Dimensions Forged Flanges to ANSI B 16.5

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Dimensions of Forged Flanges to ANSI B16.5: A Complete Guide

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ANSI B16.5 is a widely recognized standard that governs the dimensions, tolerances, materials, and pressure ratings of pipe flanges and flanged fittings. This standard applies to flanges made from materials such as forged steel, cast iron, and alloys, and is used in industries like oil and gas, chemical processing, power generation, and construction.

This article provides a detailed overview of the dimensions of forged flanges as per the ANSI B16.5 standard, including the types of flanges, pressure classes, and dimensional specifications.

What Are Forged Flanges?

Forged flanges are mechanical components used to connect pipes, valves, pumps, and other equipment in a piping system. They are manufactured by forging, a process that involves shaping metal using compressive forces, resulting in a product with superior strength and durability.

Key Features of Forged Flanges:

  • High Strength: Forging enhances the mechanical properties of the material, making the flange suitable for high-pressure applications.
  • Dimensional Accuracy: Forged flanges are manufactured with precise dimensions to ensure a tight and reliable seal.
  • Corrosion Resistance: Often made from materials like stainless steel or alloy steel, forged flanges offer excellent resistance to corrosion and wear.

Types of Flanges Covered Under ANSI B16.5

The ANSI B16.5 standard includes several types of flanges, each designed for specific applications. The most common types are:

  1. Weld Neck Flange (WN):
    • Designed for high-pressure and high-temperature applications.
    • Features a long tapered hub that provides excellent stress distribution.
  2. Slip-On Flange (SO):
    • Slides over the pipe and is welded in place.
    • Suitable for low-pressure applications.
  3. Socket Weld Flange (SW):
    • Designed for small-diameter, high-pressure systems.
    • The pipe is inserted into the flange and welded around the socket.
  4. Threaded Flange (TH):
    • Screwed onto the pipe using threads.
    • Ideal for low-pressure applications and systems where welding is not possible.
  5. Blind Flange (BL):
    • Used to close the end of a pipe or a vessel.
    • Does not have a bore and is ideal for high-pressure systems.
  6. Lap Joint Flange (LJ):
    • Used with a stub end to allow easy assembly and disassembly.
    • Suitable for systems requiring frequent maintenance.
  7. Ring-Type Joint Flange (RTJ):
    • Features a groove for a metal ring gasket, providing a leak-proof seal.
    • Commonly used in high-pressure and high-temperature applications.

Pressure Classes of ANSI B16.5 Flanges

ANSI B16.5 flanges are categorized into pressure classes, which indicate the maximum pressure the flange can withstand at a given temperature. The standard pressure classes are:

  • Class 150
  • Class 300
  • Class 400
  • Class 600
  • Class 900
  • Class 1500
  • Class 2500

The pressure rating of a flange decreases as the operating temperature increases. For example, a Class 150 flange can handle higher pressure at 100°F than at 500°F.

Dimensional Specifications of Forged Flanges to ANSI B16.5

The dimensions of forged flanges as per ANSI B16.5 include the following key parameters:

  1. Nominal Pipe Size (NPS):
    • Refers to the size of the pipe the flange is designed to fit.
    • Ranges from 1/2 inch to 24 inches under ANSI B16.5.
  2. Outside Diameter (OD):
    • The total diameter of the flange, measured across its widest point.
  3. Bolt Circle Diameter (BCD):
    • The diameter of the circle formed by the centers of the bolt holes.
  4. Number of Bolt Holes:
    • The number of holes drilled into the flange for bolting.
  5. Bolt Hole Diameter:
    • The diameter of each bolt hole.
  6. Flange Thickness (T):
    • The thickness of the flange, excluding the raised face.
  7. Raised Face Height (RF):
    • The height of the raised face, which provides a sealing surface for the gasket.
  8. Hub Diameter and Length (for Weld Neck Flanges):
    • The diameter and length of the hub, which connects the flange to the pipe.

Dimensional Table for ANSI B16.5 Flanges (Class 150)

Below is a summary of the dimensions for Class 150 flanges as per ANSI B16.5. Dimensions are in inches.

NPS OD BCD Bolt Holes Bolt Hole Diameter Flange Thickness (T) Raised Face Height (RF)
1/2 3.50 2.38 4 0.63 0.38 0.06
3/4 3.88 2.75 4 0.63 0.44 0.06
1 4.25 3.12 4 0.63 0.50 0.06
1 1/2 5.00 3.88 4 0.75 0.56 0.06
2 6.00 4.75 4 0.75 0.69 0.06
3 7.50 6.00 4 0.75 0.81 0.06
4 9.00 7.50 8 0.75 0.94 0.06
6 11.00 9.50 8 0.88 1.00 0.06
8 13.50 11.75 8 0.88 1.12 0.06
10 16.00 14.25 12 1.00 1.19 0.06
12 19.00 17.00 12 1.00 1.25 0.06
14 21.00 18.75 12 1.13 1.38 0.06
16 23.50 21.25 16 1.13 1.44 0.06
18 25.00 22.75 16 1.25 1.56 0.06
20 27.50 25.00 20 1.25 1.69 0.06
24 32.00 29.50 20 1.38 1.88 0.06

Dimensional Variations for Higher Pressure Classes

  • Class 300: Thicker flanges and larger bolt holes compared to Class 150.
  • Class 600: Designed for higher pressure, with increased flange thickness and bolt circle diameter.
  • Class 900 and Above: Includes additional reinforcements, such as larger hubs and thicker flanges, to handle extreme pressure and temperature conditions.

Applications of Forged Flanges to ANSI B16.5

Forged flanges manufactured to ANSI B16.5 standards are used in a wide range of industries and applications, including:

  1. Oil and Gas:
    • High-pressure pipelines, offshore platforms, and refineries.
  2. Chemical Processing:
    • Corrosive and high-temperature environments.
  3. Power Generation:
    • Steam and gas turbines, boilers, and heat exchangers.
  4. Water Treatment:
    • Pumping stations and desalination plants.
  5. Construction:
    • HVAC systems and structural piping.

Advantages of Forged Flanges to ANSI B16.5

  1. High Strength:
    • Forging enhances the mechanical properties of the flange, making it suitable for demanding applications.
  2. Dimensional Accuracy:
    • ANSI B16.5 ensures precise dimensions for reliable connections.
  3. Wide Range of Pressure Ratings:
    • Available in multiple pressure classes to suit various operating conditions.
  4. Corrosion Resistance:
    • Materials like stainless steel and alloy steel offer excellent resistance to rust and wear.
  5. Versatility:
    • Suitable for a variety of industries and applications.

Conclusion

The ANSI B16.5 standard provides a comprehensive framework for the design and manufacture of forged flanges, ensuring they meet the stringent requirements of modern piping systems. By understanding the dimensions, pressure classes, and types of flanges covered under this standard, engineers and project managers can select the right flange for their specific application, ensuring safety, reliability, and efficiency in their piping systems.

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