Article
For most piping, ASME B16.5 is the flange standard. But when a line goes above 24", B16.5 stops and ASME B16.47 takes over. B16.47 has two series that look similar and are not interchangeable, which is a common source of costly mistakes.
Size ranges
| Standard | Sizes | Classes |
|---|---|---|
| ASME B16.5 | NPS 1/2" to 24" | 150, 300, 400, 600, 900, 1500, 2500 |
| ASME B16.47 | NPS 26" to 60" | Series A: 150–900; Series B: 75–900 |
Series A and Series B
- Series A – based on the former MSS SP-44 standard. Heavier flanges with fewer, larger bolts. Common in process plants and pipelines.
- Series B – based on the former API 605 standard. Lighter and more compact, with more, smaller bolts.
For the same size and class, the outside diameter, bolt circle, bolt count and bolt size differ between the series. A Series A flange will not bolt to a Series B flange.
Why the series must be stated
An enquiry for "30 inch Class 150 weld neck flange" is incomplete. The supplier must know Series A or Series B, and the mating equipment, such as a valve or vessel nozzle, must use the same series. If you are replacing an existing flange, measure the OD, bolt circle and number of bolts to identify it.
Blind flanges and other types
B16.47 covers weld neck and blind flanges. Slip-on, lap joint and other types above 24" are usually made to MSS SP-44 tables or custom drawings, and need to be agreed with the supplier.
A complete description
Weld Neck Flange 30" Class 150 RF, ASME B16.47 Series A, bore to 12.7 mm wall, ASTM A182 F304L – 2 nos
Frequently asked questions
What standard covers flanges above 24 inch?
ASME B16.47 covers NPS 26" to 60" flanges in Series A and Series B.
Are Series A and Series B flanges interchangeable?
No. They have different outside diameters, bolt circles and bolt patterns.
Which series is heavier?
Series A (from MSS SP-44) is generally heavier than Series B (from API 605).
Key takeaways
- B16.5 covers up to 24"; B16.47 covers 26" to 60".
- Always state Series A or Series B for large flanges.
- Series A and B are not interchangeable.
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