°C, creep causes the relaxation of the residual stress of the expansion joint, which will soon cause the expansion joint to fail. Although the welding method can withstand higher temperatures, high-temperature cyclic stress can easily cause fatigue cracks in the weld joint, so it is necessary to consider the use of expansion welding. For occasions with high sealing requirements, or those with vibration, fatigue loads, and those with gap corrosion and composite tube sheets, expanding first and then welding can improve the fatigue resistance of the weld, and the tube wall fits the hole wall of the tube plate, which can prevent cracks during welding. However, the residual lubricating oil in the expanded tube can easily produce pores during the welding process, seriously affecting the quality of the weld. Welding first and then expanding eliminates the need to clean the remaining oil stains after expanding the pipe, but the position of the expanded pipe during expansion after welding is higher, and expansion joints must be kept within the range of 10~12mm, otherwise the weld will be damaged. In expansion welding combined structures, strength expansion and sealing welding are commonly used.

Reprinted from the China Mechanical CAD Forum. The connection forms of tubes and tube sheets are as follows:: Expansion joint, welding, strength expansion + sealing welding and strength welding + sticking expansion. 3.1 Weld first and then expand. The pipe plate groove is easy to clean before welding. The air in the gap between the pipe and the pipe plate can be eliminated from the front and back sides during welding. This is very beneficial to prevent the weld from producing pores and ensure the quality of the welded joint. At the same time, post-expansion can prevent the residual stress after expansion from relaxing and avoid relaxation due to the influence of high welding temperature. However, for pipes and tube-sheet joints with poor weldability, the weld bead is prone to micro-cracks during expansion, and may even cause the weld bead to burst. In this case, deep expansion should be used (that is, the pipe mouth does not expand around 10 to 15 mm) to avoid the expansion joint from the weld bead, thereby reducing the impact of the expansion joint on the weld bead. This is also the biggest shortcoming of the welding first and then expansion process. Experimental research shows that using the first expansion and then welding process, the leakage rate of the pipe and tube plate after welding is about 10 times higher than that of the first welding and then expansion process. Moreover, the inspection results show that the weld seam has a uniform appearance, a metallic luster, and beautiful shape. There are very few pores and lack of fusion during color inspection. Therefore, the process of welding first and then expansion is often used in foreign countries. 3.2 Expansion first and then welding adopts the process of expansion first and then welding. Since a large amount of oil, rust and other debris will be left at the pipe end and groove during expansion, although it must be cleaned before welding, due to the narrow pipe bridge and the fact that the pipe protrudes from the tube plate, it is difficult to ensure thorough cleaning of the groove. When welding, these leftover debris will undergo violent chemical changes. Moisture and air will expand locally due to heat, and form pressure in the gap between the pipe and the pipe hole. Since the back side is blocked after expansion, these pressurized gases can only be discharged from one side of the weld bead. The metal in the molten state during welding has no strength at all, and the gas can easily pass through the weld bead, especially at the closing arc. The gas rushes out of the weld bead and causes the weld metal to boil, causing the weld to be uneven and even honeycomb-shaped. At the same time, it also oxidizes the surface of the weld, causing defects such as lack of fusion. During the cooling process of the weld, some gases fail to escape the weld surface in time, thus forming pores inside the weld. In addition, the high temperature generated during welding will cause the expanded parts to deform, causing the residual stress and elastic deformation generated during the expansion process to disappear, which may reduce or even eliminate the expansion force. Experimental research results show that the leakage rate of the process of expansion first and then welding is about 10 times that of welding first and then expansion. Our long-term mass production practice has also proved that there are indeed many shortcomings in expanding first and then welding, especially when the welding process performance is poor, the problem is more serious, such as the matching of 20MnMo, 15CrMo and austenitic stainless steel pipes. 　　Based on the above analysis, although the process of expansion first and then welding can be used, domestic and foreign manufacturing usage shows that it is more advantageous to use the process of welding first and then expansion. When designing and manufacturing, priority should be given to the welding first and then the expansion process. For pipe materials with poor weldability, a 10 to 15 mm non-expansion area can be left at the pipe mouth.

