Flare fittings are a specialized type of hydraulic and compression tube fitting used primarily with metal tubing, such as steel and stainless steel, but they can also be used with other materials. The defining feature of a flare fitting is the flaring or expansion and deformation of the tube’s end. This flared end is pressed against a fitting and secured by a precisely fitting nut, ensuring a leak-free connection.
The process of creating a flare in tubing is a forging operation, typically done as a cold working procedure. To assemble, a flare nut secures the flared tubing’s tapered end to a correspondingly tapered fitting, creating a durable, leak-tight seal. These connections are highly reliable, making them ideal for critical and hard-to-reach locations.
The tool for flaring tubing consists of a die that holds the tube, and a mandrel or rolling cone is used to form the flare by cold working the tube end.
There are several common standards for flare fittings, including the 45° SAE flare, the 37° JIC flare, and the 37° AN flare. Each has its specific applications and compatibility.
For high-pressure situations, flare joints are often double-flared for extra strength. This process involves folding the tube wall over itself before forming the bell end, preventing the stretching and potential cracking that can occur with single flares. This double thickness flare is formed by first creating a radial outward bubble at the tube end, which is then shaped axially by a conical tool.
SAE 45° flare fittings meet SAE J512 standard, and are widespread in automotive applications, as well as in plumbing, refrigeration, and air conditioning systems. These fittings, often made of brass, are not interchangeable with AN/JIC connections due to the different flare angles.
JIC 37° flare fittings meet SAE J514/ISO 8434-2 standard, typically made of steel or stainless steel, are used in higher pressure hydraulic systems. They are not suitable for applications requiring AN connections, which have different quality standards.
AN 37° flare fittings comply with MIL-F-5509 specifications and AS4841and are usually specified for military and aerospace applications and can be made from various materials. While the AN (Army/Navy) standard has evolved, these fittings are often still referred to by their original name.
Flared fittings provide an alternative to solder-type joints, offering the advantage of being mechanically separable without the need for an open flame. For example, copper tubing used for gases like propane, liquefied petroleum gas, or natural gas, often employs single 45°-flare type brass fittings, as per NFPA 54/ANSI Z223.1 National Fuel Gas Code. While model codes generally permit the use of flare fitting joints, it’s important to consult the local authority (AHJ) for specific applications.
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