Views: 0 Author: Site Editor Publish Time: 2026-03-18 Origin: Site
WN flanges, also known as welding neck flanges, have a long, tapered hub that is used to be butt-welded directly to the pipe. Its primary purpose is to provide a strong, leak-proof, and reusable connection in a piping system, particularly in services involving high pressure, extreme temperatures, or cyclic loading.
This guide introduces a comprehensive technical analysis into WN flange dimensions, types, and weight specifications.
1. Superior Stress Distribution
The hallmark of the WN flange is its tapered hub. As the hub tapers toward the pipe's diameter, it provides reinforcement to the flange itself and transfers the stress to the pipe. This is particularly advantageous in environments prone to "line surge" or mechanical vibrations.
2. High Resistance to Fatigue
Because the connection is a butt weld, the internal bore of the flange can be machined to match the pipe's inside diameter exactly. This eliminates turbulence and erosion at the joint, significantly increasing the fatigue life of the piping system compared to slip-on or socket-weld flanges.
3. Durability Under Extreme Conditions
In our facility, we often manufacture WN flanges from advanced nickel alloys and stainless steels. These materials, combined with the WN design, allow the flange to operate reliably in cryogenic temperatures or high-heat environments where thermal expansion could otherwise cause joint failure.
4. Ease of Inspection
The butt-weld joint between a WN flange and a pipe is easily inspected via Radiographic Testing (RT) or Ultrasonic Testing (UT). This "full penetration" weld capability ensures that the integrity of the joint can be verified to the highest safety standards—a requirement in the oil and gas and nuclear industries.
Dimensional specifications for Weld Neck flanges from NPS 1/2 to NPS 24 are strictly governed by the ASME B16.5 standard. Below are comprehensive dimension tables for WN flanges in several common pressure classes, as derived from the ASME B16.5 standard.
Table 1: ASME B16.5 Class 150 WN Flange Dimensions
NPS | DN | Flange OD (O) mm | Thickness (tf) mm | Raised Face Dia. (R) mm | Hub Dia. (X) mm | Length thru Hub (Y) mm | Bolt Circle (W) mm | No. of Bolts | Bolt Hole Dia. (I) mm |
1/2 | 15 | 90 | 11.2 | 34.9 | 30 | 48 | 60.3 | 4 | 15.9 |
3/4 | 20 | 100 | 12.7 | 42.9 | 38 | 51 | 69.9 | 4 | 15.9 |
1 | 25 | 110 | 14.3 | 50.8 | 49 | 54 | 79.4 | 4 | 15.9 |
1 1/4 | 32 | 115 | 15.9 | 63.5 | 59 | 57 | 88.9 | 4 | 15.9 |
1 1/2 | 40 | 125 | 17.5 | 73.0 | 65 | 60 | 98.4 | 4 | 15.9 |
2 | 50 | 150 | 19.1 | 92.1 | 78 | 64 | 120.7 | 4 | 19.1 |
2 1/2 | 65 | 180 | 22.4 | 104.8 | 90 | 70 | 139.7 | 4 | 19.1 |
3 | 80 | 190 | 24.3 | 127.0 | 108 | 70 | 152.4 | 4 | 19.1 |
4 | 100 | 230 | 24.3 | 157.2 | 135 | 76 | 190.5 | 8 | 19.1 |
6 | 150 | 280 | 25.4 | 215.9 | 188 | 89 | 241.3 | 8 | 22.4 |
8 | 200 | 345 | 28.4 | 269.7 | 240 | 102 | 298.5 | 8 | 22.4 |
