This article provides a comprehensive comparison of ASME B16.47 Series A and Series B flanges to help you select the right flange for your application. It covers key differences in characteristics, fasteners, types, cost, usage, weight, pressure ratings, dimensions, and designations.

Highlight

• Series A flanges are larger, heavier and more expensive
• Series B flanges need more but smaller bolts
• Series A handle more load, Series B have less flange movement
• Series A for new piping, Series B for retrofits
• Series B lacks >300 pressure classes that Series A offers

Characteristics of ASME B16.47 Flanges Series A and B Flanges

Series A flanges are much heavier, thicker, and more robust than Series B flanges for the same pressure rating and size. This allows Series A flanges to withstand more external loading. The fastener quality requirement for Series A flanges is lower than for Series B. For example, a Class 150 Series A flange needs just 28 x 1-1/4 in bolts versus 44 x 3/4 in bolts for a Series B flange. Both types include blind and weld neck raised face flanges, but only Series A includes ring type joint flanges from Class 300-900.

Cost Comparison of ASME B16.47 Flanges

Series A flanges typically cost more than Series B flanges. In one industrial survey, the average cost of a 24 in, 300# Series A flange was $1,950 versus $1,275 for a Series B flange. The higher cost of Series A flanges reflects their larger size, weight, and material requirements compared to Series B flanges. However, the lower upfront cost of Series B flanges must be weighed against their potential limitations in durability and pressure handling.

Pressure Ratings and Sizes

Series A and B flanges are both available in sizes from NPS 24-60 in. Series B includes the unique 75 psi pressure class not offered in Series A. Series A includes higher pressure classes from 300-900 psi that are not available in Series B In December 2022, ASME proposed expanding B16.47 to include sizes up to NPS 100 for both Series A and B flanges.

Usage Guidance for ASME B16.47 Flanges

• Series A flanges are well-suited for new pipeline and equipment installations that require maximum strength.
• Series B flanges are often used for retrofit, replacement, and low-criticality piping where cost is a larger factor.
• Heavy industry and high temperature/pressure applications typically require Series A flanges.
• For standard water, air, or gas pipelines, Series B flanges may suffice at a lower cost.

Design and Dimensions

The larger size of Series A flanges results in a larger bolt circle diameter, thicker flange, wider outer diameter, and larger bolt diameters. The compact size of Series B flanges allows more bolts in a smaller space, but with less flange rigidity. In December 2022, ASME proposed adding oval welded neck flanges to B16.47 to improve flexibility.

Original Designations

Originally, Series A carbon steel flanges were known as MSS SP44 flanges. Series B flanges were originally designated as API 605 flanges. Over time, the ASME B16.47 specification has become the standard for large diameter steel flanges.

Conclusion

Selecting the right ASME B16.47 flange involves weighing factors like strength, cost, pressure class, pipeline criticality, and ease of installation. Series A flanges are strongest but cost more, while Series B trade some strength for smaller size and lower cost. Consider both versions for your application.