Weld Neck Flange Dimensions
A long tapered hub butt-welded to the pipe, so the flange bore matches the pipe bore exactly. The taper moves the stress concentration away from the flange face, which is why weld neck flanges are the standard choice for high-pressure, cyclic and high-temperature service.
- Standard
- ASME B16.5
- Abbreviation
- WN
- Pressure classes
- 7
- Size range
- NPS 1/2 – NPS 24
- Typical service
- High pressure, high temperature, cyclic loading, hydrogen and lethal service.
Dimensions by pressure class
Strengths
- Bore matches the pipe, so no turbulence or crevice at the joint
- Full-penetration butt weld is radiographable
- Best fatigue and thermal-shock performance of any B16.5 flange
Limitations
- Must be ordered to a specific schedule — the bore is machined to it
- Most expensive type, and the longest
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 weld neck flange?
High pressure, high temperature, cyclic loading, hydrogen and lethal service.
What pressure classes does a weld neck flange come in?
ASME B16.5 publishes the weld neck 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.