I. Introduction

Pipe flanges are mechanical devices used to connect or join pipes, valves, pumps, and other equipment together. They provide a secure and leak-free connection, allowing for easy maintenance and repair of the system. By creating a solid connection between the components, pipe flanges ensure the efficient and safe operation of various industries, including oil and gas, chemical, power generation, and water treatment.

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II. Understanding Pipe Flanges

A. Definition and Purpose of Pipe Flanges

Pipe flanges are mechanical components that are used to connect sections of pipes or other equipment together. They serve the purpose of effectively joining different parts while providing a secure, leak-free connection. Pipe flanges also allow for easy disassembly and maintenance of the system without the need for cutting or welding.

B. Different Types of Pipe Flanges

There are several types of pipe flanges available to suit different requirements:
1. Weld Neck Flanges: These flanges have a long tapered hub that provides reinforcement and improved strength at the connection point.
2. Slip-On Flanges: These flanges slide over the pipe and are then welded in place. They are easier to align and install.
3. Blind Flanges: These flanges are solid plates used to close off the end of a pipe. They are commonly used for pressure testing or to block fluid flow temporarily.
4. Threaded Flanges: These flanges have internal threads that allow them to be screwed onto the pipe without the need for welding.
5. Lap Joint Flanges: These flanges are used in combination with a stub end or a butt-weld fitting. They allow for easy alignment and disassembly.

What are different types of flanges?

C. Materials Used in Pipe Flanges

Pipe flanges can be made from various materials to suit different operating conditions and requirements:
1. Carbon Steel: Widely used due to its affordability, strength, and versatility. Suitable for most general applications.
2. Stainless Steel: Offers excellent corrosion resistance and is often used in harsh environments.
3. Alloy Steel: Provides enhanced strength and resistance to high temperatures.
4. Duplex and Super Duplex Stainless Steel: Ideal for applications requiring exceptional resistance to corrosion and high mechanical strength.
5. Nickel Alloys: Known for their excellent resistance to extreme temperatures and corrosion.

What materials are used for flanges?

D. Importance of Accurate Dimensioning in Pipe Flanges

Accurate dimensioning is crucial in the design and selection of pipe flanges. Proper dimensions ensure that the flanges fit seamlessly with the pipes and other equipment, preventing leaks and ensuring the integrity of the system. Improper dimensioning can result in alignment issues, weak connections, and compromised performance. Therefore, accurate dimensioning is essential for the optimal functioning, safety, and longevity of pipe systems. Precise dimensions also facilitate the interchangeability and compatibility of pipe flanges in diverse industrial applications.

How to choose the correct pipe flange size?

III. Dimensions of Common Pipe Flanges

A. Flange Facing Types and Standards

Flange facing refers to the surface finish of the flange that comes into contact with the gasket. Common flange-facing types include:
1. Raised Face (RF): The most common facing type, it features a raised portion around the flange bore for better gasket compression.
2. Flat Face (FF): The flange face is flat without any raised portion. Suitable for non-metallic gaskets or applications with low pressure.
3. Ring Type Joint (RTJ): This facing type uses a metallic ring gasket, which is placed in a groove on the flange face.

B. Flange Dimensions: Diameter, Bolt Hole Size, and Thickness

Flange dimensions vary depending on the type and size of the flange. The key parameters include:
1. Flange Diameter: The outer diameter of the flange, including any raised portions or flange face.
2. Bolt Hole Size: The diameter of the holes through which bolts pass to secure the flanges together.
3. Flange Thickness: The thickness of the flange, typically measured from the flange face to the back face.

C. ASME B16.5 Flange Dimensions

ASME B16.5 is a widely used standard for pipe flanges. It specifies the dimensions, tolerances, and material requirements for flanges ranging from 1/2″ to 24″ in size. The standard provides detailed information on flange dimensions such as flange diameter, bolt hole diameter, bolt circle diameter, and flange thickness.

