What Is ASME B16.5?
ASME B16.5 is the American National Standard covering pipe flanges and flanged fittings from NPS 1/2 through NPS 24, in pressure classes 150, 300, 400, 600, 900, 1500, and 2500. It defines dimensions, tolerances, materials, marking, testing, and pressure-temperature ratings for forged steel flanges including weld neck, slip-on, blind, socket weld, lap joint, and threaded types. Flanges NPS 26 and larger are covered by ASME B16.47.
Pressure-Temperature Ratings (Ambient Temperature, A105 Carbon Steel)
Maximum allowable working pressure at ambient temperature (Min. to 38°C) for Group 1.1 materials (e.g., A105) per Table 2-1.1:
| Pressure Class | Bar (SI) | Psi (US Customary) |
|---|---|---|
| Class 150 | 19.6 | 285 |
| Class 300 | 51.0 | 740 |
| Class 400 | 68.0 | 985 |
| Class 600 | 102.0 | 1,480 |
| Class 900 | 153.1 | 2,220 |
| Class 1500 | 255.1 | 3,705 |
| Class 2500 | 425.1 | 6,170 |
Ratings decrease as temperature rises. At 425°C the Class 150 rating for carbon steel drops below 6 bar — always consult the full table for your service temperature.
Material Temperature Limits
| Material | Standard Group | Temperature Range | Note |
|---|---|---|---|
| A105 (carbon steel) | 1.1 | -29°C to 425°C | Prolonged use above 427°C not recommended (graphitization) |
| F304 / F316 (stainless) | 2.2 / 2.3 | up to 538°C | Higher temperature rating group |
| A350 LF2 (low temp) | 1.1 | -46°C to 425°C | Low-temperature service |
Flange Types Covered
- Weld Neck (WN) — NPS 1/2–24, all classes; highest integrity, butt-welded
- Slip-On (SO) — NPS 1/2–24; fillet welded both sides
- Blind (BL) — NPS 1/2–24; closes piping ends
- Socket Weld (SW) — NPS 1/2–4 only; for small-bore high-pressure lines
- Lap Joint (LJ) — NPS 1/2–24; used with stub ends
- Threaded (TH) — NPS 1/2–24; for non-welded connections
Standards That Work With ASME B16.5
- ASME B16.47 — Large-Diameter Steel Flanges (NPS 26–60)
- Our Full Flange Range
- ASME B16.20 / B16.21 Gaskets for Flanged Joints
FAQ
What sizes does ASME B16.5 cover?
ASME B16.5 covers flanges and flanged fittings from NPS 1/2 through NPS 24. Larger sizes NPS 26 through 60 are covered by ASME B16.47.
What pressure classes are available?
Class 150, 300, 400, 600, 900, 1500, and 2500. Ratings are defined in Tables 2-1.1 through 2-3.19 by material group and temperature.
Can carbon steel A105 flanges be used above 425°C?
ASME B16.5 Note (1) to Table 2-1.1 advises against prolonged use of A105 above 427°C due to graphitization. For higher temperatures use stainless steel (F304/F316) or alloy materials.
Need ASME B16.5 Flanges for Your Project?
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