Understanding ANSI/ASME B16.5 and B16.47 Standards

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The American National Standard Institute (ANSI) Sectional Committee B16 has been defining publishing safety and dimensional standards for piping systems since 1922. Sectional Committee B16 was reorganized as an ASME (American Society of Mechanical Engineers) standards committee in 1982 with the first publication of the standards under the ASME/ANSI designation in 1988. Today, these standards are reviewed and approved under the ASME B16 designation by the ASME B16 Standards Committee. They are then approved for publication by ANSI as American National Standards. The ASME B16.5 and ASME B16.47 standards cover most of the flanges used in modern industrial piping systems up to nominal pipe size (NPS) 60 inches.

1. About ASME B16.5

The ASME B16.5 Pipe Flanges and Flanged Fittings covers the standard requirements for pressure-temperature ratings, materials, and dimensions, tolerances, and marking, testing procedures, and designating openings for pipe flanges and flanged fittings.

Included are:

B16.5 covers Threaded, Slip-on, Lapped, Blind, and Weld Neck flanges.
Flanges with pressure class designations 150, 300, 400, 600, 900, and 1500 in sizes NPS 1/2 through NPS 24, and class 2500 in sizes NPS 1/2 through NPS 12.
Flanged fittings with pressure class 150 and 300 in sizes NPS 1/2 through NPS 24.
Flanged fittings with pressure class 400, 600, 900, and 1500, and class 2500 in sizes NPS 1/2 through NPS 12 in accordance with Non-Mandatory Appendix E.

ASME B16.5 is limited to flanges and flanged fittings made from forged or cast materials. Blind flanges and certain reducing flanges may also be made from plate materials. Common materials include ASTM A105 carbon steel, 304L, and 316L stainless steel.

Typical Applications of ASME B16.5

ASME B16.5 flanges are widely used in industries that require medium to high-pressure piping systems, which include following industries:

Oil and gas processing
Petrochemical plants
Refining and chemical production
Power generation
Food and beverage manufacturing
Marine and offshore systems
Water treatment facilities

2. About ASME B16.47

The ASME B16.47 – Large Diameter Steel Flanges standard applies to blind and weld-neck flanges from sizes NPS 26 through NPS 60. It covers requirements for pressure-temperature ratings, materials, dimensions and tolerances, marking, and testing. Flanges covered include pressure class designations 75, 150, 300, 400, 600, and 900 with requirements provided in both SI (Metric) and U.S. Customary Units, with bolt diameters and bolt hole sizes expressed in inch units.

This standard is limited to weld-neck flanges made from cast or forged materials, and blind flanges made from cast, forged, or plate materials.

3. The Difference Between ASME B16.5 and ASME B16.47

Differentiating ASME B16.47 Series A and Series B

Slip-ons, threaded, and socket weld are not covered by the ANSI/ASME B16.47 standard and are instead manufactured to industry (non-ANSI/ASME) standards. These “industry standard” designs are based on B16.47 bolt patterns and dimensions vary by manufacturer. Always confirm details before fabrication.

The main differences include:

ASME B16.5 covers smaller pipe sizes (NPS ½–24″) and includes a wider variety of flange types.
ASME B16.5 offers higher pressure classes (up to 2500) compared to ASME B16.47, which is limited to class 900.
ASME B16.47 applies only to large-diameter flanges (NPS 26–60″) and is divided into Series A ( blind & weld neck flanges) and Series B (blind and weld neck flanges) for different performance needs.
ASME B16.47 Series A & B: Bolt hole count, bolt hole circumference, thickness.

ASME B16.47 Series A	ASME B16.47 Series B
ASME B16.47 Series A flanges are thicker, heavier, and are based on the Manufacturers Standardization Society (MSS) Standard Practice (SP)-44 flange design. Typical applications of Series A include environments such as transmission pipelines, offshore facilities, power plants, refineries, and heavy industrial process systems.	ASME B16.47 Series B covers flanges originally designed per the American Petroleum Institute Standard 605, which was last published in 1988 before being discontinued with the further development of the B16.47 standard. Series B flanges are more compact with smaller bolt circle diameters then Series A flanges. Due to this, the two series are generally not interchangeable. Typical applications of Series B include pipeline repairs and retrofits, low-to-moderate stress environments, cost-sensitive infrastructure projects, and expansion of existing systems.

ASME B16.47 Series A

ASME B16.47 Series B

ASME B16.47 Series A flanges are thicker, heavier, and are based on the Manufacturers Standardization Society (MSS) Standard Practice (SP)-44 flange design.

Typical applications of Series A include environments such as transmission pipelines, offshore facilities, power plants, refineries, and heavy industrial process systems.

ASME B16.47 Series B covers flanges originally designed per the American Petroleum Institute Standard 605, which was last published in 1988 before being discontinued with the further development of the B16.47 standard. Series B flanges are more compact with smaller bolt circle diameters then Series A flanges. Due to this, the two series are generally not interchangeable.

Typical applications of Series B include pipeline repairs and retrofits, low-to-moderate stress environments, cost-sensitive infrastructure projects, and expansion of existing systems.

Flange Specification Comparison Table

Feature	ASME B16.5	ASME B16.47 Series A	ASME B16.47 Series B
Size Range	NPS ½ – 24″	NPS 26 – 60″	NPS 26 – 60″
Pressure Class	150 – 2500	150 – 900	75 – 900
Flange Types Covered Under Spec	TH, SO, LAP, BL, WN	BL	WN
External Load Capacity	High	Highest	Lower
Typical Applications	Refining, power, process	Offshore, high stress	Pipelines, maintenance

4. Choosing the Right Flange

Selecting the right flange depends on the demands of the system and the conditions it will operate under. Choosing between ASME B16.5 and ASME B16.47 (Series A and Series B) depends on several factors, including:

Pipe diameter
Pressure class
Mechanical loads
Application criticality
Costs and project budget
New construction vs. retrofit

General Guidance

ASME B16.5 is suitable for most medium- to high-pressure process piping under 24 inches.
ASME B16.47 Series A is considered the best fit for large-diameter, high-load systems, or when safety margins are a priority.
ASME B16.47 Series B is suitable for cost-sensitive, low- to moderate-stress, or retrofit applications.

5. Final Note

Understanding the differences between ASME B16.5 and B16.47 helps engineers specify the correct flange standard for specific applications. Our sales team at API can answer any questions about your imported and domestic (AIS) ANSI/ASME requirements. Depending on its application, they can also recommend alternative products that may be better suited for your system. We also provide custom flange solutions tailored to your project specifications. Get connected with a dedicated sales representative today! Or call us at 503.692.3800.