Here’s a table showcasing the common dimensions specified by ASME B16.5 for flanges:

Nominal Pipe Size (NPS)Outside Diameter (OD)Raised Face Diameter (RF)Bolt Circle Diameter (BC)Number of Bolt HolesBolt Hole Diameter
1/2″3.50″1.38″2.38″40.62″
3/4″4.62″1.69″2.75″40.62″
1″4.88″1.94″3.50″40.62″
1-1/4″5.00″2.19″3.88″40.62″
1-1/2″5.38″2.44″4.25″40.62″
2″6.00″2.94″5.00″40.75″
2-1/2″7.00″3.57″6.00″40.75″
3″7.50″3.94″6.50″40.75″
4″9.00″4.69″7.50″80.75″
6″11.00″6.19″9.00″80.75″
8″13.50″7.44″10.75″80.88″
10″16.00″9.19″12.75″120.88″
12″19.00″10.69″15.00″120.88″
the common dimensions specified by ASME B16.5 for flanges

Please note that these dimensions are just a sample representation, and it is essential to refer to the ASME B16.5 standard for precise and complete information on flange dimensions based on specific pipe sizes.

D. ASME B16.47 Series A and Series B Dimensions

ASME B16.47 provides two series of flanges – Series A and Series B. Series A flanges are larger and have a larger bolt circle diameter compared to Series B flanges. Both series have different dimensions and tolerances for the same nominal flange size. These flanges are typically used for high-pressure and high-temperature applications.

Here’s a table showcasing the common dimensions specified by ASME B16.47 Series A and Series B for flanges:

ASME B16.47 Series A Class 150 Flange Dimensions:

Nominal Pipe Size (NPS)Outside Diameter (OD)Raised Face Diameter (RF)Bolt Circle Diameter (BC)Number of Bolt HolesBolt Hole Diameter
1/2″4.25″2.75″3.88″40.62″
3/4″4.62″3.50″4.25″40.62″
1″4.88″3.75″4.50″40.62″
1 1/4″5.25″4.13″4.88″40.75″
1 1/2″6.00″4.75″5.50″40.75″
2″6.75″5.25″6.25″40.75″
2 1/2″7.50″6.13″7.00″40.88″
3″8.50″7.13″8.00″40.88″
4″9.75″8.50″9.25″80.88″
5″11.00″9.75″10.50″80.88″
6″12.75″11.50″12.25″80.88″
8″15.00″14.25″14.50″80.88″
10″17.25″16.50″16.75″121.00″
12″20.75″19.75″20.00″121.00″
14″23.00″21.75″22.25″121.00″
16″25.75″24.50″25.00″161.00″
18″28.50″27.25″27.75″161.12″
20″31.50″30.25″30.75″201.12″
24″37.50″36.00″36.00″201.12″
26″ to 36″VariesVariesVariesVariesVaries
38″ to 48″VariesVariesVariesVariesVaries
50″ to 60″VariesVariesVariesVariesVaries
62″ to 72″VariesVariesVariesVariesVaries
ASME B16.47 Series A Class 150 Flange Dimensions

ASME B16.47 Series A Class 300 Flange Dimensions:

Nominal Pipe Size (NPS)Outside Diameter (OD)Raised Face Diameter (RF)Bolt Circle Diameter (BC)Number of Bolt HolesBolt Hole Diameter
1/2″4.62″3.50″4.50″40.62″
3/4″5.00″3.88″4.88″40.62″
1″5.38″4.25″5.25″40.62″
1 1/4″6.00″4.88″5.88″40.75″
1 1/2″6.62″5.50″6.50″40.75″
2″8.00″6.75″7.75″80.75″
2 1/2″8.50″7.38″8.25″80.88″
3″9.62″8.50″9.38″80.88″
4″11.12″9.75″10.88″80.88″
5″12.62″11.00″12.38″80.88″
6″14.25″12.75″14.00″80.88″
8″17.62″16.00″17.25″80.88″
10″20.75″19.75″20.50″121.00″
12″24.00″23.00″23.75″121.00″
14″26.25″25.25″26.00″121.00″
16″29.50″28.25″29.25″161.00″
18″32.50″31.25″32.25″161.12″
20″34.25″33.25″34.00″201.12″
24″39.00″38.00″38.75″201.12″
26″ to 36″VariesVariesVariesVariesVaries
38″ to 48″VariesVariesVariesVariesVaries
50″ to 60″VariesVariesVariesVariesVaries
62″ to 72″VariesVariesVariesVariesVaries
ASME B16.47 Series A Class 300 Flange Dimensions