10 | 250 | 405 | 30.2 | 323.8 | 292 | 108 | 362.0 | 12 | 25.4 |
12 | 300 | 485 | 31.8 | 381.0 | 342 | 117 | 431.8 | 12 | 25.4 |
Table 2: ASME B16.5 Class 300 WN Flange Dimensions
NPS | DN | Flange OD (O) mm | Thickness (tf) mm | Raised Face Dia. (R) mm | Hub Dia. (X) mm | Length thru Hub (Y) mm | Bolt Circle (W) mm | No. of Bolts | Bolt Hole Dia. (I) mm |
1/2 | 15 | 95 | 12.7 | 34.9 | 38 | 51 | 66.7 | 4 | 15.9 |
3/4 | 20 | 115 | 14.3 | 42.9 | 48 | 56 | 82.6 | 4 | 19.1 |
1 | 25 | 125 | 15.9 | 50.8 | 54 | 60 | 88.9 | 4 | 19.1 |
1 1/4 | 32 | 135 | 17.5 | 63.5 | 64 | 64 | 98.4 | 4 | 19.1 |
1 1/2 | 40 | 155 | 19.1 | 73.0 | 70 | 67 | 114.3 | 4 | 22.2 |
2 | 50 | 165 | 20.7 | 92.1 | 84 | 68 | 127.0 | 8 | 19.1 |
2 1/2 | 65 | 190 | 23.9 | 104.8 | 100 | 75 | 149.2 | 8 | 22.2 |
3 | 80 | 210 | 27.0 | 127.0 | 117 | 78 | 168.3 | 8 | 22.2 |
4 | 100 | 255 | 30.2 | 157.2 | 146 | 84 | 200.0 | 8 | 22.2 |
6 | 150 | 320 | 35.0 | 215.9 | 206 | 97 | 269.9 | 12 | 22.2 |
8 | 200 | 380 | 39.7 | 269.9 | 260 | 110 | 330.2 | 12 | 25.4 |
10 | 250 | 445 | 46.1 | 323.8 | 321 | 116 | 387.4 | 16 | 28.6 |
12 | 300 | 520 | 49.3 | 381.0 | 375 | 129 | 450.8 | 16 | 31.8 |
Table 3: ASME B16.5 Class 600 WN Flange Dimensions
NPS | DN | Flange OD (O) mm | Thickness (tf) mm | Raised Face Dia. (R) mm | Hub Dia. (X) mm | Length thru Hub (Y) mm | Bolt Circle (W) mm | No. of Bolts | Bolt Hole Dia. (I) mm |
1/2 | 15 | 95 | 14.2 | 34.9 | 38 | 51 | 66.5 | 4 | 15.7 |
3/4 | 20 | 118 | 15.7 | 42.9 | 48 | 57 | 82.6 | 4 | 19.1 |
1 | 25 | 124 | 17.5 | 50.8 | 54 | 62 | 88.9 | 4 | 19.1 |
1 1/2 | 40 | 155 | 22.4 | 73.2 | 70 | 73 | 114.3 | 4 | 22.4 |
2 | 50 | 165 | 25.4 | 92.1 | 84 | 84 | 127.0 | 8 | 19.1 |
3 | 80 | 210 | 31.8 | 127.0 | 117 | 100 | 168.1 | 8 | 22.4 |
4 | 100 | 273 | 38.1 | 157.2 | 146 | 114 | 215.9 | 8 | 25.4 |
6 | 150 | 356 | 47.8 | 215.9 | 206 | 140 | 292.1 | 12 | 28.4 |
8 | 200 | 419 | 55.6 | 269.7 | 260 | 162 | 349.3 | 12 | 31.8 |
10 | 250 | 508 | 63.5 | 323.8 | 321 | 184 | 431.8 | 16 | 35.1 |
12 | 300 | 559 | 66.5 | 381.0 | 375 | 200 | 489.0 | 20 | 35.1 |
Note: The flange bore (B) is specified by the purchaser to match the pipe's inside diameter, which is dependent on the pipe schedule. The raised face height is typically 2 mm (1/16 in) for Class 150 and 300, and 6.4 mm (1/4 in) for Class 600 and above, and is included in the flange thickness (tf).
Weld Neck flanges are categorized by their connection method and face type.
1. Raised Face (RF) Weld Neck Flanges
The Raised Face (RF) flange is the most common type used in process plant applications, featuring a small additional thickness on the flange face to concentrate pressure on a smaller gasket area.
By raising the gasket surface above the bolting circle face, this type ensures that more clamping force is applied to the gasket. In our stainless steel production line, RF flanges are typically finished with a serrated surface to "bite" into the gasket for a superior seal.
