Technical Specification of Long Weld Neck Flange

1. What is a Long Weld Neck(LWN) flange?

According to ASME B16.5, a long weld neck flange, abbreviated as "LWN", is also called straight hub welding flange which is an extension of welding neck flange and has straight hubs of uniform wall thickness. Usually, its "flange body" has the same dimensions as that of a welding neck flange in same class and size. The LWN flange is a special flange used for nozzles on pressure vessel. The straight pipe hub is integrally forged & constructed with the flange body.

Unless specified by users, the length through hub shall be 9 inches(228.6mm) for 4" and smaller sizes and 12 inches(304.8mm) for 5" and larger sizes. The bore diameter of a LWN flange shall be equal to a regular weld neck flange. Other bore diameters may be furnished as per end user's requirement but they shall not exceed the bore of the same size and class lapped flange.

2. Advantages of using LWN flanges?

1) Time and cost saving: since the straight pipe-hub and flange are forged integrally, there will be less welding job during the fabrication of pressure vessel whilst cost of radiographic test(RT) on welding can be reduced accordingly.

2) The integral construction of a LWN flange provides good conformity and easier traceability of material. Thus only one Mill Test Certificate(MTC) is required. This unique construction also eliminates a weld seam between flange and pipe barrel, resulting in reinforced strength and toughness.

3. Common materials for LWN flanges?

Carbon Steel: ASTM A105(N), DIN C22.8

Stainless Steel: ASTM A182 F304(L), F316(L), F321, F51

Low Allow Steel: ASTM A182 F5, F11, F22, F9, F91 ASTM A350 LF2
High Pressure Service: ASTM A694 F42, F46, F48, F50, F52, F56, F60, F65, F70

Nickel Alloy: Inconel 600, Inconel 625, Monel 400, Hastelloy C276

4. Pressure ratings available

You can view the technical drawing, dimensions and weight details by clicking the class designation below:

150LB 300LB 400LB 600LB

900LB 1500LB 2500LB

Views: Author：hbmetals Date:15/03/25