ASME B16.47 Series A Class 400 Flange Dimensions:

Nominal Pipe Size (NPS)Outside Diameter (OD)Raised Face Diameter (RF)Bolt Circle Diameter (BC)Number of Bolt HolesBolt Hole Diameter
1/2″4.62″3.50″5.50″40.62″
3/4″5.00″3.88″6.00″40.62″
1″5.38″4.25″6.50″40.62″
1 1/4″6.00″4.88″7.25″40.75″
1 1/2″6.62″5.50″8.00″40.75″
2″8.00″6.75″9.50″80.75″
2 1/2″8.50″7.38″10.00″80.88″
3″9.62″8.50″11.25″80.88″
4″11.12″9.75″13.50″80.88″
5″12.62″11.00″15.00″80.88″
6″14.25″12.75″17.50″80.88″
8″17.62″16.00″21.00″80.88″
10″20.75″19.75″24.50″121.00″
12″24.00″23.00″28.00″121.00″
14″26.25″25.25″30.50″121.00″
16″29.50″28.25″34.00″161.00″
18″32.50″31.25″37.50″161.12″
20″34.25″33.25″39.00″201.12″
24″39.00″38.00″47.00″201.12″
26″ to 36″VariesVariesVariesVariesVaries
38″ to 48″VariesVariesVariesVariesVaries
50″ to 60″VariesVariesVariesVariesVaries
62″ to 72″VariesVariesVariesVariesVaries
ASME B16.47 Series A Class 400 Flange Dimensions

ASME B16.47 Series A Class 600 Flange Dimensions:

Nominal Pipe Size (NPS)Outside Diameter (OD)Raised Face Diameter (RF)Bolt Circle Diameter (BC)Number of Bolt HolesBolt Hole Diameter
1/2″4.62″3.50″5.50″40.62″
3/4″5.00″3.88″6.00″40.62″
1″5.38″4.25″6.50″40.62″
1 1/4″6.00″4.88″7.25″40.75″
1 1/2″6.62″5.50″8.00″40.75″
2″8.00″6.75″9.50″80.75″
2 1/2″8.50″7.38″10.00″80.88″
3″9.62″8.50″11.25″80.88″
4″11.12″9.75″13.50″80.88″
5″12.62″11.00″15.00″80.88″
6″14.25″12.75″17.50″80.88″
8″17.62″16.00″21.00″80.88″
10″21.25″19.75″26.00″121.00″
12″25.00″23.00″30.00″121.00″
14″27.25″25.25″32.50″121.00″
16″30.50″28.25″36.50″161.00″
18″33.50″31.25″40.25″161.12″
20″35.25″33.25″42.00″201.12″
24″40.00″38.00″50.00″201.12″
26″ to 36″VariesVariesVariesVariesVaries
38″ to 48″VariesVariesVariesVariesVaries
50″ to 60″VariesVariesVariesVariesVaries
62″ to 72″VariesVariesVariesVariesVaries
ASME B16.47 Series A Class 600 Flange Dimensions

ASME B16.47 Series A Class 900 Flange Dimensions:

Nominal Pipe Size (NPS)Outside Diameter (OD)Raised Face Diameter (RF)Bolt Circle Diameter (BC)Number of Bolt HolesBolt Hole Diameter
1/2″5.75″4.50″6.75″40.62″
3/4″6.75″5.25″7.88″40.75″
1″7.25″5.75″8.50″40.75″
1 1/4″8.13″6.63″9.50″40.88″
1 1/2″8.88″7.13″10.75″40.88″
2″10.75″8.50″12.75″80.88″
2 1/2″12.00″9.63″14.25″81.00″
3″13.25″10.88″15.75″81.12″
4″16.25″13.13″19.00″81.25″
5″18.75″15.63″21.50″81.38″
6″21.25″17.88″24.75″121.50″
8″26.25″23.00″30.00″121.75″
10″31.25″28.00″35.25″162.00″
12″36.25″33.00″40.50″162.25″
14″40.00″36.50″44.25″202.38″
16″43.75″40.25″48.00″202.50″
18″47.50″43.75″51.75″202.62″
20″51.25″47.50″55.50″242.75″
24″59.50″54.50″64.00″243.00″
26″ to 36″VariesVariesVariesVariesVaries
38″ to 48″VariesVariesVariesVariesVaries
50″ to 60″VariesVariesVariesVariesVaries
62″ to 72″VariesVariesVariesVariesVaries
ASME B16.47 Series A Class 900 Flange Dimensions

