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. No	Parameter	ASME B16.47 Series A Flanges	ASME B16.47 Series B Flanges
1	Origin	Earlier Series A flanges were known as MSS SP 44 flanges.	These flanges were known as API 605 flanges.
2	Dimension	Flange 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.
3	Strength	ASME 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.
4	Fastener Requirement	The 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.
5	Ring type joint Types	Available from Class 300 through Class 900	Does not exist.
6	Pressure Class 75	Not available for series A flanges	Available for Series B flanges
7	Flange Weight	The weight of ASME B16.47, series A flanges are more. So, they exert more load on piping supports.	Weight is comparatively less
8	Cost	More expensive.	cheaper.
9	Industry Use	More frequently used. Used for critical applications.	Less frequently used. Normally used for non-critical applications.

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.

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