Flanges

The Slip-On flange has a low hub because the pipe slips into the flange prior to welding. It is welded both inside and out to provide sufficient strength and prevent leakage. Slip-on flanges are all bored slightly larger than the outside diameter of the matching pipe. They are preferred over welding neck flanges by many users due to their lower initial cost, but total cost after installation is probably not much less than that of the welding neck flange because of the additional welding involved.

The welding neck flange is normally referred to as the “high hub” flange. It is designed to transfer stresses to the pipe, thereby reducing high stress concentrates 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.

The blind flange is a flange without a bore. It is used to close off the ends of a piping system and/or pressure vessel opening. It also permits easy access to the interior of a line or vessel once it has been sealed and must be reopened.

The threaded flange is similar to the slip-on flange, but the bore is threaded. Its advantage is that it can be assembled without welding, expanding its use in low pressure services at ordinary atmospheric temperatures, and in highly explosive areas where welding creates a hazard.

The socket welding flange is similar to a slip-on flange except it has a bore and counter-bore dimension. The counter-bore is slightly larger than the outside 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 inside diameter of the matching pipe. A restriction is built into the bottom of the bore which allows the pipe to rest on, eliminating any restrictions in flow.