Flanged valves use a raised surface mated to a groove for added strength in heavy-duty pipelines. Flange types include tongue and groove, raised face, ring-type joint, flat face, and tongue-and-groove groove. Different flange designs are not interchangeable, and mixing them can cause valve failure and dangerous leaks.
A flanged valve is a special type of valve in which a raised surface, usually in the shape of a lip or ring at the end of the valve fitting, is mated to a groove on the liner to which it attaches. This gives the valve connection added strength in heavy-duty pipelines such as those used in the chemical and petroleum industries. Visual illustrations of what a flange looks like can commonly be seen on railroad car wheels or those of city streetcars, where the steel lip or flange of the wheel fits within a groove on the track along which it runs. Flange dimensions and joints are manufactured to conform to one of several dominant standards, which include the British Standard (BS) adopted by European Standard (EN) 1092 in June 2007, to which the American Society of Mechanical Engineers standard ( ASME) compliant. A flanged valve can also be made to similar American National Standards Institute (ANSI) specifications that are widely used in the United States.
Flange types widely used in industrial settings usually follow one of five dominant shapes, including tongue and groove (M&F), raised face (RF), ring-type joint (RTJ), flat face (FF), and tongue-and-groove. – Groove (T&G). There are also several major types of flange valve designs that use these flange shapes, including ball valves, butterfly valves, check valves, and gate/sluice valves. Flange fittings are also made from one of four primary metals, including steel, cast iron, aluminum, or copper. The primary purpose that the flange connection serves on any flange valve design is that it increases the surface area of the mating surfaces, which increases the tensile strength of the material constituting the connection. Both the inside and outside diameter of a flange face are measured accurately to measure this force and evaluate the valve.
The RF flange system is considered to be the most popular design, in which a ring is raised above the flat circular surface of a connection plate which is bolted in line to a series of pipes. The flange size in the RF design is directly proportional to the pressure the flange fitting is built to handle, with the ASME B16.5 flange pattern, for example, having a flange height of 1.6 millimeters (0.063 or 1/16 inch), which can handle volumetric pressure up to 136 kilograms (300 pounds). A 6.4 millimeter (0.25 inch) overhanging RF flange is rated to handle a pressure level up to 1,134 kilograms (2,500 pounds). The installation of an RF flanged valve also includes a spiral wound stainless steel gasket which is placed inside the pipe where the flanged valve mates with the grooved joint on the opposite fitting. This gasket is wrapped together with graphite and Teflon tape, which strengthens the strength of the flange valve connection and the pipe joint in general.
Other types of flanges are used for very specific purposes. The FF flange valve has a flat face constructed of a less flexible but strong material, usually cast iron. FF flanges such as ASME B31.1 must be custom fitted to carbon steel facings and joints or the brittle nature of the iron flange can crack.
Ring joint flange designs are some of the more complicated and, in some cases, use steel grommets or gaskets that prevent the flange from making physical contact with the joint. A broken flange valve can easily result if the technician squeezes the gasket after tightening the connection, as some RTJ flanges are meant to contact the opposing coating and some are not. The RTJ design is mainly used in high pressure and high temperature applications.
While flange designs often look very similar, and an ANSI flange can look a lot like an ASME flange upon visual inspection, they are not to be mixed and matched. If RTJ, T&G or F&M designed flanged valve fittings are bolted together, the contact surfaces will not mate precisely and the valve will fail. As of 2011, there are also no seals with different flange settings on each side, such as F&M on one side and RTJ on the other, so dangerous leaks can also occur from bad seals in a faulty assembly.
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