1. Theoretical basis for tube sheet calculation

 

The structure of shell and tube heat exchangers is complex, and there are many factors that affect the strength of the tube sheet. In particular, the tube sheet of fixed tube sheet heat exchangers is subjected to the most complex force. The design specifications of various countries basically consider the tube sheet as a circular flat plate that bears uniformly distributed loads, is placed on an elastic foundation, and is uniformly weakened by the tube holes (Figure 1).

 

Due to the many factors that affect the strength of the tube sheet, it is difficult and complex to accurately analyze the strength of the tube sheet. Therefore, various countries simplify and assume the formula for calculating the thickness of the tube sheet to obtain an approximate formula.

 

The loads that cause stress on the tube sheet include pressure (tube side pressure Pt, shell side pressure Ps), thermal expansion difference between the tube and shell, and flange torque. The mechanical model of the calculation method for the tube sheet of the heat exchanger is shown in Figure 2.

 

1.1 The design specifications of various countries consider the following factors to varying degrees for the tube sheets:

1) Simplifying the actual tube sheet into a homogeneous equivalent circular flat plate based on equivalent elasticity weakened by regular arrangement of tube holes and reinforced by tubes has been adopted by most countries' tube plate specifications today.

2) The narrow non piping area around the tube sheet is simplified as a circular solid plate based on its area.

3) The edge of the tube sheet can have various types of connection structures, which may include shell side cylinders, channel cylinders, flanges, bolts, gaskets, and other components. Calculate according to the actual elastic constraint conditions of each component on the edge of the tube sheet.

4) Consider the effect of flange torque on the tube sheet.

5) Consider the temperature difference stress caused by the thermal expansion difference between the heat exchange tube and the shell side cylinder, as well as the temperature stress caused by the temperature difference at various points on the tube sheet.

6)Calculate various equivalent elastic constants and strength parameters converted from porous plates with heat exchange tubes to equivalent solid plates.

 

 

1.2 Theoretical basis for GB151 tube sheet calculation

The mechanical model considers the tube plate as an axial symmetry structure and assumes that the tubesheets at both ends of the heat exchanger have the same material and thickness. For fixed tube sheet heat exchangers, the two tube sheets should also have the same boundary support conditions.

 

1) The supporting effect of tube bundle on tube sheet

Consider the tube sheet as an equivalent circular flat plate uniformly weakened and placed on an elastic foundation. This is because in the structure of shell and tube heat exchangers, the diameter of the majority of tubes is relatively small compared to the diameter of the tube sheet, and the number of tubes is sufficient. It is assumed that they are uniformly distributed on the tube sheet, so the support effect of each discrete heat exchange tube on the tube sheet can be considered uniform and continuous, and the load borne by the tube sheet is also considered uniformly distributed.

 

The tube bundle has a restraining effect on the deflection and rotation angle of the tube sheet under external loads. The restraining effect of the tube bundle can reduce the deflection of the tube sheet and lower the stress in the tube sheet. The tube bundle has a restraining effect on the angle of the tube sheet. Through analysis and calculation of actual parameters, it was found that the restraining effect of the tube bundle on the angle of the tube sheet has a very small impact on the strength of the tube sheet and can be completely ignored. Therefore, this

 

The specification does not consider the constraint effect of tube bundles on the corner of the tube sheet, but only considers the constraint effect of tube bundles on the deflection of the tube sheet. For fixed tube sheet heat exchangers, the tube reinforcement coefficient K is used to represent the tube sheet.

 

The bending stiffness of the perforated tube plate is η D

The elastic foundation coefficient N of the tube bundle represents the pressure load required to be applied on the surface of the tube plate to cause unit length deformation (elongation or shortening) of the tube bundle in the axial direction.

