Commonly found in plumbing applications, metal flanges provide a quick and easy method for joining lengths of pipe to one another. A flange consists of an external ring around one end of a structure, pipe, or tube that contains matching boltholes for easy assembly. In contrast, pipes that require joining but lack any flanges normally involve either welding or soldering as the joining method. There are several different types of metal flanges available to cover a wide variety of applications. These include the copper flange, iron flange, and stainless steel flange; these are implemented as structural flanges, plumbing flanges, and even microwave flanges. The types of metal flanges one may encounter often depends on their applications or uses. For example, water pipes generally use a copper or stainless steel flange, since a ductile iron flange can fail over time due to the natural result of rust forming when water reacts with iron. In other words, the product passing through any given flanged system dictates the appropriate materials used in the construction of the flanges, as well as in the tubing or piping itself.
Since such a wide variety of applications exists, one would expect a challenge in matching up specific sizes of metal flanges. A system of uniformity, however, helps make this task rather simple. In the U.S., a classification system from the American Society for Mechanical Engineers (ASME) helps to discern between these choices by providing a set of standards to follow when certain projects require it. For example, when a plumber or other mechanical contractor needs to repair or replace sections of an established plumbing system, any metal flanges he or she encounters are already classified into certain sizes. This makes replacement as easy as ordering the appropriate ASME flanges. ASME is only an American piping standard, however, while other countries typically have their own classification systems. For example, the PN/DIN classification is used in many parts of Europe; the JIS/KS classification in Japan or Korea; and the BS10 in Britain or Australia. While an ASME flange will mate to another ASME flange, it is unlikely that it would match one from another country's classification system. The types of metal flange designs may also change with each application. For example, high-pressure connections may incorporate a "tongue-and-groove" interface. An application of this sort consists of two mating metal flanges protruding slightly into another flange, which greatly reduces the chances of pressure seeping out of the connection. This can be crucial if the product leaking out happens to be something dangerous, like a flammable gas.