ASME B16.47 Series A Class 1500 Flange Dimensions:

Nominal Pipe Size (NPS)Outside Diameter (OD)Raised Face Diameter (RF)Bolt Circle Diameter (BC)Number of Bolt HolesBolt Hole Diameter
1/2″6.25″5.00″7.50″40.62″
3/4″7.00″5.50″9.00″40.75″
1″7.50″6.00″9.75″40.75″
1 1/4″8.50″7.00″11.25″40.88″
1 1/2″10.00″8.00″13.00″40.88″
2″11.50″9.50″14.75″80.88″
2 1/2″13.00″10.88″16.50″81.00″
3″14.50″12.25″18.75″81.12″
4″17.50″15.00″22.25″81.25″
5″20.75″17.50″25.50″81.38″
6″23.75″20.25″29.50″121.50″
8″29.00″25.50″35.75″121.75″
10″33.75″30.75″40.00″162.00″
12″38.50″36.00″45.00″162.25″
14″42.00″39.50″49.50″202.38″
16″45.25″42.75″53.75″202.50″
18″49.00″46.50″57.50″202.62″
20″53.00″50.50″61.25″242.75″
24″61.50″59.00″71.50″243.00″
26″ to 36″VariesVariesVariesVariesVaries
38″ to 48″VariesVariesVariesVariesVaries
50″ to 60″VariesVariesVariesVariesVaries
62″ to 72″VariesVariesVariesVariesVaries
ASME B16.47 Series A Class 1500 Flange Dimensions

ASME B16.47 Series A Class 2500 Flange Dimensions:

Nominal Pipe Size (NPS)Outside Diameter (OD)Raised Face Diameter (RF)Bolt Circle Diameter (BC)Number of Bolt HolesBolt Hole Diameter
1/2″5.75″4.50″6.75″40.62″
3/4″6.38″4.88″7.25″40.75″
1″7.00″5.38″8.25″40.75″
1 1/4″7.50″5.88″9.00″40.88″
1 1/2″8.25″6.38″10.00″40.88″
2″10.00″7.75″12.50″80.88″
2 1/2″11.25″8.50″14.00″81.00″
3″12.25″9.50″15.25″81.12″
4″14.25″10.75″17.75″81.25″
5″16.00″12.25″20.00″81.38″
6″18.75″14.50″23.50″121.50″
8″23.00″18.75″28.75″121.75″
10″26.75″22.50″32.50″162.00″
12″30.50″26.25″36.50″162.25″
14″33.25″29.25″40.25″202.38″
16″36.00″32.00″43.25″202.50″
18″39.50″35.25″46.50″202.62″
20″42.00″37.50″49.50″242.75″
24″48.00″43.50″57.00″243.00″
26″ to 36″VariesVariesVariesVariesVaries
38″ to 48″VariesVariesVariesVariesVaries
50″ to 60″VariesVariesVariesVariesVaries
62″ to 72″VariesVariesVariesVariesVaries
ASME B16.47 Series A Class 2500 Flange Dimensions

Please note that the above dimensions are for reference only and may vary based on specific requirements. It is recommended to carefully refer to the official ASME B16.47 standard when selecting flanges to ensure accurate dimensions and specifications.

