This comprehensive guide delves into the world of flanged and dished tank heads, essential tank components used in a multitude of industries. Whether you're involved in vessel design, manufacturing, or maintenance, understanding the nuances of flanged and dished heads – including their types, ASME standards, and applications – is crucial. This article provides a deep dive into flanged and dished tank head and dish design, materials, and manufacturing processes, and is worth reading because it will equip you with the knowledge to make informed decisions when selecting the right dish for your specific application, ensuring safety, efficiency, and longevity of your vessel.
A flanged and dished head, often shortened to F&D, is a crucial end tank component used to close the ends of cylindrical tanks or vessels. It is also commonly referred to as a dish. The name describes its shape: a dish section that provides strength to contain the pressure vessel's contents, and a flange that allows it to be bolted or welded to the tank shell. Flanged and dished heads are preferred over flat plates because the curved shape offers significantly superior resistance to internal pressure. The dish helps distribute the stress evenly, preventing localized stress concentrations that could lead to failure. The flanged and dished head provides a robust and reliable solution for containing pressure in various industrial applications.
Flanged and dished heads are specifically designed to withstand internal pressure within a vessel. The curved dish shape and flanged edge provide structural integrity, preventing deformation or failure under pressure. This design ensures the safe containment of liquids, gases, or other materials stored within the tank. The dish acts as a structural element, distributing the load and minimizing stress points, resulting in a safer and more durable vessel.
The versatility of flanged and dished heads extends to their adaptability to different tank shapes and sizes. They can be manufactured to fit a wide range of diameters and thicknesses, allowing for customization based on specific vessel requirements. Additionally, flanged and dished heads can be constructed from various materials, including carbon steel, stainless steel, and other alloys, to suit the properties of the contained substances.
Vessel heads come in several common shapes, each offering different performance characteristics and suitable for specific applications. The most common types include Elliptical Heads, torispherical heads, and hemispherical heads.
Elliptical Heads: Also known as ellipsoidal heads or semi elliptical, these elliptical dished heads are characterized by a semi-ellipsoidal shape. Typically, the ratio of the major axis to the minor axis is 2:1. Elliptical tank head is fabricated in a way that it offer a good balance between cost, strength, and space efficiency. They provide about twice the strength of a hemispherical dished head of the same thickness.
Torispherical Heads: These torispherical heads consist of a central spherical cap (the dish), a knuckle radius, and a cylindrical flange. The knuckle radius is the transition area between the dish and the flange. Torispherical heads are more economical than elliptical heads but less resistant to pressure. They are a common choice for general-purpose tanks and vessels.
Hemispherical Heads: Hemispherical heads are spherical in shape, resembling half a sphere (hemisphere head). These hemispherical tank heads offer the highest pressure resistance for a given thickness and diameter. However, they are also the most expensive to manufacture. Hemispherical heads are typically used in high-pressure applications.
The choice between these types of vessel heads depends on factors such as operating pressure, tank size, material cost, and space constraints. For instance, in high-pressure applications, hemispherical heads are often the preferred choice due to their superior strength, despite the higher cost.
| Head Type | Description | Advantages | Disadvantages | Common Applications |
|---|---|---|---|---|
| Elliptical | Semi-ellipsoidal shape, typically 2:1 ratio | Good balance of strength, cost, and space efficiency | Less pressure resistant than hemispherical heads | General purpose tanks, moderate pressure applications |
| Torispherical | Central spherical cap, knuckle radius, and flange | More economical than elliptical heads, suitable for general use | Less pressure resistant than elliptical heads or hemispherical heads | General purpose tanks, lower pressure applications |
| Hemispherical | Spherical shape, half a sphere | Highest pressure resistance for a given thickness and diameter | Most expensive to manufacture | High-pressure applications, specialized vessels |
The selection of materials for steel dished heads depends on several factors, including the operating environment, the properties of the contained substance, and the required strength and corrosion resistance. Carbon steel and stainless steel are two of the most common materials used in the fabrication of steel dished heads.
