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

Weld neck flanges are the most reliable flange style for high-pressure and high-temperature 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 weld neck flanges in ASTM A105, A350 LF2, and A182 F304/F316-compatible carbon steel grades, manufactured to ASME B16.5, B16.47 Series A/B, and customer drawings. We machine, mark, and pack flanges for oil and gas, power generation, petrochemical, and shipbuilding projects worldwide.

Product Overview

Our carbon steel weld neck flanges are forged or formed from killed carbon steel, normalized or stress-relieved as required, and finish-machined on CNC lathes. Raised face (RF), flat face (FF), ring-type joint (RTJ), and tongue-and-groove facings are available. Each flange is marked with heat number, size, rating, standard, and grade for full traceability. We provide mill test certificates to EN 10204 3.1 standard, with 3.2 or third-party inspection available on request.

Specifications

Parameter	Details
Size range	1/2″ – 60″ (DN15 – DN1500)
Pressure class	150# – 2500# (PN6 – PN420)
Standards	ASME B16.5, ASME B16.47 Series A/B, MSS SP-44, API 6A, EN 1092-1 Type 11
Facing	RF, FF, RTJ, TG, customized
Materials	ASTM A105, A105N, A350 LF2/LF3, A694 F52-F70, A182 F304/316 (on request), 20# / Q235 / 16Mn (GB)
Surface finish	RF serrated 125–250 AARH, machined spiral or concentric serration
Coating	Black paint, rust-preventive oil, hot-dip galvanized, yellow or epoxy coating
Threads / holes	Drilled and reamed per standard, bolt circle and flange thickness to ASME tables

Dimensional and Weight Reference (ASME B16.5, RF, A105)

NPS	OD (mm)	Thickness (mm)	Hub OD (mm)	Bore (mm)	Weight approx. (kg)
2″ 150#	152	19.1	62	49	2.2
4″ 150#	229	24.0	114	98	6.0
6″ 150#	279	25.4	168	146	10.5
8″ 150#	343	28.6	219	191	17.0
6″ 300#	318	36.6	174	146	21.0
12″ 300#	483	47.7	324	289	68.0

Weights are approximate for standard ASME B16.5 raised-face weld neck flanges in ASTM A105. Exact weight depends on bore schedule, facing type, and any supplemental machining. Contact us for a detailed weight list for containers or bill of materials.

Available Grades and Equivalents

ASTM A105 / A105N: The standard forged carbon steel for ambient and high-temperature service. Normalized version (N) is recommended for sour service or when improved toughness is required.

ASTM A350 LF2: Low-temperature carbon steel for service down to −46°C. Required for cryogenic and arctic pipelines.

ASTM A694 F52–F70: High-yield forged flanges for high-strength transmission pipeline service.

GB 20# / Q235 / 16Mn: Chinese standard equivalents supplied when the customer accepts domestic-grade certification.

Manufacturing Standards and Quality Control

All flanges are produced under an ISO 9001 quality system. Raw forgings are sourced from qualified mills with EN 10204 3.1 material certificates. Machining is performed on CNC vertical and horizontal lathes to ensure bolt-hole patterns, flange thickness, and hub dimensions meet the specified standard. Each flange undergoes dimensional inspection, visual inspection, and marking verification. Optional tests include hardness testing, Charpy impact testing, ultrasonic examination, and magnetic particle inspection.

Chemical analysis: per heat, reported on MTC.

Mechanical testing: tensile, yield, elongation per heat-treatment batch.

Dimensional inspection: 100% of finished flanges.

Visual inspection: surface defects, marking, and facing condition.

Optional NDT: UT, MT, PT per ASTM or customer specification.

Applications

Oil and gas pipelines, refineries, and offshore platforms

Power plants, boilers, and heat-recovery steam generators

Petrochemical reactors, columns, and heat exchangers

Shipbuilding and marine piping systems

Water treatment, desalination, and process piping

Packaging and Shipping

Weld neck flanges are packed in seaworthy wooden pallets or steel cages, separated by size and rating to prevent mixing. Facing surfaces are protected with cardboard or plastic caps to avoid damage. Smaller sizes are bundled and strapped; larger sizes are shipped loose or crated. Each pallet is labeled with heat number, size, rating, quantity, and destination. We ship FOB, CFR, CIF, or DAP according to your preference.