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Malleable fittings are a type of pipe fitting generally made of iron. These items are commonly used for electrical conduit and various plumbing connections. The malleable fitting gets its name from the type of iron from which it is cast — white iron. Upon casting, it is a very brittle metal. Through the process of annealing, the white iron is softened into one of the three forms of malleable iron.
Blackheart malleable iron is used in production of malleable plumbing fittings. The blackheart iron gives the malleable fitting its dark color, and these connectors are commonly known as black pipe fittings. In some cases, a malleable fitting is galvanized to protect the pipe fitting from corrosion. Galvanization is a process in which a zinc coating is applied to the fitting. The malleable pipe fitting is usually threaded to make assembly of pipes and fittings easier. Basic joints can be made using hand tools and malleable fittings while more crucial joints may employ thread sealants.
The plumbing industry used malleable fittings and pipes for many years until copper, PVC, and PEX pipe became more economical. Due to concerns about chemicals such as zinc leaching into drinking water, galvanized malleable fittings are no longer commonly found in home plumbing systems. While the malleable fitting is still in use for high pressure applications, modern construction tends to use the less expensive and safer pipe fitting options for other applications.
Modern malleable fitting usage is primarily restricted to the plumbing of gas lines and high pressure steam used for heating and industrial application. Threaded fittings and pipes make malleable fittings suitable for creating tight connections using hand tools and thread sealants. These airtight joints with the ability to withstand high internal pressures are necessary for the safe delivery of gases or steam. The use of malleable iron pipe and fittings for the transmission of steam first became popular in the United States during the 1840s. The malleable fitting was primarily used in the construction of steam radiator heating systems at that time.
Galvanized malleable fittings are commonly used in outdoor electrical conduit applications. The zinc coating of the galvanized malleable fitting provides resistance to corrosion which could compromise the conduit and leave electrical wiring exposed. The natural strength and rigidity of the galvanized iron pipe and fittings serve to protect the electrical wiring from physical damage caused by crushing or abrasion.