 

the pipe reinforcement coefficient K and substitute it into the expressions D and N, so that ν P=0.3:

This coefficient indicates the strength of the elastic foundation relative to the tube plate's inherent bending stiffness, reflecting the enhanced load-bearing capacity of the tube bundle on the plate. It is a crucial parameter that characterizes the strengthening effect of the tube bundle on the plate. If the elastic foundation of the plate is weak, the enhancing effect of the heat exchange tubes is minimal, resulting in a small K value. Consequently, the plate's deflection and bending moment distribution resemble those of ordinary circular plates lacking an elastic foundation. Specifically, when K equals zero, the plate becomes an ordinary circular plate. Based on the theory of elastic foundation circular plates, the plate's deflection is not solely determined by the tube's strengthening coefficient K, but also by its peripheral support and additional loads, quantitatively represented by the total bending moment coefficient m.

 

When the periphery of the tube sheet is simply supported, MR=0, then m=0; When the periphery of the tube sheet is fixed, the corner of the edge of the tube sheet φ R=0, from which a specific value of m can be obtained (the expression is omitted); When the periphery of the tube plate only bears the action of bending moment, i.e. VR=0, then m=∞.

Under certain boundary support conditions, as the K value gradually increases, the deflection and bending moment of the tubesheet exhibit a attenuation and wavy distribution from the periphery to the center. The larger the K value, the faster the attenuation and the more wave numbers. During the process of increasing K value, when passing through a certain boundary K value, new waves will appear in the distribution curve. At the center of the plate, the curve changes from concave (or concave) to concave (or concave). Solving the derivative equation of the distribution curve can obtain the K boundary value of the curve with an increase in wave number.

 

Taking the simple support around the tube sheet as an example, as the strengthening coefficient K of the tube increases, the radial bending moment distribution curve and the boundary K value when new waves appear are shown in Figure 31. At the same time, it can be seen that the radial extreme value also moves away from the center of the tube sheet towards the periphery as the K value increases.

 

For the elastic foundation plate with peripheral fixed support, the radial bending moment distribution shows a similar trend with the change of K value, as shown in Figure 3. The difference from a simply supported boundary is that the maximum radial bending moment of the elastic foundation plate supported by a fixed boundary is always located around the circular plate, while the extreme point of the second radial bending moment moves away from the center of the plate and towards the periphery as K increases.

 

For floating head and filled box heat exchanger tube sheets, the modulus K of the tube bundle is similar to the elastic foundation coefficient N of the fixed tube sheet, which also reflects the strengthening effect of the tube bundle as an elastic foundation on the tube sheet.

 

2) The weakening effect of tube holes on tube sheets

The tube sheet is densely covered with dispersed tube holes, so the tube holes have a weakening effect on the tube sheet. The weakening effect of tube holes on the tube sheet has two aspects:

 

The overall weakening effect on the tube sheet reduces both the stiffness and strength of the tube sheet, and there is local stress concentration at the edge of the tube hole, only considering peak stress.

 

This specification only considers the weakening effect of openings on the overall tube sheet, calculates the average equivalent stress as the basic design stress, that is, approximately considers the tube sheet as a uniformly and continuously weakened equivalent circular flat plate. For local stress concentration at the edge of the tube hole, only peak stress is considered. But it should be considered in fatigue design.

 

The tube hole has a weakening effect on the tube sheet, but also considers the strengthening effect of the pipe wall, so the stiffness weakening coefficient is used η And strength weakening coefficient μ。 According to elastic theory analysis and experiments, this specification stipulates η and μ＝ 0.4.

 

3) Equivalent diameter of tube sheet layout area

The calculation of the reinforcement coefficient for fixed tube sheets assumes that all pipes are uniformly distributed within the diameter range of the cylinder. In fact, under normal circumstances, there is a narrow non pipe area around the tube sheet, which reduces the stress at the edge of the tube sheet.

 

The tube layout area is generally an irregular polygon, and now the equivalent circular pipe layout area is used instead of the polygonal pipe layout area. The value of the equivalent diameter Dt should make the supporting area of the tube on the tube sheet equal. The diameter size directly affects the stress magnitude and distribution of the tube plate. In the stress calculation of the fixed tube sheet in GB151, the stress located at the junction of the annular plate and the pipe layout area is approximately taken as the stress of the full pipe layout tube plate at a radius of Dt/2. Therefore, the standard limits this calculation method to only be applicable to situations where the non pipe layout area around the tube plate is narrow, that is, when the non dimensional width k of the non pipe layout area around the tube sheet is small, k=K (1)- ρ t) ≤ 1.

