The Difference Between ASME B16.47 Series A and Series B Flanges

ASME B16.47(Large Diameter Steel Flanges) is a standard for large diameter steel flanges sized from NPS 26 through NPS 60. ASME B16.47 standard covers pipe flanges in sizes 26” through 60” and in pressure class ratings 75, 150, 300, 400, 600, and 900. Then, ASME B16.47 is further divided into ASME B16.47 Series A and ASME B16.47 Series B flanges for Blinds and Weldnecks.  The latest version provides dimensions and ratings in both metric and inch units. The ASME B16.47 inherently incorporate MSS SP-44: Steel Pipeline Flanges and API 605: Large Diameter Carbon Steel Flanges. Therefore, the MSS SP-44 flanges are designated as ASME B16.47 Series A flanges, while API 605 flanges are designated as ASME B16.47 Series B flanges within this standard. Materials covered in this standard are as that in ASME B16.5 except for nickel alloys which means they share the same pressure-temperature chart for the selection of flange materials.

The designation formerly referred to as MSS SP-44 flanges are now considered ASME B16.47 Series A flanges, while API 605 flanges are now ASME B16.47 Series B flanges. Materials covered in this standard are the same as ASME B16.5 except for nickel alloys. Due to this, they share the same pressure-temperature chart for the selection of flange materials.

The Difference Between ASME B16.47 Series A and Series B Flanges

ASME B16.47 Series A flanges are thicker, heavier and stronger than their Series B counterparts. They also can often handle more external loading than Series B. Series A flanges tend to be more costly than Series B flanges. ASME B16.47 Series B flanges need more but smaller fasteners, such as bolts & nuts. They also usually have a smaller bolt circle diameter than Series A flanges. Generally, there is less flange movement after installation due to the smaller bolt circle diameter. Both Series A and B define weld neck flanges and blind flanges in raised face type. However, Series A defines ring type joint (RTJ) flanges from Class 300 through Class 900 within this standard while Series B does not.

Series A flanges are popular for new pipeline projects or equipment. Meanwhile, many choose Series B flanges for refurbishment or replacement jobs.

Conclusions

Standard weld neck, slip-on, blind, etc. flanges are covered by standard B16.5 for sizes up to 24″ nominal pipe. Sizes 26″ and bigger are covered by B16.47 series A or series B for weldneck and blind flanges. Series A flange is heavier, thicker and cost more whereas series B flange has more bolt holes and is lighter cheaper than series A. API605 flange and series B flanges are same thing.