Long weld neck flanges
A long weld neck flange replaces a flange welded to a length of pipe with a single forging. Fabricators use them as nozzles on pressure vessels, columns and heat exchangers, and as instrument connections.
A long weld neck (LWN) flange has a straight, extended barrel in place of the short tapered hub of a standard weld neck flange, so the flange and its nozzle neck are one forging. Fabricators use them as nozzles on pressure vessels, columns, tanks and heat exchangers, where the thick barrel also reinforces the opening. The flange end follows ASME B16.5 drilling and facing; the neck length, bore and wall are to the purchaser's drawing, including heavy barrel versions with a thicker neck. We forge and machine long weld necks in A105, A350 LF2, 304L, 316L and duplex, with an EN 10204 3.1 mill test report for every heat.
Why a single forging
A nozzle built from a weld neck flange and a length of pipe has a butt weld at the hub, which has to be welded, examined and sometimes heat treated. A long weld neck has no such joint, and its barrel can be made thicker than standard pipe, which helps carry the reinforcement the vessel code asks for at the opening and the loads that connected piping puts on the nozzle. Pressure vessels in the US are designed to the ASME Boiler and Pressure Vessel Code, Section VIII, and the vessel designer sets the nozzle dimensions.
What we need on the drawing
| Item | Why it matters |
|---|---|
| NPS and class | Sets the flange drilling and thickness to ASME B16.5 |
| Facing | Raised face, flat face or ring type joint |
| Neck length | From the flange face to the weld end |
| Bore | Matches the nozzle inside diameter on the vessel drawing |
| Barrel outside diameter or wall | Standard or heavy barrel, as the reinforcement calculation needs |
| Weld end | Plain end or weld bevel to your detail |
| Material and tests | Grade, heat treatment and any impact or corrosion tests |
Where they are used
- Nozzles on pressure vessels, columns and reactors in refineries, chemical and pharmaceutical plants.
- Shell and channel nozzles on shell and tube heat exchangers.
- Thermowell and instrument connections that need a long, strong neck.
- Tank nozzles where a flange must stand off the shell.
Grades
| Grade | Specification | Typical service |
|---|---|---|
| A105 | ASTM A105 | Carbon steel vessels and exchangers |
| A350 LF2 | ASTM A350, Charpy tested at -50 °F | Low temperature vessels |
| F304L, F316L | ASTM A182 | Stainless vessels and exchangers |
| Duplex S32205, super duplex S32750 | ASTM A182 F60 and F53 | Chloride and seawater service |
How to order
Send the nozzle drawing with each line; a typical line reads: "Long weld neck flange RF, NPS 3, Class 300, neck length and bore to drawing, ASTM A182 F316L, 6 pcs". Send the type, size, class, facing, bore or schedule, material and quantity for each line, and we quote every line as specified. Every order ships from our works in Gujarat, India, with an EN 10204 3.1 mill test report for every heat; ordering from India explains the documents, marking, packing and customs.
Frequently asked questions
Is there a standard length for a long weld neck?
No dimensional standard covers the neck. The flange end follows ASME B16.5 and the neck length, bore and wall come from your drawing or nozzle schedule.
What is a heavy barrel long weld neck?
A long weld neck whose barrel wall is thicker than standard, usually to carry nozzle reinforcement or piping loads. Give the barrel outside diameter and bore, or the wall thickness, on the drawing.
Can you supply long weld necks in stainless and duplex?
Yes, in 304L, 316L, duplex S32205 and super duplex S32750, checked by PMI and recorded on the certificate.
Sources
- ASME B16.5, Pipe Flanges and Flanged Fittings, NPS 1/2 through NPS 24 Metric/Inch Standard
- ASME Boiler and Pressure Vessel Code, Section VIII, Division 1, Rules for Construction of Pressure Vessels
- ASTM A105/A105M; ASTM A350/A350M; ASTM A182/A182M