ASME B16.5 vs B16.47
Two standards govern most flanges in the oil and gas, petrochemical, and power industries. Understanding when to use ASME B16.5 versus B16.47 is critical for procurement, engineering, and project planning.
Overview: Two Standards, Different Ranges
ASME B16.5 covers pipe flanges and flanged fittings from NPS 1/2" through NPS 24". It is the most commonly used flange standard in the world, covering pressure classes 150, 300, 600, 900, 1500, and 2500.
ASME B16.47 covers large-diameter steel flanges from NPS 26" through NPS 60". It was created to standardize the large flanges that were previously covered by MSS SP-44 and API 605. B16.47 has two series: Series A (formerly MSS SP-44) and Series B (formerly API 605).
Key Differences at a Glance
| Feature | ASME B16.5 | ASME B16.47 |
|---|---|---|
| Size Range | NPS 1/2" – 24" | NPS 26" – 60" |
| Pressure Classes | 150, 300, 600, 900, 1500, 2500 | 150, 300, 400, 600, 900 |
| Series | Single series | Series A & Series B |
| Flange Types | WN, SO, BL, SW, THD, LJ | WN, BL primarily |
| Facing | RF, FF, RTJ, LF, LM, LG, LT, LE | RF, RTJ primarily |
| Typical Use | General industrial piping | Large-bore pipelines, compressors, turbines |
B16.47 Series A vs Series B
Within B16.47, there are two distinct series with different dimensional requirements:
Series A (MSS SP-44)
- • Thicker, heavier flanges
- • Larger bolt circle diameter
- • More bolts, larger bolt diameter
- • Higher pressure capacity
- • Higher cost
- • Common in offshore, refinery, high-stress applications
Series B (API 605)
- • Thinner, lighter flanges
- • Smaller bolt circle diameter
- • Fewer bolts, smaller bolt diameter
- • Lower pressure capacity
- • Lower cost
- • Common in water treatment, HVAC, lower-stress applications
Important
Series A and Series B flanges are NOT interchangeable. They have different bolt circle diameters, bolt sizes, and flange thicknesses. Always verify which series is specified on drawings and RFQs.
When to Use Each Standard
Use ASME B16.5 When:
- • Pipe size is NPS 24" or smaller
- • You need slip-on, threaded, or socket weld flanges
- • Pressure class is 1500 or 2500
- • You need flat face (FF) or lap joint (LJ) flanges
- • General industrial piping, chemical plants, oil refineries
Use ASME B16.47 When:
- • Pipe size is NPS 26" or larger
- • Large-bore pipeline connections
- • Compressor and turbine inlet/outlet piping
- • Water treatment plants with large diameter piping
- • Power plant cooling water systems
The Overlap Zone: NPS 22" – 24"
There is a small overlap where both standards cover the same sizes. ASME B16.5 goes up to NPS 24", and B16.47 Series A starts at NPS 26" (though some manufacturers produce B16.47 flanges in NPS 22" and 24" as well).
In this overlap zone, B16.5 flanges are generally preferred because they offer more flange types (SO, SW, THD) and higher pressure classes. However, if the project specifies B16.47, follow the specification.
Common Mistakes to Avoid
Mixing Series A and Series B
Never mix Series A and Series B flanges in the same connection. The bolt patterns are different and they will not mate properly.
Assuming same pressure class = same dimensions
A Class 300 B16.5 flange and a Class 300 B16.47 flange have completely different dimensions. Pressure class numbers are not comparable across standards.
Using B16.5 flanges above NPS 24"
B16.5 does not cover sizes above NPS 24". For larger sizes, you must use B16.47 or industry-specific standards like AWWA C207.
Frequently Asked Questions
Can I replace a B16.47 Series A flange with Series B?▼
What is the largest flange size in ASME B16.5?▼
Which standard is more common in the oil and gas industry?▼
Are B16.47 flanges more expensive than B16.5?▼
Calculate Flange Weight by Standard
Use our free flange weight calculator with ASME B16.5 dimensional data for all pressure classes from 150 to 2500.