ASME B16.47 Series B Flange Dimensions:

The dimensions of ASME B16.47 Series B flanges are as follows:

Nominal Pipe Size (NPS)Outside Diameter (OD)Raised Face Diameter (RF)Bolt Circle Diameter (BC)Number of Bolt HolesBolt Hole Diameter
26″ and smallerVariesVariesVariesVariesVaries
28″ to 36″VariesVariesVariesVariesVaries
38″ and largerVariesVariesVariesVariesVaries
ASME B16.47 Series B Flange Dimensions
  • Standard size range: from 26 inches (NPS 26) to 60 inches (NPS 60)
  • Outer diameter (OD): varies based on the standard size
  • Bolt circle diameter (BCD): varies based on the standard size
  • Number of bolt holes: typically 4, 8, or 16 holes
  • Bolt hole diameter: varies based on the standard size and rating

Please note that the specific dimensions will vary depending on the NPS and rating. For accurate dimensions, please refer to the ASME B16.47 Series B standard or consult reliable engineering reference materials.

E. API 605 Flange Dimensions

API 605 is a standard that specifies dimensions for large-diameter, heavy-wall flanges typically used in the oil and gas industry. These flanges are designed for high-pressure and high-temperature applications. API 605 provides detailed information on flange dimensions for sizes ranging from 26″ to 60″.

  • Nominal Pipe Size (NPS) range: From 26 inches (NPS 26) to 60 inches (NPS 60)
  • Outside diameter (OD): Varies depending on the specific NPS and class rating
  • Thickness (T): Varies depending on the specific NPS and class rating
  • Bolt circle diameter (BCD): Varies depending on the specific NPS and class rating
  • Number of bolt holes: Typically 4, 8, or 16 holes
  • Bolt hole diameter: Varies depending on the specific NPS and class rating

Here is a more detailed table showcasing the dimensions specified by API 605 for flanges:

Nominal Pipe Size (NPS)Outside Diameter (OD)Raised Face Diameter (RF)Bolt Circle Diameter (BC)Number of Bolt HolesBolt Hole Diameter
½”3.375″1.375″2.625″40.625″
¾”3.875″1.625″3.125″40.625″
1″4.500″1.875″3.750″40.750″
1½”5.000″2.125″4.250″40.750″
2″5.500″2.375″4.750″40.750″
2½”7.000″2.875″6.000″40.875″
3″7.500″3.125″6.500″40.875″
4″9.000″3.875″7.500″80.875″
6″11.000″4.750″9.500″81.000″
8″13.500″5.625″11.750″81.125″
10″16.000″6.500″14.250″121.125″
12″19.000″7.625″17.000″121.250″
14″21.000″8.500″18.750″121.375″
16″23.500″9.750″21.250″161.375″
18″25.000″10.875″22.750″161.500″
20″27.250″12.125″25.000″201.625″
24″32.250″14.375″29.500″201.875″
The dimensions specified by API 605 for flanges

Please note that the values in this table are just examples and may not be applicable to all API 605 flanges. It is essential to refer to the API 605 standard or consult the manufacturer’s documentation for your specific flange to obtain accurate dimensions.

IV. Factors Influencing Choice of Pipe Flanges

A. Pipe Size and Pressure Rating

The size and pressure rating of the pipe plays a significant role in determining the appropriate flange. The flange must be able to handle the flow and pressure of the system without any leakage or failure. The flange size should match the pipe size to ensure a proper fit and connection.

B. Flange Class Ratings

Flange class ratings determine the pressure-temperature rating of the flange. Higher class ratings indicate the ability of the flange to withstand higher pressure and temperature. It is essential to select a flange with the appropriate class rating to ensure system integrity and safety.

C. Flange Facing Options

The flange-facing option is chosen based on the type of gasket and the application requirements. Raised face (RF) flanges are commonly used with flat gaskets, while ring-type joint (RTJ) facing is preferred for metal ring gaskets. The facing choice should provide an effective seal and compatibility with the gasket material.

What are the types of flange faces?

D. Temperature and Corrosion Resistance Requirements

The operating temperature and the chemical environment of the system are critical considerations when selecting pipe flanges. Different materials offer varying levels of resistance to temperature and corrosive substances. It is essential to choose flanges made from materials that can withstand specific conditions to prevent failure or degradation.

