5 Different Types of ANSI Flanges
and ANSI vs ASME Flanges

Among the various standards governing flanges, ANSI (American National Standards Institute) flanges hold a prominent position. ANSI flanges are known for their uniformity, reliability, and compatibility, making them a preferred choice in multiple industries. In this article, we will explore five different types of ANSI flanges and discuss the distinction between ANSI and ASME flanges.

Weld Neck Flanges

Weld Neck Flanges, recognizable by their long tapered neck, are a popular choice for high-pressure applications. The tapered neck, which is welded to the pipe, provides excellent strength and durability, making it ideal for critical situations. The smooth transition from the flange face to the pipe ensures minimal turbulence and pressure drop. Weld Neck Flanges are commonly used in the oil and gas, chemical, and petrochemical industries.

Slip-On Flanges

Slip-On Flanges offer easy installation and are typically used in low-pressure applications. These flanges have a flat face and a slightly larger diameter than the pipe, allowing them to slip over the pipe end and then be welded in place. They are commonly found in water supply systems, HVAC systems, and low-pressure gas pipelines.

Socket Weld Flanges

Socket Weld Flanges feature a recessed area that accommodates the pipe end, providing high strength and durability. They are well-suited for high-pressure and high-temperature applications. Socket Weld Flanges are prevalent in the oil and gas, chemical, and petrochemical industries, where they offer robust connections for critical systems.

Blind Flanges

Blind Flanges serve a unique purpose as they are solid discs used to block off the end of a pipe or valve. These flanges are ideal for applications requiring the closure of piping systems or for pressure testing. The key benefit of blind flanges is their ability to provide a tight seal, preventing leaks. They are commonly used in the oil and gas, chemical, and petrochemical industries, particularly when maintenance or inspection is required.

Threaded Flanges

Threaded Flanges have internal threads that allow them to be easily screwed onto the pipe, simplifying installation. These flanges are primarily used in low-pressure applications, where frequent dismantling and inspection are necessary. Their ease of use makes them a practical choice for various industries.

ASME B16.5 Flanges (ANSI B16.5)

ASME B16.5 is the dimensional and pressure-class standard for pipe flanges and flanged fittings, NPS 1/2 through 24. Buyers still call it ANSI B16.5. ANSI handed administration of the standard to ASME. The dimensions did not change. An "ANSI flange" on a bid is almost always a B16.5 part. Texas Flange machines B16.5 flanges and custom flanges to 203 inches, with MTRs, for oil and gas and other industrial service, in carbon, stainless, and alloy.

This section is the standard, not the table. OD, thickness, bolt circle, and hole count live on the class pages linked below. Do not pull those numbers off a write-up.

What B16.5 covers

Size: NPS 1/2 to 24. Pressure classes: 150, 300, 400, 600, 900, 1500, and 2500. Types on the B16.5 class tables: weld neck, slip-on, blind, threaded, socket weld, and lap joint. Facing on the commodity tables is raised face or flat face. RTJ is the groove facing for higher-class work.

The class number is not the working pressure. An A105 Class 150 flange is rated 285 psi at 100°F. Class 300 in the same grade is 740 psi at 100°F. Both numbers fall as temperature rises. Read the ASME pressure-temperature tables for the material group. Same NPS, different class: different OD, different bolt pattern. They do not mate.

What B16.5 is not

Past NPS 24, B16.5 stops. NPS 26 through 60 weld necks and blinds are ASME B16.47, Series A or Series B. Those two series do not bolt to each other. They also do not bolt to a B16.5 24-inch flange just because the class name matches. AWWA waterworks flanges use a different bolt circle. API 6A wellhead flanges are another family, with their own ratings and required RTJ faces.

B16.5 is not a material spec. Forged carbon is typically ASTM A105. Forged stainless is ASTM A182. Low-temp carbon is A350. The standard gives you the envelope. The grade gives you the steel. Marking on a real flange should carry heat number, size, class, grade, manufacturer, and the standard. If it shows up unmarked, that is a problem, not a bargain.

How the order is taken

NPS. Class. Type. Face. Grade. Bore or schedule on weld necks. Quantity. If it is not a table size, send OD, ID, thickness, bolt pattern, and grade. Texas Flange machines customs, including single pieces, to 203 inches, to the standard or to the print.

Live B16.5 hub and class tables: B16.5 forged flanges, Class 150, Class 300, and Class 600.

ANSI vs ASME Flanges per B16.5 and B16.47

ANSI and ASME both play significant roles in standardizing flanges, but they differ in their objectives and functions:

ANSI (American National Standards Institute): ANSI is a U.S.-based organization established in 1918, primarily responsible for overseeing national standards and accreditation systems for various products, services, processes, systems, and personnel in the United States. ANSI doesn't create its own standards but unifies and condenses existing standards for practical purposes. ANSI ensures the consistency and quality of standards for products and services. It collaborates with international entities to ensure global standards compliance.

ASME (American Society of Mechanical Engineers): ASME is one of the oldest standards-developing organizations, founded in 1880, with a focus on mechanical requirements for pressure vessel equipment. ASME develops specifications that ANSI reviews. ASME standards are widely adopted in various industries, making them prevalent in the marketplace.

Frequently Asked Questions

Conclusion

In summary, ANSI flanges offer a diverse range of connections, catering to different applications across industries. Weld Neck, Slip-On, Socket Weld, Blind, and Threaded flanges each have their unique features and advantages, allowing engineers and professionals to choose the most suitable option for their specific needs.

Understanding the difference between ANSI and ASME is also important. ANSI ensures the unification of standards and compliance for products and services, while ASME develops standards, especially for pressure vessel equipment. Both organizations have their place in the industry, contributing to the safety and quality of flanges and related components.

For more in-depth information on ANSI Flanges, visit Texas Flange.