Types and Applications

Slip-On Weld Flange
         The flange is slipped over the pipe or tube and welded (usually both inside and outside) to provide strength and to prevent leaks. These flanges are at the low cost end of the scale, and do not require high accuracy when cutting the pipe or tube to length. They can sometimes have a boss or hub, and can be made with a bore to suit pipe or tube.

Weld Neck Flange
         This flange is designed to be joined to a piping system by butt welding. It is relatively expensive because of its long neck, but is preferred for high stress applications. The neck transmits stresses to the pipe, reducing stress concentrations at the base of the flange. The gradual transition of thickness from the base to the neck to the wall thickness at the butt weld provides important reinforcement of the flange. The bore of the flange matches the bore of the pipe, reducing turbulence and erosion.

Threaded Flange
         This is similar to the slip-on flange in outline, but the bore is threaded, thus enabling assembly without welding. This obviously limits its application to relatively low pressure piping systems. The flange may be welded around the joint after assembly, but this is not considered a satisfactory method of increasing its use in pressure applications.

Socket Weld Flange
         This is similar to a slip-on flange in outline, but the bore is counter-bored to accept the pipe. The diameter of the remaining bore is the same as the inside diameter of the pipe. The flange is attached to the pipe by a fillet weld around the hub of the flange. An optional internal weld may be applied in high stress applications. Its biggest use is in high pressure systems such as hydraulic and steam lines.

Lap Joint Flange
         This is again similar to a slip-on flange, but it has a radius at the intersection of the bore and the flange face, and no raised face, to accommodate a lap joint stub end. The face of the stub end forms the gasket face of the flange. This type of flange is used in applications where sections of the piping system need to be dismantled quickly and easily for inspection or replacement, because the stub end is welded to the pipe, not the flange. As the flange is not welded to the pipe, this allows for easy alignment to the mating flange.

Blind Flange
         This is a flange without a bore and is used to shut off a piping system or vessel opening. It also permits easy access to vessels or piping systems for inspection purposes.

Loose Flange
         This is usually used with a pressed collar, where the flange is placed behind the collar before the collar is welded to the pipe or tube. The flange is not welded, and thus allows for easy alignment. As the flange is not in direct contact with the liquid, alternative materials can be used for the flange.