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WELDING NECK FLANGES are distinguished from other types by their long tapered hub and gentle
transition of thickness in the region of the butt weld joining them to the pipe. The long
tapered hub provides an important reinforcement of the flange proper from the standpoint of
strength and resistance to dishing. The smooth transition from flange thickness to pipe wall
thickness effected by the taper is extremely beneficial under conditions of repeated bending,
caused by line expansion or other variable forces and produces an endurance strength of welding
neck flanged assemblies equivalent to that of a butt welded joint between pipes, which, in
practice, is the same as that of unwelded pipe. Thus this type of flange is preferred for
every severe service condition, whether this results from high pressure or from sub-zero or
elevated temperature, and whether loading conditions are substantially constant or fluctuate
between wide limits.
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