welding neck flange,socket weld flange,ansi flange:

Weld Neck or Welding Neck Flanges:
The weld neck flange is normally referred to as the "high hub" flange. It is designed to transfer stresses to the pipe, thereby reducing high stress concentrations at the base of the flange. The welding neck flange is the best designed butt-welded flange of those currently available because of its inherent structural value. It is expensive because of the design.

Socket Weld or Socket Welding Flange:
The socket welding flange is similar to a slip-on flange except it has a bore and a counter bore dimension. The counter bore is slightly lager than the outer diameter of the matching pipe, allowing the pipe to be inserted into the flange similar to a slip-on flange. The diameter of the smaller bore is the same as the inner diameter of the matching pipe. A restriction is built into the bottom of the bore which sets as a shoulder for the pipe to rest on. This eliminates any restriction in flow when using a socket welding flange.