Weld Neck Flange — ASME B16.5
Also written WNRF
Weld neck flange — a flange with a long tapered hub that is butt-welded to the pipe. Choose a weld neck flange for high pressure, high or low temperature and cyclic loading. The tapered hub moves stress away from the flange face, and the full-penetration butt weld can be radiographed.
- ASME B16.5
- 23 grades
- EN 10204 3.1 / 3.2
Reviewed by the Kanak Steel & Engineering Co. technical team · Updated October 2026
What is a weld neck flange?
A weld neck flange is a flange with a long tapered hub that is butt-welded to the pipe. Choose a weld neck flange for high pressure, high or low temperature and cyclic loading. The tapered hub moves stress away from the flange face, and the full-penetration butt weld can be radiographed.
Standards for weld neck flanges
Weld Neck Flange: What to Know Before Ordering
- Bore must match the pipe schedule — state it on the order
- Hub length and taper per ASME B16.5 / B16.47 tables
- Most common facing: raised face; RTJ for high-pressure classes
Weld Neck Flange Materials & Grades
| Grade | Material standard | Best for |
|---|---|---|
| Inconel 825 weld neck flange | ASTM B564 | Sulphuric and phosphoric acid service, chloride stress-corrosion cracking and sour gas |
| SS 904L weld neck flange | ASTM A182 F904L | Dilute sulphuric acid, phosphoric acid and chloride-bearing cooling water |
| SS 304 weld neck flange | ASTM A182 F304 | General corrosion resistance, food, water and architectural work |
| SS 304L weld neck flange | ASTM A182 F304L | Welded tanks, piping and vessels in general corrosive service |
| SS 310 / 310S weld neck flange | ASTM A182 F310 | Furnaces, burners and heat treatment at high temperature |
| SS 316 / 316L weld neck flange | ASTM A182 F316L | Chloride-bearing process fluids, marine air and pharmaceutical service |
| SS 321 weld neck flange | ASTM A182 F321 | High-temperature service between 425 and 815 °C |
| SS 347 weld neck flange | ASTM A182 F347 | Welded high-temperature piping in refineries and power plants |
| Duplex 2205 weld neck flange | ASTM A182 F51 / F60 | Strength with chloride resistance at a stainless-steel budget |
| Super Duplex 2507 weld neck flange | ASTM A182 F53 | Seawater and high-chloride service where strength also matters |
| Inconel 600 weld neck flange | ASTM B564 | High-temperature oxidation, caustic and nuclear service |
| Inconel 625 weld neck flange | ASTM B564 | Seawater, high strength and high temperature in one alloy |
| Inconel 718 weld neck flange | project / purchase specification dependent | Very high strength at temperatures up to about 650 °C |
| Incoloy 800 / 800H / 800HT weld neck flange | ASTM B564 | Furnaces, petrochemical heaters and high-temperature piping |
| Hastelloy C276 weld neck flange | ASTM B462 / B564 | The most aggressive mixed acids, wet chlorine and hypochlorite |
| Hastelloy C22 weld neck flange | ASTM B462 / B564 | Mixed oxidising and reducing acids, and weld overlays |
| Monel 400 weld neck flange | ASTM B564 | Seawater, hydrofluoric acid and marine service |
| Monel K500 weld neck flange | project / purchase specification dependent | High-strength pump shafts, bolting and springs in seawater |
| Super Duplex S32760 weld neck flange | ASTM A182 F55 | Seawater firewater, injection and offshore piping |
| ASTM A106 Gr B weld neck flange | ASTM A105 | High-temperature process and steam piping in refineries and power plants |
| ASTM A333 Gr 6 weld neck flange | ASTM A350 LF2 | Cold-climate and refrigerated piping down to −45 °C |
| ASTM A335 P11 weld neck flange | ASTM A182 F11 | Steam and hot-oil piping up to about 550 °C |
| ASTM A335 P22 weld neck flange | ASTM A182 F22 | High-pressure steam and hydrogen service up to about 580 °C |
Other flanges
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.
Weld neck flange — questions buyers ask
What is a weld neck flange?
A weld neck flange is a flange with a long tapered hub that is butt-welded to the pipe. Choose a weld neck flange for high pressure, high or low temperature and cyclic loading. The tapered hub moves stress away from the flange face, and the full-penetration butt weld can be radiographed.
Why is the bore important on a weld neck flange?
The flange bore is machined to the inside diameter of the pipe schedule, so the weld is smooth inside. A wrong bore leaves a step that disturbs flow and complicates the weld.
Which grades are 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 weld neck flange dimensions?
ASME B16.5 · B16.47. The material standard depends on the grade.
Sources: the ASTM / ASME specifications named on this page and producer datasheets · Last updated October 2026