2. Flat Face (FF) Weld Neck Flanges
Flat Face (FF) flanges have a machining surface that is in the same plane as the bolting circle face and are primarily used with cast iron or brittle equipment.
The objective of an FF flange is to avoid the "bending moment" that occurs when bolting RF flanges together. If you are connecting a stainless steel WN flange to a cast iron pump or valve, an FF flange is mandatory to prevent cracking the cast iron component.
3. Ring Type Joint (RTJ) Weld Neck Flanges
RTJ flanges feature a deep groove machined into their face, designed to house a metal ring gasket that creates a "metal-to-metal" seal under high pressure.
These are the heavyweights of the industry. Typically found in Class 600 and higher, RTJ WN flanges are used in oilfield drilling and high-pressure gas systems. The integrity of the seal increases as the internal pressure increases, making them incredibly reliable in volatile conditions.
4. Long Weld Neck (LWN) Flanges
Long Weld Neck flanges feature a straight, heavy-walled barrel instead of a tapered hub, functioning essentially as a nozzle for pressure vessels or tanks.
Because the "neck" is much longer and thicker than a standard WN flange, it provides extra reinforcement and eliminates the need for a separate piece of pipe when connecting a flange directly to a vessel wall.
5. Reducing Weld Neck Flanges
Reducing WN flanges are used to change the pipe size at a flange connection point without the need for a separate concentric reducer.
This type is highly efficient for saving space in tight manifold configurations. The hub of the flange matches the larger pipe diameter, while the bore and the face transition to a smaller size.
The weight varies significantly based on the material density; therefore, the chart below provides weights based on Stainless Steel 304/316. The following table lists approximate weights for common sizes in Class 150 and Class 300 ratings.
NPS (inch) | Class 150 Weight (kg) | Class 150 Weight (lbs) | Class 300 Weight (kg) | Class 300 Weight (lbs) |
1/2 | 0.5 | 1.1 | 0.7 | 1.5 |
1 | 0.8 | 1.8 | 1.1 | 2.4 |
2 | 1.6 | 3.5 | 2.3 | 5.1 |
4 | 3.9 | 8.6 | 5.8 | 12.8 |
6 | 6.8 | 15.0 | 10.5 | 23.1 |
8 | 10.5 | 23.1 | 16.8 | 37.0 |
10 | 15.2 | 33.5 | 24.5 | 54.0 |
12 | 21.8 | 48.1 | 35.0 | 77.2 |
14 | 27.5 | 60.6 | 45.2 | 99.6 |
16 | 35.0 | 77.2 | 58.5 | 129.0 |
18 | 43.5 | 95.9 | 72.0 | 158.7 |
20 | 54.0 | 119.0 | 88.5 | 195.1 |
24 | 78.5 | 173.1 | 125.0 | 275.6 |
Note: Weights are theoretical and based on stainless steel density. Actual weights may vary slightly due to manufacturing tolerances and material mill variations.
Oil and Gas Industry
In upstream exploration and downstream refining, fluids are often under extreme pressure. WN flanges, particularly in duplex or super-duplex stainless steel, are used in wellhead equipment and high-pressure manifolds where they must resist both internal pressure and external corrosive environments.
Petrochemical and Chemical Processing
In systems handling corrosive acids or volatile organic compounds, the leak-proof nature of the WN butt-weld connection is essential. Using Hastelloy C276 for the WN flange ensures that the connection point is as corrosion-resistant as the rest of the piping system.
Power Generation
In both nuclear and fossil fuel power plants, steam lines operate at temperatures exceeding 500℃. The WN flange’s ability to handle thermal expansion and contraction without developing leaks makes it the standard for high-pressure steam distribution.
Desalination and Marine Applications
For offshore platforms and desalination plants, the mechanical strength of the WN flange is coupled with high-alloy materials (like 6-Moly stainless steel) to resist chloride-induced stress corrosion cracking and pitting.
We offer full traceability, material test certificates, and custom machining to meet your specifications.
