Difference between ASME B16.47 Series A and Series B Flanges

ASME B16.47 is an American standard for large-diameter steel flanges. This standard covers the design of flanges from NPS 26 to NPS 60. For lower sizes i.e, up to NPS 24, ASME B16.5 has to be referred. ASME B16.47 provides pressure-temperature ratings, materials, dimensions, tolerances, marking, and testing for pipe flanges with rating class designations 75, 150, 300, 400, 600, and 900. The Standard also includes the requirements and recommendations regarding flange bolting, flange gaskets, and flange joints.

What is ASME B16.47 Flange Series?

The ASME B16.47 standard provides the use of two types of flange series.

  • Series A flanges and
  • Series B flanges.

Series A specifies flange dimensions for general-use flanges whereas Series B specifies flange dimensions for compact flanges. Series A flanges have larger bolt circle diameters than Series B flanges.

This is to be noted that Series A and Series B flanges are not interchangeable. So, the user must take care of the compatibility issues that may arise by mistake. In most cases, flanged valves, equipment bolted between flanges, and flanged equipment are compatible with only one series of these flanges.

Difference between ASME B16.47 Series A and Series B Flanges

The following table provides the major differences between ASME B16.47 Series A and Series B flanges.

Sr. NoParameterASME B16.47 Series A FlangesASME B16.47 Series B Flanges
1OriginEarlier Series A flanges were known as MSS SP 44 flanges.These flanges were known as API 605 flanges.
2DimensionFlange Outer diameter, Bolt Circle Diameter, Flange Thickness, Bolt Diameter, etc. are larger for Series A Flanges for the same pressure rating class.B16.47 Series B flanges are compact as compared to series A flanges.
3StrengthASME B16.47 Series A flanges are comparatively stronger. Hence, can handle more external loading before leakage.Load bearing for the same pressure class is relatively less.
4Fastener RequirementThe quality requirement is less but bigger size. For example, as seen in Fig. 1, a 30-inch class 150 series A flange needs 28 bolts of 1-1/4 inch diameter.The quantity of fasteners is more. For example, a 30-inch class 150 Series B flange requires 44 bolts with a diameter of 3/4 inch.
5Ring type joint TypesAvailable from Class 300 through Class 900Does not exist.
6Pressure Class 75Not available for series A flangesAvailable for Series B flanges
7Flange WeightThe weight of ASME B16.47, series A flanges are more. So, they exert more load on piping supports.Weight is comparatively less
8CostMore expensive.cheaper.
9Industry UseMore frequently used. Used for critical applications.Less frequently used. Normally used for non-critical applications.
ASME B 16.47 Series A vs Series B

Dimensional Comparison for ASME B16.47 Series A and Series B Flanges

Refer to Fig. 1 which shows the comparative dimensions for a 30″ (150 class) Series A and Series B ASME B16.47 flanges.

ASME B 16.47 Series A vs Series B Flange Dimensions
Fig. 1: ASME B 16.47 Series A vs Series B Flange Dimensions

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Anup Kumar Dey

I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

6 thoughts on “Difference between ASME B16.47 Series A and Series B Flanges

  1. for nominal sizes greater than 60″, which class is followed?
    i have pipe diameter ranging upto 125″
    need to order the blind flanges accordingly.

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