Selecting the right ASME B16.5 weld neck flange is critical for high-temperature and high-pressure piping systems. This guide covers full flange dimension tables, pressure class selection logic, and practical engineering tips.
Why Choose ASME B16.5 Weld Neck Flange for High-Pressure Piping?
The weld neck flange (or welding neck flange) remains the top choice for severe service conditions. Its tapered hub design provides distinct advantages over slip-on or threaded types.
Superior stress distribution – The tapered hub minimizes stress concentration at the hub-to-pipe junction. This allows the flange to handle pressure surges and thermal cycling without fatigue failure.
Full weld joint integrity – Butt-welded connections enable 100% radiography or ultrasonic testing. Weld strength matches the pipe itself. This makes it ideal for flammable, toxic, or critical media.
Full standard compliance – All dimensions follow ASME B16.5-2020. Classes covered: 150, 300, 400, 600, 900, 1500, and 2500. Facing types include RF, FF, RTJ, T/G, and M/FM.
How to Select the Right ASME B16.5 Flange Pressure Class
Before reviewing ASME B16.5 weld neck flange dimensions, confirm the correct pressure class. The Class rating combines temperature and pressure limits. Higher Class means thicker walls, larger bolt circles, and greater strength.
ASME B16.5 Weld Neck Flange Class Selection Quick Reference
| Pressure Class | Typical Pressure Range | Recommended Applications |
| Class 150 | ≤ 2.0 MPa | Water, fire protection, low-pressure steam, air |
| Class 300 | ≤ 5.0 MPa | Refinery process lines, medium-pressure steam, chemicals |
| Class 400 | Medium-high | Intermediate duty between Class 300 and 600 |
| Class 600 | ≤ 10.0 MPa | Gas transmission, boiler feedwater, heat exchangers |
| Class 900 | Very high | Reactor connections, cryogenic, ultra-high steam |
| Class 1500 | Extra high | Nuclear primary loops, extreme temperature systems |
| Class 2500 | Extreme | Special reactors, military/defense piping |
Important: Always verify against material allowable stress at your design temperature. A105, F304, and F316 have different ratings at the same temperature. Contact our engineers for full temperature-pressure tables.
ASME B16.5 WN Flange Dimensions – Class 150 & Class 300
Below are the standard flange dimension tables for Class 150 and Class 300. All measurements conform to ASME B16.5.
Legend:
A = Flange outside diameter (OD)
C = Flange thickness at hub
E = Weld Neck OD (pipe OD)
J = Bolt circle diameter
H = Number of bolt holes
Weight = Approximate theoretical net weight
For sizes 14″ and larger: Hub length and neck thickness are buyer-specified. These depend on mating pipe wall thickness and welding procedure. We offer custom machining per your drawings.
Class 150 Weld Neck Flange Dimensions
| Nominal Pipe Size | A | B | C | D | E | F | G | H | I | J | Weight | |
| inch | mm | mm | mm | mm | mm | mm | mm | mm | Holes | mm | mm | kg / piece |
| 1/2 | 21.30 | 88.90 | 15.70 | 11.20 | 47.80 | 21.30 | 30.20 | 35.00 | 4 | 15.70 | 60.45 | 0.48 |
| 3/4 | 26.70 | 98.60 | 20.80 | 12.70 | 52.30 | 26.70 | 38.10 | 42.90 | 4 | 15.70 | 69.85 | 0.71 |
| 1 | 33.40 | 108.0 | 26.70 | 14.20 | 55.60 | 33.50 | 49.30 | 50.80 | 4 | 15.70 | 79.25 | 1.01 |
