ANSI / ASME Flanges


The current ANSI / ASME flange specifications of B16.5 and B16.47 trace their roots to the old B16.1 specification from decades past, which consisted primarily of cast iron. This specification in turn was developed from the original AESC / ASA committee B16 in the 1920s. These modern specifications are the result of countless hours of engineering and design to form a standard which could be utilized worldwide. Our most commonly requested flange specification, ANSI / ASME flanges continue to be the most widely used type of steel flange across various industries. The pressure vessel and fabrication sectors use these in abundance in their pressurized applications to retain and transport air, water, and a variety of other chemicals. Often found in refineries, ANSI / ASME flanges are a critical component in their infrastructure, and are primarily used to connect piping, valves, and other fittings which compose the bulk of a piping assembly. The 150# class of steel flanges is the most popular for low pressure and vacuum applications, as the design has proven to be effective in applications which require an occasional fluctuation in the temperature and pressure of the environment.

*ANSI stands for “American National Standards Institute”

“ASME Stands for “American Society of Mechanical Engineers”

These are organizations representing quality control and engineering requirements. Read on to understand the differences between the two.


Although both organizations are known internationally for their standards, the primary difference between them is in their objectives. two organizations can be clearly seen in their mission and vision. As an American institute, ANSI is responsible for the accreditation of specifications in the United States. Though ANSI doesn’t develop standards its own standards, they are tasked with unifying existing standards and condensing them for practical purposes. ANSI was originally founded in 1918 with members from government agencies, businesses, and academic institutions. ANSI oversees the standards developed by these organizations for the creation of products and services, and thereby ensures the consistency of these standards for quality and public utilization. To maintain the standard set by the United States as a global power, ANSI is involved in working with international standards organizations for global compliance requirements and checking for quality requirements developed within those foreign product lines.

On the other hand, the American Society of Mechanical Engineers is one of the oldest standards developing organizations. ASME actually builds out specifications for ANSI to review. They were founded in 1880 as a result of various mechanical requirements to build pressure vessel equipment. ASME has members nationwide in various companies, and all of these members have an engineering background. ASME has developed several hundreds of standards for mechanical devices, and almost all of the products provided by Texas Flange will likely adhere to the ASME standard given its popularity. If you order a flange or fitting from us, it is likely that you are getting a product which adheres to ASME B16.5, B16.47, or B16.9 due to your project requirements.

For reference, head on over to:

*ANSI stands for “American National Standards Institute” and more information can be found on their website:

**ASME Stands for “American Society of Mechanical Engineers” and more information can be found on their website:


Texas Flange stocks a wide variety of flanges in all sizes and specifications.