copper plumbing SS fittings and AL tanks

[fusto]

In reading the latest installments on the Kaholee project I noticed Tim, that your not using stainless bushings or nipples between the brass/bronze fittings and the aluminum tank?
Any particular reason?
I'm curious 'cause i just had this exact issue come up at work, and I'm seeking other intelligent opinions.

Here's the backstory:
Our yard did a big fuel job on a 42' Riviera last fall, replacing the two aluminum tanks with new and all new tank fittings and plumbing. When we did the work we put in new brass/bronze tank fittings and called it good. Thats how the tanks were plumbed originally, so we just did it the same.

Just this week I got a call from the owner (I'm the lead mechanic, lucky me...); a potential buyer had a pre-purchase survey done and the seller/owner said we had to redo all the new tank fittings because we didn't use a SS bushing between the brass/bronze fittings and the aluminum tank. ABYC says its required and the surveyor noted it in his findings.
ABYC sez:

33.18.3.3 Metals and metal alloys used in a fuel system
shall be selected to minimize galvanic action.
NOTE: The copper based alloys normally used for fuel
fittings and lines are acceptable for direct coupling with all
fuel tank materials listed in TABLE IV , except aluminum.

33.18.3.3.1 Copper-base alloy components shall be
separated from contact with aluminum tanks or fitting
plates by means of a galvanic barrier, such as 300 series
stainless steel.

Well, long story short we're getting the tanks pumped out (100 gal. each) and were going to have to undo all the hard plumbed fittings we put in. Unfortunately for me the parquet sole that we cut out for tank access originally is now reinstalled. So this "warranty" job is going to cost my dept a lot of time.

I agree with SS bushings between copper alloy fittings and AL tanks if its in a wet bilge-y area or somewhere where it could potentially get salt water on it.
The only way you'll get any corrosion between copper and aluminum is in the presence of salt water. The original 20+ year old tank fittings when the boat came in had no corrosion at all. They were dry as a bone.
So to me this is unnecessary, but to the owner and the surveyor (and ABYC) this is mandatory. Which makes me responsible.

Opinions?

[JonnyBoats]

ABYC is not alone on this. Take a look at Bill Seifert's book Offshore Sailing: 200 Essential Passagemaking Tips.

I guess the real moral of the story is to align expectations prior to starting the job. Appearently the owner expected your yard would do the job in conformance with ABYC standards. That probably should have been stated in the work order/contract.

Playing the devils advocate, remember that what is "necessary" may be as much a function of what an insurance company requires as what is required by good seamanship. How would you feel if you took your car in for a repair and the mechanic installed something which made your car fail a state mandated inspection?

[Tim]

In reading the latest installments on the Kaholee project I noticed Tim, that your not using stainless bushings or nipples between the brass/bronze fittings and the aluminum tank?
Any particular reason?

ABYC sez:

33.18.3.3 Metals and metal alloys used in a fuel system
shall be selected to minimize galvanic action.
NOTE: The copper based alloys normally used for fuel
fittings and lines are acceptable for direct coupling with all
fuel tank materials listed in TABLE IV , except aluminum.

33.18.3.3.1 Copper-base alloy components shall be
separated from contact with aluminum tanks or fitting
plates by means of a galvanic barrier, such as 300 series
stainless steel.

Well, I sheepishly admit that I was unaware of that particular ABYC standard. I've been looking at brass fuel line fittings on aluminum tanks on virtually all boats for so long that, frankly, it never occurred to me to even check that it was acceptable. It's simply how most of them are done, in my experience. That's no excuse for not knowing it should be otherwise, but that's my story and I'm sticking to it. Sometimes, convention can overwhelm a need to run to the rule book for every little thing.

The logic that leads to the apparently incorrect assumption, of course, is this: all commonly available fuel fittings for marine use are brass; a large percentage of fuel tanks, both OE and aftermarket, are aluminum, typically equipped with standard brass fuel fittings; therefore, brass fuel fittings are OK.

I note also that the ABYC standard indicates the need for a galvanic barrier, "such as (emphasis mine) 300 series stainless steel". What else, I wonder aloud, constitutes an acceptable galvanic barrier? Clearly, stainless steel is not the only option, or else the standard would have been written as such. Is pipe dope a galvanic barrier at all?

On the other hand, we all know how stainless steel and aluminum can react in a saltwater environment; we also know how stainless steel and brass or bronze can react in a saltwater environment. Is adding stainless steel into this mix truly a way to eliminate potential corrosion, or is it just setting up a different potential? (A legitimate, not rhetorical, question)

One never stops learning!

[Figment]

Doesn't Loc-Tite make a thread compound for use with diesel?

[Tim]

I have an inquiry in with ABYC to request clarification on this standard, particularly as to what constitutes a "barrier" against galvanic action.

[Figment]

sigh. Leave it to Tim to suck all the fun out of our flailing, floundering, and guessing by going straight to the source for an actual "answer".

Stifling. Positively stifling! There is absolutely no room for the Creative Process around here any more!

Oh, what's the point of it all?

(too dramatic? nah.)

[Rachel]

I probably just haven't had enough coffee yet today, but I thought Kaholee's tank was stainless steel, not aluminum as Fusto's customer's tank was.

