The scope of ASME B16.5 standard
Applicable objects: Cast or forged flanges or flange parts (including blind plates and some reduced-diameter flanges).
The standard covers pressure grades: 150, 300, 400, 600, 900, 1500, and 2500 (but 2500 corresponds only to NPS ½ -12 ").
Built-in connection methods of flange types: weld neck, Slip-on, Socket-weld, thread, Lap joint, blind plate, etc.
The following is the main size information table of ASME B16.5 Class 150 and 300 flanges from NPS ½ "to 24", Including Outside Diameter (OD) and Pitch Circle Diameter PCD, Bolt Hole Diameter and Number of Bolt Holes.
ASME B16.5 Class 150 Flange Dimensions
Below is the size chart for ASME B16.5 Class 150 flanges from NPS ½″ to 24″.
| NPS (″) | Outside Diameter (OD) (″) | Pitch Circle Diameter (PCD) (″) | Bolt Hole Diameter (″) | Number of Bolt Holes |
| ½ | 3.50 | 2.38 | 0.62 | 4 |
| ¾ | 3.88 | 2.75 | 0.62 | 4 |
| 1 | 4.25 | 3.12 | 0.62 | 4 |
| 1¼ | 4.62 | 3.50 | 0.62 | 4 |
| 1½ | 5.00 | 3.88 | 0.62 | 4 |
| 2 | 6.00 | 4.75 | 0.75 | 4 |
| 2½ | 7.00 | 5.50 | 0.75 | 4 |
| 3 | 7.50 | 6.00 | 0.75 | 4 |
| 3½ | 8.50 | 7.00 | 0.75 | 8 |
| 4 | 9.00 | 7.50 | 0.75 | 8 |
| 5 | 10.00 | 8.50 | 0.88 | 8 |
| 6 | 11.00 | 9.50 | 0.88 | 8 |
| 8 | 13.50 | 11.75 | 0.88 | 8 |
| 10 | 16.00 | 14.25 | 1.00 | 12 |
| 12 | 19.00 | 17.00 | 1.00 | 12 |
| 14 | 21.00 | 18.75 | 1.12 | 12 |
| 16 | 23.50 | 21.25 | 1.12 | 16 |
| 18 | 25.00 | 22.75 | 1.25 | 16 |
| 20 | 27.50 | 25.00 | 1.25 | 20 |
| 24 | 32.00 | 29.50 | 1.38 | 20 |
ASME B16.5 Class 300 Flange Dimensions
Below is the size chart for ASME B16.5 Class 300 flanges from NPS ½″ to 24″.
| NPS (″) | Outside Diameter (OD) (″) | Pitch Circle Diameter (PCD) (″) | Bolt Hole Diameter (″) | Number of Bolt Holes |
| ½ | 3.75 | 2.62 | 0.62 | 4 |
| ¾ | 4.62 | 3.25 | 0.62 | 4 |
| 1 | 4.88 | 3.50 | 0.62 | 4 |
| 1¼ | 5.25 | 3.88 | 0.62 | 4 |
| 1½ | 6.12 | 4.50 | 0.75 | 4 |
| 2 | 6.50 | 5.00 | 0.75 | 8 |
| 2½ | 7.50 | 5.88 | 0.75 | 8 |
| 3 | 8.25 | 6.62 | 0.75 | 8 |
| 3½ | 9.00 | 7.25 | 0.88 | 8 |
| 4 | 10.00 | 7.88 | 0.88 | 8 |
| 5 | 11.00 | 9.25 | 0.88 | 8 |
| 6 | 12.50 | 10.62 | 0.88 | 12 |
| 8 | 15.00 | 13.00 | 0.88 | 12 |
| 10 | 17.50 | 15.25 | 1.00 | 16 |
| 12 | 20.50 | 17.75 | 1.00 | 20 |
| 14 | 23.00 | 20.25 | 1.12 | 20 |
| 16 | 25.50 | 22.50 | 1.12 | 20 |
| 18 | 28.00 | 24.75 | 1.25 | 20 |
| 20 | 30.50 | 27.00 | 1.25 | 24 |
| 24 | 34.00 | 30.50 | 1.38 | 24 |
Note: The number of bolt holes increases with the increase in size, and the smallest size is 4 holes.
Comparison of dimensions for each pressure rating
Class 150: Relatively thin, commonly used in standard industry.
Class 300: Thicker than 150, with enlarged bolt holes and hole circles.
Class 600/900: Heavier, more holes, and larger hole diameters.
Class1500/2500: Maximum thickness, only used for high pressure and within the diameter limit of NPS.
Design and selection suggestions
Selection sequence: Determine NPS → Select pressure rating → Select flange type → Check the corresponding size table.
Bolt matching: Ensure that the material and length of the bolts are consistent with the flange grade and surface type.
Material and pressure-temperature rated: For flanges of the same grade made of different materials, the working pressure varies with temperature.
Interface compatibility: Ensure that the surface type (RF/PF/RJ/TG) is consistent with that of the matching equipment to avoid leakage risks.