The Weld Neck flange (WN flange) is the most reliable flange type in piping engineering. Its most distinctive feature is a long, gradually tapered hub that smoothly transitions from the flange ring to the butt weld bevel end. This design provides a gradual stiffness change between the flange and the pipe, greatly distributing stress concentration at the flange root under bending moments and pressure. Compared to slip‑on or socket weld flanges, the weld neck flange offers much higher fatigue life, making it ideal for high pressure, high temperature, thermal cycling, vibration, and hazardous media (e.g., hydrogen, H₂S, high‑pressure steam).
The flange is joined to the pipe by a V‑groove or U‑groove butt weld, which can be 100% radiographed or ultrasonic tested. The weld strength equals that of the base material, and there is no leakage path. Furthermore, the weld neck flange is typically bored to match the pipe I.D. (full bore), eliminating abrupt changes in flow, reducing turbulence, erosion, and pressure loss. Sealing faces can be RF, FF, RTJ, MFM, etc., as required.
The weld neck flange is suitable for all nominal pipe sizes, but it is almost the only choice for larger diameters (NPS 4″ and above) and higher pressure classes (Class 900 and above).
Why Choose Us / Advantage
Warranty – EN 10204 3.1/3.2 material certificate and 18‑month warranty; dimensional inspection report and heat treatment records included.
Customization – Non‑standard hub length, special bevel angles, special materials (duplex 2205/2507, Inconel, Hastelloy) available per drawing.
Fast delivery – Forged blanks for common carbon/stainless WN flanges (Class 150/300) in stock; machining 10‑15 days; high‑grade custom orders 25‑35 days.
Rigorous testing – PMI and hardness testing on each piece; optional UT, MT/PT; 100% dimensional check on weld bevels.
Export packaging – Flange face coated with anti‑rust oil and fitted with plastic protectors; hub and body wrapped with stretch film + plywood case, suitable for long sea freight.
Technical Data
★ Standard: ANSI/ASME B16.5, GB/T 9117, DIN 2633
★ Body Material: Carbon Steel (A105); Stainless Steel (304, 316, 304L, 316L)
★ Pressure Class: Class 150, 300, 600, 900, 1500, 2500 (PN16~PN160)
★ Size Range: DN15 ~ DN2000 (1/2" ~ 80")
★ Face Type: Raised Face (RF)
★ Surface Treatment: Anti-rust oil (carbon steel) / Pickling & passivation (stainless steel)
Applications
● Petrochemical – Hydrotreater/reactor feed/effluent lines, high‑temperature high‑pressure separators, FCC units
● Thermal power – Main steam piping, reheat steam piping, high‑pressure feedwater systems
● Nuclear power – Primary coolant system (Reactor Coolant Loop), steam generator nozzles
● Natural gas industry – Long‑distance transmission pipelines, compressor stations, LNG terminals
● Metallurgy & chemicals – High‑temperature corrosive media (sulfuric acid, nitric acid, hot oil service)
● High‑pressure fluid transport – Oilfield water injection, CO₂ pipelines, supercritical fluid piping