Or am I confusing that with Britton's water tanks?

Rachel

[Tim]

Pour another cup, Rachel.

Kaholee's fuel tank is aluminum.

[fusto]

Playing the devils advocate, remember that what is "necessary" may be as much a function of what an insurance company requires as what is required by good seamanship. How would you feel if you took your car in for a repair and the mechanic installed something which made your car fail a state mandated inspection?

Oh I agree completely. Thats why we agreed to make it right.

And I think it does say in our contract somewhere that we do conform to ABYC standards. I even knew somewhere in the back of my muddled brain about this standard, but couldnt access the information at the right time. I'm ABYC certified in Diesels, electrical, refrigeration and corrosion. So I know most of the standards in the ABYC manual by heart. They just sometimes get a bit jumbled.

My complaint is with this standard in general. Anybody who knows anything about corrosion knows that copper, aluminum and stainless in saltwater can be a nasty mess.
I usually agree with ABYC but sometimes I think they are a bit vague and misdirected.
I'll be interested to see what they say in response to Tim's query.

[Hirilondë]

Doesn't Loc-Tite make a thread compound for use with diesel?

I don't know who makes it, but if anyone wants a real answer I can find out monday, but there is a thread goop called Gazoila specifically for fuel tanks/lines/etc.. I don't believe it counts as a barrier for galvanic corrosion though.

As I understand it the only material the Coast Guard blesses for fuel tanks is aluminum. Stainless steel welds are quite subjective to corrosion is why they don't like it.

[Rachel]

Okay, I'm awake now. Sorry about that!

[JonnyBoats]

Doesn't Loc-Tite make a thread compound for use with diesel?

For what it is worth, Bill Seifert in his book recommends RectorSeal for this application.

[JonnyBoats]

The following Coast Guard Boating Safety Circular http://www.uscgboating.org/recalls/pdfs/BSC79.pdf may provide some background information. In particular:

Aluminum and copper, in the presence of moisture, always create a very bad galvanic cell and special efforts must be made to avoid any direct contact. This can be done by inserting a 300 Series stainless steel fitting between the aluminum tank and any copper or brass fittings.

[bcooke]

Or am I confusing that with Britton's water tanks?

Britton's water and waste tanks are stainless.
Britton's fuel tank are aluminum.

(I expected the aluminum tank to be cheaper than the stainless water tanks - that was definitely not the case)

I have been asking around and all my sources say bronze is okay with aluminum. With a little prompting, they all agree however that stainless is probably best. The problem is that the available fittings in stainless is pretty limited.

This bushing idea is interesting. Are we saying that as long as the aluminum is physically separated from any copper (I am assuming the copper content in bronze/brass is the concern) with stainless then we have the best setup? Does fuel -gas or diesel- act as any sort of electrical connection between the two dissimilar metals?

With that thought I think I can find a stainless elbow to mate with the aluminum tank and then a bronze/brass pipe-to-hose adapter leading into the hose that covers the rest of the fuel system. The idea of three metals connected together sounds counter-intuitive though.

-Britton

[bcooke]

As per usual, I posted and then read the link. That is a really good link. If anyone wants to install a fuel tank I suggest taking the time to read it. It brings up several key points concerning the installation of an aluminum tank and a brief comparison of other materials.

And I think the link answered my question as well.

-Britton

[Tim]

So, if anyone's keeping up with this thread, here's a brief update.

A couple weeks ago, I received a response from ABYC to my query regarding the standard in question. There's certainly no earth-shattering new information to be had, unfortunately. Next time, I'll ensure that the proper barbs are simply welded on to the tank.

Copper and aluminum corrode almost immediately in the presence of water. I suggest stainless, as an intervening barrier or plastics if practical (marelon, etc.) aluminum barbs welded directly to the tank are preferable.

So, yesterday I replaced the direct brass-aluminum contact on the fuel tank with 316 stainless fittings--elbows and bushings as required. So Kaholee's tank installation is now up to snuff as far as ABYC H-33.18.3.3.1 is concerned.

[bcooke]

The answer you received mentioned plastic between aluminum and copper.

Could that work when we are talking about a fuel line? I was under the impression that the different heat expansion rates between metal and plastic made mixing metals and plastic a poor choice in this application. Or maybe with the proper dope/sealant on the threads it isn't really an issue.

-Britton

P.S. I like it when you get ahead of me and I can learn from your experiences. Having to wait for warmer weather has an advantage after all. :-)

[Tim]

It's sort of a moot point, since it's not as if there is a wide variety of appropriate plastic or Marelon fuel line fittings available. The Forespar catalog shows some barbed fittings with tapered male threads that would fit in a fuel tank, though they don't (on that page, at least) indicate that they're meant for fuel systems.

Obviously, certain plastics must be suitable for fuel containment, as evidenced by plastic fuel tanks and containers. Marelon, being a fiberglass product, is probably fuel resistant, but I don't know for sure and see no real reason to find out right now.

The crux of the response was that stainless steel was the recommendation, or, even better (but not possible in my case), welded aluminum barbs. So stainless it is. Good enough for me.