Turn 3 Among the heat exchanger systems in petrochemical and chemical equipment, shell-and-tube heat exchangers have always dominated chemical production and use due to their advantages of solid structure, high reliability, and strong adaptability. However, due to the complexity of its structure and the diversity of use conditions, heat exchangers often suffer from various forms of failure. From a structural analysis, the connection between the tube bundle and the tube sheet is more likely to fail. ； From the analysis of the use process parameters, corrosion stress, temperature difference stress, oscillation of the tube bundle, etc. will all cause partial or overall failure of the heat exchanger. 1. The connection form of the pipe and the tube sheet. The connection between the pipe and the tube sheet should ensure good tightness to prevent leakage at the connection, resulting in loss of heat and products, and even endangering the safety of people and equipment. ； At the same time, it should be ensured that it can withstand a certain axial force to prevent the pipe from coming out of the tube sheet. The traditional connection method between pipe and tube sheet is expansion joint, welding and expansion welding combined. 1.1 Expansion joints 1.1.1 Mechanical rolling expansion method The use of mechanical rolling expansion method for connection is likely to cause over-expansion or under-expansion of the heat exchange tube, and the inner wall of the heat exchange tube is prone to work hardening. Structures with slotted holes or flanges (see Figure 1) are used in situations with high pull-off resistance and sealing requirements, and are not suitable for working at high temperatures. Under the influence of temperature difference changes, the residual stress of the tube at the expansion joint gradually disappears, thereby reducing the sealing performance and pull-off resistance, causing the connection between the heat exchange tube and the tube plate to fail. The advantage is that the expansion joint structure is relatively simple, making it easy to replace and repair pipes. The general applicable conditions are pressure ≤ 4 MPa and temperature ≤ 300 ℃. 1.1.2 Hydraulic expansion joint The stress distribution during hydraulic expansion joint is relatively uniform, and it has the characteristics of high productivity, low labor intensity and good sealing performance. Hydraulic expansion joints have particularly strict requirements on the accuracy of pipe holes and grooves. 1.1.3 Blasting pipe expansion uses the radial force during the explosion to tighten the pipe, and at the same time uses the axial force during the explosion to throw the residue out of the pipe. 1.2 Welding The welding method is easy to process, has good connection strength, and can ensure the tightness and pull-off resistance of the connection under high temperature and high pressure (see Figure 2). After the connection is welded, the residual thermal stress and stress concentration existing in the pipe and tube sheet may cause stress corrosion and fatigue damage, causing the connection between the pipe and the tube sheet to fail and leak. Therefore, it is necessary to grind the pipe end during welding and clean the dirt in the welding area to prevent node contamination. 1.3 Combined use of expansion welding Expansion welding and welding methods have their own advantages and disadvantages. The use of expansion welding combined method can not only improve the fatigue resistance of the joint, but also eliminate stress corrosion and gap corrosion and increase the service life. Expansion welding connections can be divided into the following types according to different expansion and welding requirements.: Strength welding + expansion, strength welding + strength expansion, strength expansion + sealing welding, strength expansion + expansion + sealing welding, strength welding + strength expansion + expansion, etc. The latter two methods are used for thick tube sheets. In addition, "positioning expansion" is used before strength welding, that is, the pipe is expanded and positioned in the pipe hole before welding and other processes. The various expansion welding combinations mentioned above should be selected according to working conditions such as connection strength requirements, sealing requirements, tube plate thickness and corrosion. The strength welding mentioned here refers to the entire connection strength between pipes and tube sheets, and also ensures the tightness of the weld. ； Sealing welding is simply to prevent medium leakage ； The function of strength expansion is the same as that of strength welding, while bonding expansion only eliminates the gaps between pipe holes in order to prevent gap corrosion.

The connection between the tube plate and the heat exchange tube The connection between the heat exchange tube and the tube plate (hereinafter referred to as the "pipe joint") is usually a place where failure and leakage of the heat exchanger are prone to occur. If the connection quality is not good, it will directly affect the normal process operation and the service life of the heat exchanger. There are many reasons for connection failure, such as: ①Pipe joints fail due to stress relaxation at high temperatures. ②Failure due to medium corrosion. ③Fatigue failure of pipe joints due to fluid-induced vibration in pipes. ④Improper operation and temperature fluctuations can cause fatigue damage. ⑤Failure due to stress corrosion cracking. ⑥Pipe joints themselves have varying degrees of quality hazards. Therefore, great attention should be paid to the design and construction of joints. The main ways to connect heat exchange tubes and tube sheets include expansion joints, welding, and a combination of expansion welding, which are introduced below. (1) Expansion connection There are two types of expansion joints: strength expansion and adhesive expansion. The expansion joint methods can be mainly divided into two categories: mechanical expansion joints and flexible expansion joints. Mechanical expansion joints