Weld neck flanges are a flanges with a heavy welding neck which is hot formed from a circular section of steel plate having a small co-axial hole in the center.
Specifications :
ANSI B 16.5 from 1/2" to 24" and classes150 to 2500 (complete range)
Applications :
Recommended for orifice flanges. These work as substitute for slip-on-flanges in the cases where the diameter of the tube is very small and working pressure is very high.