| 11/4 | 42.20 | 117.3 | 35.10 | 15.70 | 57.15 | 42.20 | 58.70 | 63.50 | 4 | 15.70 | 88.90 | 1.33 |
| 11/2 | 48.30 | 127.0 | 40.90 | 17.50 | 62.00 | 48.30 | 65.00 | 73.15 | 4 | 15.70 | 98.60 | 1.72 |
| 2 | 60.30 | 152.4 | 52.60 | 19.10 | 63.50 | 60.45 | 77.70 | 91.90 | 4 | 19.10 | 120.7 | 2.58 |
| 21/2 | 73.00 | 177.8 | 62.70 | 22.40 | 69.85 | 73. 15 | 90.4 | 104.6 | 4 | 19.10 | 139.7 | 4.11 |
| 3 | 88.90 | 190.5 | 78.00 | 23.90 | 69.85 | 88.90 | 108.0 | 127.0 | 4 | 19.10 | 152.4 | 4.92 |
| 31/2 | 101.6 | 215.9 | 90.20 | 23.90 | 71.40 | 101.6 | 122.2 | 139.7 | 8 | 19.10 | 177.8 | 6.08 |
| 4 | 114.3 | 228.6 | 102.40 | 23.90 | 76.20 | 114.3 | 134.9 | 157.2 | 8 | 19.10 | 190.5 | 6.84 |
| 5 | 141.3 | 254.0 | 128.3 | 23.90 | 88.90 | 141.2 | 163.6 | 185.7 | 8 | 22.40 | 215.9 | 8.56 |
| 6 | 168.3 | 279.4 | 154.2 | 25.40 | 88.90 | 168.4 | 192.0 | 215.9 | 8 | 22.40 | 241.3 | 10.6 |
| 8 | 219.1 | 342.9 | 202.7 | 28.40 | 101.6 | 219.2 | 246.1 | 269.7 | 8 | 22.40 | 298.5 | 17.6 |
| 10 | 273.0 | 406.4 | 254.5 | 30.20 | 101.6 | 273.0 | 304.8 | 323.8 | 12 | 25.40 | 362.0 | 24.0 |
| 12 | 323.8 | 482.6 | 304.8 | 31.75 | 114.3 | 323.8 | 365.3 | 381.0 | 12 | 25.40 | 431.8 | 36.5 |
| 14 | 355.6 | 533.4 | To be specified by the Purchaser | 35.10 | 127.0 | 355.6 | 400.1 | 412.7 | 12 | 28.40 | 476.3 | 48.4 |
| 16 | 406.4 | 596.9 | 36.60 | 127.0 | 406.4 | 475.2 | 469.9 | 16 | 28.40 | 539.8 | 60.6 | |
| 18 | 457.2 | 635.0 | 39.60 | 139.7 | 457.2 | 505.0 | 533.4 | 16 | 31.75 | 577.9 | 68.3 | |
| 20 | 508.0 | 698.5 | 42.90 | 144.5 | 508.0 | 558.8 | 584.2 | 20 | 31.75 | 635.0 | 84.5 | |
| 24 | 609.6 | 812.8 | 47.80 | 152.4 | 609.6 | 663.4 | 692.1 | 20 | 35.10 | 749.3 | 115 | |
Class 300 Weld Neck Flange Dimensions
| Nominal Pipe Size | A | B | C | D | E | F | G | H | I | J | Weight | |
| inch | mm | mm | mm | mm | mm | mm | mm | mm | Holes | mm | mm | kg / piece |
| 1/2 | 21.30 | 95.20 | 15.70 | 14.20 | 52.30 | 21.30 | 38.10 | 35.00 | 4 | 15.70 | 66.55 | 0.75 |
| 3/4 | 26.70 | 117.3 | 20.80 | 15.70 | 57.15 | 26.70 | 47.70 | 42.90 | 4 | 19.00 | 82.50 | 1.26 |
| 1 | 33.40 | 123.9 | 26.70 | 17.50 | 62.00 | 33.50 | 53.80 | 50.80 | 4 | 19.00 | 88.90 | 1.52 |
| 1 1/4 | 42.20 | 133.3 | 35.10 | 19.00 | 65.00 | 42.20 | 63.50 | 63.50 | 4 | 19.00 | 98.50 | 2.03 |
| 1 1/2 | 48.30 | 155.4 | 40.90 | 20.60 | 68.30 | 48.30 | 69.85 | 73. 15 | 4 | 22.30 | 114.3 | 2.89 |
| 2 | 60.30 | 165. 1 | 52.60 | 22.30 | 69.85 | 60.45 | 84.00 | 91.90 | 8 | 19.00 | 127.0 | 3.4 |
| 2 1/2 | 73.00 | 190.5 | 62.70 | 25.40 | 76.20 | 73.15 | 100.0 | 104.6 | 8 | 22.30 | 149.3 | 5.17 |
| 3 | 88.90 | 209.5 | 78.00 | 28.40 | 79.25 | 88.90 | 117.3 | 127.0 | 8 | 22.30 | 168.1 | 6.93 |
| 3 1/2 | 101.6 | 228.6 | 90.20 | 30.20 | 81.00 | 101.6 | 133.3 | 139.7 | 8 | 22.30 | 184.1 | 8.67 |
| 4 | 114.3 | 254.0 | 102.4 | 31.70 | 85.80 | 114.3 | 146.0 | 157.2 | 8 | 22.30 | 200.1 | 11.2 |
| 5 | 141.3 | 279.4 | 128.3 | 35.00 | 98.50 | 141.2 | 177.8 | 185.7 | 8 | 22.30 | 234.9 | 15.1 |
| 6 | 168.3 | 317.5 | 154.2 | 36.50 | 98.50 | 168.4 | 206.2 | 215.9 | 12 | 22.30 | 269.7 | 19.1 |
| 8 | 219.1 | 381.0 | 202.7 | 41.10 | 111.2 | 219.2 | 260.3 | 269.7 | 12 | 25.40 | 330.2 | 29.9 |
