stop these compression fitting leaking

[garyfdl]

Originally Posted by Uncle Bob

Ahh, I get it now, you are advising that no thread should ever require any sealing product regardless.

No... I. Did. Not.

Originally Posted by Uncle Bob

the advice to seal the threads was NOT the flare portion of the fitting so your advice may not be appropriate.

If i misunderstood your original post, I apologize. (That's still no reason to put words in my mouth. )

Originally Posted by Uncle Bob

perchance you glance at the original photo you will see a fitting with TWO threaded ends, one is the thread for the flare nut, the other appears to be a standard gas thread, this is the thread that would require some sealant, IMHO.

(There's is also no reason to be condescending.) Agreed. The "standard gas thread", if the OP is in the US, is most likely NPT - National Pipe Thread. FWIW teflon tape was (as I understand it) developed to seal this type of thread. I'll also throw in that teflon 'infused' pipe dope is preferable to teflon tape, and is more 'forgiving' to mis-application than is teflon tape.

[Scrimshaw4]

Make sure you use fuel rated Teflon tape. Regular plumbers Teflon tape will breakdown and leak over time when exposed to diesel fuel.

[garyfdl]

Originally Posted by Scrimshaw4

Make sure you use fuel rated Teflon tape. Regular plumbers Teflon tape will breakdown and leak over time when exposed to diesel fuel.

Did not know this, but not surprised. Diesel is aggressive towards a lot of polymeric compounds.

My rwo cents to this is: unless you know how to properly use teflon tape, and are using the correct type, stay away from it altogether and use a suitable 'dope' (brush-on) sealant.

[Bowdrie]

Originally Posted by garyfdl

Did not know this, but not surprised. Diesel is aggressive towards a lot of polymeric compounds.

My rwo cents to this is: unless you know how to properly use teflon tape, and are using the correct type, stay away from it altogether and use a suitable 'dope' (brush-on) sealant.

You make a good point.
Going thru the "Permatex" products, (and perhaps I missed something,) I found only one product that had diesel listed in the MSDS data.
That is part#80632, commonly available at your favorite auto parts store.
It's a paste with PTFE, and I've had good success with it.
I'm sure their are other brands, I'm just used to the Permatex product line.
Their "Aviation" sealant can give good service, but it it's messy to use, it leaps right out of the bottle and gets over everything.

[Bycrick]

Detail. NPT stands for National Pipe Tapered. As opposed to NPS or National Pipe Straight.

[garyfdl]

Originally Posted by Bycrick

Detail. NPT stands for National Pipe Tapered. As opposed to NPS or National Pipe Straight.

My bad. I stand corrected.

(It's been a while. )

[hirondeller]

There has been a 'back & forth' in this string about the suitability of copper for diesel, (and maybe propane gas). Here is my two cents:

I owned a propane barbecue in Texas with deteriorated copper lines that completely clogged the regulator with black flakes. Why? High sulfur fuels react with copper to form black copper sulfide. This material flakes off in the pipe.
If your copper fittings stay bright when you are using copper with fuels you are OK. If the fittings look black switch to bright plated, or stainless steel. DONT USE GALVANIZED, Zn also reacts with sulfur in fuels.
In the USA diesel is 'de-sulfurized' to prevent acid rain (sulfates appear aafter combustion). Not necessarily so elsewhere. If you tank up outside the USA think about using 'no copper' lines.

[4runner]

I would replace that section with a foot of rubber fuel line that’s approved for use with marine diesel fuel and be sure to use two T-Bolt hose clamps. Be sure the fuel line is approved for use with hose clamps- not all are.

Good luck—

[b.needalman]

You should be concerned about what caused the failure. Presumably, the fittings were in place were in place for some time before they failed.

I have heard that hard lines, particularly fuel lines, should not be used on boats. Vibration accelerates metal fatigue and causes failure over time.

A diesel leak is a serious thing. In the best case, the boat will stink. In the worst case, the boat will catch fire. Seek qualified professional advice.
https://www.uscgboating.org/assets/1...YC.1002.01.pdf

[Dieseldude]

Originally Posted by hd002e

I have these compression fittings in my diesel fuel lines and they leak, it is not kuch but it is enough to make everything greasy and stinky. How do i compat the mess? Any tricks? Thank you!

There have been some great replies posted already. But just would like to add a bit. Of course, as others have posted, the fitting pictured is a flare fitting. These are one of the most reliable tube fittings available. If fitted correctly they will hold tight for a very long time. They seal on the flared surface, so no teflon tape is required. Teflon tape in fuel and hydraulic systems is a hazard, as it can get into the system and cause blockages.


There was at least one posting that copper tubing should not be used around diesel engines. But I have seen copper lines on engines that has been there for years, and it has lasted fine. Well secured copper line is quite durable. It is much easier to bend, cut, and flare than steel. Of course the initial cost of steel is lower. I would chose copper over steel for any line that runs close to the bilge or through any watery or moisture prone area.


