Threaded Flanges

Welding Neck Flanges:The welding neck flange is normally referred to as the "high hub" Flange. It is designedto transfer stresses to the pipe, thereby reducing high stress concentrationsat the base of the Flange. The welding neck flange is the best designed butt-weldedflange of those currently available because of its inherent structuralvalue. It is expensive because of the design.Threaded (Screwed) Flanges:The threaded flange is similar to the slip-on flange, but the bore is threaded. Itschief merit is that it can be assembled without welding, explaining its use inlow pressure services at ordinary atmospheric temperatures and in highly explosiveareas where welding create a hazard.Slip-on Flanges:The slip-on flange has a low hub because the pipe slips into the flange prior towelding. It is welded both inside and out to provide sufficient strength and preventleakage. Slip-on flanges are all bored slightly larger that the O.D. of thematching pipe. They are preferred over welding neck flanges by many users due totheir lower initial cost, but final installation cost is probably not much lessthan that of the welding neck flange because of the additional welding involved.Lap joint Flanges:The lap joint flange is practically identical to a slip-on flange except it has aradius at the intersection of the bore and flange race. This radius is necessaryto have the flange accommodate a lap joint stub end. Normally, a lap joint flangeand a lap joint stub end are mated together in an assembly system.Blind Flanges:The blind flange is a flange without a bore. It is used to close off the ends ofa piping system and/or a pressure vessel opening. It also permits easy access tothe interior of a line or vessel once it has been sealed and must be reopened.Socket Welding Flanges:The socket welding flange is similar to a slip-on flange except it has a bore anda counter bore dimension. The counter bore is slightly lager than the O.D. of thematching pipe, allowing the pipe to be inserted into the flange similar to aslip-on flange. The diameter of the smaller bore is the same as the I.D. of thematching pipe. A restriction is built into the bottom of the bore which sets asa shoulder for the pipe to rest on. This eliminates any restriction in flow whenusing a socket welding flange.