Learn how to use a simple tool to flare pipe and make sure your flare fitting connections are installed properly.
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How to Use a Pipe Flaring Tool

When it comes to distributing A/C refrigerant, gas, fuel-oil or very high-pressure water through soft copper or aluminum pipe, there's really only one worthy alternative to soldering: flare fittings. Where soldering with an open flame could prove difficult or dangerous (a real possibility when working with gas and oil lines), flare fittings allow for a strong mechanical joint capable of withstanding pressures in the 450-3000 psi range, depending on the pressure rating of the materials being used.

Typically brass or steel, flare fittings are composed of a threaded body with flared ends, and a nut. They utilize a corresponding flare at the end of the pipe to create their highly secure connection. Creating that flared end is accomplished by using a special tool.

Pro Tip: Flaring is typically only done with malleable metal tubing like soft/annealed copper and aluminum. In situations where only hard copper pipe is available, you can still flare the pipe ends, but they will need to be annealed first. Annealing hard copper pipe is a fairly advanced skill; if you aren't comfortable with it, leave it to a pro.

Pipe flaring tools are very simple in both design and operation. They consist of two separate parts: a die block (or "flare form") with openings for different pipe sizes, and a flared cone attached to a yoke. As the cone is pressed into the pipe end, it shapes the soft metal into the 45° flare that the fitting calls for.

Heads up! Always be certain that you're using the correct flaring tool: in addition to plumbing/HVAC applications, flare connections are used in industry and the automotive world (brake lines, etc.). The angle of those flares, however, is 37.5° - not 45° as used in "home" applications.

Flaring Steps

Step 1: Cut your copper or aluminum using a tube cutter to ensure a clean cut - hacksaws and other cutting tools can make for an uneven cut or burrs, which will compromise the flare.
Step 2: Use a deburring tool or abrasive cloth to remove any burrs and debris in and around the pipe end.
Step 3: Slide the flare nut onto the pipe, with the tapered end facing away from the end of the pipe to be flared. The nuts need to be on the pipe before both ends are flared.
Step 4: Insert the pipe into the corresponding hole in the die block. Your flare should turn out fine with the pipe end flush against the block (some users insist on leaving just a bit sticking out - about an 1/8-1/16 of an inch).
Step 5: Tighten the wingnut closest to the pipe first.
Step 6: Then tighten the far wingnut.
Step 7: Place the yoke onto the die block - it should hook or clamp into place on the underside of the block.
Step 8: Position it so that the cone is directly above the pipe to be flared. Turn the handle to move the cone toward the pipe.
Step 9: Keep turning until the cone is fully seated in the pipe and can be tightened no further (without great force).
Step 10: Back the cone out and take off the yoke.
Step 11: Remove the pipe from the die block. The newly flared pipe-end should be smooth and even.
Step 12: Check it out against the fitting body, ensuring that the flare sits fully and evenly on the fitting, without reaching the threads.

Problems? Problems usually come up as the result of the pipe slipping in the block while it's being flared. Should there be any issues, you can simply cut the pipe below the end in question, and try again.

When finally installing the new flare fitting, make sure that you do not use any joint sealing compounds or tape on the threads. You can use a drop of threading oil to help make connecting your fitting easier. Always leak test after any new connection - this is especially critical if you're dealing with a gas or oil line.

As with any new skill, you should probably do a few practice runs on any spare bits of soft copper tubing you might have lying around; if you're buying new tubing, get an extra foot to play around with. When it comes to crunch time, it will pay off!

Pipe flaring tool

Purchase this handy, easy to use tool for flaring pipe - $16.11


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Frequently Asked Questions

Q. "Where do you use compression versus flare fittings?"
A. We prefer flare with soft tubing over 3/8" OD in size and compression fittings on all hard copper and soft tubing 3/8" OD and smaller. Don't use compression fittings on gas connections at all as most codes do not allow it nor do we recommend it.

Q. "What is the flare degree of the flare fittings you offer?"
A. The fittings we offer are SAE 45° flare with the exception of the 15/16"-16 flare cap found on our gas-related products page. The 15/16"-16 are 45° flare, but are not SAE fittings.

Q. "Are flare fittings suitable for natural gas connections?"
A. Brass and copper pipe or tubing must not be used where the gas contains more than an average of 0.3 grams of hydrogen sulfide per 100 scf (standard cubic feet) of gas (0.7 mg/100) according to section 1208.5.2.3 of the 2012 Uniform Plumbing Code and section 54.5.6.2.3 of the NFPA (National Fire Protection Association) fuel gas code. Since natural gas can contain some hydrogen sulfide, the brass flare fittings we offer are not recommended. Galvanized and black steel pipe and fittings can be used if it is standard weight Schedule 40 or thicker.

Q. "Why do you only offer a 15/16" flare cap and no other 15/16" flare fittings?"
A. The 15/16" - 16 thread flare fitting is used strictly for natural and propane flexible gas connectors and not for water or with fittings used in automobiles. Up until the 1980's, 5/8" O.D. SAE (Society of Automotive Engineer) standardized flare fittings were used for natural gas and propane flexible gas connections.

5/8" O.D. SAE Flare fittings were too close in size to 1/2" iron pipe size (IPS) fittings and pipe nipples. Because of this, 1/2" IPS couplings were often being used to connect to 5/8" O.D. SAE Flare fittings and IPS nipples into flexible gas connectors which then would not properly seal causing a small gas leak.

To alleviate this type of safety issue, the American gas industry implemented the 15/16" threaded flare fitting with fine threads (16 threads per inch) to be used on 5/8" O.D. (outside diameter) tubing.

The flare fittings we offer are SAE 45° flare with the exception of the 15/16"-16 gas flare fittings. The 15/16"-16 are 45° flare, but are not SAE fittings.

Q. "How can I measure my flare fitting to know if it is 15/16"-16 flare or another size?"
A. The 15/16"-16 male flare thread measures 15/16" diameter from the outside of the male threads. The flare threads have 16 threads per inch. The actual opening through the fitting is 1/2" inside diameter for the gas to flow through. Gas appliance connectors larger than 1/2" O.D. use special flare fittings designed for gas use only.

Q. "Why shouldn't I use PTFE thread sealing tape or pipe joint compound on my flare threads?"
A. PTFE tape and pipe joint compound (also known as "pipe dope") should only be used on "IPS" ("iron pipe size") threads, which are normal pipe threads. IPS threads make their seal along the threads themselves; when a piece of IPS-threaded pipe is screwed into a fitting, PTFE tape and/or pipe dope is used to assist that seal on the threads. Flare fittings, on the other hand, seal on the beveled ends of the fittings, and so using pipe dope or tape on flare threads could actually prevent the fittings from making an adequate seal.


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