ASME B16.5 vs B16.47: Flange Size Limits
ASME B16.5 and ASME B16.47 are the two ASME standards that define dimensions, tolerances, and pressure-temperature ratings for steel pipe flanges. The fundamental distinction is size range: B16.5 covers NPS 1/2 through NPS 24, while B16.47 covers NPS 26 through NPS 60 for large-diameter applications.
When Each Standard Applies
ASME B16.5 is the standard flange specification for the vast majority of process piping in refineries, chemical plants, power stations, and offshore platforms. It defines seven pressure classes (150 through 2500) and covers the most common flange types: weld neck, slip-on, blind, socket weld, threaded, and lap joint.
ASME B16.47 is used for large-diameter piping systems such as main headers, columns, heat exchangers, storage tank nozzles, and pipeline terminal connections where flange sizes exceed NPS 24. It includes two series: Series A (derived from MSS SP-44) and Series B (derived from API 605).
Specifications and Properties
| Feature | ASME B16.5 | ASME B16.47 |
|---|---|---|
| Size range | NPS 1/2 to NPS 24 | NPS 26 to NPS 60 |
| Pressure classes | 150, 300, 600, 900, 1500, 2500 | 75, 150, 300, 400, 600, 900 |
| Series | Single series | Series A (MSS SP-44) and Series B (API 605) |
| Flange types | WN, SO, BL, SW, THD, LJ | WN, BL (primarily) |
| Face types | RF, FF, RTJ | RF, RTJ |
| Pressure-temperature ratings | Table 2 (by material group) | Same methodology as B16.5 |
| Bolt hole pattern | Standard per NPS and class | Different between Series A and Series B |
| Series A vs B | N/A | Series A: larger OD, more bolts; Series B: compact, fewer bolts |
| Material groups | 1.1 through 3.17 | Same as B16.5 |
| Marking | Size, class, material, heat number | Size, class, series (A or B), material, heat number |
Comparison: Series A vs Series B (B16.47)
| Feature | Series A (MSS SP-44) | Series B (API 605) |
|---|---|---|
| Origin | MSS SP-44 | API 605 |
| Flange OD | Larger | Smaller (more compact) |
| Number of bolt holes | More | Fewer |
| Bolt diameter | Larger | Smaller |
| Hub profile | Longer hub | Shorter hub |
| Weight | Heavier | Lighter |
| Pressure integrity | Higher bolt load capacity | Adequate for rated pressure |
| Cost | Higher | Lower |
| Common application | High-integrity, critical services | General pipeline and tank nozzles |
Overlap at NPS 24
NPS 24 is covered by both B16.5 and B16.47. The B16.5 NPS 24 flange and the B16.47 NPS 24 flange (available in some pressure classes) have different dimensions. The project specification must clearly identify which standard applies at NPS 24 to avoid mismatch.
For flange rating tables and dimensional data, including B16.5 weld neck flange sizes and B16.47 large flange sizes, refer to the full guides.
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