The Large Diameter Weld Neck Flange is engineered for large bore pipeline systems that demand a strong, reliable connection at high flow rates. Produced from forged carbon steel, stainless steel and alloy steel billets, these oversized flanges maintain dimensional accuracy and mechanical integrity even at diameters up to 72 inch, making them ideal for main trunk lines, water transmission and major industrial piping.

Manufactured to ASME B16.5 and ASME B16.47 standards, each large diameter weld neck flange undergoes precision machining to guarantee flatness of the sealing face and concentricity of the bolt circle. The extended weld neck hub provides a gradual transition that supports full penetration butt welding, minimizing stress at the joint and delivering a leak-tight seal under sustained operating pressure.

Product Specifications

Key Advantages

• Available in diameters from 24 inch up to 72 inch
• Precision machined sealing face for leak-tight performance
• Full penetration butt weld hub for high joint strength
• Forged billet construction ensures uniform mechanical properties
• Dimensional control to ASME B16.5 and B16.47 tolerances
• Custom face drilling and bolt circle patterns available
• Suitable for high flow main trunk lines and transmission systems
• Complete traceability with mill test certificates

Frequently Asked Questions

Q: What is the maximum diameter available for a large diameter weld neck flange?

A: We manufacture large diameter weld neck flanges up to 72 inch. For diameters beyond 48 inch, flanges are typically supplied as custom-forged rings machined to ASME B16.47 Series A or Series B dimensions according to your piping specification.

Q: How do you ensure flatness on a large diameter sealing face?

A: Each large diameter weld neck flange is precision machined on large-bore CNC lathes and verified with a coordinate measuring machine. The raised face is machined with a controlled surface finish to ensure a reliable gasket seal under operating pressure.

Q: Can you produce large diameter flanges with custom bolt patterns?

A: Yes, we offer custom face drilling and bolt circle patterns to match non-standard mating equipment. Simply provide your drawing or specification, and our engineering team will confirm feasibility and lead time.

Manufacturing & Quality Control

Large diameter weld neck flanges are forged from carefully selected billets and machined on large-bore CNC turning centers. After machining, the sealing face flatness and bolt circle concentricity are verified with a coordinate measuring machine to ensure perfect alignment with mating equipment. Each flange is marked with heat number, material grade and pressure class for full traceability from billet to finished product.

Q: How are large diameter flanges packed and shipped?

A: Large diameter weld neck flanges are packed on reinforced steel pallets with protective edge guards and weather-resistant wrapping to prevent damage during transport. We coordinate with ocean freight and land carriers experienced in oversized cargo to deliver your flanges safely to the project site.

     TOBO GROUP sales head offce in Shanghai. 

     We are one of the Professional manufacturers Exporter  Pipeline products  in China .Our company was established in 1998, the plant covers 550, 000 square meters and a construction area of 6,8,000square meters, existing 260 workers and 45 technicians. 

      We have five branch factories which can supply the best quality pipes, tubes, fittings flanges and related accessories. Now, it owns a number of advanced pipe production equipments, metal, forging, machining, cold forming, hot extrusion, such as heat treatment process, producing 60, 000 tons of pipe fittings. Company with a variety of detection devices, such as nondestructive testing, chemical analysis, metallographic examination, physical experiments. The technical is very strength, our main products contain fittingsforged socket welding fittings and threaded fittings, pipe weld and the materials of the products contain stainless steel ,duplex-stainless steel alloy steel.

       In addition, we are authorized by more than 120 top-class mills from South Korea,Japan and China like JFE,SUMITOMO,POSCO,BAOSTEEL, TISCO,LISCO,.TPCO,HENGYANG VALIN and so on .

Our main products as follows:

• Stainless steel pipe & tube

(seamless pipe / welded pipe / square pipe /  rectangular tube,duplex stainless / inconel tube)

• Carbon / alloy steel pipe & tube

(seamless pipe / ERW / SSAW / LSAW / UOE / hollow section pipe / Galvanized Pipe)

• Tubing and casting

(line pipe,water pipeline,gas pipeline,oil pipeline)

• Special steel tube

(copper tube/titanium tube/aluminium tube/nickel alloy )

• steel bar 

(round bar/angle steel /flat steel/channel steel/steel wire)

• Pipe Fittings

(eblows, equal / reducing tees, concentric/eccentric reducers, caps, crosses, bends, dish end/end cup, stub ends, unions, couplings / hex couplings, swage nipples , nipples, hex. plug, sockolet, weldolet, thredolet, etc)

• Flange

(DIN flange/ AISI flange/blind flange/welding flange/stainless flange/slip on flange)

• steel sheet / coil

(stainless steel/carbon steel/alloy steel/galvanized steel/aluminium )

• Valve

(ball valve/gate valve/butterfly valve/globe valve/swing check valve/ check valve) 

      In order to comply with the global modernization services development trends and eliminating the varieties distress of the global enterprise‘s purchase in the consumables.. We coordinate the pressure pipe manufacturer which with the scale of production,quality control and high cost performance (has passed ISO 9001 quality series attestation, ccs, DNV,PED/97/23/EC,AD2000-WO,special equipment manufacturing license,ASME-SA182.through a variety of effective assort mechanism to make up the shortage of supply and Post-processing of VAT enterprise, and to supply high quality pipe fittings, because of the superior quality and good service, we have established long term business cooperation with more than 60 countries and areas,which covers Europe, Africa, South America, North America, Middle East, Taiwan and South East Asia and so on.

      With many years effort and support from our valuable customers, these products have obtained a big market share in the world. 

      Our business principle is "Superior quality, Competitive price, Timely delivery and Considerate service " Standing to the principle of “Enterprises focus on the core business”, TOBO will actively promotes the globalization of business strategy approach, using advanced supply chain management technology to service for clients with higher quality and more competitiveness ‘ s products. At the same time, we sincerely reply your inquiry, honesty waiting for your visiting and wish to have cooperation with you at the any time. We welcome all the customers to contact us for more information. We assure you, with our technical knowledge and experience, our company will be one of your Stable, Continuate business parters in China.

 info@tobo-group.com