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Weld Neck Flanges (WN) are long-tapered-hub pipe connectors that butt-weld directly to the pipe, providing the highest structural integrity among the six standard flange types. They are the preferred choice for high-pressure, high-temperature, and cyclic-service applications where the bolted joint must remain leak-tight under thermal cycling, vibration, or pressure surge.
As an ASME B16.5 flange manufacturer and supplier based in Hebei, China, we produce Weld Neck flanges to ASME B16.5 (1/2"–24", Class 150–2500), ASME B16.47 (26"–60", Class 75–900), EN 1092-1 Type 11 (PN 10–160), JIS B2220 5K–63K, and GB/T 17241 / HG/T 20592 (Chinese chemical standard). All dimensions, tolerances, and weld-end preparations are produced per the governing standard's dimensional schedule. Hub length and bore diameter match the mating pipe schedule (typically ASME B36.10 / B36.19 for ASME standards).
The defining feature of the Weld Neck design is the tapered hub that distributes mechanical stress from the flange face to the pipe body through a gradual transition. This reduces stress concentration at the weld joint by 30–60% compared to slip-on or plate flanges, making WN flanges mandatory for:
- Power plant main steam and reheat lines (Class 600+, 540°C+) - Hydrocracker and catalytic cracker reactor nozzles - LNG and LPG cryogenic piping (16MnDR / A350 LF2 to -46°C) - Sour-service hydrocarbon gathering (NACE MR0175 / ISO 15156 compliance) - High-cycle fatigue applications (FPSO swivel stacks, subsea manifolds)
Pressure class selection follows the standard pressure-temperature rating table. ASME B16.5 Class 150 flanges are rated for 285 psi at 38°C (carbon steel) up to Class 2500 at 6170 psi. EN 1092-1 PN 16 to PN 100 covers most European refinery and chemical service. We provide full pressure-temperature derating curves per ASME B16.5 Table 2-1.1 (Group 1.1 carbon steel) and Table 2-3.1 (Group 1.9 low-temperature carbon steel) on request.
Manufacturing process: forged billet (preferred for Class 600 and above) or rolled plate (Class 150–300). Hub taper is machined to ASME B16.5 §6.1 tolerances. Weld-end preparation is per ASME B16.25 (default 37.5° bevel, 1.6 mm land, 1.6 mm root face). Machined surfaces including the gasket contact face, bolt circle, and bolt holes are produced on CNC vertical turning lathes with surface finish Ra 3.2–6.3 μm (125–250 μin) for RF (raised face) and Ra 0.8–1.6 μm for RTJ (ring type joint) grooves.
Materials stocked for Weld Neck flanges include ASTM A105 (carbon steel, -29°C to +425°C), A350 LF2 (low-temperature carbon steel, -46°C to +345°C, normalized), A182 F11/F22/F91 (Cr-Mo alloy for high-temperature power), 16MnDR (Chinese low-temp, -46°C, GB 150 compliant), 304/316/316L stainless, and duplex F51/F55. Each heat is supplied with EN 10204 3.1 mill test certificate showing chemical composition, mechanical properties, and NACE MR0175 compliance when applicable.
PED 2014/68/EU CE-marking is available under Module H (full quality assurance) or Module A2 (production quality assurance) for EU-bound shipments. We supply to oil & gas NORSOK M-650 / M-630 requirements when specified, and to ASME Section VIII Division 1 / Division 2 (U-stamp, U2-stamp) for pressure vessel nozzle applications. ASME U-stamp / U2-stamp certification available for pressure vessel nozzle applications.
Shipping is from Shanghai, Qingdao, or Ningbo to major ports in 14–30 days. Custom clearance documents include commercial invoice, packing list, certificate of origin (China Chamber of Commerce notarized), MTC EN 10204 3.1, and third-party inspection certificates (SGS / BV / TUV / Intertek) on request.
Weld Neck flanges have a long tapered hub that is butt-welded to the pipe, distributing stress through the tapered transition. Slip-On flanges have a short hub and are fillet-welded at the pipe outside diameter only. WN flanges offer 30-60% lower stress concentration at the weld joint and are rated for Class 600 and above. Slip-On flanges are dimensionally defined in ASME B16.5 through Class 600 and are preferred for low-pressure, low-temperature service where fabrication speed matters more than fatigue life.
Use Weld Neck flanges when: (1) service temperature exceeds 425°C (e.g. power plant main steam), (2) pressure exceeds Class 600 / PN 100, (3) the system experiences thermal cycling or vibration (cyclic service), (4) service is cryogenic (-29°C or below), (5) NACE MR0175 sour service is specified, or (6) the application is subsea or offshore. Plate (PL) flanges are typically limited to PN 25 / Class 300 ambient temperature. Slip-On (SO) flanges are dimensionally defined through Class 600 per ASME B16.5 but are not recommended for thermal cycling at high class.
Standard ASME B16.5 sizes 1/2" through 24" in A105 carbon steel with RF facing require no MOQ for stocked items. Custom alloys (A350 LF2, F11, F22, F91, 16MnDR, duplex, 316L) typically require MOQ 50 pieces per size-class-material combination. Large-bore ASME B16.47 Series A and B (26"–60") require MOQ 5 pieces per size due to forging die setup costs.
Yes. All A350 LF2 Class 1 and 16MnDR Weld Neck flanges are supplied NACE MR0175 / ISO 15156 compliant by default, with documented hardness testing per NACE MR0175 §6.2 (HRC 22 maximum for sour service). For H2S-containing service, A350 LF2 Class 2 may be required. We provide per-batch hardness test reports and can supply chloride stress corrosion cracking (SCC) compliance documentation for austenitic stainless steels per NACE MR0175 §6.3.
Standard stocked sizes in A105 carbon steel Class 150-300 ship in 15-20 days from order confirmation. Non-stocked Class 600+ flanges, large-bore B16.47, and custom alloys (F11/F22/F91/LF2/16MnDR/duplex) ship in 25-45 days depending on forging mill availability. Sea freight from Shanghai/Qingdao/Ningbo to Middle East ports (Jebel Ali, Dammam, Hamad) is 14-21 days. To South Asia (Mundra, Karachi, Chittagong) is 10-18 days. To Europe (Rotterdam, Hamburg, Genoa) is 28-35 days. Air freight is available for urgent orders at 5-7x ocean freight cost.
No. ASME B16.5 Class 600 and Class 900 flanges have different dimensional schedules (different bolt circle diameters, different bolt hole counts, different flange thicknesses). A Class 600 flange used at Class 900 conditions will fail catastrophically. Always specify the exact pressure class when ordering. We can machine a Class 900 flange from Class 600 stock only if the bolt circle diameter matches, most cases it does not.
Weld Neck Flanges (WN) are long-tapered-hub pipe connectors designed to butt-weld directly to the pipe, providing the highest structural integrity for high-pressure, high-temperature, and cyclic-service applications. They conform to ASME B16.5 (1/2" to 24" NPS) and ASME B16.47 (>26" NPS), with pressure ratings from Class 150 (285 PSI at 100 deg F) to Class 2500 (6,670 PSI at 100 deg F), materials ranging from A105 carbon steel to 16MnDR low-temperature alloy, and operating temperatures spanning -46 deg C (cryogenic LNG) to 540 deg C (power-plant steam). They are the preferred specification for refining, hydrocracker, and high-pressure steam service.
Source: ASME B16.5-2020; EN 1092-1:2018.
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