What is ASME B16.5 Standard?
ASME B16.5 is the most widely adopted international standard covering pipe flanges and flanged fittings for industrial piping systems. It defines standardized dimensions, pressure-temperature ratings, materials, tolerances, and testing requirements for flanges ranging from NPS 1/2” to 24”.
Compliance with ASME B16.5 guarantees interchangeability, structural safety, and consistent performance across global industries. This standard ensures that flanges from different manufacturers can be safely connected and used together in the same piping system.
Types of ASME B16.5 Flanges
ASME B16.5 classifies flanges into several main types to suit different connection methods and service conditions:
- Weld Neck Flanges
- Slip-On Flanges
- Blind Flanges
- Socket Weld Flanges
- Lap Joint Flanges
- Threaded Flanges
Each type serves specific applications, among them weld neck flanges are widely recognized as the most reliable flanges for high-pressure, high-temperature, and critical service environments.
ASME B16.5 Flange Pressure Ratings
Pressure classes are one of the most important parameters of ASME B16.5 flanges. They represent the maximum allowable working pressure under designated temperature conditions.
The standard pressure ratings include:
- Class 150
- Class 300
- Class 600
- Class 900
- Class 1500
- Class 2500
Higher pressure classes require thicker bodies, larger bolt circles, and stronger structural design to withstand extreme operating pressures and temperatures.
ASME B16.5 Weld Neck Flange
An ASME B16.5 weld neck flange, commonly abbreviated as WN flange, is distinguished by its long, tapered hub that provides a smooth transition from the flange to the pipe wall. This hub is welded directly to the pipe, creating an extremely strong and durable joint.
The design effectively reduces stress concentration, improves flow characteristics, and enhances resistance to vibration, fatigue, and thermal cycling. For these reasons, weld neck flanges are widely used in the most demanding and critical piping systems worldwide.
Besides, ASME B16.5 weld neck flanges are available in several common sealing face types to suit different sealing requirements. They are: Raised Face (RF), Ring Type Joint (RTJ), Flat Face (FF), Tongue and Groove (T&G), and Male and Female (M&F). Among these, RF is the most popular for general service, while RTJ is typically used for high-pressure and high-temperature applications.
Key Dimension Terms Explained
To accurately use flange dimension charts, it is essential to understand the following terms:
- NPS: Nominal Pipe Size
- OD: Outside Diameter of the flange
- BCD: Bolt Circle Diameter
- Hub Dia: Hub diameter at the welding end
- Bore: Inner diameter matching the pipe schedule
- Flange Thk: Flange thickness
- RF Height: Raised Face height for sealing performance
All these dimensions are strictly defined under the ASME B16.5 standard.
ASME B16.5 WN Flange Dimensions Class 150
Class 150 is the most commonly used pressure rating for general industrial applications, offering an excellent balance of performance, cost, and ease of installation.
Below is the standard dimension table for ASME B16.5 Class 150 weld neck flanges:
NPS 1/2-4
| NPS | A | B | C | D | E | F | G | H | I | J |
| inch | inch | inch | inch | inch | inch | inch | No. of Holes | inch | inch | |
| mm | mm | mm | mm | mm | mm | mm | mm | mm | ||
| 1/2 | 3.500 | 0.620 | 0.440 | 1.880 | 0.840 | 1.190 | 1.380 | 4 | 0.620 | 2.380 |
| 88.90 | 15.70 | 11.20 | 47.80 | 21.30 | 30.20 | 35.00 | 15.70 | 60.45 | ||
