Metal Marine Tanks (mainly welded aluminum)

Steel and aluminum boatbuilding. See: "Boatbuilding Methods", in left-hand column of the Home page, for information about alloys.

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Jetmetal
Posts: 4
Joined: Wed Oct 31, 2018 8:52 am
Location: Bozeman

Re: Metal Marine Tanks (mainly welded aluminum)

Post by Jetmetal » Thu Mar 07, 2019 8:01 pm

Thank you! And yes I am planning on doing a 1/2"npt fitting in the tank and then the SS reducers I like that idea and I completely agree with your reasons behind it!
As for the hose and pipe ID OD stuff and the the nightmare that is NPT I often get mix up so thank you for the clarification on it.
I am going to go with the 1 1/2" Hose I'm pretty sure I found the fittings I will need I will figure out how to post pictures so I can show you and make sure I'm thinking of it all right.
On the topic of weld in fittings in the tank I am still a bit unclear on what exactly your cutting the NPT thread coupler in half for? Is that just to make it shorter? Your not cutting it hmmm how to explain?? Are you cutting it length wise? To make to halfs? Then welding the 2 in?
That's about it for me tonight thank you for your time I will gather some pictures and information before we go any farther with parts ordering.

Kevin Morin
Posts: 738
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: Metal Marine Tanks (mainly welded aluminum)

Post by Kevin Morin » Fri Mar 08, 2019 7:20 pm

jetmetal,
dedicated tank fittings like these https://www.fueltankparts.com/fuel-tank ... tings.html are lower profile extending from the tank face or top surface. There is some thread down inside the tank allowing the ST El or other hose adapter to remain closer to the tank top- often a preferred choice.

The picture shows the flange type, 1/2 couplers and full ht. couplers - I buy the full ht coupler and cut in half. I usually shop online at the time I'm planning a project and buy the needed couplers from a fitting supplier with competitive pricing.

I use pipe couplers and cut them on the band saw- along their middle & at 90 to their body- this results in two (2) fittings for welding for one purchase. The fittings are lower profile- less sticking up and as I mentioned I often weld the bottom/inside tank portion to a draw pipe or downcomer with a butt weld.

Hope this clears up my confusing writing?

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

Jetmetal
Posts: 4
Joined: Wed Oct 31, 2018 8:52 am
Location: Bozeman

Re: Metal Marine Tanks (mainly welded aluminum)

Post by Jetmetal » Sat Mar 16, 2019 8:20 am

Yes that clears it all up thank you.
It's been a few days since I responded because of what I am trying to accomplish in a short amount of time.
The fuel tank is in the parts collection stage and I have been hard at work on the boat.
AT SD-312 fitted in last week😎
It took a bit more work as the boat was designed for a Kodak 3 stage.
Hope all is well for you in Alaska

Kevin Morin
Posts: 738
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: Metal Marine Tanks (mainly welded aluminum)

Post by Kevin Morin » Mon Apr 15, 2019 10:33 am

After some conversation about tanks' construction I thought I'd mention some links to some of the parts available online?

I typically use aluminum pipe couplers, cut in half on the band saw as my tank wall weld in fittings. But... they're not for everyone! In the following links there are flange type fittings that will allow the weld area to be much farther from the threads than a pipe coupling allows. This allows the tanks' fittings to be put in with MIG if that is the only welding power supply available.

Also, we've discussed down comers/fuel draw pipes and other fittings types for different functions as part of the marine tank. These links also provide at least a source for most of the other fittings.

Tanks' fill fittings come in two general groups: one, a fitting where the cap is on the tank and removed to fill that tank; two, a hose system of some or another configuration to a remote fill/deck fill fitting and cap. Both of those are here too.

So, if you're planning a stand alone tank, Iike Yofish's tank on his adjacent build thread- then several types of caps are shown. On the other hand if, as Yofish mentions, the tank were below deck; a hose to pipe adapter would be needed so the hose can originate at a deck fill fitting on the gunwale or some other location.

Following are some links to various suppliers- I'm not recommending them, just noting their addresses and suggesting you contact them individually to learn about their products?
https://www.fueltankparts.com/fuel-tank ... ories.html
https://www.mcmaster.com/weld-on-tank-fittings
https://www.alumitank.com/parts/tankfittings.php?s=24
https://www.buyfittingsonline.com/
https://www.amazon.com/Thread-Fitting-C ... ay&sr=8-10

A few more notes as regard SS pipe fittings:
SS tends to gall or fuse when threaded together- due to very small (micro level) "hairs" of metal left from most thread cutting operations. To avoid this potentially expensive and tiresome event: take a mild steel/carbon steel/"black iron" pipe fitting and apply valve grinding compound to the threads. Use that fitting to thread into all the female SS fittings including valves, bushings, 90's and so on.... Any female fitting of SS- and when the threads are well dressed with valve grinding compound- hand tighten the threads and work those two fittings back and forth from hand tight -tightening and loosing a dozen times to 'lap' or smooth the micro hairs off the SS.

Do this with the male fittings as well using any mild steel female coupler or fitting as the dressing tool. By very finely lapping ALL SS fittings using NPT profile threads (not needed on SAE O-ring, JIC or other straight cut threads- but not bad practice with SS bolts if Nylon Locking Nuts will be used?) - then the likelihood of galling these alloy of fittings is greatly reduced.

When installing them together, a teflon pipe sealant that both lubricates one fitting to the other and seals the tapered threads for future fluid containment is best. This will also act as a parting agent if the two fittings need to be separated in the future and allows the SS to engage another 1/4 or 1/2 turn deeper into the other gender fitting when making up.

SS will gall and seize in aluminum too- sometimes. By dressing the SS threads with lapping compound and the engagement of SS to aluminum can be increased without resorting to the longest pipe cheater bar you can fit on the makeup wrench- those joints will seal better at lower torque and separate better when and if they need to be removed for future maintenance.

Another note about SS fittings in any use in an aluminum tank (or boat anywhere) is to passivate the SS using gels and liquids containing acid(s) for this purpose.
https://www.delstar.com/passivating
https://www.mmsonline.com/articles/how- ... teel-parts

the idea is simply to use a chemical solution to help the SS metal surfaces to become less reactive and more stable by increasing a film on the part that is less reactive with any other metal. Aluminum and SS will and do react to one another- if at all possible 316L is preferred of other alloys but many times a part is much more expensive in this alloy compared to the more common 304 alloy?

This is actually all the more reason to passivate SS especially if the 304 or more reactive alloy is used- this chemical immersion is very helpful to keep the reaction to aluminum minimized.

I'd hoped to have provided some sources and examples of parts to use in building a welded aluminum tank? While not advocating any specific vendor for fittings - welded or threaded; these are examples of some of the products you'd expect to use on tank project.

If there are any questions about the remarks, or 'best practices' I've advocated here? Please don't hesitate to post so I can help to clarify my remarks or answer and questions this post creates?

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

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