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Old 02-27-2017, 05:00 PM   #1
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Cracked 3/8" Flare Nuts

I installed a new fridge in the 69 Globetrotter. I had to reroute a couple of the propane lines. I tighten the fittings, pressurized, and checked every joint for leaks.

Much to my surprise I found two 3/8" flare nuts that were cracked! They were leaking gas of course. Neither one were the nuts I had loosed.

Last winter I had the entire propane distribution piping down while I redid the belly pan in this old Globetrotter. I reassembled the piping, tightened the fittings, and checked for leaks. All was good after I fixed a couple of leaks I found.

Has anyone ever experienced a cracked flare nut?

David
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Old 02-27-2017, 05:37 PM   #2
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Yes, they've been overtorqued.
Some people believe that if a little torque is good.... a LOT must be BETTER!

Use a bit of thread lube paste/sealant and tighten only enough to seal the fitting. Re-tighten after the first trip, and then they should not need further.
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Old 02-27-2017, 05:41 PM   #3
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Yes 3 of them actually. Supreme PIA to repair. You can either replace the line, nuts and all( you will need a flaring tool for this job), or cut the line, replace the flare nuts and install a splice fitting with ferrule sleeves. I have done it both ways. When I replaced the water heater the line needed to be changed anyway (different layout) so new line.
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Old 02-27-2017, 05:49 PM   #4
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Don't use those machined flare nuts. Only use forged flare nuts for propane.
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Old 02-27-2017, 06:03 PM   #5
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Don't use those machined flare nuts. Only use forged flare nuts for propane.
DITTO!!!!!!

Also....NEVER USE ANY TYPE OF SEALANT OR THREAD LOCK ON A FLAIR FITTING!!!!! (sorry Boxite, but RVIA and the gas industry say NO) as pressure on the flair is what creates the seal and NOT THE THREADS.

Typically, they should be finger tight and then tightened '2 flats', which means an additional 1/3 of a rotation (every flair nut has 6 'flats'). Test with soapy water and make sure that they are properly sealed. Any additional rotation of the flare nut will begin to stretch the threads and negatively affect their clamping power..... and compromise the seal.

If you have to remove a flair and the re-tighten, it is then finger tight and '1 flat' or rotation, or 1/6 of a rotation.

The same tightening requirements are followed by the hydraulics industry, as in leveling jacks for motor homes and slide-out rooms. All of their flair fittings at the end of their hoses use the identical tightening regimen......and they are good to 3000PSI.
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Old 02-27-2017, 06:24 PM   #6
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2nd the no to thread sealant, tape. Have never seen a flair nut split and don't really see how over tightening would cause it? Do like the looks of that forged nut and does resemble what comes on a pre made gas flex.
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Old 02-27-2017, 11:26 PM   #7
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From The Copper Tube Handbook: "No material (e.g., pipe joint compound) should be applied to the mating surfaces of the flare fitting and the flared tube end before attaching the flare nut to the fitting body. "

I knew that! I guess I wasn't thinking while drinking! (I was only thinking of the threaded-portion but certainly didn't express that detail!)

Thanks for the correction/reminder.
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Old 02-28-2017, 06:13 AM   #8
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I was under the impression that double flares were now required by RVIA. Is that still the case? I installed all new propane lines on our 66 last year and found the doubles to seal without issue when tightened as lewster stated. Good luck.
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Old 03-02-2017, 07:23 PM   #9
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Thank you folks for your good replies. I was not aware of the forged flare nuts and will look for them at the store. And I was not aware of the torque to tighten requirements. Maybe I broke these flare nuts by getting them too tight. A guy can get a 3/8" flare nut too tight easily since it requires a 3/4" open end wrench across the flats. Too easy to torque it too tight. I'll always remember the 3 flats if virgin, 1 flat if tightened. It is the first time I've seen crrcked flare nuts. And they could be over 40 years old. Old things like me crack pretty easily when over torqued.

David
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Old 03-02-2017, 07:33 PM   #10
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Originally Posted by dbj216 View Post
Thank you folks for your good replies. I was not aware of the forged flare nuts and will look for them at the store. And I was not aware of the torque to tighten requirements. Maybe I broke these flare nuts by getting them too tight. A guy can get a 3/8" flare nut too tight easily since it requires a 3/4" open end wrench across the flats. Too easy to torque it too tight. I'll always remember the 3 flats if virgin, 1 flat if tightened. It is the first time I've seen crrcked flare nuts. And they could be over 40 years old. Old things like me crack pretty easily when over torqued.

David
That's 2 flats if new........................ 3 will start to stretch the threads.
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Old 03-02-2017, 07:35 PM   #11
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Hi bubba l: I don't know the requirements for compression fittings, which I assume your reference to "double flare". I agree compression fittings are pretty darn good. They save time as you don't have to swage a flare at every connection.

