ASME B16.5 Class 150 — NPS 3/4" Flange Dimensions
An ASME B16.5 Class 150 NPS 3/4" flange (DN 20) is a forged steel pipe flange rated to19.6 bar (285 psi) at ambient temperature for Group 1.1 carbon steel. It is used in process piping systems wherever the design pressure and temperature fall within the Class 150 pressure-temperature rating envelope defined in ASME B16.5.
| Dimension | Imperial (in) | Metric (mm) |
|---|---|---|
| Flange OD | 3.88" | 98.6 mm |
| Bolt Circle Diameter (BCD) | 2.75" | 69.8 mm |
| Number of Bolt Holes | 4 | — |
| Bolt Hole Diameter | 0.62" | 15.7 mm |
| Bolt Size (stud) | 1/2" | 12.7 mm |
| Raised Face OD | 1.69" | 42.9 mm |
| Minimum Thickness | 0.50" | 12.7 mm |
| Approx. Weight — Weld Neck (kg) | 1.8 kg | — |
Disclaimer: These dimensions are provided for reference only. Always verify against the current edition of ASME B16.5 before using in engineering calculations, fabrication drawings, or procurement documents.
Common Materials
Class 150 NPS 3/4" flanges are typically carbon steel ASTM A105 (forged) or stainless steel ASTM A182 F304 / F316L. For elevated temperatures above 340 °C (650 °F), chrome-moly grades such as A182 F11 or F22 are specified. Confirm the material group against the ASME B16.5 pressure-temperature tables for your design conditions. Use the Flange Weight Calculator to estimate weights for different materials and flange types.
Frequently Asked Questions
What is an ASME B16.5 Class 150 NPS 3/4" flange?
A forged steel pipe flange conforming to ASME B16.5, NPS 3/4" (DN 20), pressure class 150. The flange OD is 3.88" (98.6 mm) with 4 bolt holes on a 2.75" bolt circle. It is rated to approximately 19.6 bar (285 psi) at ambient for Group 1.1 carbon steel.
What material is a Class 150 NPS 3/4" flange?
Common materials include ASTM A105 (carbon steel, forged), ASTM A182 F304/F316L (stainless steel), and ASTM A182 F11/F22 (chrome-moly alloy for high-temperature service). The choice depends on the fluid service, maximum design temperature, and corrosion requirements.
How does Class 150 differ from Class 300 for NPS 3/4"?
Class 150 is rated to 19.6 bar (285 psi) at ambient, while Class 300 is rated to 51.1 bar (740 psi). The Class 300 flange for NPS 3/4" has a larger OD and heavier bolting to achieve the higher pressure rating. Always confirm the required class from the piping design specification before procurement.