Flanges are important connecting components in piping systems, capable of achieving stable connections, easy disassembly and assembly, and ensuring good sealing performance under various operating conditions. The selection of flanges requires comprehensive consideration of factors such as pressure rating, temperature conditions, medium properties, and installation requirements. Among various types of flanges, weld neck flanges (WN) have become the most widely used type due to their excellent mechanical properties and sealing performance. This article will focus on analyzing their structural characteristics, performance advantages, and typical applications to provide reference for your procurement decisions.
Introduction to Weld Neck Flanges
Weld neck flanges are a type of neck flange that are connected to pipes using a welded joint. Their structural feature is a relatively high neck height, which effectively enhances the flange’s rigidity and pressure-bearing capacity. In terms of connection methods, the flange is connected to the pipeline using welding technology. First, the flange neck is butt-welded to the pipeline end to form an integrated structure. This connection method ensures excellent strength and sealing performance between the flange and the pipeline, enabling it to withstand high pressure and temperature conditions. It is widely applied in high-pressure, high-temperature, and critical industrial pipeline systems across industries such as petroleum, chemicals, power generation, and metallurgy.
Why WN Flanges Dominate?
Superior Structural Integrity
•The tapered hub provides optimal stress distribution
•Reduces stress concentration by up to 60% compared to slip-on flanges (ASME B31.3 Process Piping Code)
Unmatched Leak Prevention
•Butt-welded connection ensures maximum sealing reliability
•Leak rate below 0.0005% in standard hydrostatic tests (API 6A specification)
Exceptional Durability
•Average service life of 20+ years in harsh environments
•Withstands temperature ranges from -196°C to +650°C
Specification of Weld Neck Flanges
| Shape Type | Regular and Long Neck |
| Sealing Face | RF, FF, RTJ |
| Size Range | 1/2″ – 48″/ DN15 – DN1200 |
| Pressure Rating | Class 150, 300, 600, 900, 1500, 2500lb |
| Standard | ASME B16.5, ASME B16.47 Series A/B |
Material Selection Guide
| Materials | Standard | Grade |
| Carbon Steel | ASTM A105/105N | – |
| Stainless Steel | ASTM A182 | F304/304L/304H、F316/316L、F317、F310S、F321、F347、F904L |
| Duplex Stainless Steel | ASTM A182 | F44/F51/F53/F55/F60 |
| Pipeline Steel | ASTM A694 | F42/46/52/56/65/70 |
| Alloy Steel | ASTM A182 | F5/F9/F11/F12/F22/F91/F92 |
| Low Temperature Steel | ASTM A350 | LF2/LF3 |
ASME B16.5 Weld Neck Flanges Dimension
There are seven pressure ratings for weld neck flanges, covering 150#, 300#, 400#, 600#, 900#, 1500#, and 2500.
Class 300 Weld Neck Dimension
| 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 | |
Industry-Specific Applications
Industry-Specific Applications:
•Oil and Gas Industry
•Offshore platforms
•Oil and gas pipelines
•Refining facilities
Chemical and Petrochemical Industry
•High-pressure reactors, heat exchangers, steam pipes
•Critical connections in corrosive medium pipelines
Frequently Asked Questions (FAQs):
What is the difference between weld neck flanges and lap joint flanges?
Weld neck flanges provide permanent, high-strength connections through butt welding. Lap joint flanges feature a rotatable ring and stub end secured by bolts, enabling easy disassembly for low-pressure maintenance work. Weld neck flanges excel in sealing reliability, while lap joint flange versions offer installation flexibility.
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