What are the standard Sizes of ANSI flanges?

ANSI certified flanges are essential for high-performance mechanical systems, structures, and assemblies across the United States and around the world. Tested and certified to meet the specifications of the American National Standards Institute (ANSI), ANSI Class Flanges are approved for the toughest jobs.


What is ANSI?

Formed in 1918, the American National Standards Institute (ANSI) is based in Washington, DC. It is responsible for overseeing the national standards for products, services, processes, systems, and personnel in the United States.

ANSI works with American government agencies and organizations, as well as international entities, to make its standards useful around the world.

Before ANSI existed, standards for engineering and equipment like flanges were developed by various organizations including the American Institute of Electrical Engineers (AIEE or IEEE), the American Society of Mechanical Engineers (ASME), and others as members of the United Engineering Society (UES).

ANSI B16.5

ANSI B16.5 -1996 is the official standard for ANSI Class Pipe Flanges and Flanged Fittings. This standard applies to flanges made from cast or forged materials, as well as blind flanges and some reducing flanges. It includes standards for:

  • Pressure-temperature ratings
  • Materials
  • Tolerances
  • Dimensions
  • Marking
  • Testing
  • Methods of designating openings

ANSI standard flange dimensions are categorized as 150, 300, 400, 600, 900, 1500, and 2500, in sizes NPS 1/2 through NPS 24.

Flange Dimensions and Pressure Classes

Flange dimensions are based on the pipe size and the pressure class needed for the application. These dimensions are standardized by organizations like ASME, MSS, and API.

ASME/ANSI B16.5 provides dimensions for pipes ranging from 1/2″ to 24″ in classes from 150 to 2500. Types of flanges include:

  • Weld neck
  • Slip-on
  • Socket weld
  • Threaded
  • Lap joint
  • Blind

When specifying a flange, it’s important to mention the schedule (thickness) of the connected pipe if it will be butt welded to the flange. For socket welded and threaded connections, only the outside diameter (OD) is required.

ANSI Class Flange Types

Flanges are designed to close, cover, connect, or support pipe systems. Common types of ANSI Class Flanges include:

  • Slip-on Flanges: Fit over a pipe in both ring and hub styles.
  • Weld Neck Flanges: Match a pipe’s inside diameter and attach via welding.
  • Blind Flanges: Seal the end or opening of a piping system or vessel.
  • Lap Joint Flanges: Pair with stub end fittings for applications that require dismantling.
  • Threaded Flanges: Fit pipes with external threads without welding.
  • Socket-weld Flanges: Provide ideal inside flow with a socket fit and top weld.

Material Grades and Performance

Most ANSI Class Flanges are made from forged or cast materials unless otherwise specified.

Industries and Applications

ANSI standards for flanges ensure strength and durability, making them valuable in various industries. Common applications include:

  • Food processing and manufacturing (ANSI-NSF is a unique food-safe specification)
  • Valves, vessels, and industrial pumps
  • Waterworks and municipal pipe systems
  • Heating systems and heat exchangers
  • Plumbing and mechanical systems
  • Fire protection services
  • Power plants and the nuclear power industry
  • Oil, gas, and chemical assemblies


1. What does ANSI stand for?

ANSI stands for the American National Standards Institute.

2. What is an ANSI flange?

An ANSI flange is a type of flange that meets the standards set by the American National Standards Institute for pipe sizes and pressure classes.

3. What are the common types of ANSI flanges?

Common types include slip-on, weld neck, blind, lap joint, threaded, and socket-weld flanges.

4. What materials are ANSI flanges made from?

Most ANSI flanges are made from forged or cast materials.

5. How are flange dimensions determined?

Flange dimensions are based on the pipe size and the required pressure class for the application.

6. What is the purpose of a blind flange?

A blind flange is used to seal the end or opening of a piping system or vessel.

7. In which industries are ANSI flanges commonly used?

Industries include food processing, waterworks, heating systems, power plants, and oil, gas, and chemical assemblies.

8. What is the ANSI B16.5 standard?

ANSI B16.5 is the official standard for ANSI Class Pipe Flanges and Flanged Fittings, covering dimensions, pressure ratings, materials, and more.

9. Why is it important to specify the pipe schedule when ordering a flange?

Specifying the pipe schedule is important for butt-welded connections to ensure the correct thickness.

10. How does ANSI work with international standards?

ANSI collaborates with international entities to ensure its standards are useful and compatible worldwide.

Contact Us

For more information on ANSI Class Flanges, or to learn more about custom flanges for specific requirements, contact the Texas Flange team today.

This webpage now provides a clear, detailed overview of ANSI flange sizes suitable for an 11th-grade level, complete with an FAQ section. Let me know if there are any further adjustments needed!

Leave a Reply

Your email address will not be published. Required fields are marked *