A weld neck flange (also known as a high-hub flange and tapered hub flange) is a type of flange. There are two designs. The regular type is used with pipes. The long type is unsuitable for pipes and is used in process plant. A weld neck flange consists of a circular fitting with a protruding rim around the circumference. Generally machined from a forging, these flanges are typically butt welded to a pipe. The rim has a series of drilled holes that permit the flange to be affixed to another flange with bolts.
Such flanges are suitable for use in hostile environments that have extremes of temperature, pressure or other sources of stress. The resilience of this type of flange is achieved by sharing the environmental stress with the pipe with which it is welded. This type of flange has been used successfully at pressures up to 5,000 psi.
Socket-weld pipe flanges are typically used on smaller sizes of high pressure pipes. These pipe flanges are attached by inserting the pipe into the socket end and applying fillet weld around the top. This allows for a smooth bore and better flow of the fluid or gas inside of the pipe. Slip on Pipe flanges with a hub have published specifications that range from 1/2" thru 24".Elite flange provides Socket Weld pipe flanges in all material grades, specifications and sizes.Socket Weld pipe flanges are typically provided with a raised face, flat face, or RTJ facing. When a raised face is necessary for socket weld pipe flanges, the standard height is 1/16" for socket weld pipe flanges under 400#. For socket weld pipe flanges of 400# and up, the standard socket weld pipe flange raised face height is 1/4".
The Slip On type flanges are attached by two fillet welds, inside as well as outside the flange. The calculated strength from a Slip On flange under internal pressure is of the order of two-thirds that of Welding Neck flanges, and their life under fatigue is about one-third that of the latter. Normally, these flanges are of forged construction and are provided with hub. Sometimes, these flanges are fabricated from plates and are not provided with the hub.The disadvantage of the flange is that a combination of flange and elbow or flange and tee is not possible because named fittings have not a straight end that complete slid in the Slip On flange.
The Lap joint flanges are used with stub ends when piping is of a costly material. For example, in a stainless steel pipe system, a carbon steel flange can be applied, because flange will not come in contact with the product in the pipe. The stub ends will be butt-welded to the piping and the flanges are kept loose over the same. The inside radius of these flanges is chamfered to clear the stub end radius.These flanges are nearly identical to a Slip On flange with the exception of a radius at the intersection of the flange face and the bore to accommodate the flanged portion of the Stub End. Their pressure-holding ability is little, if any, better than that of Slip On flanges and the fatigue life for the assembly is only one tenth that of Weld Neck flanges. Thus this flange connections are applied in low-pressure and non critical applications.
Blind Flanges are manufactured without a bore and used to blank off the ends of piping, Valves and pressure vessel openings.From the standpoint of internal pressure and bolt loading, blind flanges, particularly in the larger sizes, are the most highly stressed flange types.However, most of these stresses are bending types near the center, and since there is no standard inside diameter, these flanges are suitable for higher pressure temperature applications.
Threaded flanges are used on pipe lines where welding cannot be carried out. A threaded flange or fitting is not suitable for a pipe system with thin wall thickness, because cutting thread on a pipe is not possible. Thus, thicker wall thickness must be chosen.ASME B31.3 Piping Guide says: Where steel pipe is threaded and used for steam service above 250 psi or for water service above 100 psi with water temperatures above 220° F, the pipe shall be seamless and have a thickness at least equal to schedule 80 of ASME B36.10.Socket welding and threaded flanges are not recommended for service above 250°C and below -45 C.
The Reducing flanges are used to connect between larger and smaller sizes without using a reducer. In case of reducing flanges, the thickness of the flange should be that of the higher diameter. These flanges normally come in blind, slip-on, threaded and weld neck flanges. They are available in all pressure classes and provide a good alternative to connecting two different sizes of pipe. This type of flange should not be used if an abrupt transition would create unwanted turbulence, such as at a pump.