These weld-neck flanges are 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, or hub, transmits stresses to the pipe, reducing stress concentrations at the base of the flange. The gradual transition of thickness from the base of the hub 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.

These socket weld flanges are similar to a slip-on flange in outline, but the bore is counter –bored to accept pipe. The diameter of the remaining bore is the same as the inside diameter of the pipe. The socket weld flanges are attached to the pipe by a fillet weld around the hub of the flange. An optional interval weld may be applied in high stress application. It’s biggest use in high pressure systems such as hydraulic and steam lines.

These threaded flanges are similar to a slip-on flange in outline, but the bore is threaded, thus enabling assembly without welding. This obviously limits its applications 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 applications.

The slip on flanges are slipped over the pipe then welded both inside and outside to provide sufficient strength and prevent leakage. These slip on flanges are used in preference to weld necks by many users because of its lower cost and the fact that less accuracy is required when cutting pipe to length.

These are blind flanges without bore and are used to shut off a piping system or vessel opening. These blind flanges also permits easy access to vessels or piping system for inspection purposes. Blind flanges can be supplied with or without hubs at the manufacturers option.  Spectacle Blank (also called a Figure 8 Blank) This is a pressure retaining plate with one solid end and one open end connected with a web or tie-bar. In normal operation, the open end forms the seal between two flanges and permits normal flow of fluid through pipe work. If the solid end is swung into position it effectively blanks off the pipe and halts the flow.

This is again similar to a slip-on flanges, but it has a radius at the intersection of the bore and the lap-joint flanges face to accommodate a lap stub end. The face on the stub end forms the gasket face of the flange. This type of flange is used in applications where sections of piping systems need to be dismantled quickly and easily for inspection or replacement.

The function of an orifice flange is to provide access to a line for meeting off gases or liquids. An orifice plate is clamped between a pair of flanges when installed in a line and the whole assembly is referred to as an orifice flange union. Jack-screws within the assembly facilitate removal of the orifice plate. The orifice plate, the metering device, consists of a thin plate with a concentric, square edge, circular hole in the center. Two pressure tap-holes are drilled in each orifice flange to measure pressure differences through the orifice.