ASME B16.47-2025 · NPS 26–60
ASME B16.47 Series A vs Series B — large-diameter flanges
Above NPS 24 the American standard is ASME B16.47, published in two dimensionally different series: Series A (the former MSS SP-44 outline) and Series B (the former API 605 outline). The pressure class and nominal size can be identical while the outside diameter and bolt circle are not — so the series has to be on the purchase order.
This page compares the two outlines, then links to the full dimension tables and to the 2025 pressure–temperature, material and tolerance data.
Series A vs Series B at a glance
| Series A | Series B | |
|---|---|---|
| Origin | Former MSS SP-44 | Former API 605 |
| Outside diameter | Larger for the same size and class | More compact |
| Bolt pattern | More bolts, larger circle | Fewer bolts, smaller circle |
| Typical use | New large-bore piping, headers, vessel nozzles | Space- and weight-constrained layouts |
| Classes | 150, 300, 400, 600, 900 | 150, 300, 400, 600, 900 (Class 75 in 2025 tables) |
| Interchangeable | No | No |
ASME B16.47-2025 · Class 150
| Nominal size | Series A OD mm | Series B OD mm | OD difference mm | Series A bolt circle mm | Series B bolt circle mm | Series A bolts | Series B bolts | Series A thickness mm | Series B thickness mm |
|---|---|---|---|---|---|---|---|---|---|
| 26″ / DN 650 | 870 | 786 | 84 | 806.4 | 744.5 | 24 × Ø34.9 | 36 × Ø22.2 | 66.8 | 39.9 |
| 30″ / DN 750 | 984 | 887 | 97 | 914.4 | 846.1 | 28 × Ø34.9 | 44 × Ø22.2 | 73.2 | 42.9 |
| 36″ / DN 900 | 1168 | 1057 | 111 | 1085.8 | 1009.6 | 32 × Ø41.3 | 44 × Ø25.4 | 88.9 | 50.8 |
| 42″ / DN 1050 | 1346 | 1226 | 120 | 1257.3 | 1171.4 | 36 × Ø41.3 | 48 × Ø28.6 | 95.2 | 57.2 |
| 48″ / DN 1200 | 1511 | 1392 | 119 | 1422.4 | 1335.1 | 44 × Ø41.3 | 44 × Ø31.8 | 106.4 | 63.5 |
| 60″ / DN 1500 | 1854 | 1726 | 128 | 1759 | 1662.1 | 52 × Ø47.6 | 52 × Ø34.9 | 130.3 | 74.6 |
The two series are never interchangeable within the same nominal size and class. Dimensions are from the site's B16.47 datasets; verify against the edition named in your specification.
Dimension tables and reference data
ASME B16.47 Series A dimensions
NPS 26–60 · Classes 150–900
ASME B16.47 Series B dimensions
NPS 26–60 · Classes 150–900
Pressure–temperature ratings
Verified against ASME B16.47-2025
Material groups
Verified against ASME B16.47-2025
Tolerances
Verified against ASME B16.47-2025
Marking
Verified against ASME B16.47-2025
Edition changes
Verified against ASME B16.47-2025
B16.47 selection questions
Is ASME B16.47 Series A the same as MSS SP-44?
Series A reproduces the dimensions of the former MSS SP-44 large-diameter flange standard. When a project specifies MSS SP-44, a B16.47 Series A flange is dimensionally equivalent — but the purchase order should still name the standard and series so the inspection report matches.
Is Series B the same as API 605?
Series B reproduces the former API 605 dimensions, with a smaller outside diameter and a different bolt pattern than Series A for the same size and class. A Series B flange will not bolt to a Series A flange, so the series must always be stated.
Which series should I specify?
Specify the series of the mating flange or the project standard. Series A is the common choice for new large-bore piping; Series B is chosen where the smaller outside diameter reduces weight or fits a restricted space. If you are replacing an existing flange, measure the bolt circle and count the bolts before ordering.
What changed in ASME B16.47-2025?
The 2025 edition mostly revised table titles to show the unit system, revised pressure–temperature ratings for several material groups, and added a Group 2.13 duplex material table. The 2025 edition is the current edition; read the edition named in your specification. See the 2025 change summary on this site for the record numbers.