 

Whether it is a fixed tube sheet heat exchanger, or a floating head or filled box heat exchanger, when calculating the area of the tube layout area, it is assumed that the tubes are uniformly covered within the range of the tube layout area.

 

Assuming there are n heat exchange tubes with a spacing of S. For a triangular arrangement of tube holes, the supporting effect of each tube on the tube sheet is the hexagonal area centered on the center of the tube hole and with S as its inner tangent diameter, i.e;

 

For tubes with square arrangement of tube holes, the supporting area of each tube on the tube sheet is a square area centered on the center of the tube hole and with S as the side length, i.e. S2.

 

The tube sheet layout area is the area enclosed by connecting the supporting area of the outermost tube of the tube sheet, including the supporting area of the outermost tube itself.

 

For a single pass heat exchanger tube sheet with uniformly distributed heat exchange tubes, the supporting area of all n heat exchange tubes on the tube sheet is the area of the tube layout area.

 

4) Consider the bending effect of the tube sheet, as well as the tensile effect of the tube sheet and flange along their central plane.

 

5) Assuming that when the flange deforms, the shape of its cross-section remains unchanged, but only the rotation and radial displacement of the center of gravity around the ring section. Due to this rotation and radial displacement, the radial displacement at the connection point between the flange and the center surface of the tube sheet should be coordinated and consistent with the radial displacement along the center surface of the tube sheet itself.

 

6) Due to temperature expansion difference γ The axial displacement of the shell wall caused by the shell side pressure ps and the tube side pressure pt should be coordinated and consistent with the axial displacement of the tube bundle and tube sheet system around the tube sheet.

 

7) The corner of the tube sheet edge is constrained by the shell, flange, channel, bolt, and gasket system, and its corner should be coordinated and consistent at the connection part.

 

8) When the tube sheet is also used as a flange, the influence of flange torque on the stress of the tube sheet is considered. In order to ensure sealing, it is stipulated that the flange stress needs to be checked for the extended part of the tube sheet that also serves as a flange. At this time, when calculating the flange torque, it is considered that the tube sheet and flange jointly bear the external force moment, so the ground force moment borne by the flange will be reduced.

 

 

About us

Wuxi Changrun has provided high-quality tube sheets, nozzles, flanges, and customized forgings for heat exchangers, boilers, pressure vessels, etc. to many well-known petrochemical enterprises at home and abroad. Our customers include PetroChina, Sinopec, Chevron, Bayer, Shell, BASF, etc. Send your drawings to sales@wuxichangrun.com We will provide you with the best quotation and the highest quality products.

 

What is overlay welding?

Overlay welding is a surface treatment process that uses heating sources such as arcs to heat metal or alloy materials, and then heats and melts them on the surface of the base materials to fill the other material and form a layer of metal coating. By depositing materials with certain properties on the surface of the workpiece, the surface characteristics of the workpiece can be changed. The purpose of overlay welding is not to connect the workpiece, but to use welding methods to deposit one or several layers of materials with the desired performance on the workpiece. This process method is widely used in various industrial sectors, mainly for repairing worn and cracked parts, or modifying the surface of workpieces to obtain special properties such as wear resistance, heat resistance, and corrosion resistance of the deposited layer. In order to effectively utilize the function of the overlay layer, it is hoped that the overlay welding method adopted will have smaller base material dilution, higher deposition speed, and excellent overlay performance, namely high-quality, efficient, and low dilution rate overlay welding technology.

 

 

Application of overlay welding technology to Tube Sheet

 

The main function of weld overlay tube sheet is to enhance the mechanical properties and wear resistance of the base material. In industries such as chemical plants and power plants, many equipment may experience issues such as wear and corrosion during operation, which seriously affect the stability and lifespan of the equipment. By using the method of overlay welding, the equipment can be reinforced and repaired, greatly extending its service life. weld overlay tube sheets are widely used in petrochemical, coal chemical, refining, oil and gas transportation, marine environment, power, heating and other projects. For more detailed information on welded overlay tube sheet, please click (What is overlay welded tube sheet?)

