Grounding Aluminum Gas Tanks

Designs for inboard or outboard power

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steveh41
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Re: Grounding Aluminum Gas Tanks

Postby steveh41 » Wed Dec 06, 2017 8:33 pm

Kevin, you're very welcome. I appreciate your insight and info on galvanized fasteners...

Regards,

Steve
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Milhouse
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Re: Grounding Aluminum Gas Tanks

Postby Milhouse » Wed Dec 06, 2017 11:14 pm

Kevin thank you for the detailed reply!

First of all I must have had one to many last night and been influenced by the name of the post because I will be using stainless tanks, I don't know why I wrote Aluminum...Is what you said all still applicable or are there totally different design considerations?

These tanks will get wet for sure, they are open to the weather (see pic) so I think that the idea in the link of plastic strips and 5200 will be used so that there is not crevice corrosion (didn't know that was a thing till now!)

There will be two ~10 gal tanks (they will take the place of the two shown in the pic below (taken before they were cut out)). Since they are small it seems that tabs + mat + epoxy will be sufficient to keep them in place

Does the fill need a ground too? It is ~12" away but floating and separated by the rubber fill hose.

In summary: 1/4" Fiber Reinforced plastic sheet + 5200 for the bottom, Tabs + Mat + Epoxy to secure the tank, Ground on the tank, dual wire senders
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tanks.jpg
Jim
16' Ski Boat Restoration
17' Overnighter Sloop

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Kevin Morin
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Re: Grounding Aluminum Gas Tanks

Postby Kevin Morin » Thu Dec 07, 2017 5:00 pm

Milhouse,
SS tanks will not the exact concerns of aluminum because of a couple of factors. #1 Nickel alloy steel is less reactive than marine aluminum in a galvanic comparison due to the higher position on the galvanic scale. That means the fittings and bolts of SS will be much less galvanically reactive than SS to Alum.

#2 Also, while SS is subject to crevice corrosion as are all commercial marine alloys except silicon bronze (??? not sure???), the surface of the SS can easily be passivated to reduce its reactivity with and DE-aereated water that has become acidic. Again, relative position on the galvanic scale comes into play in your favor.

One super CAUtion: ALL SS NPT (national pipe threads, originating hundred years ago in England) seal by ''jamming" one fitting into another- so torque=seal. That is a problem for SS.

Why? SS machines with a tiny (nearly microscopic) 'burr' - tiny strands of hardened SS like hairs that curl up from the machine tools' cutting edge. These tiny strands are a major pain in the stern- but they can be dealt with very easily and without any problems IF (and only if) you'll take time to treat them with the respect that SS pipe threads need.

The burrs (sometimes called knap/whiskers/hairs) can be removed very easily- but if they are not - then it is extremely TOO COMMON for SS pipe thread fittings to seize up- to 'gall' or fuse to one another at the surfaces of the threads! Anyone who's put together industrial SS fittings systems of pipe & tube has experienced this problem first hand.

First, take a carbon steel fitting of exactly the same size and type fitting as will make up with your tank fittings. ie. 1-1/2" (FNPT) fill fitting will end up with a ST.90 or a King nipple so use a 1-1/2" male pipe nipple in carbon steel to lap the threads inside the tanks welded on fill.

Use fine valve grinding compound https://www.amazon.com/Permatex-80037-V ... B000HBM80M and put the (grit in grease) abrasive on the male nipple threads and simply hand thread the parts together and then 1/2 turn in and out just before the parts are tight.

This will cut the burrs off the SS machined threads. Rinse the tank with solvent or acetone very thoroughly after all the threaded openings have been lapped clean of machining burrs.

Reverse the process with the male ends of any fittings that will attach by using a pipe coupler as the lapping tool - rinsing all the threads of any trace of grinding/lapping compound before attempting to fit the external King nipples or other adapters to tank.

Before final assembly- using passivating gel to treat all the surfaces of the tank- then rinse and assemble. These steps will help reduce many headaches for those not used to working in SS.

Finally - spend time researching your thread 'goop' -there are many fine products available, but some for SS aren't gasoline or fuel proof so the application of any thread sealant/lubricant should be done after you know what to use- and that may require some testing?

hope these remarks bout my many (MAny) mistakes help you at avoid the one's I've made?

Cheers,
Kevin Morin
Kenai, AK
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Milhouse
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Re: Grounding Aluminum Gas Tanks

Postby Milhouse » Thu Dec 07, 2017 8:48 pm

Thank you again Kevin! That is a wealth of information. I will try and keep this all in mind!

Would you still elevate the tank off the deck with 5200 and fiber reinforced plastic to eliminate water getting trapped under causing crevice corrosion it or is the passivization you mentioned good enough to cover the bases? Elevating it still seems like a good practice to me, is it overkill?
Jim
16' Ski Boat Restoration
17' Overnighter Sloop

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Re: Grounding Aluminum Gas Tanks

Postby Kevin Morin » Fri Dec 08, 2017 4:04 pm

Milhouse, I'd still use bedding to isolate the tanks from directly laying on the fiber glassed decks. I'm not as concerned with crevice corrosion when the bedding strips are glued to the tank- keeping out moisture from the interface- but passivating SS is just good practice- let the installation outlive us all and the boat.

If the decks will be awash in either rain of wind spray? I'd raise them up just to allow the lower surfaces to dry out once in a while!

