Socket welding flange, a popular type of pipe flange, was initially developed for use on small-sized high- pressure piping. The fabrication of this type of flange is similar to that of a slip-on flange. However, the internal pocket of a socket weld flange allows for a smooth bore and better fluid flow. When provided with an internal weld, the static strength of this flange is equal to slip-on flange, but the fatigue strength is 50% greater than double welding slip-on flanges. Smooth bore conditions in such a flange can easily be attained without having to bevel the flange face and, after welding, to reface the socket weld flange as would be required with slip-on flanges. For this reason, the internally welded flange is popular in chemical process piping.
The Socket weld Flanges is similar to a slip-on flange, except that it has a bore and a counter bore. These act as a socket, holding the pipe in place before welding, hence the name. The counter bore is slightly larger than the OD of the matching pipe, allowing the pipe to be inserted into the flange, while the diameter of the smaller bore is the same as the ID of the matching pipe. This difference in bore size acts only as a restriction to the depth insertion of the pipe, and therefore eliminates any restriction in flow.