Class 900 Socket Weld Flange Dimensions
ASME B16.5 dimensions and bolting for the Class 900 socket weld flange, NPS 1/2 through NPS 24.
- Standard
- ASME B16.5
- Flange type
- Socket Weld Flange
- Pressure class
- Class 900
- Size range
- NPS 1/2 – NPS 24
- Raised face height
- 0.25 in (6.3 mm)
- Rating at 100 °F (A105)
- 2220 psig (153.1 bar)
Dimensions are given in inches, with the millimetre equivalent beneath in grey.
| Size | Flange OD | Thickness | Bolt circle | Bolts | Bolt dia. | Raised face OD |
|---|---|---|---|---|---|---|
| NPS 1/2 | 4.75120.65 mm | 0.8822.35 mm | 3.2582.55 mm | 4 | 3/4 in | 1.3835.05 mm |
| NPS 3/4 | 5.12130.05 mm | 1.0025.40 mm | 3.5088.90 mm | 4 | 3/4 in | 1.6942.93 mm |
| NPS 1 | 5.88149.35 mm | 1.1228.45 mm | 4.00101.60 mm | 4 | 7/8 in | 2.0050.80 mm |
| NPS 1 1/4 | 6.25158.75 mm | 1.1228.45 mm | 4.38111.25 mm | 4 | 7/8 in | 2.5063.50 mm |
| NPS 1 1/2 | 7.00177.80 mm | 1.2531.75 mm | 4.88123.95 mm | 4 | 1 in | 2.8873.15 mm |
| NPS 2 | 8.50215.90 mm | 1.5038.10 mm | 6.50165.10 mm | 8 | 7/8 in | 3.6291.95 mm |
| NPS 2 1/2 | 9.62244.35 mm | 1.6241.15 mm | 7.50190.50 mm | 8 | 1 in | 4.12104.65 mm |
| NPS 3 | 9.50241.30 mm | 1.5038.10 mm | 7.50190.50 mm | 8 | 7/8 in | 5.00127.00 mm |
| NPS 4 | 11.50292.10 mm | 1.7544.45 mm | 9.25234.95 mm | 8 | 1 1/8 in | 6.19157.23 mm |
| NPS 5 | 13.75349.25 mm | 2.0050.80 mm | 11.00279.40 mm | 8 | 1 1/4 in | 7.31185.67 mm |
| NPS 6 | 15.00381.00 mm | 2.1955.63 mm | 12.50317.50 mm | 12 | 1 1/8 in | 8.50215.90 mm |
| NPS 8 | 18.50469.90 mm | 2.5063.50 mm | 15.50393.70 mm | 12 | 1 3/8 in | 10.62269.75 mm |
| NPS 10 | 21.50546.10 mm | 2.7569.85 mm | 18.50469.90 mm | 16 | 1 3/8 in | 12.75323.85 mm |
| NPS 12 | 24.00609.60 mm | 3.1279.25 mm | 21.00533.40 mm | 20 | 1 3/8 in | 15.00381.00 mm |
| NPS 14 | 25.25641.35 mm | 3.3885.85 mm | 22.00558.80 mm | 20 | 1 1/2 in | 16.25412.75 mm |
| NPS 16 | 27.75704.85 mm | 3.5088.90 mm | 24.25615.95 mm | 20 | 1 5/8 in | 18.50469.90 mm |
| NPS 18 | 31.00787.40 mm | 4.00101.60 mm | 27.00685.80 mm | 20 | 1 7/8 in | 21.00533.40 mm |
| NPS 20 | 33.75857.25 mm | 4.25107.95 mm | 29.50749.30 mm | 20 | 2 in | 23.00584.20 mm |
| NPS 24 | 41.001041.40 mm | 5.50139.70 mm | 35.50901.70 mm | 20 | 2 1/2 in | 27.25692.15 mm |
Flange thickness excludes the raised face. Bolt diameter is nominal; stud bolts are normally ASTM A193 B7 with A194 2H nuts.
ASME B16.5 publishes socket weld flanges through NPS 3 only. Rows above NPS 3 in the table are the corresponding slip-on dimensions, shown so the bolt pattern can still be looked up; a socket weld flange is not available in those sizes.
In NPS 1/2 through NPS 2 1/2 the Class 900 flange is dimensionally identical to the Class 1500 flange.
Common questions
How many bolts does a Class 900 socket weld flange use?
NPS 1/2 takes 4 × 3/4 in; NPS 3/4 takes 4 × 3/4 in; NPS 1 takes 4 × 7/8 in; NPS 1 1/4 takes 4 × 7/8 in; NPS 1 1/2 takes 4 × 1 in. Bolt count rises with size — see the table above for the full range.
What pressure is a Class 900 flange rated for?
Class is a designation, not a pressure. A Class 900 flange in A105 carbon steel is rated 2220 psig (153.1 bar) at 100 °F, and that rating falls as metal temperature rises. In stainless the same class starts lower at ambient but holds up far better in the heat — see the P-T rating tables.
Will a Class 900 flange bolt to a Class 150 flange?
No. Bolt circle diameter, bolt count and bolt size all change with class, so flanges of different classes in the same NPS will not mate. The only exceptions inside B16.5 are the deliberate ones the standard calls out, such as Class 400 sharing Class 600 dimensions in NPS 1/2 through 3 1/2.