| 3/4 | 3.880 | 0.820 | 0.500 | 2.060 | 1.050 | 1.500 | 1.690 | 4 | 0.620 | 2.750 |
| 98.60 | 20.80 | 12.70 | 52.30 | 26.70 | 38.10 | 42.90 | 15.70 | 69.85 | ||
| 1 | 4.250 | 1.050 | 0.560 | 2.190 | 1.320 | 1.940 | 2.000 | 4 | 0.620 | 3.120 |
| 108.0 | 26.70 | 14.20 | 55.60 | 33.50 | 49.30 | 50.80 | 15.70 | 79.25 | ||
| 1-1/4 | 4.620 | 1.380 | 0.620 | 2.250 | 1.660 | 2.310 | 2.550 | 4 | 0.620 | 3.500 |
| 117.3 | 35.10 | 15.70 | 57.15 | 42.20 | 58.70 | 63.50 | 15.70 | 88.90 | ||
| 1-1/2 | 5.000 | 1.610 | 0.690 | 2.440 | 1.900 | 2.560 | 2.880 | 4 | 0.620 | 3.880 |
| 127.0 | 40.90 | 17.50 | 62.00 | 48.30 | 65.00 | 73.15 | 15.70 | 98.60 | ||
| 2 | 6.000 | 2.070 | 0.750 | 2.500 | 2.380 | 3.060 | 3.620 | 4 | 0.750 | 4.750 |
| 152.4 | 52.60 | 19.10 | 63.50 | 60.45 | 77.70 | 91.90 | 19.10 | 120.7 | ||
| 2-1/2 | 7.000 | 2.470 | 0.880 | 2.750 | 2.880 | 3.560 | 4.120 | 4 | 0.750 | 5.500 |
| 177.8 | 62.70 | 22.40 | 69.85 | 73.15 | 90.40 | 104.6 | 19.10 | 139.7 | ||
| 3 | 7.500 | 3.070 | 0.940 | 2.750 | 3.500 | 4.250 | 5.000 | 4 | 0.750 | 6.000 |
| 190.5 | 78.00 | 23.90 | 69.85 | 88.90 | 108.0 | 127.0 | 19.10 | 152.4 | ||
| 3-1/2 | 8.500 | 3.550 | 0.940 | 2.810 | 4.000 | 4.810 | 5.500 | 8 | 0.750 | 7.000 |
| 215.9 | 90.20 | 23.90 | 71.40 | 101.6 | 122.2 | 139.7 | 19.10 | 177.8 | ||
| 4 | 9.000 | 4.030 | 0.940 | 3.000 | 4.500 | 5.310 | 6.190 | 8 | 0.750 | 7.500 |
| 228.6 | 102.4 | 23.90 | 76.20 | 114.3 | 134.9 | 157.2 | 19.10 | 190.5 |
NPS 5-24
| NPS | A | B | C | D | E | F | G | H | I | J |
| inch | inch | inch | inch | inch | inch | inch | No. of Holes | inch | inch | |
| mm | mm | mm | mm | mm | mm | mm | mm | mm | ||
| 5 | 10.00 | 5.050 | 0.940 | 3.500 | 5.560 | 6.440 | 7.310 | 8 | 0.880 | 8.500 |
| 254.0 | 128.3 | 23.90 | 88.90 | 141.2 | 163.6 | 185.7 | 22.40 | 215.9 | ||
| 6 | 11.00 | 6.070 | 1.000 | 3.500 | 6.630 | 7.560 | 8.500 | 8 | 0.880 | 9.500 |
| 279.4 | 154.2 | 25.4 | 88.90 | 168.4 | 192.0 | 215.9 | 22.40 | 241.3 | ||
| 8 | 13.50 | 7.980 | 1.120 | 4.000 | 8.630 | 9.690 | 10.62 | 8 | 0.880 | 11.75 |
| 342.9 | 202.7 | 28.40 | 101.6 | 219.2 | 246.1 | 269.7 | 22.40 | 298.5 | ||
| 10 | 16.00 | 10.02 | 1.190 | 4.000 | 10.75 | 12.00 | 12.75 | 12 | 1.000 | 14.25 |
| 406.4 | 254.5 | 30.20 | 101.6 | 273.0 | 304.8 | 323.8 | 25.40 | 362.0 | ||
| 12 | 19.00 | 12.00 | 1.250 | 4.500 | 12.75 | 14.38 | 15.00 | 12 | 1.000 | 17.00 |
| 482.6 | 304.8 | 31.75 | 114.3 | 323.8 | 365.3 | 381.0 | 25.40 | 431.8 | ||
| 14 | 21.00 | 1.380 | 5.000 | 14.00 | 15.75 | 16.25 | 12 | 1.120 | 18.75 | |
| 533.4 | 35.10 | 127.0 | 355.6 | 400.1 | 412.7 | 28.40 | 476.3 | |||
| 16 | 23.50 | 1.440 | 5.000 | 16.00 | 18.00 | 18.50 | 16 | 1.120 | 21.25 | |
| 596.9 | 36.60 | 127.0 | 406.4 | 475.2 | 469.9 | 28.40 | 539.8 | |||
| 18 | 25.00 | 1.560 | 5.500 | 18.00 | 19.88 | 21.00 | 16 | 1.250 | 22.75 | |
| 635.0 | 39.60 | 139.7 | 457.2 | 505.0 | 533.4 | 31.75 | 577.9 | |||
| 20 | 27.50 | 1.690 | 5.690 | 20.00 | 22.00 | 23.00 | 20 | 1.250 | 25.00 | |
| 698.5 | 42.90 | 144.5 | 508.0 | 558.8 | 584.2 | 31.75 | 635 | |||
| 24 | 32.00 | 1.880 | 6.000 | 24.00 | 26.12 | 27.25 | 20 | 1.380 | 29.50 | |
| 812.8 | 47.80 | 152.4 | 609.6 | 663.4 | 692.1 | 35.10 | 749.3 |
All dimensions are for reference only. Slight tolerances may vary between manufacturers.
ASME B16.5 WN Flange Weight Chart for All Classes
Flange weight is critical for quotation, shipping cost calculation, container loading, and structural design. Weight increases significantly with pressure class due to thicker material and larger dimensions.