 

 

 

 

Application of overlay welding technology on flanges

The flange adopts an overlay welding process to combine the two materials, ensuring that the pipeline transportation medium is corrosion-resistant and meets the pressure requirements under working conditions, while greatly reducing material costs. The base material of flanges is generally carbon steel, alloy steel, pipeline steel, etc; The cladding layer is generally made of corrosion-resistant alloys such as stainless steel, duplex steel, nickel based alloys, titanium materials, copper materials, etc. The weld overlay flanges are suitable for connecting two different materials, but they exhibit excellent corrosion and wear resistance. For example, in fields such as chemical, petroleum, natural gas, and pharmaceuticals, if it is necessary to connect materials with good corrosion resistance and the connection part is required to withstand high temperature and high pressure environments, then overlay welding flanges is a very good choice. Weld overlay clad flanges are suitable for situations with high requirements for connection methods. For example, in equipment such as pipelines and vessels that require sealing, overlay welding flanges have been widely used because they can effectively avoid leakage issues at the connection points.

 

The advantages of overlay welding flanges

1. Long lifespan: One of the advantages of welded overlay flanges is their good durability, as they can maintain a long service life in harsh environments.

2. Corrosion resistance: Due to the use of materials with good corrosion resistance as welding rods for overlay welding flanges, they can effectively resist the corrosion of strong acidic or alkaline substances.

3. High temperature and high pressure resistance: The welding material of the overlay welding flange can withstand high temperature and high pressure environments, and the connection part will not leak, so it has good applications in extreme temperature or air pressure working environments.

 

 

 

Application of overlay welding technology on pipes and fittings

In the modern industrial field, steel pipes and fittings are widely used in industries such as petroleum, chemical, and power. However, due to long-term use and environmental factors, the inner walls of pipelines often suffer from wear and corrosion, posing a threat to their normal operation. To solve this problem, pipeline inner wall overlay welding technology is usually used.

 

The benefits of overlay welding on the inner wall of pipes and fittings

1. Superior wear resistance: High performance wear-resistant materials are used for welding, which can effectively resist the wear and corrosion of the inner wall of the pipeline, and extend the service life of the pipe and fitting.

2. Strong corrosion resistance: Special alloy materials are used for overlay welding, which has good corrosion resistance and can effectively prevent corrosion and rust on the inner wall of pipes and fittings.

3. High welding quality: Advanced welding technology is adopted to ensure the bonding strength and density between the overlay layer and the original inner wall of the pipeline, avoiding the risk of leakage caused by welding quality issues.

4. Easy to operate: The inner wall welding technology of pipes and fittings has the characteristic of easy operation, without the need to disassemble the pipes, only local repairs need to be carried out inside the pipes, greatly saving maintenance time and costs.

5. Environmental protection and energy conservation: Compared with the traditional method of replacing pipes, pipeline inner wall welding technology has lower energy consumption and smaller environmental impact, which meets the green and environmental protection requirements of modern industrial production.

 

 

What is condenser?

The condenser is one of the main heat exchange equipment in refrigeration equipment. The function of the condenser is to cool and condense the high-temperature and high-pressure refrigerant discharged from the compressor into liquid. The heat released by the refrigerant in the condenser is carried away by the cooling medium (water or air).

 

What is condenser Tube Sheet?

The condenser tube sheet is a component of heat exchange in various industries, including power plants, chemical plants, refrigeration systems, and HVAC (Heating Ventilating and Air Conditioning). Its main function is to provide safe connections for the condenser tubes and promote effective heat transfer. Therefore, the working state of the condenser tube sheet directly affects the performance and efficiency of the condenser. Let's explore in more detail the importance and application of condenser tube sheets.

 

In power plants

Firstly, condenser tube sheets are crucial in power plants, where they play a vital role in converting steam into water and facilitating the generation of electricity. The tube sheets offer structural support for the condenser tubes, allowing the transfer of heat from the steam to the cooling medium, typically water. This heat transfer process is essential for converting high-pressure steam into liquid water, which can then be recycled and reused in the power generation cycle.

