ASME B16.5 is the standard most US buyers have in mind when they say pipe flanges. It sets dimensions, tolerances, marking and pressure-temperature ratings for flanges and flanged fittings in a defined size range.
What B16.5 covers
B16.5 applies to flanges and flanged fittings from NPS 1/2 through NPS 24. Larger flanges are covered by ASME B16.47. Related standards deal with gaskets, line blanks, weld ends and orifice flanges.
| Standard | Covers |
|---|---|
| ASME B16.5 | Pipe flanges and flanged fittings, NPS 1/2 to 24 |
| ASME B16.47 | Large-diameter steel flanges, NPS 26 to 60 (Series A and Series B) |
| ASME B16.48 | Line blanks: spectacle blinds, paddle blanks and paddle spacers |
| ASME B16.20 | Metallic gaskets: ring joint, spiral-wound and metal-jacketed |
| ASME B16.21 | Nonmetallic flat gaskets |
| ASME B16.25 | Buttwelding ends |
| ASME B16.36 | Orifice flanges |
Pressure classes
B16.5 defines seven classes: 150, 300, 400, 600, 900, 1500 and 2500. A class is a dimensional and rating designation, not a pressure in psi. Allowable pressure at a given temperature depends on the material group and the rating tables.
For copper nickel: the rating basis for a copper-nickel flange comes from the governing piping code and the project specification. Do not assume the allowable pressure from carbon-steel tables. Confirm the rating basis with your piping designer when you specify the class.
Flange types in B16.5
Face types
| Face type | Abbreviation | Typical use |
|---|---|---|
| Raised face | RF | Most common; gasket seats on the raised area |
| Flat face | FF | Mating with flat-faced equipment or cast components |
| Ring-type joint | RTJ | Higher-pressure joints using a metal ring gasket |
The standard also describes other facings such as male and female, and tongue and groove. When two flanges mate, the facings must be compatible. See RF vs RTJ flanges for the practical differences.
Dimensions, material and testing are separate things
B16.5 is a dimensional and rating standard. The material comes from an ASTM or ASME material specification, and testing and documentation come from your purchase order or project specification. Keeping these separate avoids confusion when you request a quotation.
Sizing a quotation
To quote a copper-nickel flange against B16.5 we need NPS, class, facing, flange type, alloy and quantity. For weld neck flanges we also need the pipe wall thickness or schedule. Send your requirement and we will confirm what is available.
FAQs
What size range does ASME B16.5 cover?
NPS 1/2 through NPS 24. ASME B16.47 covers larger sizes.
Is Class 150 the same as 150 psi?
No. Class is a designation. Allowable pressure depends on the material and temperature.
Does B16.5 cover copper nickel pressure ratings?
Confirm the rating basis for copper-nickel flanges with your piping designer and the governing code. It should not be read from carbon-steel tables.