Below is the approximate weight chart for ASME B16.5 weld neck flanges across all standard pressure classes, based on carbon steel material:
| NPS | 150LB | 300LB | 400LB | 600LB | 900LB | 1500LB | 2500LB |
| 1/2 | 0.91 | 0.91 | 1.36 | 1.36 | 3.18 | 3.18 | 3.63 |
| 3/4 | 0.91 | 1.36 | 1.59 | 1.59 | 3.18 | 3.18 | 4.09 |
| 1 | 1.14 | 1.82 | 1.82 | 1.82 | 3.86 | 3.86 | 5.9 |
| 1 1/4 | 1.14 | 2.27 | 2.5 | 2.5 | 4.54 | 4.54 | 9.08 |
| 1 1/2 | 1.81 | 3.18 | 3.63 | 3.63 | 6.36 | 6.36 | 12.71 |
| 2 | 2.72 | 3.63 | 4.54 | 4.54 | 10.9 | 10.9 | 19.07 |
| 2 1/2 | 4.54 | 5.45 | 6.36 | 6.36 | 13.17 | 16.34 | 23.61 |
| 3 | 5.22 | 8.17 | 8.17 | 8.17 | 16.34 | 21.79 | 42.68 |
| 3 1/2 | 5.45 | 9.1 | 11.8 | 11.8 | / | / | / |
| 4 | 7.49 | 12.03 | 13.62 | 16.8 | 23.15 | 31.33 | 66.28 |
| 5 | 9.53 | 16.34 | 17.71 | 30.87 | 39.04 | 59.93 | 110.78 |
| 6 | 11.8 | 20.43 | 22.45 | 33.14 | 49.94 | 74.46 | 171.61 |
| 8 | 19.07 | 31.33 | 35.41 | 50.85 | 84.9 | 123.94 | 261.5 |
| 10 | 24.52 | 45.4 | 49.94 | 85.81 | 121.67 | 206.12 | 484.87 |
| 12 | 39.95 | 64.47 | 72.64 | 102.6 | 168.89 | 313.26 | 730.03 |
| 14 | 51.76 | 93.52 | 105.78 | 157.54 | 255.15 | / | / |
| 16 | 64.47 | 113.05 | 133.78 | 218.97 | 310.99 | / | / |
| 18 | 74.9 | 138.92 | 163.44 | 251.97 | 419.5 | / | / |
| 20 | 89.44 | 167.53 | 202.03 | 313.26 | 528.46 | / | / |
| 24 | 121.67 | 235.63 | 290.56 | 443.56 | 956.58 | / | / |
Weights are approximate. Actual weight may differ by material, production process, and manufacturer.
Advantages of ASME B16.5 WN Flange
Weld neck flanges provide outstanding advantages over other flange types:
- Extremely high structural strength and long service life
- Excellent resistance to high pressure, high temperature, and vibration
- Smooth bore design reduces flow resistance and turbulence
- Low stress concentration at the welded joint
- Outstanding performance under thermal cycling and fatigue loads
- Suitable for critical, hazardous, and heavy-duty applications
- Fully compatible with all standard ASME B16.5 materials and pressure classes
These benefits make weld neck flanges the top choice for critical piping systems.
Common Materials for ASME B16.5 Weld Neck Flange
ASME B16.5 weld neck flanges are manufactured in a full range of materials to meet different working conditions:
- A105: Carbon steel for general-purpose applications
- A350 LF2: Carbon steel for low-temperature service
- A182 F304 / F316: Stainless steel for corrosion resistance
- A182 F11, F22, F91: Alloy steel for high-temperature and high-pressure service
Material selection depends on medium, temperature, pressure, and environmental requirements.
Typical Applications
ASME B16.5 weld neck flanges are used across nearly all major industries:
- Oil and gas gathering and transmission pipelines
- Petroleum refineries and petrochemical plants
- Thermal power and nuclear power facilities
- Chemical processing and pharmaceutical systems
- High-pressure boiler and utility piping
- Water treatment, metallurgy, and marine applications
They are the preferred flange type for projects that demand safety, stability, and long-term reliability.
Conclusion
ASME B16.5 remains the global foundation standard that ensures safety, compatibility, and performance for industrial pipe flanges. Among all flange designs, the weld neck flange represents the highest level of structural integrity, sealing reliability, and versatility for extreme working conditions.
Accurate understanding of dimensions, pressure ratings, and weight data is essential for proper flange selection, cost control, system safety, and long-term operational stability. Adhering to ASME B16.5 standards helps minimize risks, improve interchangeability, and ensure consistent performance across entire piping systems.
For customized flange solutions, precise dimensional data, optimized material selection, detailed weight lists, test reports, or formal quotations tailored to your project requirements, we recommend working with a qualified and experienced ASME B16.5 flange manufacturer. Professional support ensures full compliance with industry standards and project specifications.