| 10 | 273.0 | 444.5 | 254.5 | 47.70 | 117.3 | 273.0 | 320.5 | 323.8 | 16 | 28.40 | 387.3 | 42.7 |
| 12 | 323.8 | 520.7 | 304.8 | 50.80 | 130.0 | 323.8 | 374.6 | 381.0 | 16 | 31.70 | 450.8 | 61.8 |
| 14 | 355.6 | 584.2 | To be specified by the Purchaser | 53.80 | 142.7 | 355.6 | 425.4 | 412.7 | 20 | 31.70 | 514.3 | 85.8 |
| 16 | 406.4 | 647.7 | 57.15 | 146.0 | 406.4 | 482.6 | 469.9 | 20 | 35.00 | 571.5 | 106 | |
| 18 | 457.2 | 711.2 | 60.45 | 158.7 | 457.2 | 533.4 | 533.4 | 24 | 35.00 | 628.6 | 131 | |
| 20 | 508.0 | 774.7 | 63.50 | 162.0 | 508.0 | 587.2 | 584.2 | 24 | 35.00 | 685.8 | 158 | |
| 24 | 609.6 | 914.4 | 69.85 | 168.1 | 609.6 | 701.5 | 692.1 | 24 | 41.10 | 812.8 | 230 | |
Download Class 400 to Class 2500 Weld Neck Flange Dimension PDF
For complete dimensional data on higher pressure classes, download the official PDF sheets below:
Class 400 Weld Neck Flange Dimensions (PDF)
Class 600 Weld Neck Flange Dimensions (PDF)
Class 900 Weld Neck Flange Dimensions (PDF)
Class 1500 Weld Neck Flange Dimensions (PDF)
Class 2500 Weld Neck Flange Dimensions (PDF)
Applications for ASME B16.5 Forged Flanges
ASME B16.5 forged flanges are specified across multiple sectors:
Petrochemical & Refining – High-temperature reactor feeds, catalytic cracking, hydrogen service.
Power Generation – Supercritical steam lines, nuclear auxiliary systems, HRSG piping.
Pharmaceutical & Fine Chemical – Sanitary, corrosion-resistant, dead-leg-free systems.
Marine & Offshore – Seawater piping, platform process lines.
Heavy Machinery & Metallurgy – Furnace connections, hydraulic systems.
Pre-fabricated spool service: We supply flanges pre-welded to pipes, elbows, and tees. This eliminates field fit-up and reduces installation time.
Why Source ASME B16.5 Steel Flanges from ZIZI ENGINEERING?
Rigorous Quality Control
Incoming material retesting per batch.
Mechanical property verification on finished flanges.
100% compliance with ASME, EN, JIS, and other global standards.
Full Traceability & ISO 9001 Certification
Complete process control: forging → machining → heat treatment → surface finishing → inspection.
Full material certificates and dimensional reports included.
Third-party inspections (SGS, BV, TÜV) supported.
Custom Sizes & Fast Turnaround
Non-standard orders: Machined precisely to your drawings.
Emergency orders: A105, F304, F316L blanks always in stock.
No MOQ: Single-piece orders welcome.
One-Stop Piping Component Supply
We also supply elbows, tees, reducers, caps, forged fittings, stud bolts, and gaskets – including RTJ oval/octagonal rings in soft iron, 10#, 304, 316L, and Inconel.
FAQ
Q: Can Class 150 and Class 300 flanges be interchanged?
A:No. Bolt circles, OD, and thickness differ. Always match flange, gasket, and bolting ratings.
Q: Why is hub length not listed for 14″ and larger?
A:Hub length depends on the mating pipe wall and weld bevel. It must be specified by the designer. We manufacture per your drawing.
Q: Do you supply RTJ gaskets?
A:Yes. We supply all standard oval and octagonal ring gaskets, plus stud bolts, spiral wound gaskets, and non-asbestos gaskets.
Q: Is the table weight accurate for shipping?
A:It is a theoretical net weight. Use it for estimation only; actual weight may vary slightly.