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.
Welding Neck Flanges are easy to recognize as the long tapered hub, that goes gradually over to the wall thickness from a pipe or fitting. The long tapered hub provides an important reinforcement for use in several applications involving high pressure, sub-zero and / or elevated temperatures. The smooth transition from flange thickness to pipe or fitting wall thickness effected by the taper is extremely beneficial, under conditions of repeated bending, caused by line expansion or other variable forces.These flanges are bored to match the inside diameter of the mating pipe or fitting so there will be no restriction of product flow. This prevents turbulence at the joint and reduces erosion. They also provide excellent stress distribution through the tapered hub.The Weld neck flanges are attached by butt-welding to the pipes. These are used mainly for critical services where all the weld joints need radiographic inspection. While specifying these flanges, the thickness of the welding end also should be specified along with flange specification.
A weld neck flange (WN flange) means a flange has a neck for weld with the pipe, it is easily to recognized by their long tapered neck on the flange (The neck is also called hub in the weld neck flange). The tapered neck can supply a high strength reinforcement to support flange and pipe. It means the weld neck flange is suitable to used in high pressure and extremely temperature situation.
The weld neck flange is connected with the pipe from the neck in butt welding method, that means the neck should be have same material and same outer diameter and wall thickness with the pipe. The butt welding joint could provide a strong connection between the pipes and flanges which is better for high pressure application.