What is a blind flange? Blind flange dimensions

A blind flange is a type of pipe fitting used to seal the end of a piping system or pressure vessel openings to prevent the flow of fluids or gases. Unlike other flanges, a blind flange has no bore or opening, making it ideal for applications requiring complete isolation. Here’s a detailed introduction to blind flanges:

1. Definition and Purpose

A blind flange is a solid disk-shaped component used to block off a pipeline, valve, or vessel’s opening. It is bolted in place and provides a secure seal to prevent leakage.

2. Key Features

• Solid Design: Unlike other flanges, blind flanges do not have a central hole, making them suitable for sealing off sections of a piping system.
• High Strength: Typically made from robust materials such as stainless steel, carbon steel, or alloy steel to withstand high pressure and temperature conditions.
• Versatility: Can be used in various industries, including oil and gas, petrochemical, power generation, and water treatment.

3. Applications

• Pipeline Maintenance: Used to temporarily or permanently close off sections of a pipeline for maintenance or repair.
• Pressure Testing: Employed during pressure testing of pipelines and vessels to isolate sections and test for leaks.
• Isolation and Protection: Used to isolate piping components or equipment from the rest of the system during shutdowns or maintenance.

4. Installation and Maintenance

• Installation: Typically bolted to matching flanges on the piping system using gaskets to ensure a leak-proof seal.
• Maintenance: Regular inspection is required to check for signs of wear, corrosion, or damage to ensure continued reliability and safety.

5. Standards and Specifications

Blind flanges are manufactured according to various industry standards to ensure compatibility and performance, including:

• ASME (American Society of Mechanical Engineers)
• ANSI (American National Standards Institute)
• DIN (Deutsches Institut für Normung)
• JIS (Japanese Industrial Standards)

6. Advantages

• Effective Sealing: Provides a secure seal, preventing leaks and ensuring system integrity.
• Durability: Made from high-strength materials to withstand harsh operating conditions.
• Easy Installation: Can be easily installed or removed for maintenance purposes.

7. Considerations

• Material Compatibility: Ensure the material of the blind flange matches the material of the piping system to prevent galvanic corrosion.
• Pressure Rating: Select a blind flange with an appropriate pressure rating for the application to avoid failure under operating conditions.
• Gasket Selection: Use the correct type of gasket to achieve a proper seal and prevent leaks.

In summary, blind flanges are essential components in piping systems, providing reliable sealing capabilities for various industrial applications. Proper selection, installation, and maintenance are crucial to ensuring their effective performance and longevity.

Blind flanges come in various types to accommodate different sealing requirements, pressure ratings, and material compatibility. Here are the main types of blind flanges:

1. Raised Face (RF) Blind Flange:

• Description: This type of blind flange has a small raised section around the bore where the gasket is placed. The raised face helps to concentrate the sealing pressure on a smaller area, enhancing the seal’s effectiveness.
• Common Use: Frequently used in applications where a higher sealing efficiency is needed, such as in oil and gas, petrochemical, and high-pressure systems.

2. Flat Face (FF) Blind Flange:

• Description: The entire face of this flange is flat and even with the bolt circle. It provides a full-contact surface for the gasket.
• Common Use: Typically used with cast iron or other brittle materials that can be damaged by the high stress concentrated on a raised face. Common in low-pressure applications and systems where pipe and flange materials are less flexible.

3. Ring-Type Joint (RTJ) Blind Flange:

• Description: Features a groove cut into its face to accommodate a metal ring gasket. This design allows for a very tight metal-to-metal seal, suitable for high-pressure and high-temperature environments.
• Common Use: Ideal for oil and gas industries and other applications where leak-tight seals are critical, especially under high-pressure conditions.

4. Threaded (Screwed) Blind Flange:

• Description: This flange has a threaded bore that matches the external threads on the pipe. It can be screwed onto the pipe end without welding.
• Common Use: Used in low-pressure, non-critical applications where welding is not feasible or practical. Suitable for small diameter piping systems.

5. Lap Joint Blind Flange:

• Description: Used with a stub end or lap joint stub end. The flange itself does not come into contact with the fluid and can be rotated to align with the bolt holes of the mating flange.
• Common Use: Common in systems where frequent dismantling for inspection and cleaning is required, or in systems where the material of the flange must match the pipe material for corrosion resistance.

6. Spectacle Blind Flange:

• Description: This type consists of a pair of discs connected by a small section of metal. One disc is solid (acting as a blind), and the other is a ring (acting as a spacer). It allows for easy switching between open and closed positions.
• Common Use: Often used in systems requiring frequent isolation and where space constraints allow for the swinging of the spectacle blind to change the status from open to closed.

7. Reducing Blind Flange:

• Description: This flange combines the features of a blind flange and a reducing flange. It has a solid center with an outer diameter of a larger flange but can connect to a pipe of a smaller size.
• Common Use: Used in systems where it is necessary to terminate a larger diameter pipe and then reduce the connection to a smaller diameter pipe, all while maintaining a sealed end.

Material Variations:

• Carbon Steel Blind Flanges: Suitable for high-temperature and high-pressure environments.
• Stainless Steel Blind Flanges: Ideal for corrosive environments due to their resistance to rust and corrosion.
• Alloy Steel Blind Flanges: Used in high-temperature and high-pressure applications where added strength and durability are required.
• Plastic Blind Flanges: Used in low-pressure applications or where chemical resistance is crucial.

Choosing the right type of blind flange depends on the specific requirements of the application, including pressure, temperature, material compatibility, and the need for frequent maintenance or inspection. Proper selection ensures the integrity and safety of the piping system.

