Sealing copper fuel pipe joints

[Tim O]

So as part of my major clean of my fuel delivery system, I’ve removed the piework and shut-off gate valve which attaches at one end to tank outlet, turns through two 90 degree bends, then reduces down to join the 6mm copper fuel pipe.

It was full of sludge which I’ve now scrubbed out and sluiced clean with clean diesel.

My question is whether on reassembly I should use any kind of jointing compound or Teflon thread. It appears there was sone kind of reddish “paste” used before but my thoughts are that bits of that could get into fuel. Both Nigel Calder’s book and Don Seddon’s Diesel l Troubleshooter advise NOT to use any sealant on metal joints so I’m minded to follow that advice...

Any thoughts?

 

[FlyingGoose]

replace the olive , this is enough to create a new seal, as it does on gas seals , dremel it off and buy new from band q, and do not tighten to much as this ll cause the olive to fail.
then test . plumbers thread tape perhaps but unsure of the diesel eating away at it

 

[rogerthebodger]

First of all copper should not be used with diesel as it can cause sludge to develop so I would replace all that copper/brass pipe, valve and fittings with stainless steel.

Threaded fittings can be sealed with loctite and not PTFE tape incase any take gets into the fuel system.

Compression fittings should not need and sealant.

 

[FlyingGoose]

Hey Roger can you explain in easy words why copper attracts the sludge and stainless des not and would then fabric diesel pipes work best, asking as all my pipes are copper for tank, return , generator, and had the sludge bug this year .
cheers

 

[jamie N]

FG, I experienced a bit of this a few years ago, and enclosed some stuff about it then. I hope that it helps.

Edit: I see that the link is 'U/S' right now, but IIRC it cut the RON and made it a great deal less flammable.
It should be remembered of course, that mine was in a copper tank.

 

[rogerthebodger]

Hey Roger can you explain in easy words why copper attracts the sludge and stainless des not and would then fabric diesel pipes work best, asking as all my pipes are copper for tank, return , generator, and had the sludge bug this year .
cheers

Have a look at this

Copper vs. Diesel

And

Diesel fuel piping? - Pipelines, Piping and Fluid Mechanics engineering - Eng-Tips

There gas been several posts on the forum about the reactions between copper/zinc and diesel fuel.

 

[thinwater]

Hey Roger can you explain in easy words why copper attracts the sludge and stainless des not and would then fabric diesel pipes work best, asking as all my pipes are copper for tank, return , generator, and had the sludge bug this year .
cheers

The ASTM, ISO, and every major engine manufacture recommends strongly against copper and zinc for this reason. The science is old and well known. We use them because they are convenient and inexpensive. They work out so long as you turn your fuel often enough and use an effective metal deactivator.

copper fitting poor practice for fuel systems

It's a weird issue. Personally, I just avoid copper as much as practical and use StarTron with diesel, which seems to help agood bit with copper corrosion.

The other cure is to run the engine more! Too many sailor pride themselves on only running the engine for a few minutes. I get it. But that doesn't turn the fuel over often enough, if you have a big tank.

 

[PCUK]

Yes, copper can cause a reaction with diesel but in the real world diesel flowing through a tube will not affect the copper. My previous boat has the same copper that was fitted. 30 years age. Hundreds of thousands of boats worldwide use copper fuel piping so why worry about a theoretical threat?

 

[thinwater]

Yes, copper can cause a reaction with diesel but in the real world diesel flowing through a tube will not affect the copper. My previous boat has the same copper that was fitted. 30 years age. Hundreds of thousands of boats worldwide use copper fuel piping so why worry about a theoretical threat?

ASTM, ISO, Cumins, Cat, Yamar....

Not theoretical, real. I've seen it in standby systems quite a few times. I've not worked on enough under-utilized sailboats to say.

Saying that "hundreds of thousands of boats worldwide use copper fuel piping" without trouble is a plainly false assumption. Many, many thousands have fuel problems and threads are very common. We just fail to clearly identify one of the causes.

If you use the boat regularly and burn throught he fuel once or twice season this will likely never affect you. The science says this too. If you read the links you would have seen this. It was for standby or rare use. The real world, as you say, involves many boats that don't move for 8 months, don't move every year, and many that only burn 1/4 tank each year.

 

[FlyingGoose]

Have read the articles given I am happy to start to add to my to do list , thanks for the info I think!! as I ripe out my lines and start replacing them need to do this anyways as the generator fuel line is just silly long and running all over the place , so good excuse to the wife that it needs all replacing, Having a look on the interweb , am going to boy racer my old perkins with fancy blue connectors , love it , thanks again great info

 

[Tim O]

I’ve already got it in mind to replace the pipe work with proper flexible fuel hose BUT that’s not going to happen right away for financial and time reasons so in the short term I was planning to just pop this back on as it is while I save up for that job.

So, is it ESSENTIAL to replace the olives here or might the existing ones probably be ok? Haven’t measured the pipe work but looks about 1” reducing down to 5/16” (6mm) at the small end.

 

[RivalRedwing]

To my mind it is not essential to replace the olives if the male and female components are still the same (just don't over-tighten). Don't use PTFE tape but a smear of anaerobic pipe sealant such as Loctite 542 can be beneficial.