Carbon Steel Long Weld Neck Flange — Factory Direct Supplier | Huaxia-Steel

Carbon steel long weld neck flanges — also known as long-hub flanges or LWN flanges — are the preferred connection method for high-pressure piping systems where the extended hub provides reinforcement against bending stresses, thermal expansion and cyclic fatigue. The long tapered neck acts as a gradual stress-reducing transition between the pipe and the flange ring, eliminating the stress concentration that occurs at abrupt geometry changes.

Huaxia-Steel manufactures ASME B16.5 and B16.47 Series A & B long weld neck flanges from ASTM A105, A350 LF2 and A694 carbon steel forgings, with pressure classes from 150 to 2500 and sizes from 1/2" to 60" NPS. All flanges are heat-treated, ultrasonically tested and dimensionally verified to guarantee leak-free performance in the most demanding oil, gas and power applications.

Product Overview

The defining feature of a long weld neck flange is the extended hub length, which is typically 2–4 times the nominal pipe wall thickness longer than a standard weld-neck flange. This extra length provides several engineering advantages:

Reinforced bore: The hub reinforces the pipe end against ovalisation during welding and hydrotest
Thermal stress reduction: The gradual taper reduces thermal-stress concentration at the pipe-to-flange junction
Fatigue resistance: Smooth stress distribution extends cyclic-life by 300–500 % compared with slip-on flanges
Instrument compatibility: The extended hub can be drilled for thermowell or sampling-probe insertion

Huaxia-Steel long weld neck flanges are forged on 5,000-tonne hydraulic presses with minimum 4:1 forging ratio, ensuring grain-flow alignment parallel to the hub axis for maximum fatigue strength. Final machining is performed on CNC lathes with live tooling for bolt-hole drilling and facing.

Specifications and Dimensions

Parameter	Specification
Standard	ASME B16.5, ASME B16.47 Series A / Series B
Pressure class	150, 300, 400, 600, 900, 1500, 2500
Size range	1/2" – 60" NPS (B16.47 Series A&B)
Facing	Raised Face (RF), Ring-Type Joint (RTJ), Flat Face (FF)
Hub length	Standard long-hub or custom length per drawing
Bore	Pipe bore, tap bore, or reduced bore
Surface finish	RF: 125–250 AARH; RTJ: 63 AARH max
Coating	Black oxide, rust-preventive oil, hot-dip galvanized, PTFE coated

For pipeline applications requiring high-integrity gaskets, we supply long weld neck flanges with RX or BX ring grooves machined to API 6A dimensional tolerances. Groove hardness is controlled to 150–190 HB to prevent galling during make-and-break operations.

Material Grades and Selection Guide

Grade	Standard	Service Temp.	Typical Application
ASTM A105	ASME B16.5	−29°C to 425°C	General process piping, water, steam
ASTM A105N	ASME B16.5	−29°C to 425°C	Normalised for improved notch toughness
A350 LF2 Cl.1	ASME B16.5	−46°C to 345°C	Low-temperature process piping
A350 LF2 Cl.2	ASME B16.5	−46°C to 345°C	Quenched & tempered for higher strength
A694 F52	ASME B16.5	−29°C to 260°C	API 5L pipeline matching grade
A694 F60	ASME B16.5	−29°C to 260°C	High-strength transmission pipeline
A694 F65	ASME B16.5	−29°C to 260°C	Ultra-high-pressure gas pipeline

For subsea and deep-water applications, we supply long weld neck flanges with clad overlays (316L, Inconel 625 or 825) applied by explosive bonding or weld overlay. Clad flanges eliminate the need for corrosion-resistant alloy piping in aggressive service while maintaining the structural strength of carbon steel.

Manufacturing Standards and Quality Assurance

Forging: 5,000-tonne hydraulic press, 4:1 minimum forging ratio, longitudinal grain flow
Heat treatment: Normalising at 880°C±15°C or Q&T per ASTM A961
Machining: CNC turning, bolt-circle drilling, facing and grooving in one setup
NDE: 100 % UT per ASTM A388 for all pressure classes; MT or PT for surface flaws
Hardness test: 100 % HB or HRC verification on hub and ring
Dimensional inspection: CMM on OD, BCD, bolt holes, face runout and hub concentricity
PMI: XRF spectrometry on every heat to confirm chemistry
Traceability: Heat number, serial number and project code stamped on every flange

Applications

High-pressure steam lines in thermal power plants
Crude oil and refined product transmission pipelines
Natural gas compressor station suction and discharge piping
Offshore platform process risers and flowlines
Refinery hydrocracker and hydrotreater reactor nozzles
Nuclear feedwater and main steam piping (A105N with ASME N-stamp)
Cryogenic LNG loading and unloading arms (A350 LF2)

Packaging and Shipping

Long weld neck flanges are individually wrapped in corrosion-inhibitor VCI film and stacked on engineered wooden cradles to prevent hub bending during transit. Bolt holes are protected with plastic plugs to prevent thread damage. Each shipment includes a packing list, mill test certificate, heat-treatment chart, NDE report and dimensional inspection sheet. For sea freight, containers are loaded with dunnage and lashing to prevent movement.

Standard lead time is 4–5 weeks for A105 and A350 LF2 grades. A694 grades and clad overlays require 6–8 weeks. Emergency air-freight service is available for project-critical spares.