What Is ASME B16.47?

ASME B16.47 covers large-diameter steel flanges in sizes NPS 26 through NPS 60. It picks up where ASME B16.5 leaves off (NPS 24 is the upper limit of B16.5). The standard defines two distinct dimensional series—Series A and Series B—which are NOT interchangeable. This is the most common source of errors when ordering large flanges.

What ASME B16.47 Covers

Parameter	Detail
Size range	NPS 26 to NPS 60
Pressure classes	75, 150, 300, 400, 600, 900
Series	Series A (MSS SP-44) and Series B (API 605)
Flange types	WN, blind, slip-on (Series B only for SO)
Face types	RF, RTJ
Materials	Same ASTM material groups as B16.5
P/T ratings	Same tables as ASME B16.5
Origin	Series A from MSS SP-44; Series B from API 605

Series A vs Series B at a Glance

Feature	Series A (MSS SP-44)	Series B (API 605)
OD	Larger	Smaller
Thickness	Thicker	Thinner
Weight	Heavier	Lighter
Bolt circle	Larger	Smaller
Number of bolts	More	Fewer
Cost	Higher	Lower
Structural integrity	Higher	Adequate for most services
Common use	Refineries, petrochemical	Pipeline, storage tanks

Common Mistake

Series A and Series B flanges of the same NPS and class have different bolt patterns and ODs. They cannot be bolted together. Always confirm which series is specified in the piping class before ordering. Mixing series on a single line is a costly construction error.

Size and Class Coverage

NPS	Available Classes
26	150, 300, 400, 600, 900
28	150, 300, 400, 600, 900
30	150, 300, 400, 600, 900
32	150, 300, 400, 600, 900
34	150, 300, 400, 600
36	150, 300, 400, 600
38-42	150, 300
44-48	150, 300
50-60	150

Class 75 is available for some sizes in Series B only.

For full dimensional tables, see the ASME B16.47 flange dimensions reference page.

Pro Tip

Large-diameter flanges are typically custom-manufactured. Lead times of 12-20 weeks are common, and stock availability is limited to popular sizes (NPS 26, 30, 36 in Class 150 and 300). Plan procurement early in the project schedule.

Relationship to ASME B16.5

ASME B16.47 uses the same pressure-temperature rating tables as ASME B16.5. A Class 300 NPS 30 flange per B16.47 has the same allowable pressure at a given temperature as a Class 300 NPS 6 flange per B16.5—the ratings are independent of size. The standards also share the same material groups, gasket specifications, and facing requirements.

Read the full guide to flanges