Long Weld Neck Flange

Standard specifications: Mainly follow HG/T20615-2009 (China Chemical Standard) and ASME B16.5 (US Standard), and some designs also comply with international standards such as ISO 7005-1.
Material selection: Common materials include carbon steel, stainless steel (such as 304/316L), alloy steel, and duplex steel (such as 2205). For special working conditions, Hastelloy or titanium alloy materials can also be used.
Production process: The integral forging or die forging process is used, combined with high-precision CNC lathe processing to ensure the density and dimensional accuracy of the flange.

Long Weld Neck Flanges are usually used in the following scenarios:
Energy and chemical industry: petroleum refining high-pressure pipelines, LNG storage and transportation systems, and pickling equipment circulation loops.
Electricity and nuclear power: Ultra high voltage transmission steel pipe towers and cooling systems for nuclear power plants must meet the first level welding seam standard.
Ships and pharmaceuticals: seawater cooling system, sterile fluid delivery, surface polished to Ra ≤ 0.8 μ m to meet hygiene requirements.
General Industry: High temperature boilers, pressure vessels, and pipeline connections for repeated loads.

Welding method:
Manual gas shielded welding (GTAW/SMAW): used for root welding of small-sized flanges or complex working conditions.
Automatic submerged arc welding (SAW): Suitable for double-sided penetration welding of large diameter flanges, without the need for root cleaning, with high efficiency and a weld qualification rate of 98%.
Groove design: Single-sided V-shaped or U-shaped groove is usually adopted, with blunt edge ≥7mm and gap between joints of 0-1mm to ensure full penetration of the weld seam and prevent burn-through.
Quality control: 100% X-ray (RT) and ultrasonic (UT) inspection, hydrostatic pressure test up to 1.5 times the working pressure, materials must be certified according to EN 10204 3.1.

Advantages:
High load-bearing capacity: The neck structure disperses stress, reduces leakage risk, and is suitable for high-pressure systems above PN16MPa.
Easy installation: on-site welding eliminates the process of weld seam inspection, especially suitable for modular equipment with limited space.
limitations:
High cost: The welding workload is large, the consumption of welding rods is high, and the processing cycle is long.
Weak fatigue resistance: Not recommended for pipelines with frequent bending or sudden temperature changes.