Blind flange dimensions are typically standardized according to various international standards, such as ASME, ANSI, DIN, and JIS. Here, I’ll provide an overview of common dimensions for blind flanges based on ASME/ANSI B16.5 standards for pipe flanges and flanged fittings. These dimensions include various pressure classes (150, 300, 600, 900, 1500, and 2500).

Key Dimensions of a Blind Flange:

1. Diameter (D): The outer diameter of the flange.
2. Bolt Circle Diameter (BC or BCD): The diameter of the circle on which the bolt holes are located.
3. Number of Bolt Holes (n): The number of bolt holes in the flange.
4. Bolt Hole Diameter (d): The diameter of each bolt hole.
5. Thickness (T): The thickness of the flange.
6. Raised Face Diameter (R): The diameter of the raised face portion (for raised face flanges).

Sample Dimensions for ASME/ANSI B16.5 Blind Flanges (in inches):

Class 150:

Class 300:

Class 600:

Important Considerations:

1. Material Selection: Choose the appropriate material based on the application’s temperature, pressure, and fluid type.
2. Pressure Class: Ensure the flange’s pressure rating matches the system’s requirements.
3. Standards Compliance: Verify that the blind flange complies with the relevant standards and specifications.

For precise and detailed dimensions, always refer to the relevant standard (e.g., ASME B16.5) and consult with the manufacturer or supplier to ensure compatibility and proper fit for your specific application.

Blind flange specifications encompass various parameters such as dimensions, materials, pressure ratings, and standards to ensure they meet the requirements for different applications. Here is an overview of key specifications for blind flanges, based on the ASME/ANSI B16.5 standard.

Key Specifications for Blind Flanges:

1. Dimensions:

• Outside Diameter (D): The overall diameter of the flange.
• Thickness (T): The thickness of the flange.
• Bolt Circle Diameter (BC or BCD): The diameter of the circle on which the bolt holes are located.
• Number of Bolt Holes (n): The number of bolt holes in the flange.
• Bolt Hole Diameter (d): The diameter of each bolt hole.
• Raised Face Diameter (R): The diameter of the raised face (if applicable).
• Hub Diameter (if applicable): For specific types of blind flanges with a hub.

2. Pressure Classes:

• Blind flanges are rated by their pressure class, which denotes the maximum pressure they can withstand. Common pressure classes include:
  • Class 150
  • Class 300
  • Class 600
  • Class 900
  • Class 1500
  • Class 2500

3. Materials:

• Carbon Steel: Suitable for high-pressure applications.
• Stainless Steel: Resistant to corrosion and suitable for harsh environments.
• Alloy Steel: Used in high-temperature and high-pressure applications.
• Other Materials: Such as copper-nickel, duplex stainless steel, and plastic for specific applications.

4. Standards and Codes:

• ASME B16.5: Covers pipe flanges and flanged fittings for sizes NPS 1/2 through NPS 24.
• ASME B16.47: Covers large diameter steel flanges for sizes NPS 26 through NPS 60.
• DIN Standards: German standards for flanges.
• JIS Standards: Japanese standards for flanges.

5. Surface Finish:

• Raised Face (RF): A small raised area around the bore of the flange.
• Flat Face (FF): A flat sealing surface.
• Ring Type Joint (RTJ): A groove for a metal ring gasket.

Example Specifications for ASME B16.5 Blind Flanges (in inches):

Class 150 Blind Flanges:

Class 300 Blind Flanges:

Notes:

• Gasket Selection: Ensure the correct gasket type is used for the flange face type to achieve a proper seal.
• Bolt Material and Size: Match the bolt material and size to the flange specifications and application requirements.
• Corrosion Allowance: If applicable, consider a corrosion allowance when determining the final flange thickness.

For precise and application-specific specifications, always refer to the detailed guidelines provided in the relevant standards (ASME, ANSI, DIN, JIS) and consult with manufacturers or suppliers to ensure compatibility and compliance with all requirements.

Conclusion

Blind flanges are essential components in piping systems, providing secure and effective sealing solutions for the ends of pipelines, valves, or vessels. Their versatility and robustness make them suitable for various industrial applications, including oil and gas, petrochemical, power generation, and water treatment.

Key Takeaways:

1. Purpose and Design: Blind flanges are solid, round plates without a central bore, used to block the end of a pipe or opening, ensuring no flow of fluids or gases.
2. Types and Specifications:
   • Types: Common types include Raised Face (RF), Flat Face (FF), Ring-Type Joint (RTJ), Threaded, Lap Joint, Spectacle Blind, and Reducing Blind flanges.
   • Dimensions: Key dimensions include outside diameter, thickness, bolt circle diameter, number of bolt holes, and bolt hole diameter.
   • Materials: Typically made from carbon steel, stainless steel, alloy steel, and other materials suited to the application’s requirements.
   • Pressure Classes: Rated for different pressure levels (Class 150, 300, 600, 900, 1500, and 2500) to match the operating conditions.
3. Standards and Compliance: Blind flanges are manufactured to adhere to international standards such as ASME B16.5, ASME B16.47, DIN, and JIS, ensuring compatibility and reliability.
4. Installation and Maintenance: Proper installation with appropriate gaskets and bolts is crucial for achieving a leak-proof seal. Regular inspection and maintenance ensure continued performance and safety.
5. Calculation of Thickness: The thickness of a blind flange is determined based on the design pressure, material allowable stress, and safety factors. Using standard formulas and guidelines helps in ensuring the flange can withstand the required pressure.

In summary, selecting the right blind flange involves understanding the specific requirements of the application, including pressure, temperature, material compatibility, and adherence to relevant standards. Proper selection, installation, and maintenance of blind flanges contribute to the safety and efficiency of piping systems, providing reliable sealing solutions for various industrial applications.