LWN (long weld neck flange) is considered a specialty steel flanges because of its protruding neck, also referred to as a hub. The neck extends from the flat surface of the flange and receives and guides the pipe into place — the neck serves as an extension of the boring. Tapering the neck provides extra reinforcement for use in high-pressure or extreme and fluctuating temperature applications. Tapering the flange reduces the steel's thickness so that the opening of the neck blends with the pipe it receives — the tapered neck appears to be an extension of the pipe.
Uses
LWN steel flanges are largely used in the petroleum and chemical industries but can also be used in residential and commercial buildings where fluctuating temperatures and high stress are expected, such as a main water or gas source.Long neck steel flanges are used under conditions where line or pipe expansion creates bending or repeated changes in the pipe. Because a long neck flange is used in pressurized applications, the flange may have additional pressure connections and may be referred to as an orifice flange. The flange supports free product flow when bored to match the diameter of the pipe it will receive. Long weld neck flanges are attached using V-shaped welds known as butt welds.
Standards
Manufacturers of steel flanges follow specific production standards when designing or machining a flange. Dimensional tolerances and dimensions for long neck orifice flanges are covered in the American Society of Mechanical Engineers section 36 of publication B16. AMSE publication B.16 covers pipes and fittings made of steel, cast iron, cast bronze and wrought copper.