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Old 03-02-2013, 18:57   #1
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Aluminum Alloys

Need to patch a fuel tank. The plate says the tank is made of 5052 aluminum but all I can get locally is 6061. Google tells me the main difference is 6061 has Si in the alloy, otherwise both have the same metals just slightly different ratios.

So can I patch the 5052 alloy tank with a piece of 6061 and 6061 welding or will the tank rot and the boat explode?
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Old 03-02-2013, 19:01   #2
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Re: Aluminum alloys

Hell, I have some 1/8" 5052 in my shop. Where are you located?
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Old 03-02-2013, 19:37   #3
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Re: Aluminum alloys

'Tis a good plate, most frames and stringers (extruded) in aluminium boats construction are 6061-T6 Nice and strong and anneals well. is fine if you cannot match with some 5052, fuel won't know the difference.... go see Delmarrey!
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Old 03-02-2013, 19:51   #4
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Re: Aluminum alloys

From your profile I see your in FL. There are a few alum tank mfgr's in FL.

Boyd Welding 2811 NW 8th PL, Ocala FL 34475

Contact RDS

and so on Aluminum Tanks in Florida (FL) on ThomasNet.com
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Old 03-02-2013, 20:22   #5
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Re: Aluminum alloys

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Originally Posted by delmarrey View Post
From your profile I see your in FL. There are a few alum tank mfgr's in FL.

Boyd Welding 2811 NW 8th PL, Ocala FL 34475

Contact RDS

and so on Aluminum Tanks in Florida (FL) on ThomasNet.com
Yep, FL. Almost as far from you as one could be in the US.

Also the one place in FL that not close to anything marine. Hard to believe but it's about 2 hours to the nearest West Marine, the nearest boat yard or even salt water.

I can order some 5052 from Online Metal Store | Small Quantity Metal Orders | Metal Cutting, Sales & Shipping | Buy Steel, Aluminum, Copper, Brass, Stainless | Metal Product Guides at OnlineMetals.com but the local shop has plenty of 6061 laying around. Just for once it would be nice to fix something on the boat without waiting 3-5 days for my package to arrive from Defender/Jamestown/West or driving for a few hours to get stuff.

So if 5052 and 6061 can live together happily then I get at least one easy repair. If not, back to mail order again.
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Old 03-02-2013, 21:03   #6
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Re: Aluminum Alloys

They weld together fine. as said, most extrusions in alum boats are 6061 welded on 5052 hull plate etc....
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Old 03-02-2013, 21:20   #7
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Re: Aluminum Alloys

Thanks all. To the welder it goes.
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Old 04-02-2013, 10:30   #8
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Re: Aluminum Alloys

If the tank is 1/8" aluminum, I would consider going 5/32 or even 3/16 on the new bottom plating. Especially if the holes are in the bottom plate, not the corner welds. the cost would be very minimal and should wseld with no issues.
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Old 04-02-2013, 10:41   #9
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Re: Aluminum Alloys

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If the tank is 1/8" aluminum, I would consider going 5/32 or even 3/16 on the new bottom plating. Especially if the holes are in the bottom plate, not the corner welds. the cost would be very minimal and should weld with no issues.
Very good suggestion. I didn't mike it but to my calibrated eyeball it looks like 1/8" and the leaks are indeed pinholes on the bottom plate. I'm thinking from acids formed by gunk in the tank eating holes in the Al.

I found a reference in another thread to the CFR specs for fuel tanks and even diesel it required 0.250" for under 80 gal. Mine are only 40 gal each but I still think 0.125 is a little on the light side. I guess back in 1984 1/8 was considered good enough.
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Old 04-02-2013, 10:45   #10
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Re: Aluminum Alloys

Actually 1/8 and 5/32 are still used today even in certified gas tanks to 120 gallons. We used to buy them all athe time. Maybe the CFR only applies to commercial or military?
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Old 04-02-2013, 12:54   #11
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Re: Aluminum Alloys

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Actually 1/8 and 5/32 are still used today even in certified gas tanks to 120 gallons. We used to buy them all athe time. Maybe the CFR only applies to commercial or military?
Not sure what limits on vessels subject to the regs. Thanks to Delmarrey for posting the original information. Here's a link to the original regs.


46 CFR 58 : MAIN AND AUXILIARY MACHINERY AND RELATED SYSTEMS [ 46 CFR 58 ] : (SHIPPING [ 46 CFR ])

Fuel tanks are section 58.50. I glanced through briefly but didn't see anything about where this applies but I think it was for any vessel. Maybe you have the patience to read through the pages to see.
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Old 04-02-2013, 13:19   #12
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Re: Aluminum Alloys

Make sure the tank is not on rubber pads as that is what causes corrosion.
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Old 04-02-2013, 14:01   #13
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Re: Aluminum Alloys

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Make sure the tank is not on rubber pads as that it what causes corrosion.
Thanks. Not on rubber. Main supports are lengths of angle welded to both sides of the length of the top of the tank screwed into plywood braces that are glassed into the hull. Bottom of the tank is not touching anything.

Both tanks are leaking in almost the same spot, on the bottom at the lowest point in the tank right by the pickup tube and a few couple of inches from any edge and nowhere near any brackets or supports. Boat sat a lot and stayed in the water every winter in NY so I'm guessing picked up a lot of moisture from condensation. When I bought the boat it had a lot of grunge in the bottom so again, my guess is the grunge and water formed an acid that ate through the tank from the inside. Also from the outside where the tank leaks the metal is smooth and shiny so again must be from the inside out.

I'm going to get a grinder and cut out the leaking section so I can get a good look at inside area.
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Old 04-02-2013, 15:11   #14
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Re: Aluminum Alloys

A skil saw will cut that aluminum too. (enclosed eye protection)
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Old 04-02-2013, 15:47   #15
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Re: Aluminum Alloys

Ive patched a couple of tanks with edge leaks with alminum angle iron welded along the edges, worked well and it was all I could find where we were at the time! just a thought
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