are the most traditional. Flexible expansion joints include hydraulic expansion joints, liquid bag expansion joints, rubber expansion joints, explosive expansion joints, etc. Below, we focus on the mechanical expansion method. The principle is to use a roller expander, insert it into the end of the pipe and then rotate it, so that the diameter of the pipe expands and plastic deformation occurs, while the tube plate only produces elastic deformation. After the pipe expander is taken out, the elasticity of the tube plate recovers, and the pipe is tightened. An extrusion force is generated between the tube plate and the pipe to fit together, thereby achieving the purpose of fastening and sealing. According to this principle, the hardness of the tube sheet is required to be higher than the hardness of the tube head. The difference in hardness is usually achieved by selecting different tube sheet and tube materials. In addition, appropriate "expansion" must be ensured. "Under-expansion" cannot guarantee the mechanical strength and sealing of the connecting joint, while "over-expansion" will cause the pipe wall to be excessively thin and prone to rupture, or cause excessive deformation or even plastic deformation of the tube plate hole bridge, resulting in tube plate deformation. The German Linde Company stipulates that the degree of strength expansion is when the increase in the inner diameter of the pipe reaches 18% of the pipe wall thickness. ； The expansion degree of sticking expansion is that the increase in the inner diameter of the pipe reaches 3% of the pipe wall thickness. In order to improve the connection strength and tightness, a circumferential groove is usually opened on the wall of the pipe hole. When the pipe is expanded, the pipe undergoes plastic deformation and the pipe wall at the groove is embedded in the groove. This not only improves the pull-off strength, but also improves the tightness. Generally, when the pressure is high, grooves must be made. Previously, relevant domestic standards stipulated that when the operating pressure p≤0.6MPa, no grooves could be made to save processing costs. GB151-1999 only stipulates that when the outer diameter of the heat exchange tube is ≤14mm, the tube hole is not allowed to be grooved. In addition, of course, there is no need to groove for expansion. The structural type and size of mechanically expanded pipes are specified in GB151-1999. The regulations on the slot size of the strength expansion structure are to meet the need to open two slots in a thinner tube sheet (such as 25mm thickness) ； This size can be changed when the tube sheet is thicker ； For mechanical expansion, a 3mm wide groove is feasible. However, when using flexible expansion joints, the width of the groove must be widened, and the formula in Article 105 of the "Capacity Regulations" should be followed, groove width = (1.1~1.3), where d is the average diameter of the heat exchange tube ； δ is the wall thickness of the heat exchange tube. like: Ø 25×2.5mm heat exchange tube, the slot width should be 8.7mm~10.3mm. The minimum expansion length L for strength expansion should be the nominal thickness of the tube sheet minus 3mm or 50mm, whichever is smaller. The longer L is, the greater the pull-off strength is, but if it exceeds 50mm, it is meaningless to know from experiments. This is because the length of 50mm is enough to ensure that the pipe will not pull off, but will only break. Therefore, there is no need to expand the pipe too long. For composite tube sheets, when grooving the tube hole, a groove should be made in the cladding part of the tube hole, see Figure 1.2-70 (d). For thicker tube sheets, in order to prevent gap corrosion, in addition to the 50mm strength expansion, the remaining parts can be expanded, see Figure 1.2-70 (c). The tightness of the expansion joint is also related to the surface roughness of the tube hole. GB151-1999 stipulates that when the heat exchange tube is expanded and connected to the tube plate, the surface roughness Ra value of the tube hole shall not be greater than 12.5 μm. Of course, there is no need to set excessively high requirements, which will only increase manufacturing costs. Expansion joints have the characteristics of convenience, simplicity, low cost, and easy pipe replacement, so they are widely used. They are mostly used in situations where leakage of the medium between pipes and shells will not cause adverse consequences or where welding is difficult. The expansion connection is more limited by temperature than by pressure, because as the temperature increases, the stiffness of the pipe and tube sheet decreases, the expansion joint stress relaxes, and the thermal expansion stress increases, which can easily cause joint relaxation and leakage. Japan's Mitsubishi Heavy Industries Co., Ltd. recommends that when the pressure is not high, the expansion joint can be extended to 350°C. If the temperature is not high, but considering the pressure, the United States has used 35MPa ； Among the 300,000 tons/year ammonia synthesis equipment imported from France, most of the medium-pressure and medium-temperature heat exchangers with a design pressure of 3.0~4.7 MPa and a temperature of 250~460°C adopt an expansion joint structure. The applicable temperature range of expansion joints used by Japan's Ishikawashima Harima Heavy Industries Co., Ltd. is shown in Table 1.2-7. Table 1.2-7 Maximum operating temperature for expansion joints of different materials. Maximum operating temperature of pipe material and tube plate material/℃ Aluminum carbon steel 93 Copper carbon steel 177 Navy brass carbon steel 177 90-10 copper-nickel alloy carbon steel 204 80-20 copper-nickel alloy carbon steel 232 70-30 copper-nickel alloy carbon steel 268 70-30 nickel-copper alloy carbon steel 288 Austenitic stainless steel carbon steel 260 In Appendix A of the ASME Code, A99 A-1 General (d) (3) describes the pipe joints when the heat exchange tubes and tube sheets are made of materials with different expansion coefficients as follows: When