Carbon Steel: Carbon steel is a popular choice due to its strength, weldability, and relatively low cost. It is suitable for a wide range of applications where corrosion is not a primary concern. Different grades of carbon steel are available, each offering varying levels of strength and ductility. Carbon steel heads are often coated or painted to provide corrosion protection.
Stainless Steel: Stainless steel is selected for its excellent corrosion resistance, making it ideal for applications involving corrosive substances or environments. Stainless steel is also used in applications where hygiene is critical, such as in the food, beverage, and pharmaceutical industries. Stainless steel heads are more expensive than carbon steel heads but offer a longer service life in corrosive conditions. Quality stainless steel provide additional strength to head.
Other materials, such as aluminum, nickel alloys (inconel®), al6xn or duplex 2205, and other specialty alloys, may be used for specific applications requiring exceptional corrosion resistance, high-temperature strength, or other unique properties. For example, vessels used in the chemical processing industry may require vessel heads made from exotic alloys to withstand aggressive chemicals.
The mechanical properties of the selected material are also a critical consideration. Factors such as tensile strength, yield strength, and elongation must be carefully evaluated to ensure that the dish head can withstand the design pressure and operating conditions without failure.
ASME (American Society of Mechanical Engineers) standards play a vital role in the design, fabrication, inspection, and testing of flanged and dished heads. These standards ensure the safety, reliability, and consistency of pressure vessels and their tank heads. The most relevant ASME standard for flanged and dished heads is the ASME Boiler and Pressure Vessel Code (BPVC), specifically Section VIII, Division 1.
The ASME BPVC provides detailed requirements for the design and manufacturing of pressure vessels, including asme tank heads. It covers aspects such as material selection, welding, non-destructive examination, and overpressure protection. Adherence to ASME standards is essential for several reasons:
Safety: ASME standards are designed to prevent vessel failures, which can have catastrophic consequences. By following ASME guidelines, manufacturers can ensure that their vessels are safe to operate.
Reliability: ASME standards promote consistency and reliability in vessel design and manufacturing. This reduces the risk of premature failure and extends the service life of the vessel.
Regulatory Compliance: In many jurisdictions, compliance with ASME standards is mandatory for pressure vessels. Failure to comply can result in fines, penalties, and even the shutdown of operations.
Industry Acceptance: ASME standards are widely recognized and accepted throughout the industry. Compliance with ASME standards provides assurance to customers and stakeholders that the vessel meets rigorous quality and safety requirements.
Heads are ASME compliant and are designed for the best mechanical vessels.
In addition to Section VIII, Division 1, other ASME standards may be relevant depending on the specific application. For example, Section IX covers the qualification of welders and welding procedures.
The diameter of a dished tank head is a critical factor influencing its design, material selection, and overall performance. As the diameter increases, the surface area of the dish also increases, leading to higher stresses under internal pressure. This relationship has several important implications:
Thickness Requirements: Larger diameter heads typically require greater thickness to withstand the same internal pressure. The thickness calculation is governed by ASME standards and takes into account the material strength, diameter, and design pressure.
Material Selection: For larger diameter heads, stronger materials may be necessary to keep the thickness within reasonable limits. Stainless steel or other high-strength alloys may be required in place of carbon steel to reduce weight and cost.
Manufacturing Considerations: Manufacturing larger diameter heads can be more challenging, requiring specialized equipment and techniques. The forming process may need to be done in multiple stages to avoid excessive thinning or distortion of the metal. The diameter and the knuckle radius are important aspects in the manufacturing of the head.
Cost: The cost of a dished head generally increases with diameter. Larger heads require more material, more complex manufacturing processes, and more extensive testing and inspection.
Navigation through the manufacturing process can be complicated.
Understand your needs before going into any specifics.
The dish radius or knuckle radius of the dish are also closely related to the diameter of the head. The radius of the dish affects the stress distribution and the overall strength of the head. Smaller radiuses result in higher stresses but can also reduce the overall height of the vessel. The knuckle radius helps to reduce stress concentrations at the junction between the dish and the flange.
Cold formed tank heads are manufactured through a process that involves shaping metal plates at room temperature using specialized machinery. This method offers several advantages, including improved mechanical properties, tighter tolerances, and reduced material waste compared to hot forming.