 

In chemical plants

In chemical plants, condenser tube sheets are used for various purposes, such as cooling and condensing volatile substances, recovering valuable chemicals or solvents, and facilitating heat exchange in chemical processes. The tube sheets provide a stable platform for the condenser tubes, ensuring efficient heat transfer and enabling the separation and collection of desired substances from gas or vapor streams.

 

In refrigeration systems

Condenser tube sheets also find application in refrigeration systems, where they aid in the cooling and condensation of refrigerants. These systems rely on the expansion and compression of refrigerants to transfer heat from the conditioned space to the surrounding environment. The condenser tube sheets help facilitate this heat transfer process by providing a surface for the refrigerant to release heat, enabling its transition from a high-pressure vapor to a low-pressure liquid state.

 

In HVAC

In HVAC (Heating, Ventilation and Air Conditioning) systems, condenser tube sheets are utilized in air-cooled condensers. These systems use the condenser tube sheets to support the tubes through which the refrigerant flows. As the refrigerant releases heat to the ambient air, it condenses into a liquid state before flowing back to the evaporator, enabling the cooling and conditioning of indoor spaces.

 

The material of condenser tube sheets

To ensure the effective functioning of condenser tube sheets, proper material selection is essential. Factors such as corrosion resistance, strength, and thermal conductivity play a significant role in determining the suitable material for the tube sheet. Stainless steel, carbon steel, copper alloys, and titanium are commonly utilized due to their excellent corrosion resistance and mechanical properties.

 

Regular inspection and maintenance of condenser tube sheets are critical to identify any signs of corrosion, erosion, or leaks. Timely repairs or replacements can prevent system failures and ensure prolonged operational efficiency.

 

In conclusion, wuxichangrun condenser tube sheets are essential components in various industries, enabling efficient heat transfer, condensation, and cooling processes. Their proper selection, installation, and maintenance are crucial to maintaining optimal system performance, energy efficiency, and reliability.

 

What is the function of overlay welded tube sheets?

 

In industrial applications, corrosion resistance and structural integrity are very important, and welded overlay tube sheets have become essential components. Overlay welding also known as cladding, is a process of coating a corrosion-resistant alloy on the surface of a based materials. This technology provides an effective solution to protect the tube sheet from the impact of corrosive environments and extends its service life. And it can greatly reduce costs.

 

The main purpose of overlay welding tube sheets is to improve the performance and durability of heat exchangers, boilers, and other equipment using tube sheets. The following are some main advantages and precautions related to overlay welded tube sheets:

 

Corrosion Resistance:

By cladding a layer of corrosion-resistant alloy to the tube sheet's surface, the weld overlay layer protects against corrosion caused by corrosive fluids, high temperatures, or harsh operating conditions. This corrosion resistance helps to minimize maintenance requirements and maximizes the service life of the equipment. Common corrosion-resistant overlay metals include copper, titanium, nickel, cobalt based alloys, and austenitic stainless steel. For example, stainless steel overlay welding is used on the inner walls of petrochemical containers. When welding, workers should pay attention to the dilution rate of the based plate on the welding layer to ensure the alloy content required for corrosion resistance of the welding layer.

 

Material Compatibility:

Weld overlay tube sheets allow for the selection of different materials for the base material and the cladding layer. This flexibility enables the use of cost-effective base materials while ensuring optimal corrosion resistance and compatibility with the process fluids or gases. The chemical composition of the welding material should be similar as the base materials to ensure that the welding layer has good corrosion resistance and wear resistance. The welding material should have sufficient strength and toughness to ensure the structural performance and durability of the welding layer. The overlay welding material should have good welding performance, including melting point, fluidity, wettability, etc. The welding material should have good crack resistance to ensure that the welding layer will not crack due to vibration and deformation during operation. The welding material should have a certain degree of wear resistance to ensure that the welding layer does not excessively wear during operation.