Sure wish some of the legitimate fiberglass hands on this Forum would reply! Don't want you to pay attention to anything I say outside metal- that's where I've had experience, others here have many glass projects, from boats to repairs and modifications to their credit- so they'd know more than I about the glass part of planning.

Cheers,
Kevin Morin
Kenai, AK
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Re: Grounding Aluminum Gas Tanks

Postby Mr Hot Rod » Fri Dec 08, 2017 8:27 pm

Here's a link to show how we installed our aluminium fuel tanks using David Pascoe's method :


Image

Image

Image

Hope this helps !
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Re: Grounding Aluminum Gas Tanks

Postby Milhouse » Fri Dec 08, 2017 10:10 pm

Thanks Paul! The pictures and explanation about how to laminate the fiberglass spacers for the bottom is very helpful!

I'm ashamed to admit this but I totally feel dumb because now that I look at the tanks that you posted look a lot like the ones I saw in the shop. Some reason I thought they were stainless. Their website mentions they are aluminum...I think that I will be all set now (even though i'm obviously not qualified to discuss metal!) Thank you Kevin and Paul for the info. Once I get the tanks from the fabricator I'll post some pictures.
Jim
16' Ski Boat Restoration
17' Overnighter Sloop

I'd rather have a $h!tty meal than an $h!tty resume because a totally awesome resume will feed me steak one day - Steve Poltz

Kevin Morin
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Re: Grounding Aluminum Gas Tanks

Postby Kevin Morin » Sat Dec 09, 2017 2:03 pm

Milhouse, just a note of caution about the tanks shown in the photos on the site link.

That company does not appear to remove mill scale from the aluminum? As an official "Millscale Gnat-Zee!"; may I caution you to add the work to etch the tanks inside and out? I have on other threads explained the problems that can result from leaving millscale intact on aluminum sheet goods (5000 series aluminum alloys) and also noted that many well known, 'big name' boat builders don't bother to remove the mill scale!

And some of those threads show images of corrosion that results on the sides of year old boats-while comparing to 30 year boats without a trace of the same corrosion because the older boats were etched.

Can't caution enough about this widely spread but incorrect surface finish problem/practice with marine aluminum products.

Cheers,
Kevin Morin
Kenai, AK
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Milhouse
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Re: Grounding Aluminum Gas Tanks

Postby Milhouse » Sat Dec 09, 2017 4:58 pm

Thanks Kevin, I see a forum post here that you wrote discussing mill scale, I will ask the fabricators if they can remove it.
Jim
16' Ski Boat Restoration
17' Overnighter Sloop

I'd rather have a $h!tty meal than an $h!tty resume because a totally awesome resume will feed me steak one day - Steve Poltz

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Re: Grounding Aluminum Gas Tanks

Postby Milhouse » Fri Dec 15, 2017 6:06 pm

Here are some pics of the tanks. The fabricator didn't want to hear anything about mill scale though...

The fittings are aluminum so I shouldn't have to worry about de-burring them.

I'll glass them in via the tabs shortly after I paint the bilge.
Attachments
20171215_165024.jpg
20171215_165035.jpg
Jim
16' Ski Boat Restoration
17' Overnighter Sloop

I'd rather have a $h!tty meal than an $h!tty resume because a totally awesome resume will feed me steak one day - Steve Poltz

Kevin Morin
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Re: Grounding Aluminum Gas Tanks

Postby Kevin Morin » Sun Dec 17, 2017 9:21 pm

Milhouse,
just because the fabricator has no concern for you tanks' longevity, doesn't mean you shouldn't!! I'd take time to etch them, maybe even paint them outside with some primer? Then I'd wash them out with acid too, rinse with water and finally with acetone while rolling them around on horses, let them drain and air out- acetone will totally evaporate.

Not sure if you're covering the entire tank with glass/fiber or just the tabs? I'd skip that method and glass in a 'pad' or wooden block- then just use fasteners to bolt/lag screw the tank tabs to the glassed in wooden block. This way they're easily removable; in case you need to do maintenance on them? The lags can be hot dipped galvanized to reduce galvanic differential to aluminum and if SS is used? a nylon washer and sleeve can be incorporated to keep the bolt and aluminum tab from corroding one another.

Just another few cents from an old builder who's built hundreds of tanks, and done nearly as many tank repairs from pitting, inside and out! "An ounce of prevention is worth a pound of cure"

cheers,
Kevin Morin
Kenai, AK
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Milhouse
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Re: Grounding Aluminum Gas Tanks

Postby Milhouse » Wed Sep 05, 2018 10:03 pm

Thanks for all the tips! I am getting closer to getting these tanks installed.

I am trying to find an anti Siphon valve for the tank now and I see that Moller makes one that is Aluminum but it is rated for < 200HP

They recommend the brass one for > 200HP which is my situation (stock 327 should be around 225HP (Guess))

Should I use brass and potentially have a dissimilar metal situation or go with the < 200HP version? Any suggestions on other valves out there?

This one does not mention HP but should I trust West Marine? I will have < 30" of head.

I was able to find aluminum fittings for the vent line.
Jim
16' Ski Boat Restoration
17' Overnighter Sloop

I'd rather have a $h!tty meal than an $h!tty resume because a totally awesome resume will feed me steak one day - Steve Poltz


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