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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 either a mandrel or rolling cone is forced into the end of the tube to form the flare by cold working.
SAE 45° flare connections are commonly used in automotive applications as well as for refrigeration and air conditioning. SAE fittings are typically made from brass. SAE and AN/JIC connections are incompatible due to the different flare angle.
JIC 37° flare connections are used in higher pressure hydraulic applications. JIC fittings are typically steel or stainless steel. JIC fittings are not permissible where AN connections are specified, due to differing quality standards.
AN 37° flare connections are typically specified for military and aerospace applications. Fittings can be made from a large variety of materials. The “AN” standard (for Air Force / Navy) has been replaced by other military and aerospace standards, though in practice these fittings are still referred to as AN.
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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