The typical cold formed tank heads manufacturing process involves several stages:
Blanking: The process begins with cutting a circular blank from a metal plate. The diameter of the blank is determined based on the desired diameter and shape of the finished head.
Forming: The blank is then fed into a forming machine, which uses a series of dies and rollers to gradually shape the metal into the desired dish profile. This process may involve multiple passes to achieve the final shape.
Flanging: After the dish is formed, the flange is created by bending the edge of the metal plate. This is typically done using a flanging machine that applies pressure to the edge of the dish while rotating it.
Trimming: The flanged head is then trimmed to the final dimensions. This step ensures that the flange is square and that the overall diameter of the head is within specifications.
Inspection: The finished head is inspected for dimensional accuracy, surface finish, and any defects. Non-destructive testing methods, such as ultrasonic testing or magnetic particle inspection, may be used to detect internal flaws.
Polishing: After inspection, the dished head might go through a polishing stage.
Sandblast: The last thing to do is to sandblast dished head.
Cold forming improves the mechanical properties of the metal by increasing its tensile strength and yield strength. This is due to the work hardening that occurs during the forming process. The tight tolerances achievable with cold forming result in more accurate and consistent heads.
Flanged and dished heads are indispensable components in a wide array of industries, where they serve as critical closures for tanks and vessels designed to contain various substances under diverse operating conditions. Their versatility, durability, and adherence to stringent safety standards make them essential in several sectors:
Chemical Processing: In the chemical industry, vessels often handle corrosive, high-pressure, or high-temperature substances. Flanged and dished heads made from stainless steel or other specialty alloys are essential to ensure safe containment and prevent leakage or contamination.
Petroleum and Gas: Storage tanks, reactors, and separators in the petroleum and gas industry rely on flanged and dished heads to withstand high pressure and harsh environmental conditions. These heads are vital for maintaining the integrity and safety of the vessels.
Food and Beverage: Hygienic vessels in the food and beverage industry require stainless steel flanged and dished heads to prevent contamination and facilitate easy cleaning. These heads are used in storage tanks, mixing vessels, and other equipment where cleanliness is paramount.
Pharmaceutical: Similar to the food and beverage industry, the pharmaceutical sector demands high levels of cleanliness and purity. Flanged and dished heads made from stainless steel are used in reactors, storage tanks, and other equipment to ensure the safe and sterile handling of pharmaceutical products.
Water Treatment: Vessels used in water treatment plants, such as pressure filters and clarifiers, often incorporate flanged and dished heads. These heads provide the necessary strength and corrosion resistance to withstand the pressure and chemical exposure involved in water treatment processes.
Power Generation: Boilers and other pressure vessels in power plants rely on flanged and dished heads to contain high-pressure steam and water. These heads are designed to withstand extreme temperatures and pressures, ensuring the safe and efficient operation of the power plant.
Selecting the appropriate specifications and sizing for a flanged and dished head involves a careful evaluation of various factors to ensure that the head meets the requirements of the specific application. Key considerations include:
Design Pressure and Temperature: The design pressure and temperature of the vessel are crucial factors in determining the required thickness and material of the dished head. The head must be able to withstand the maximum expected pressure and temperature without deformation or failure. ASME pressure code provides guidelines for calculating the required thickness based on these parameters.
Diameter: The diameter of the dished head must match the diameter of the tank shell to ensure a proper fit. The diameter also affects the stress distribution in the head, with larger diameters generally requiring thicker heads.
Material: The material of the dished head should be selected based on the properties of the contained substance, the operating environment, and the required strength and corrosion resistance. Carbon steel, stainless steel, and other specialty alloys are commonly used.
Head Type: The choice of head type (elliptical, torispherical, hemispherical) depends on the specific application and the desired balance between cost, strength, and space efficiency.
Flange Dimensions: The dimensions of the flange, including the thickness, width, and bolt hole pattern, must be compatible with the mating flange on the tank shell.
Corrosion Allowance: A corrosion allowance may be added to the thickness of the dished head to account for material loss due to corrosion over time. This allowance is typically based on the aggressiveness of the contained substance and the expected service life of the vessel.