the smaller expansion coefficient is 70% to 90% of the larger expansion coefficient, the difference between the operating temperature and room temperature (t=21℃) shall not exceed 138℃, that is, the maximum operating temperature at this time is 159℃. When the smaller expansion coefficient is 50% to 70% of the larger expansion coefficient, the difference between the operating temperature and room temperature (t=21℃) shall not exceed 128℃, that is, the maximum operating temperature at this time is 149℃. When the smaller expansion coefficient is 50% of the larger expansion coefficient, the difference between the operating temperature and room temperature (t=21℃) shall not exceed 72℃, that is, the maximum operating temperature at this time is 93℃. The above-mentioned ASME, 99 addendum proposes the relationship between strength expansion-linear expansion coefficient-allowable operating temperature, but it is relatively general. The ratio of linear expansion coefficients of the same grade spans too much, but it illustrates the trend of temperature influence. The recommended maximum operating temperatures for expansion joints of different materials are shown in Table 1.2-8. Table 1.2-8 Maximum operating temperature of expansion joints of different materials Maximum operating temperature of heat exchange tube material tube plate material/℃ Aluminum carbon steel, low alloy steel 93 Copper (red copper, brass) Carbon steel, low alloy steel 177 90-10 copper-nickel alloy carbon steel, low alloy steel 204 80-20 copper-nickel alloy carbon steel, low alloy steel 232 70-30 copper-nickel alloy carbon steel, low alloy steel 268 70-30 Nickel-copper alloy carbon steel, low alloy steel 288 Austenitic stainless steel carbon steel, low alloy steel 260 carbon steel, low alloy steel carbon steel, low alloy steel 300 GB151-1999 stipulates the scope of application for steel joint expansion: ①Design temperature≤300℃ ； ②Design pressure≤4.0 MPa ； ③There is no severe vibration, no excessive temperature fluctuation, and no obvious stress corrosion during operation. The disadvantages of the mechanical expansion method are: ①The expansion is not easy to control. It often depends on the operator's experience. Even if an automatic tube expansion instrument is used and controlled by current (torque), the degree of expansion may not be truly controlled. Because there are many factors that affect torque, such as: Dimensional deviations, material performance deviations, differences in lubrication conditions, etc. Therefore, the strength and tightness of each joint after expansion are uneven. ②Labor intensity is high, especially for pneumatic or electric mechanical pipe expansion. ③For small-diameter or thick-walled pipes, it is difficult or impossible to expand them. Generally, the ratio of pipe wall thickness to pipe outer diameter, that is, δ/d0

Continued: (2) Welded connection For a long time, expansion connection has been widely used. Generally, welding connections are only used in harsh media such as high temperature or pressure, as well as flammable and explosive media. However, since the welding method has more advantages than the expansion method, such as: It has a wide range of applications, more reliable tightness, low requirements for tube plate hole processing (low surface roughness requirements and no need for grooves), simple and easy process conditions, etc., as well as the rapid development of welding technology. For commonly used types, the pipe ends are allowed to be welded down (melted) during construction. Full-angle welds that do not allow welding (melting) at the pipe end are used in high-pressure or harsh situations and U-shaped pipe structures. The connecting joints do not protrude from the tube plate, and are used to avoid residual liquid retention on the tube plate after the operation is stopped (such as the upper tube plate of a vertical heat exchanger), and to reduce the tube inlet resistance. Grooves are opened around the hole, which can effectively reduce welding stress and tube plate deformation. It is suitable for thin tube walls and materials that do not allow large deformation of the tube plate after welding or are prone to thermal cracks. Internal hole butt welding has two common shortcomings due to the previous types. Not only is there a gap between the pipe and the wall of the pipe hole, which is prone to gap corrosion, but the fillet weld will produce stress concentration at the welding point. Under high temperature or temperature fluctuations, it is easy to cause the weld to fail and break. ； The inner hole butt welding not only fundamentally eliminates gap corrosion, but also improves the quality of the weld and allows for non-destructive testing. This kind of joint has good stress state and significantly improves stress concentration. Especially from the perspective of fatigue strength, it is undoubtedly the best. In addition, the notch effect can be eliminated and thermal shock reduced. Its disadvantage is that it is difficult to manufacture. First of all, in order to facilitate alignment and docking, the dimensional tolerances of the tubes and tube holes are stricter. Special internal hole welding equipment is required, and ultra-short focal length and low-energy radioactive sources are required. Moreover, any weld defects are almost impossible to repair, so the manufacturing process requirements are extremely strict. Despite this, because this kind of butt joint can produce high-strength and high-quality welds, it is still used in situations where high pressure, vibration, cyclic load, thermal stress, strong corrosion, etc. may cause welded joint failure and serious consequences. The above are several typical joint types of welded connections (not all). Strictly speaking, they are all strength welding (which ensures both the sealing of the connection and the tensile strength of the connection). In addition, there are sealing welding (which only ensures the sealing of the connection). Generally, seal welding is not used alone, but is used together with expansion joints.