 

Enhanced Strength and Integrity:

Weld overlay also improves the mechanical properties of forged tube sheet, including strength and toughness. It has higher hardness and wear resistance, and can withstand longer periods of wear and impact. The cladding layer adds an extra level of protection and reinforcement to the base material, reducing the risk of failure or leakage during operation.

 

Customization and Precision:

Weld overlay tube sheets can be tailored to specific project requirements, such as the size and pattern of the tube holes, the thickness and composition of the cladding layer, and the welding techniques used. This customization allows for precise fitting and dependable performance in various applications.

 

When selecting weld overlay tube sheets, several factors should be considered:

 

1.Corrosion Environment: Assess the nature of the operating environment, including the temperature, pressure, and the types of fluids or gases being processed. This information helps determine the appropriate corrosion-resistant alloy for the cladding layer.

 

2. Base Material Compatibility: Consider the compatibility between the base material and the cladding layer to ensure optimal bonding and long-term performance. 

 

3. Cladding Thickness: Determine the appropriate thickness of the cladding layer based on the severity of the corrosion environment and the desired service life of the equipment.

 

4. Manufacturing Standards: Verify that the weld overlay tube sheets comply with relevant industry standards and quality assurance processes to ensure their reliability and performance.

 

In summary, weld overlay tube sheets play a crucial role in enhancing the corrosion resistance and durability of heat exchangers, boilers, and other equipment. The careful selection of materials, customization options, and adherence to manufacturing standards are key considerations when choosing weld overlay tube sheets for optimal performance and long-term reliability. https://www.wuxichangrun.com/

 

When purchasing tube sheets, careful consideration and comparison should be made to ensure the selection of the correct product for the intended application. Whether used in heat exchangers, boilers, or pressure vessels, tube sheets play a crucial role in the overall performance and efficiency of equipment. The following are some important factors to consider when selecting the appropriate tube sheet:

Material Selection:

The material of the tube sheet should be compatible with the fluid or gas flowing through the pipeline. Factors such as corrosion resistance, thermal conductivity, and mechanical properties should be considered. Common materials used for tube sheets include carbon steel, stainless steel, copper alloys, nickel alloys, aluminum alloys, and titanium.

 

Tube Arrangement:

The tube sheet design should accommodate the desired tube arrangement, whether it's a triangular, square, or staggered pattern. The number and size of tube holes should be carefully specified to ensure proper tube fit and alignment.

Thickness and Strength:

The tube sheet should have adequate thickness and strength to withstand the operating conditions and pressures within the equipment. The required thickness should be determined according to engineering calculations and standards, based on diameter, material, and pressure ratings.

 

Weldability:

If it is necessary to connect the tubes to the tube sheets by welding, the material should have good weldability. Some materials may require preheating or post weld heat treatment to maintain the integrity of the joint.

 

Cladding or Coating:

In applications where corrosion resistance is crucial, in order to reduce the use of high corrosion-resistant materials for the whole tube sheet, the tube sheet can be coated or clad with a higher alloy material. This provides effective protection against corrosive fluids or environments and extends the service life of the tube plate. The materials used for coatings usually include stainless steel, nickel, titanium, etc.

 

Quality Assurance:

It is important to purchase tube sheets from reputable manufacturers or suppliers who comply with industry standards and quality control processes. Wuxi Changrun has 30 years of production experience and supply flanges, tube sheets, for well-known petrochemical industry giants in various countries, including PetroChina and Sinopec, BASF, Bayer, Chevron, Mobil, etc. 

 

Customization:

In some cases, it may be necessary to customize the designed tube plate to meet specific project requirements. Collaborating with experienced engineers and manufacturers can help design and manufacture customized tube sheets. Wuxi Changrun has a professional team of engineers and technicians who can manufacture customized products according to customer needs.

 

It is recommended to consult with industry experts, engineering consultants, or equipment manufacturers to ensure that the selected forged tube sheet meets the desired performance and longevity requirements. By considering these factors, the right tube sheet can be chosen to enhance the overall efficiency and reliability of the equipment in which it is used. Get more details from www.wuxichangrun.com.