Slip-On Flange Dimensions
Slides over the outside of the pipe and is fillet-welded both inside and outside. The bore is sized to the pipe OD rather than to a schedule, so a single slip-on fits any wall thickness in that NPS.
- Standard
- ASME B16.5
- Abbreviation
- SO
- Pressure classes
- 7
- Size range
- NPS 1/2 – NPS 24
- Typical service
- Low-pressure, non-cyclic utility and water service.
Dimensions by pressure class
Strengths
- Cheaper than weld neck and tolerant of small alignment errors
- One bore fits every schedule in the size
- Shorter than a weld neck, useful in tight spaces
Limitations
- Two fillet welds instead of one butt weld; harder to inspect
- Roughly a third of the fatigue life of a weld neck
Class 150 dimensions
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 | 3.5088.90 mm | 0.4411.18 mm | 2.3860.45 mm | 4 | 1/2 in | 1.3835.05 mm |
| NPS 3/4 | 3.8898.55 mm | 0.5012.70 mm | 2.7569.85 mm | 4 | 1/2 in | 1.6942.93 mm |
| NPS 1 | 4.25107.95 mm | 0.5614.22 mm | 3.1279.25 mm | 4 | 1/2 in | 2.0050.80 mm |
| NPS 1 1/4 | 4.62117.35 mm | 0.6215.75 mm | 3.5088.90 mm | 4 | 1/2 in | 2.5063.50 mm |
| NPS 1 1/2 | 5.00127.00 mm | 0.6917.53 mm | 3.8898.55 mm | 4 | 1/2 in | 2.8873.15 mm |
| NPS 2 | 6.00152.40 mm | 0.7519.05 mm | 4.75120.65 mm | 4 | 5/8 in | 3.6291.95 mm |
| NPS 2 1/2 | 7.00177.80 mm | 0.8822.35 mm | 5.50139.70 mm | 4 | 5/8 in | 4.12104.65 mm |
| NPS 3 | 7.50190.50 mm | 0.9423.88 mm | 6.00152.40 mm | 4 | 5/8 in | 5.00127.00 mm |
| NPS 3 1/2 | 8.50215.90 mm | 0.9423.88 mm | 7.00177.80 mm | 8 | 5/8 in | 5.50139.70 mm |
| NPS 4 | 9.00228.60 mm | 0.9423.88 mm | 7.50190.50 mm | 8 | 5/8 in | 6.19157.23 mm |
| NPS 5 | 10.00254.00 mm | 0.9423.88 mm | 8.50215.90 mm | 8 | 3/4 in | 7.31185.67 mm |
| NPS 6 | 11.00279.40 mm | 1.0025.40 mm | 9.50241.30 mm | 8 | 3/4 in | 8.50215.90 mm |
| NPS 8 | 13.50342.90 mm | 1.1228.45 mm | 11.75298.45 mm | 8 | 3/4 in | 10.62269.75 mm |
| NPS 10 | 16.00406.40 mm | 1.1930.23 mm | 14.25361.95 mm | 12 | 7/8 in | 12.75323.85 mm |
| NPS 12 | 19.00482.60 mm | 1.2531.75 mm | 17.00431.80 mm | 12 | 7/8 in | 15.00381.00 mm |
| NPS 14 | 21.00533.40 mm | 1.3835.05 mm | 18.75476.25 mm | 12 | 1 in | 16.25412.75 mm |
| NPS 16 | 23.50596.90 mm | 1.4436.58 mm | 21.25539.75 mm | 16 | 1 in | 18.50469.90 mm |
| NPS 18 | 25.00635.00 mm | 1.5639.62 mm | 22.75577.85 mm | 16 | 1 1/8 in | 21.00533.40 mm |
| NPS 20 | 27.50698.50 mm | 1.6942.93 mm | 25.00635.00 mm | 20 | 1 1/8 in | 23.00584.20 mm |
| NPS 24 | 32.00812.80 mm | 1.8847.75 mm | 29.50749.30 mm | 20 | 1 1/4 in | 27.25692.15 mm |
Higher classes are on the Class 300 page and above.
Common questions
When should I use a slip-on flange?
Low-pressure, non-cyclic utility and water service.
What pressure classes does a slip-on flange come in?
ASME B16.5 publishes the slip-on flange in Class 150, Class 300, Class 400, Class 600, Class 900, Class 1500 and Class 2500, in sizes NPS 1/2 through NPS 24. Above NPS 24 large-diameter flanges are covered by ASME B16.47 instead.
Does the flange face type change these dimensions?
The flange outside diameter, bolt circle and bolting are the same whatever the face. What changes is the facing itself and the flange thickness measurement: B16.5 thickness excludes the raised face, so a Class 300 raised-face flange is 0.06 in thicker overall than the tabulated figure. Ring-type joint flanges are grooved instead and are dimensioned separately.