Continued: (3) Expansion welding combined with connection When the operating conditions (temperature, pressure, medium, etc.) have strict requirements on the connection joint between the heat exchange tube and the tube sheet, it will be difficult to meet the requirements regardless of whether the expansion connection or welding connection is used alone. Although internal hole welding can be used, it is difficult to manufacture, expensive and not widely used. At present, the method of combining expansion welding is widely used. Tests have proven that the combined use of expansion welding can not only improve the fatigue resistance of the joint, but also eliminate gap corrosion. In addition, the expansion joint can make the tube sheet temperature approach the tube side medium temperature. This is because the heat transfer surface of the tube side medium to the tube sheet is much larger than the heat transfer surface of the shell side medium to the tube sheet, especially for thick tube sheets. Therefore, the metal temperature difference on both sides of the tube sheet can be reduced, thereby alleviating the temperature difference stress of the tube sheet itself. GB151-1999 stipulates the applicable scope of expansion welding combined use: ①Occasions with high sealing performance requirements ； ②Where subjected to vibration or fatigue loads ； ③Where there is crevice corrosion ； ④Where composite tube sheets are used. In the 1970s, the heat exchangers of synthetic ammonia, urea, ethylene and other devices introduced in my country widely used the joint method of expansion welding. There are five types of connection types that can be used together with expansion welding:: ①Strength welding + expansion. ②Strength expansion + sealing welding, ③ Strength expansion + strength welding ； ④Strength expansion + sticking expansion + sealing welding ； ⑤Strength expansion + sticking expansion + strength welding. In the connection using both expansion welding and expansion welding, there is currently no unified standard and answer as to whether welding should be done first and then expanded, or whether it should be expanded first and then welded. However, since most of the traditional mechanical rolling methods are used, in most cases the process of welding first and then expansion is used. This is because lubricating oil (grease) must be used during mechanical rolling. It can easily stain the pipe head and invade the gaps of the joint. It is also difficult to clean thoroughly and will seriously affect the quality of the weld. Welding first and then expanding can avoid this disadvantage and ensure the quality of the weld. However, the welding first and then expansion process also has weaknesses. First, there is a gap between the pipe and the pipe hole. During welding, the two will be eccentrically arranged and form an uneven distribution of the annular weld bead. This will especially have a certain impact on the welding of thin-walled pipes. ； Secondly, when the pipe is expanded later, since the pipe in the expanded section and the pipe hole are ultimately concentric, this conflicts with the eccentricity of the weld, which will inevitably produce bending and squeezing effects on the weld with a large offset gap. In order to avoid the destructive effect of the expansion force on the weld, the expanded section must be separated from the weld by a certain distance. GB151-1999 stipulates that this distance is 15mm (also called the non-expansion zone). In addition, mechanical rolling will cause the pipe wall to become thinner and the pipe to elongate, and improper control will also cause damage to the weld. If the fillet weld is allowed to be welded down at the pipe end, the shrinkage of the pipe mouth and the welding nodule protruding from the inner wall will cause difficulties in future pipe expansion operations. When other pipe expansion methods that do not require lubrication are used (such as rubber pipe expansion, liquid bag expansion, explosion pipe expansion, etc.), it is also appropriate to use the first expansion and then welding process on the premise of ensuring the quality of the weld. At this time, the 15mm non-expansion zone allows for appropriate adjustments.

