Weld neck flanges are the most popular flange type with a neck extension with a weld bevel at the end. This type of flange is designed to butt weld directly to pipe to provide a superior and relatively natural form connection. In larger sizes and higher pressure classes, this is almost exclusively the type of flange connection utilized. If only one bored flange style existed in modern applications, the weld neck would be your flange of choice.

Raised Face Weld Neck Forged Flange

The weld bevel joins to a pipe end with a similar bevel in a V-type connection which allows for a uniform circular weld around the perimeter to form a unified transition. This allows for the gas or liquid within the pipe assembly to flow with minimal restriction through the flange connection. This weld bevel connection is inspected after the weld procedure to ensure that the seal is uniform and lacking anomalies.

Weld neck with matching bevel to pipe
Weld neck with matching bevel to pipe

The other noticeable feature of the weld neck flange is the tapered hub. This type of connection provides a more gradual distribution of pressure forces along the transition from the pipe to the base of the flange, helping to withstand some of the shock from use in a higher pressure and higher temperature operating environment. The mechanical stresses are limited given the extra steel material along the hub transition.

As higher pressure classes require this type of flange connection almost exclusively, weld neck flanges are often made with a ring type joint facing (otherwise known as RTJ face). This sealing surface allows for a metallic gasket to be crushed between the grooves of both connecting flanges to form a superior seal and complement the high strength weld bevel connection to the pressurized pipe assembly. An RTJ weld neck with a metal gasket connect is the primary choice for critical applications.

Ring Type Joint Octagonal Gaskets
Ring joint gaskets for RTJ weld necks

Also known as nozzle flanges or “long neck” flanges, these items were designed specifically with the pressure vessel and tank fabrication industry in mind. They are usually made as a one-piece construction with the intention of replacing a standard weld neck and pipe weld combination. The lack of a necessary weld connection is the defining feature of this flange style.

Long Weld Neck Forged Flanges

They usually have one straight thru bore with a square cut end (instead of the typical weld neck bevel). Generally, the bore size of the long weld neck is the exact same as the actual nominal pipe size but can be changed as necessary. The overall length of the nozzle flange is also up to the end user, and the body of the nozzle can be modified to some pre-existing sizes or custom sizes for additional reinforcement. The base of the neck connecting to the base of the flange is slightly radiused to alleviate the abrupt perpendicular connection between both portions of the flange and to solidify the idea of a reinforced one piece construction.

Per ASME B16.5 subsection 2.8, these flange styles are also known as “straight hub welding flanges” and are given minimal detail in the governing specification. This is due to the fact that long weld necks are chosen on a per application basis depending on the particular engineering requirements of a given tank or pressure vessel. The operating pressure, temperature, and media of the vessel are all critical factors in determining just what type of long weld neck flange connection you require.

Long Weld Neck
CAD rendering of a LWN

Aside from standard long weld necks, Texas Flange also offers a variety of nozzle connections with varying wall thicknesses. Reinforced barrel flanges in nozzle form are an option when your pressure vessel requires a stronger outlet connection and can be provided with barrel thickness you desire. Please contact us regarding your specific application as we can provide nozzle flanges in all commercially available material grades, including carbon, stainless, and nickel alloys.


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