Carbon steel welding neck flanges (WNRF) are the premium connection choice for high-pressure, high-temperature and cyclic-load piping systems. The long tapered hub transfers stress smoothly from the flange into the pipe wall, reducing stress concentration at the weld joint. Huaxia-Steel supplies carbon steel welding neck flanges in Classes 150 through 2500 to ASME B16.5 and B16.47 Series A/B with full certification and custom machining.
Product Overview
A welding neck flange is distinguished by its extended hub, which is butt-welded to the pipe. This design provides:
- Superior structural strength compared to slip-on or socket weld flanges
- Ideal fatigue resistance for cyclic pressure and temperature service
- Radiographic-friendly butt weld for 100% joint inspection
- Smooth bore matching the pipe ID, minimising turbulence and erosion
Carbon steel welding neck flanges are specified in refineries, power plants, offshore platforms and process plants where reliability is non-negotiable.
Specifications and Dimensions
| Parameter | Standard Range |
|---|---|
| Nominal pipe size (NPS) | 1/2″ – 60″ |
| Pressure class | Class 150, 300, 400, 600, 900, 1500, 2500 |
| Standards | ASME B16.5 (≤ 24″), ASME B16.47 Series A/B (≥ 26″) |
| Flange facing | Raised face (RF), flat face (FF), ring-type joint (RTJ), tongue and groove (T&G) |
| Bore type | Standard bore, extra-heavy bore, special bore to match pipe schedule |
Material Grades
| Standard | Grade | Typical Service |
|---|---|---|
| ASTM A105 | A105 | Ambient and moderate temperature, –29 °C to +425 °C |
| ASTM A350 LF2 | LF2 Cl. 1 / Cl. 2 | Low-temperature service down to –46 °C |
| ASTM A181 | Class 60 / 70 | General-purpose forged flanges |
| ASTM A694 | F42 – F70 | High-yield transmission pipeline service |
| EN 1092-1 | P250GH, P245GH, P280GH | European pressure equipment |
| JIS B2220 | SF440A, SF390A | Japanese standard piping |
Dimensional Data (Excerpt, ASME B16.5 Class 300 RF)
| NPS | OD (mm) | Thickness (mm) | Hub OD (mm) | Length thru Hub (mm) | Drilling |
|---|---|---|---|---|---|
| 2″ | 165 | 23.0 | 84 | 60 | 8 × Ø19 |
| 4″ | 254 | 31.8 | 130 | 73 | 8 × Ø22 |
| 6″ | 318 | 36.6 | 171 | 83 | 12 × Ø22 |
| 8″ | 381 | 41.1 | 215 | 92 | 12 × Ø25 |
| 10″ | 445 | 47.8 | 267 | 100 | 16 × Ø29 |
| 12″ | 521 | 50.8 | 318 | 108 | 16 × Ø32 |
Full dimensional tables per ASME B16.5 and B16.47 are available on request. Custom drilling patterns, reduced bore and long-neck variants can be engineered for vessel and heat-exchanger nozzles.
Pressure-Temperature Ratings (ASTM A105)
| Class | -29 to +38 °C | +100 °C | +200 °C | +300 °C | +400 °C | +425 °C |
|---|---|---|---|---|---|---|
| 150 | 19.8 bar | 17.9 bar | 15.9 bar | 14.2 bar | 12.6 bar | 11.8 bar |
| 300 | 51.7 bar | 46.7 bar | 41.6 bar | 37.2 bar | 33.0 bar | 30.9 bar |
| 600 | 103.4 bar | 93.4 bar | 83.1 bar | 74.4 bar | 66.0 bar | 61.8 bar |
| 900 | 155.1 bar | 140.2 bar | 124.7 bar | 111.6 bar | 99.1 bar | 92.7 bar |
Manufacturing Process
- Forging: Billets are heated and die-forged to rough hub and ring geometry
- Heat treatment: Normalizing or quench-and-temper per material grade requirement
- Rough machining: Turning OD, bore and hub profile
- Finish machining: Facing, drilling, tapping, gasket surface finish (Ra 3.2 – 6.3 µm for RF; 1.6 µm for RTJ)
- Marking: Size, class, material, heat number, standard and manufacturer stamp
- NDT: Ultrasonic test (UT) on forging body; magnetic particle (MT) or liquid penetrant (PT) on machined surfaces
Applications
- Oil and gas: Riser connectors, manifold headers, pipeline stations
- Power: Main steam lines, HP feedwater, boiler outlet headers
- Chemical: Reactor nozzles, exchanger channels, distillation column connections
- Offshore: Platform process piping, subsea jumpers (with A694 high-yield grades)
- Shipbuilding: Engine room piping, fuel oil and ballast systems
Quality Assurance
- Material certification to EN 10204 3.1 or 3.2
- Chemical analysis and mechanical testing per heat
- Dimensional inspection with CMM on critical faces
- Surface finish measurement on gasket seating surfaces
- Hardness survey on RTJ grooves and raised faces
- Positive material identification (PMI) on request
Packing and Shipping
- Individual foam or corrugated separation for faced flanges
- Plywood crates or steel frames for ocean freight
- RTJ grooves protected with plastic inserts
- Desiccant and VCI packaging for long transit
- Container stuffing with lashing and photo documentation
Why Buy Welding Neck Flanges from Huaxia-Steel?
- ASME U-stamp and ISO 9001 certified forging and machining facility
- Complete traceability from melt to finished flange
- In-stock rough forgings for fast-track delivery of common sizes
- Custom long-neck, orifice and spectacle blind flanges engineered to drawing
- Third-party witnessing by Lloyd’s, DNV, BV or SGS available
Request a quotation for carbon steel welding neck flanges. Provide NPS, pressure class, facing type, material grade, quantity and destination port. Our flange specialists will confirm dimensions, lead time and certification level within one working day.