Continued: (4) Other connection methods 1. Explosive expansion joint and explosive welding Explosive expansion joint and explosive welding use high energy * * The explosion generates high pressure in a very short time (10~12×10-6s). Under the action of the high-pressure gas shock wave, the pipe rapidly undergoes plastic deformation to firmly fit on the tube sheet. Explosive expansion joints form a wave-like mechanical connection between the pipe and the tube sheet, while explosive welding also has a certain degree of metallurgical bonding in addition to the mechanical connection. Of course, each has its own unique features in specific process methods. Explosive welding requires fairly high impact forces, at least ten times the yield limit of the metal. ①Explosive expansion joints Explosive expansion pipes have the following advantages over mechanical pipe expansion (rolling expansion): a) This technology can be used for expansion joints of thin-walled pipes, thick-walled small-diameter pipes, and situations where general mechanical expansion joints are not suitable. b) This technology does not require lubricating oil, and there is no need to worry about pores occurring during seal welding after expansion. c) Economical and efficient. Can be used to detonate thousands of joints. The cost of explosive welding of thick-walled small-diameter pipes is reduced by 30% to 40%. d) Applicable to various metals, especially stainless steel pipes and bimetallic pipes. e) The pull-off resistance is great, and the degree of embedding in the groove of the pipe hole is greater than that of mechanical rolling. For thick-walled pipes that work for a long time under high temperature and high pressure, it can be used together with seal welding to achieve good results. f) Reduce the axial elongation and deformation of the tube. g) It is easy to operate and does not require special equipment. h) Since mechanical expansion is limited by the length of the roller (cannot be too long), the length of one expansion joint generally does not exceed 60mm. ； When the expansion joint length is required to be longer, it can only be filled in two or three times, which is labor-intensive and time-consuming. However, the explosion expansion joint can be filled in one time. Application examples: Under the operating conditions of 350°C and 30 MPa, the original heat exchanger began to leak after being used for about 6 months. Later, the connection between the pipe and the tube sheet was switched to explosive expansion joint and sealing welding, and it has been used for more than 5 years without any accidents. In 1989, Lanzhou Petrochemical Machinery Factory provided an acrylonitrile cooler for a refinery in Fushun. Its design conditions were:: Tube side 0.24MPa, 480℃, shell side 4.7 MPa, 265℃ ； The thickness of the tube sheet is 215mm and the material is SA182F12 ； The heat exchange tube specification is Ø 31.8mm×3mm×6500mm, the material is SA213GrT12, and the quantity is 1916 pieces. ； The connection between the pipe and the tube sheet is strength welding + expansion, and the expansion length is 197mm. Explosive expansion is used for the expansion, and the equipment has been in good use since it was put into operation. Disadvantages of explosive expansion joints: There is a certain degree of danger and requires specialized sites and professional operations. And it is generally not used for expansion joints of U-shaped pipes, because explosion residues can easily block U-shaped pipes. ② Explosive welding is similar to explosive expansion. It has all the advantages of explosion. Compared with ordinary welding, explosive welding has its own special advantages.: a) Have better connection integrity and higher quality pass rate. The connection area of ​​explosion welding is larger than that of ordinary seal welding, and its strength and reliability are high. b) The requirements for machining tolerances are low. c) Almost all combinations of materials (carbon steel, stainless steel, aluminum, copper, titanium and various alloys) can be connected by explosion welding without gas protection. Moreover, the strength of the weld is higher than that of the base material, because explosion welding is basically a cold process. d) Explosion welding can use pipes with very thin walls, which not only saves a lot of material, but also reduces the minimum core distance required for explosion welding and improves heat conduction. e) It can be remotely controlled and is suitable for repairing heat exchangers that are exposed to radiation or are inaccessible to people, as well as for explosion welding. The main disadvantage of the explosive welding method is that it requires a tube-to-core distance that can withstand the impact force generated when the tube expands without deforming it. As with ordinary processing methods, the minimum distance between tubes that can be applied has nothing to do with the diameter of the tube, but is related to the thickness of the tube wall. The thicker the tube wall, the greater the minimum distance between tubes. When operating conditions permit, by locally thinning the pipe end to an appropriate pipe wall, a pipe with a thicker wall can be blast welded to a specific pipe center distance. 