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Flare fittings are a type of compression fitting used with metal tubing, usually soft steel, ductile (soft) copper and aluminum, though other materials are also used. Tube flaring is considered to be a type of forging operation, and is usually a cold working procedure. During assembly, a flare nut is used to secure the flared tubing's tapered end to the also tapered fitting, producing a pressure-resistant, leak-tight seal. Flared connections offer a high degree of long-term reliability and for this reason are often used in mission-critical and inaccessible locations.
The tool used to flare tubing consists of a die that grips the tube and a mandrel that is forced into the end of the tube to form the flare by cold working. The most common flare fitting standards in use today are the 45° SAE style, and the 37° AN style, also used with the JIC system. The AN/JIC style generally has a higher pressure rating for a given size tubing. SAE and AN/JIC fittings are completely incompatible due to the different flare angle. Further, AN fittings (or those complying with subsequent standards) and JIC fittings are not interchangeable for design-controlled applications due to differing quality standards. The refrigeration and air conditioning industry usually uses 45° flare connections while hydraulic hoses are usually 37 1⁄2° flare connections.
Flared fittings are an alternative to solder-type joints that is mechanically separable and doesn’t require an open flame. Copper tube used for propane, liquefied petroleum gas, or natural gas may use flared brass fittings of single 45°-flare type, according to NFPA 54/ANSI. Z223.1 National Fuel Gas Code. Many plumbing codes, towns, and water companies require copper tube used for water service to be type-L or type-K. All National Model Codes permit the use of flare fitting joints, however, the authority having jurisdiction (AHJ) should be consulted to determine acceptance for a specific application.
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