Blind Flange Dimensions
A solid disc with no bore, bolted on to close off a flanged opening. Blind flanges carry the highest stress of any flange type at a given class, because the full pressure acts across the whole unsupported disc.
- Standard
- ASME B16.5
- Abbreviation
- BL
- Pressure classes
- 7
- Size range
- NPS 1/2 – NPS 24
- Typical service
- Vessel and line closures, future tie-in points, pressure-test blanks.
Dimensions by pressure class
Strengths
- Closes a line while leaving it easy to reopen for inspection or tie-in
- Can be drilled and tapped later for a future branch
Limitations
- Highest bending stress of the six types at the same class
- Heavy in large sizes — a NPS 24 Class 600 blind is a lift
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 blind flange?
Vessel and line closures, future tie-in points, pressure-test blanks.
What pressure classes does a blind flange come in?
ASME B16.5 publishes the blind 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.