2. Hydraulic pipe expansion method and liquid bag pipe expansion method. The hydraulic pipe expansion method inserts the mandrel into the pipe end and relies on the "O" type seals provided at both ends of the mandrel to directly press high-pressure oil or water into the pipe, subjecting the pipe wall to the necessary high pressure, thereby achieving the purpose of pipe expansion. This method has gained practical application abroad (such as Germany). This method has residual liquid contamination on the inner wall of the tube, so it is not suitable for the first expansion and then welding process. ； In addition, the "O" type seal is easily damaged. In the liquid bag expansion method, high-pressure liquid is pressed into the liquid bag, and the pressure is applied to the inner wall of the pipe with the help of the expansion of the liquid bag to achieve the purpose of expanding the pipe. This method has no pollution to the tube head and has reached the stage of practical application in Japan. The advantages of these two expansion methods are: The pipe wall is uniformly stressed, the pipe has little axial elongation, and there is no work hardening. ； The grooved and expanded pipes are more embedded in the grooves, the connection strength and sealing performance are better, and the expansion length is not limited. The disadvantage is: The parts close to the surface of the tube sheet cannot be expanded, requiring high dimensional accuracy of the tube. 3. The piston in the rubber tube expansion hydraulic cylinder generates axial force under the action of oil pressure. This axial force forces the tube expansion medium (special rubber) to generate uniform radial pressure, pressing the tube against the tube plate hole wall to achieve the purpose of expansion. Advantages of rubber tube expansion method: a) The requirements for tube accuracy are relatively loose. b) No lubricant is needed, and the expansion force is even. c) Easy to operate and control. d) High production efficiency (it only takes a few seconds to expand a joint) and low production cost. Suitable for expansion joints and expansion joints of various pipe diameters, thicknesses and materials, and * * Reduce the labor intensity of workers. e) The expansion joint quality is uniform. When grooving and expanding, the internal pressure of the expanded pipe is uniform, so that the pipe is deeply embedded in the groove, obtaining greater fastening force and sealing performance, which will not be degraded even after long-term use at high temperatures. The slot width is 6~12mm and the depth is 0.5mm. The fastening force and watertightness obtained by the rubber tube expansion method far exceed that of the rolling expansion method. f) The rubber tube expansion method will not cause the thickness of the expanded tube wall to thin, and the axial elongation of the tube will be very small. Since the tubes and tube holes are deformed by uniform internal pressure, they will not cause tube sheet deformation. g) When using the rubber tube expansion method, the hardening distribution of the entire thickness of the tube is uniform, there is no work hardening on the surface of the inner wall of the tube, and there is no need to worry that the inner wall of the tube will become rough and cause a deterioration in corrosion resistance. There is no residual stress on the outer wall of the pipe and no stress corrosion cracking will occur. h) The rolling expansion method is not easy to expand pipes with thicker walls, while the rubber expansion method is easy to expand and will not cause pipe expansion cracks. i) When expansion welding is used together, the protection of the welding part is also one of the requirements for the expansion mouth. According to the fatigue test of repeated axial loading of the pipe end at normal temperature, it is shown that both rolling expansion and rubber expansion have protective effects. Compared with the pipe end that is only welded and does not expand, the fatigue life is increased by 10 times. However, because the fastening force of rolling expansion decreases and the rubber expansion decreases very little under high temperature, rubber expansion is more effective in protecting the pipe end. 4. Before expansion by the visco-expansion method, apply an epoxy mixture (epoxy resin, phosphorus benzyl dibutyl ester, polyvinyl amide plus porcelain powder or lack of powder or graphite or aluminum oxide or zinc oxide) on the expansion length of the pipe end (or pipe hole). It has good adhesion to metal and is stable against water, acid and alkali. Adhesive connections are characterized by high mechanical strength and stability against vibration loads. Epoxy mixtures also provide protection against corrosion. The operating temperature depends on the performance of the adhesive. For heat exchangers using epoxy mixtures, the operating temperature should not exceed 170~200℃. The visco-expansion method shows particular advantages for the connection of aluminum tubes and steel tube sheets. Since the strength and elastic modulus of aluminum and steel are quite different, when the pure expansion joint method is used, when the aluminum pipe has undergone plastic deformation, the steel tube plate hole has not yet reached the required elastic deformation. Therefore, it is impossible to firmly and tightly connect the aluminum pipe and steel tube plate together. The domestically developed heat exchanger with L2 aluminum tube Ø 22×2 and A3 steel tube plate is connected by visco-expansion. The mass ratio of the binder is: Epoxy resin (6101): Polyamide (650#): Quartz powder (250 mesh) = 100: 100: 40. The expansion degree Ks=4~6% (expressed by the pipe wall thickness reduction rate, if expressed by the pipe inner diameter increase rate KD, KD=1-2%) is appropriate. Test results show that the adhesive joint has high strength (the shear strength of the adhesive is generally 10~15MPa, which is 2~4 MPa greater than the allowable pull-off force of the pipe required by the general heat exchanger), and the vibration resistance is 5~10 times higher than that of the pure expansion joint (the adhesive joint is cured at room temperature for 5~7 days). The developed heat exchanger is still in good condition and has no leakage after 5 years of use. 5. Pulse expansion ① Mechanical pulse expansion method This method can expand any size, especially thick-walled pipes with a diameter of 12~60mm. Compared with the general inflation control method, its efficiency can be increased by 1 to 2 times. Belouschk method - the essence of this mechanical pulse pipe expansion method is to use the impact and rotation motion of the tool to cause plastic deformation of the metal to achieve the purpose of expansion. The impact rotation motion is provided by a pneumatic or electric device equipped with a special pulse mechanism. It is said that this method can be expanded not only at the pipe end, but also anywhere from the pipe end. The elastic chuck method uses a square pyramid and an elastic chuck to expand the pipe. This method is suitable