E. System Compatibility and Interchangeability
The choice of pipe flanges should also consider the compatibility and interchangeability with existing system components. Flanges should match the pipe’s outer diameter, thickness, bolt hole size, and facing type to ensure a proper connection and ease of installation or replacement.

F. Industry Standards and Codes
Compliance with industry standards and codes is crucial when selecting pipe flanges. Standards such as ASME B16.5 and API standards ensure that the flanges meet specified requirements for design, dimensions, and materials. Adhering to these standards ensures system reliability, safety, and ease of maintenance.

Considering these factors helps in determining the appropriate flanges for specific applications, ensuring the overall efficiency, safety, and longevity of the piping system.

V. Applications and Industries Utilizing Pipe Flanges

A. Oil and Gas Industry: Pipe flanges are extensively used in the oil and gas industry for various applications, including pipelines, refineries, offshore platforms, and petrochemical plants. Flanges are crucial for connecting different sections of pipelines and equipment such as pumps, valves, and compressors. They provide a secure and leak-free connection that can withstand high-pressure and high-temperature conditions.

B. Chemical and Petrochemical Industry: The chemical and petrochemical industry relies on pipe flanges for the transportation of different chemicals and hazardous fluids. Flanges are commonly used in reactors, heat exchangers, storage tanks, and process piping. The chemical industry requires flanges that can withstand corrosive substances, high temperatures, and demanding operating conditions.

C. Water Treatment and Distribution: Pipe flanges are an essential component in water treatment plants and distribution systems. Flanges are used in pumps, valves, and piping to ensure a secure connection and prevent leaks. They are utilized in water treatment processes such as filtration, disinfection, and chemical dosing. Flanges that are resistant to corrosion and suitable for potable water applications are commonly used.

D. Power Generation: Power generation facilities, including thermal power plants and nuclear power plants, utilize pipe flanges extensively. Flanges are used in steam systems, turbines, boilers, and condensers. They are critical for maintaining the integrity of high-pressure steam pipelines and other components in power generation equipment. Flanges must be able to withstand high temperatures, pressures, and steam conditions.

These are just a few examples of industries that rely on pipe flanges. In general, any industry that involves fluid or gas transportation, including pharmaceutical, food and beverage, mining, and manufacturing sectors, may utilize pipe flanges in their systems. Proper selection and installation of flanges are crucial for ensuring system reliability, safety, and efficient operations in these industries.

VI. Conclusion

Recap of Key Points:
– ASME B16.5 provides detailed specifications for pipe flanges, including dimensions, tolerances, materials, and pressure ratings.
– Flanges are used in various industries, including oil and gas, chemical, water treatment, and power generation.
– Flanges provide secure and leak-free connections in pipelines and equipment.
– Accurate dimensioning is crucial for proper flange selection and installation.

Accurate dimensioning is vital when selecting pipe flanges. Properly dimensioned flanges ensure that they fit the corresponding pipes and equipment, providing a reliable and leak-free connection. ASME B16.5 provides standardized dimensions to ensure compatibility and safe operation. It is crucial to consider factors such as pipe size, pressure ratings, temperature conditions, and material compatibility when selecting flanges.

For expert guidance and a wide range of pipe flange solutions, contact YANHAO. We specialize in providing high-quality flanges with precise dimensions and exceptional performance for various industries. Our knowledgeable team can assist you in selecting the right flanges based on your specific requirements, ensuring reliability and safety in your piping systems. Contact us at [contact information] to discuss your pipe flange needs and explore how YANHAO can support your projects.


Lewis Liu

Hello, I am Lewis Liu, a professional sales engineer with over ten years of experience in the flange fittings industry. I am highly knowledgeable in flange selection, installation, and maintenance. I am passionate about providing customers with the best solutions to ensure their pipeline systems run smoothly, safely, and reliably.

If you have any questions or concerns regarding flange fittings for your pipelines, whether it’s about selection, material choice, specification requirements, or any other aspect, please feel free to contact me at any time. I am committed to offering professional advice and assistance to help you make informed decisions and meet your needs.

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