Flanges · ASME B16.5 (flange end)
Long Weld Neck Flange — ASME B16.5 (flange end)
Also written LWN
Long weld neck flange — a weld neck flange with an extended straight neck, used as a vessel nozzle. Long weld neck flanges are used as nozzles on vessels and columns, with the neck welded into the shell. Standard neck lengths are 9" and 12", or made to drawing.
- ASME B16.5 (flange end)
- 23 grades
- EN 10204 3.1 / 3.2
Reviewed by the Kanak Steel & Engineering Co. technical team · Updated October 2026
Long Weld Neck Flange: What to Know Before Ordering
- Heavy-barrel and equal-barrel designs
- Neck length 9" / 12" or to drawing
- Often machined from solid bar in alloys
Long Weld Neck Flange Materials & Grades
| Grade | Material standard | Best for |
|---|---|---|
| Inconel 825 long weld neck flange | ASTM B564 | Sulphuric and phosphoric acid service, chloride stress-corrosion cracking and sour gas |
| SS 904L long weld neck flange | ASTM A182 F904L | Dilute sulphuric acid, phosphoric acid and chloride-bearing cooling water |
| SS 304 long weld neck flange | ASTM A182 F304 | General corrosion resistance, food, water and architectural work |
| SS 304L long weld neck flange | ASTM A182 F304L | Welded tanks, piping and vessels in general corrosive service |
| SS 310 / 310S long weld neck flange | ASTM A182 F310 | Furnaces, burners and heat treatment at high temperature |
| SS 316 / 316L long weld neck flange | ASTM A182 F316L | Chloride-bearing process fluids, marine air and pharmaceutical service |
| SS 321 long weld neck flange | ASTM A182 F321 | High-temperature service between 425 and 815 °C |
| SS 347 long weld neck flange | ASTM A182 F347 | Welded high-temperature piping in refineries and power plants |
| Duplex 2205 long weld neck flange | ASTM A182 F51 / F60 | Strength with chloride resistance at a stainless-steel budget |
| Super Duplex 2507 long weld neck flange | ASTM A182 F53 | Seawater and high-chloride service where strength also matters |
| Inconel 600 long weld neck flange | ASTM B564 | High-temperature oxidation, caustic and nuclear service |
| Inconel 625 long weld neck flange | ASTM B564 | Seawater, high strength and high temperature in one alloy |
| Inconel 718 long weld neck flange | ASTM B637 | Very high strength at temperatures up to about 650 °C |
| Incoloy 800 / 800H / 800HT long weld neck flange | ASTM B564 | Furnaces, petrochemical heaters and high-temperature piping |
| Hastelloy C276 long weld neck flange | ASTM B462 / B564 | The most aggressive mixed acids, wet chlorine and hypochlorite |
| Hastelloy C22 long weld neck flange | ASTM B462 / B564 | Mixed oxidising and reducing acids, and weld overlays |
| Monel 400 long weld neck flange | ASTM B564 | Seawater, hydrofluoric acid and marine service |
| Monel K500 long weld neck flange | ASTM B865 | High-strength pump shafts, bolting and springs in seawater |
| Super Duplex S32760 long weld neck flange | ASTM A182 F55 | Seawater firewater, injection and offshore piping |
| ASTM A106 Gr B long weld neck flange | ASTM A105 | High-temperature process and steam piping in refineries and power plants |
| ASTM A333 Gr 6 long weld neck flange | ASTM A350 LF2 | Cold-climate and refrigerated piping down to −45 °C |
| ASTM A335 P11 long weld neck flange | ASTM A182 F11 | Steam and hot-oil piping up to about 550 °C |
| ASTM A335 P22 long weld neck flange | ASTM A182 F22 | High-pressure steam and hydrogen service up to about 580 °C |
Other flanges
Weld neck flangeA flange with a long tapered hub that is butt-welded to the pipe.Slip-on flangeA flange that slides over the pipe and is fillet-welded inside and outside.Blind flangeA solid disc that closes the end of a pipe, valve or vessel nozzle.Socket weld flangeA flange with a counterbore socket into which the pipe is inserted and fillet-welded.Threaded flangeA flange with a tapered internal thread that screws onto threaded pipe.Lap joint flangeA loose flange that sits behind a stub end welded to the pipe.Orifice flangeA pair of weld neck or slip-on flanges with pressure taps that hold an orifice plate.Spectacle blindA figure-8 plate with one solid end and one open ring, fitted between two flanges.Reducing flangeA flange with a smaller bore than its outside dimensions, connecting to a smaller pipe.Ring type joint flangeA flange with a machined groove for a metal ring gasket.Expander flangeA weld neck flange whose hub increases the pipe size.Anchor flangeA forged ring welded into a pipeline to fix it to a structure.Swivel ring flangeA flange with a rotating ring that allows bolt holes to be aligned after welding.
Long Weld Neck Flange dimensions — ASME B16.5 Class 150 & 300
Outside diameter, thickness and bolting are set by size and class. Values in mm; thickness excludes the 1.6 mm raised face.
| NPS | Cl 150 OD | Cl 150 thickness | Cl 150 bolt circle | Cl 150 bolts | Cl 300 OD | Cl 300 thickness | Cl 300 bolt circle | Cl 300 bolts |
|---|---|---|---|---|---|---|---|---|
| ½" | 90 | 9.6 | 60.3 | 4 × ½" | 95 | 12.7 | 66.7 | 4 × ½" |
| 1" | 110 | 12.7 | 79.4 | 4 × ½" | 125 | 15.9 | 88.9 | 4 × ⅝" |
| 1½" | 125 | 15.9 | 98.4 | 4 × ½" | 155 | 19.1 | 114.3 | 4 × ¾" |
| 2" | 150 | 17.5 | 120.7 | 4 × ⅝" | 165 | 20.7 | 127.0 | 8 × ⅝" |
| 3" | 190 | 22.3 | 152.4 | 4 × ⅝" | 210 | 27.0 | 168.3 | 8 × ¾" |
| 4" | 230 | 22.3 | 190.5 | 8 × ⅝" | 255 | 30.2 | 200.0 | 8 × ¾" |
| 6" | 280 | 23.9 | 241.3 | 8 × ¾" | 320 | 35.0 | 269.9 | 12 × ¾" |
| 8" | 345 | 27.0 | 298.5 | 8 × ¾" | 380 | 39.7 | 330.2 | 12 × ⅞" |
| 10" | 405 | 28.6 | 362.0 | 12 × ⅞" | 445 | 46.1 | 387.4 | 16 × 1" |
| 12" | 485 | 30.2 | 431.8 | 12 × ⅞" | 520 | 49.3 | 450.8 | 16 × 1⅛" |
Full chart: ASME B16.5 flange dimensions.
Long weld neck flange — questions buyers ask
What is the difference between equal-barrel and heavy-barrel LWN?
Equal-barrel has a uniform neck; heavy-barrel has a thicker neck for extra reinforcement at the vessel wall.
Which grades are long weld neck flanges available in?
Inconel 825, SS 904L, SS 304, SS 304L, SS 310 / 310S, SS 316 / 316L, SS 321, SS 347, Duplex 2205, Super Duplex 2507, Inconel 600, Inconel 625, Inconel 718, Incoloy 800 / 800H / 800HT, Hastelloy C276, Hastelloy C22, Monel 400, Monel K500, Super Duplex S32760, ASTM A106 Gr B, ASTM A333 Gr 6, ASTM A335 P11, ASTM A335 P22.
Which standard covers long weld neck flange dimensions?
ASME B16.5 (flange end). The material standard depends on the grade.
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