It is easiest to start fresh with compression fittings for the whole project. I don't have any inventory of compression fittings, but I have accumulated a box full of 37 degree flare fittings. I was just relocating an existing line about 6" to connect my new fridge. So I just squeezed a new flare "horn" on the tubing I cut and tightened it up. Then I found these cracked flare nuts upstream while checking for leaks.

David
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Old 03-02-2017, 07:37 PM   #12
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Thanks lewster, I stand corrected. David
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Old 03-03-2017, 12:34 PM   #13
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Originally Posted by dbj216 View Post
Hi bubba l: I don't know the requirements for compression fittings, which I assume your reference to "double flare". I agree compression fittings are pretty darn good. They save time as you don't have to swage a flare at every connection.

It is easiest to start fresh with compression fittings for the whole project. I don't have any inventory of compression fittings, but I have accumulated a box full of 37 degree flare fittings. I was just relocating an existing line about 6" to connect my new fridge. So I just squeezed a new flare "horn" on the tubing I cut and tightened it up. Then I found these cracked flare nuts upstream while checking for leaks.

David
A double-flare is not the same as a compression-fitting.
A double-flare requires a special tool, which folds a flare back onto itself to provide greater strength and security.
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Old 03-04-2017, 04:09 PM   #14
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Thanks Boxite: I just ASSumed a double flare was Texan for compression fittings as the compression fitting insert has a flare on both sides.

You taught me a double flare is a fold over. I had never heard of that before. I read reference to them for steel brake lines. I don't know what they might look like in soft copper tubing.

Old fashioned 37 degree flare fittings in soft copper tubing seems to work for me if I don't over torque the flare nuts! All I'm trying to do is seal very low pressure gas.

David
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Old 03-04-2017, 08:12 PM   #15
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Thanks Boxite: I just ASSumed a double flare was Texan for compression fittings as the compression fitting insert has a flare on both sides.

You taught me a double flare is a fold over. I had never heard of that before. I read reference to them for steel brake lines. I don't know what they might look like in soft copper tubing.

Old fashioned 37 degree flare fittings in soft copper tubing seems to work for me if I don't over torque the flare nuts! All I'm trying to do is seal very low pressure gas.

David
David,

I use double flares any time I make flare connections. The double layer of soft copper makes for a better seal. Not sure if it is required by RVIA......but definitely suggested.

No issue with making them as the copper IS very soft...usually K or L type.

If you have never done them, I would get a double flair kit and practice on some scrap prior to the real deal...............
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Old 03-05-2017, 09:03 AM   #16
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Thank you lewster: I was totally in the dark on double flare forming. And that's after 25 years in the hydraulics industry. I'll be looking around for a double flare tool set as I've nearly worn out my current flaring tool. I'm always interested in trying something new and better.

David
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Old 03-05-2017, 02:34 PM   #17
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http://www.harborfreight.com/double-...kit-66534.html

$22. Flare capacity: 3/16 in. - 5/8 in.
Includes adapter sizes: 3/16 in., 1/4 in., 5/16 in., 3/8 in., 7/16 in., 1/2 in., 5/8 in.

It's a tool you'll only use a few times if you're a non-professional so the cheap HF tool is fine. I've used it to make repairs in the field on tractor fuel lines, brake lines, etc.
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Old 03-05-2017, 03:07 PM   #18
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I hate to say it (NOT a fan of HF) but I have used that very same tool when I did not have mine (much more precise) and it was available.

The key to making proper double flares is in the clamp mechanism. When you close tha clamp halves (empty) and tighten the wing nuts, look at the holes on the flair clamp halves to line up perfectly.

If they do...it will make a decent double flare......if not.....you get GARBAGE!

If you find a good one.......it will work for you for the very few times you will need to use it.
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Old 03-05-2017, 03:57 PM   #19
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I have used double flares on soft steel brake lines which works well. It should work on any annealed (soft) material. I read somewhere not to double flare stainless steel. Stainless steel work hardens when manipulated and could crack in a 2 stage operation like double flares require.

In my experience a bargain flaring tool is no bargain. The cheap ones don't perform. Even the Snap on and Eastman tools are at their limit during use, and performance goes down over time.

Also flare nuts are hollow and when wrenched with an open end wrench, will compress and become oval which lets the wrench slip. If you can get some flaring specific open end wrenches they grip more points and help keep the fitting from distorting. They are like a box end that has an opening to insert the wrench over the tubing. Cracked fittings are likely caused by using the wrong tool, distorting the fitting.
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Old 03-05-2017, 04:24 PM   #20
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I have bad luck w/ compression fitting esp. water and never enclose in wall as eventually it will leak. I will never use them. When comes to gas I won't take chances, either flare or black iron pipe, never galvanized pipe. I have used both dbl. flare and single, if bad flare either one will not seal. No tape or sealer with flares, if using pipe thread, yellow teflon tape for gas, white for water or teflon paste for water.
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