Dimensional standard
ASME B16.5
Pipe Flanges and Flanged Fittings (NPS 1/2 through NPS 24)
ASME B16.5 is the dimensional standard most commonly referenced for pipe flanges and flanged fittings in sizes NPS 1/2 to NPS 24. It defines flange types, pressure classes, facings, bolting patterns and marking requirements.
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What it covers
- Sizes NPS 1/2 through NPS 24 (DN 15 to DN 600).
- Pressure classes 150, 300, 400, 600, 900, 1500 and 2500.
- Flange types including weld neck, slip-on, socket weld, threaded, lap joint and blind.
- Facing types such as raised face (RF), flat face (FF) and ring-type joint (RTJ).
Practical notes
Points to specify
- Flange outside diameter, thickness, bolt circle diameter, number of bolts and bolt hole size are fixed per size and class.
- Pressure–temperature ratings depend on the material group, so the same class rating carries different allowable pressures for different materials.
- Larger flanges above NPS 24 are normally referenced to ASME B16.47 Series A or Series B instead.
Common questions about ASME B16.5
- What sizes does ASME B16.5 cover?
- NPS 1/2 through NPS 24. Above NPS 24, flanges are usually referenced to ASME B16.47.
- Does the class number mean the pressure rating in psi?
- No. Class 150, 300 and so on are rating designations. The allowable working pressure at a given temperature comes from the pressure–temperature tables for the specific material group.
- Which flange types can Omegha Steel quote to ASME B16.5?
- Weld neck, slip-on, socket weld, threaded, lap joint and blind flanges. Sizes, class, facing and material are confirmed against your enquiry before quotation.
More references
General guidance only. Work from the current published edition of the standard and your project specification; sizes, grades, classes and documentation are confirmed per enquiry.