Heads are used to meet the specifications and sizing parameters.
It is essential to consult with a qualified engineer or head manufacturers to determine the appropriate specifications and sizing for a flanged and dished head based on the specific application requirements. Contact us to discuss your needs or contact us today.
While flanged and dished heads are the most common choice for closing the ends of cylindrical vessels, there are certain situations where dished only heads, non-ASME heads, or flat heads may be more appropriate.
Dished Only Heads: Dished only heads are flanged and dished heads without the flange. These are typically used when the head is to be welded directly to the tank shell, eliminating the need for a flanged connection. Dished only heads can be more economical than flanged and dished heads in certain applications.
Non-ASME Heads: Non-ASME heads are vessel heads that do not comply with the ASME Boiler and Pressure Vessel Code. These heads may be used in applications where ASME compliance is not required, such as in low-pressure or non-critical applications. Non-ASME heads can be less expensive than ASME heads but may not offer the same level of safety and reliability.
Flat Heads: Flat heads are simple flat plates used to close the ends of vessels. Flat heads are generally not suitable for pressure vessels, as they are prone to deformation and failure under pressure. Flat heads may be used in low-pressure applications where the diameter of the vessel is small and the pressure is minimal.
The choice between these types of heads depends on factors such as operating pressure, tank size, material cost, and regulatory requirements. In general, flanged and dished heads are the preferred choice for pressure vessels due to their superior strength and reliability. Dished only heads, non-ASME heads, and flat heads should only be used in specific situations where they are appropriate for the application.
Selecting the right supplier for your tank head needs is crucial to ensuring the quality, reliability, and performance of your vessel. A reputable supplier should offer a wide range of tank head types, materials, and sizes, as well as the expertise and support to help you choose the right head for your specific application.
Here are some key factors to consider when choosing a supplier:
Experience and Reputation: Look for a supplier with a proven track record of providing high-quality tank heads and excellent customer service. Check online reviews and ask for references from other customers.
Product Range: The supplier should offer a wide range of tank head types, materials, and sizes to meet your specific needs. They should also be able to provide custom fabrication services for unique applications.
Quality Control: The supplier should have a robust quality control program in place to ensure that their tank heads meet or exceed industry standards. They should be able to provide certifications and documentation to verify the quality of their products.
Technical Support: The supplier should have a team of knowledgeable engineers and technicians who can provide technical support and guidance throughout the selection and installation process.
Price and Delivery: Compare prices from different suppliers and ensure that the supplier can deliver the tank heads on time and within budget.
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Paul Mueller Company is one of the most known tank components industries that provide polishing equipment and can help you select dished head that satisfy yours criteria.
Once you have chosen a supplier, be sure to communicate your specific needs and requirements clearly. Provide detailed information about the application, including the design pressure, temperature, material, diameter, and any other relevant factors. A good supplier will work closely with you to understand your needs and recommend the best tank head solution for your application.
To contact us and discuss your needs with our team of experts, please visit our website or call us directly. We are committed to providing high-quality tank heads and exceptional customer service to help you achieve your project goals. You can contact us today for help.
Flanged and dished heads are essential tank components used to close the ends of cylindrical tanks or vessels.
Different types of dished heads include elliptical, torispherical, and hemispherical heads, each offering different performance characteristics.
Common materials used for manufacturing steel dished heads include carbon steel and stainless steel.
ASME standards, particularly Section VIII, Division 1 of the Boiler and Pressure Vessel Code, ensure the safety and reliability of flanged and dished heads.
The diameter of the dished head significantly affects its design, material selection, and overall performance.
Cold formed tank heads are manufactured through a process that involves shaping metal plates at room temperature using specialized machinery.
Flanged and dished heads are widely used in industries such as chemical processing, petroleum and gas, food and beverage, and pharmaceutical.
Key considerations for specifications and sizing include design pressure and temperature, diameter, material, head type, and flange dimensions.
Dished only heads, non-ASME heads, and flat heads may be used in specific situations where they are appropriate for the application.
Choosing the right supplier is crucial to ensuring the quality, reliability, and performance of your tank head.
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