for expanding thick-walled pipes with a diameter of 18 to 100 mm. The expansion quality is higher than the ordinary expansion pipe method, and 4 to 5 pipes can be expanded per minute. ②The electric pulse tube expansion method is only suitable for mass-produced heat exchangers, because the high-voltage electrical equipment used is very heavy and requires a special place in the workshop. There are many electric pulse methods, and the basic principle is to use powerful instantaneous (10~20 microseconds) discharge energy to achieve expansion. The difference is simply the method of converting discharge energy into other energy. Electric explosion method——This method is to expand the tube by utilizing the electric explosion (sublimation) phenomenon caused by the thermal effect of short-time pulses of high-intensity current on the metal fusible insulating material. The biggest advantage of this method is that it can expand pipes with small diameters and thick walls. The diameter can be as small as 1~2mm, and the wall thickness of the pipe can be as high as 5~8mm. At the same time, the pipe material is not restricted. The joint can withstand a pressure of 65MPa. The basic principle of the hydroelectric tube expansion method is to store high-voltage electric energy in a capacitor, and through a high-voltage switch, a spark discharge occurs between two electrodes that extend into the liquid medium. The high-intensity radially propagating shock wave generated in the dielectric during the discharge is used to plastically deform the tube, so that the tube is fixed to the tube sheet. This method is more efficient and less noisy than mechanical tube expansion. ； Several pipes can be expanded at the same time, and the expansion depth is large at one time ； There is no difficulty in expanding thin-walled pipes, thick-walled small-diameter pipes, and thick tube plates, and the pipe wall expansion is relatively uniform. There are no restrictions on the material and diameter of the pipe (from a few millimeters to 300 millimeters), and it can be expanded anywhere from the pipe end. However, the variable physical factors that affect tube expansion are difficult to control and maintain stability, and the equipment is expensive and bulky, so its widespread application is limited. 6. The detachable inner tube is first expanded and connected to the insert with a boss. Each tube has one insert. It is pressed by the hexagonal plug nut and fixed to the small tube plate. The insert is sealed on the small tube plate with a copper pad. Each inner tube can be extracted individually.

Continued: (5) ASME-Ⅷ-1-2004 Relevant rules for welded joints of heat exchange tubes and tube sheets ASME-Ⅷ-1-2004 (UHX-15 and non-mandatory appendix A) has a detailed discussion of the welded joints of heat exchange tubes and tube sheets, from which the following conclusions can be drawn: ①The highest level of weld is: a≥1.4t. Its weld structure type is consistent with GB151-1999 5.8.3.2 Figure 34(C) in the article is basically equivalent. It can be called full strength welding. ②For the secondary weld, t≤a<1.4t. To be precise, it can be called sub-strength welding that can bear the axial load of the tube. It is not suitable for U-shaped tube heat exchanger structures (this is because the tubes in the U-shaped tube structure are not considered to support the tube plate and do not help increase the strength of the tube plate). ③The lowest level of weld is: a<t. The weld structure type is not determined according to the axial load of the pipe, but is only used as a supplementary measure to ensure no leakage in addition to strength expansion. This level of welding is generally not used in the country.

The above publication is the most complete description of the connection between tube sheet and tube that I have ever seen. I am sending it here for everyone to share!

study* ,study * , learn again * !!~~~

1) Pg is less than 4MPa, the operating temperature is less than or equal to 350 degrees, and expansion joints are generally used. Advantages: simple structure and easy pipe repair ； Disadvantages are subject to certain limitations on pressure and temperature. 2) Welding is currently widely used. The welded structure has high strength and strong pull-off resistance. ； Welding technology requirements are high. 3) Combined with expansion welding, it is used for media with high pressure, strong permeability, or corrosive media on one side. This post was last edited by jia717 on 2009-2-26 22:02 ]

1. Applicable scope of strength expansion joint: The design pressure is less than or equal to 4MPa, the design temperature is less than or equal to 300 degrees, and there is no strong vibration, no excessive temperature change and no obvious stress corrosion during operation. 2. Applicable scope of strength welding: The design pressure is less than or equal to 35MPa, but it is not suitable for occasions with large vibration and crevice corrosion. 3. Applicable scope of combined use of expansion welding: Occasions with high sealing performance requirements ； Where subjected to vibration or fatigue loads ； Where there is crevice corrosion ； Where composite tube sheets are used

The information on cm-1979 is very good and comprehensive, but I am old and cannot remember it after reading it once.

The GBl5l-l999 standard stipulates that the structure using expansion and welding is widely used because it can effectively dampen the damage to the welding joint caused by the vibration of the pipe bundle, avoid gap corrosion, and has higher strength and sealing than simple expansion or strength welding, so it is widely used. At present, conventional heat exchange tubes usually adopt the "expansion + strength welding" mode. ； However, heat exchangers that are important or have harsh operating conditions require the "strength expansion + sealing welding" mode. According to the order of expansion and welding in the process, the structure using both expansion and welding can be divided into two types: expansion first and then welding, and welding first and then expansion. Strength expansion joints are suitable for design pressure~