The flare must be carefully made. A good sharp tubing cutter is required. If the cutting wheel is blunt, get a new wheel. The cut edge must be deburred to prevent ridging and edge cracks that can cause leaks. I find that the deburring blades on tubing cutters are useless. A good counter sink bit with at least four flutes does a good deburring job internally. It can be held in vice grips and turned by hand or in an electric drill. If using a drill, turn at low speed to prevent chatter. The tubing end must be held down to keep chips from falling inside. The outer edges must be deburred with a fine file and/or medium grit emery paper.


I have not had good luck with cheap flaring tools. They often leave parting ridges by the jaw mating surfaces. This can cause leaks. Some better quality flaring tools are made by Rigid Tools. I am not happy with the performance of my Gray Tools flaring tool for 3/16 brake lines for double flares. The die is a slack fit and tips sideways, making a very bad quality flare. But my Gray does well on larger sizes. For low pressure fuel lines, I have seen single flares hold well. Whether to make a double flare or single I would leave to personal preference. Perhaps a double will be more reliable for high vibration applications. A double flaring tool kit will cost more, but it is good to have that capability.


Hopefully your damaged line has enough extra length to cut off the end and make a new flare. For short runs, making a splice with a flared union is probably not worth the effort.


A word on bending tubing: Ideally, tubing should be bent only once. It should not be repeatedly re-bent, as the metal can work harden and fatigue. I have gotten away with slight bend corrections though.


With some practice on some scrap tubing, anyone with basic mechanical skills should be able to make a good quality flare. There has been a lot of emphasis on the tube flare itself, but if you have leaks, the fitting sealing surface should be inspected for any gouging or raised burrs that can cause seeps. May need a magnifier for a good look. Steel lines can cause damage to the brass surface. Even copper can do the same if over tightened. If damaged, scrap it and use new.

[stubones99]

Copper work hardens, making a good seal harder each time it is used.

As I see it, you can either cut off the end and re-flare it like others have recommended, or if you can safely anneal it using a propane torch that will soften the copper enough to reseal the joint. If it is a fuel line, remove that section and anneal it off the boat just for safety.

To anneal copper, all you have to do is heat it enough to see the color change in the metal. It is subtle, but a good indicator. If you heat it too much, it will melt and you have to cut off the damaged part and re-flare the new end.

[Dieseldude]

Originally Posted by garyfdl

You shouldn't need to seal the threads. If the fitting leaks without the tape, it's not flared/seated properly and you're just using a band-aid instead of fixing it correctly.

To the OP:

DIY flared copper is done on soft copper tubing. Soft copper work hardens with repeated use - so every time you make up the joint and compress the copper female flare against the bronze male it gets harder - over time, that makes it difficult to get a proper seal.

There is an easy fix. Unlike steel, which gets harder when heated up and quenched, copper will get softer. SAFELY heat up the copper flare until it gets red and quench it in some water. Then take some sandpaper (120 grit is good)or a really, really, really fine wire brush on a drill or Dremmel and clean off any scale. Wipe the fitting clean and reinstall.

There has been a lot of debate amongst people about quenching copper sealing washers and flared tubing ends. Quenching makes a sudden temperature change that can cause uneven stresses in the metal. As the metal enters water, a cold region quickly progresses which may cause uneven stresses. I tend to hold to the theory that slow cooling will anneal the metal and prevent stresses of uneven quick quenching. Anyone on the form have any theory for or against quenching?

[garyfdl]

Originally Posted by Dieseldude

There has been a lot of debate amongst people about quenching copper sealing washers and flared tubing ends.

I was a hydraulic tech/systems engineer for decades. The large pumps had copper sealing washers on the high pressure (3500 PSI) lines. It was SOP to heat and quench the washers to reuse.

BUT

You can only do it a couple of times. after that, the copper thins out from the repeated crushing and they will crack/split. Flared tubes do the same thing.

[Shaneesprit]

Originally Posted by Emmalina

nothing wrong with them but you shouldn't use copper pipe for diesel !

Do you have a valid reason for saying this?

[Dieseldude]

Originally Posted by Shaneesprit

Do you have a valid reason for saying this?

Maybe this is a carry over from automotive brake lines. Copper is not strong enough for the higher pressures of an automotive break system. But for low pressure fuel lines, strength is not an issue. The softer copper tends to dampen vibrations in engine applications, so this is an advantage over steel. Steel is more difficult to make tight bends in, making it less appealing. Factory made lines are likely to be steel because it is cheaper, and for mass production, the cost of factory bending equipment for steel is recovered over the production cycle. All lines must be well secured regardless of material. All contact points must be well protected from vibration and chafing. A layer of spongy material such as rubber hose or gasket rubber will prevent chafe through. It may seem odd, but on one boat, I saw a copper line that had been secured to a steel one with a tie wrap. The steel actually chafed through and leaked while the copper was relatively unscathed. Strange, but that is what happened.