ASME Flanges
American Society of Mechanical Engineers Pipe Flange Standards
What Are ASME Flanges?
ASME (American Society of Mechanical Engineers) develops and maintains the B16 series of standards that govern pipe flanges, fittings, and valves used in piping systems worldwide. ASME flange standards define dimensions, tolerances, materials, pressure-temperature ratings, and marking requirements. These standards are referenced by piping codes such as ASME B31.1 (Power Piping) and B31.3 (Process Piping).
ASME B16.5: The Core Flange Standard
Covers pipe flanges and flanged fittings from NPS 1/2 through NPS 24. Defines seven pressure classes (150, 300, 400, 600, 900, 1500, 2500). Specifies dimensions for all six standard flange types. Includes pressure-temperature rating tables for dozens of material groups.
This is the most frequently referenced flange standard in the industry.
ASME B16.47: Large Diameter Flanges
Covers flanges NPS 26 through 60. Two series: Series A (based on MSS SP-44) and Series B (based on API 605). Series A flanges have heavier construction. Series B flanges have more bolt holes and smaller bolt sizes.
Other ASME Flange Standards
- ASME B16.36 — Orifice Flanges
- ASME B16.1 — Gray Iron Flanges
- ASME B16.42 — Ductile Iron Flanges
- ASME B16.20 — Metallic Gaskets (ring joint, spiral wound)
- ASME B16.21 — Non-Metallic Flat Gaskets
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Pressure-Temperature Ratings
Every ASME flange has a maximum allowable working pressure that varies with temperature. These ratings are found in ASME B16.5 Table 2 (for each material group). As temperature increases, the allowable pressure decreases.
Engineers must verify that the selected flange class is adequate for both the design pressure AND design temperature.
Common ASME Flange Materials
- Material Group 1.1 — Carbon Steel (A105, A350 LF2)
- Group 1.5 — C-1/2Mo (A182 F1)
- Group 1.9-1.10 — Cr-Mo Alloys (A182 F11, F22)
- Group 2.1-2.3 — Austenitic Stainless (A182 F304, F316)
Related References
- ASME B16.5 — Pipe Flanges and Flanged Fittings standard
- Flange Dimensions — Dimensional data for all flange types
- Flange Types — Overview of all flange types
- Flange Torque — Bolt torque values for flanged connections
- ANSI Flanges — ANSI flange standards and specifications