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Old 19-01-2022, 14:39   #1
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leaking steel diesel tank

steel hull and inbuilt diesel tank, absolute pinhole in weld, VERY slight seepage. Interior inaccessible. What about emptying tank, filling with CO2, applying slight vacuum pressure, grinding pinholed weld site and then run a bead over the top? or even araldite? Opinions please.
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Old 20-01-2022, 05:53   #2
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Re: leaking steel diesel tank

Hmmm.

I doubt that the CO2 is necessary - if you do set fire to diesel in the tank it will be self extinguishing when CO/CO2 fills the tank and oxygen is depleted. The bigger issue is keeping diesel oil out of the weld surface. Is the leak at the bottom of the tank or can you drain until the level of the diesel is below the leak? If so, go ahead and weld a bead.

Vacuum. It might keep oil out of the way, but it might also suck the weld into the tank. If I wanted one, I'd use a wet/dry vac on the fill pipe.

But, is the tank getting ready to form multiple leaks? If so, you have a much bigger problem to solve.

I'm tempted toward a glued on patch rather than a weld. A plate with plenty of 3M 5200 should do the job.
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Old 20-01-2022, 06:10   #3
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Re: leaking steel diesel tank

Why a glued on plate rather than just plenty of 3M 5200 or epoxygoop to plug the pinhole?
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Old 20-01-2022, 06:13   #4
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Re: leaking steel diesel tank

Araldite might work, depending upon which Huntsman ‘Araldite’ product you’re talking about.
https://www.huntsman.com/about/advanced-materials

I’d suggest you also look at J-B Weld ‘SteelStik’, or ‘TankWeld’.
https://www.jbweld.com/projects/gas-tank-repair
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Old 20-01-2022, 06:22   #5
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Re: leaking steel diesel tank

Welding on a diesel tank: Diesel oil starts producing flammable gas at about 125 F. It's -40 for gasoline. If you locally heat diesel above 125 F with a welder, and supply a spark, it can ignite. But either the rest of the diesel or the steel of the tank is going to dissipate that heat very quickly. It's like trying to set fire to a log with a butane lighter - you can get a very local flame, but not enough heat to sustain a fire. I have welded on (but not in) a filled diesel tank with no consequence. Just don't try it on a gasoline tank.
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Old 20-01-2022, 16:30   #6
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Re: leaking steel diesel tank

I had a pinhole leak in a 500 gal diesel tank on MOJO - found the leak when sandblasting the bottom. It was just a pinhole seepage, but still a leak. We filled the tank to full and then used a CO2 fire extinguisher to flush out any remaining air/oxygen. The welder then welded the pinhole, no problem. In reality, the CO2 flush was probably unnecessary - the amount of heat generated welding a pinhole leak was easily absorbed by the volume of diesel in the tank.
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Old 20-01-2022, 18:48   #7
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Re: leaking steel diesel tank

Welding over/through the seepage was ok?
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Old 20-01-2022, 20:27   #8
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Re: leaking steel diesel tank

If it's a pinhole and not a crack, and you're concerned about welding, what about drilling, tapping, and installing a bolt with thread sealant?
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Old 20-01-2022, 20:43   #9
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Re: leaking steel diesel tank

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Welding over/through the seepage was ok?
Not a problem at all.
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Old 20-01-2022, 20:55   #10
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Re: leaking steel diesel tank

Done such a repair in the past on a ~1/2" weld loss at a stainless diesel tank. After sanding around the area outside, used J-B Weld Steel reinforced epoxy. It is rated for fuel tanks repair. Worked perfectly.
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Old 20-01-2022, 21:21   #11
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Re: leaking steel diesel tank

Belzona makes an excellent series of steel re-building epoxies. One of them is designed exactly for this- canít remember the exact number. It is designed to work in oily and greasy situations. I once had a leaky steel diesel tank where it was impossible to get a welder into (without cutting a hole in the side of the boat). Managed to build a fillet of belzona in there that worked like a charm. It was 8 years ago, and as far as I know itís still working fineÖ
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Old 20-01-2022, 22:08   #12
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Re: leaking steel diesel tank

Agreed .. belzona is definitely the ticket!
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Old 21-01-2022, 03:22   #13
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Re: leaking steel diesel tank

Quote:
Originally Posted by NSboatman View Post
Belzona makes an excellent series of steel re-building epoxies. One of them is designed exactly for this- canít remember the exact number Ö
Tanks, I wasnít aware of Belzona Metal Repair / Rebuilding Compounds
https://www.belzona.com/en/products/...al-repair.aspx
? 1221 (Super E-Metal) ? ➥ https://www.belzona.com/en/products/1000/1221.aspx
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Old 21-01-2022, 04:48   #14
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Re: leaking steel diesel tank

+1 for JB or maybe the other brand. Way easier, faster, cheaper than welding.
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Old 21-01-2022, 09:10   #15
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Re: leaking steel diesel tank

Had to do that on my old boat many years ago. Welder said all he needed was to tilt tank so no fuel behind welding spot (said dissipates the heat too fast). That, and he had me sit behind him with a water hose to put out anything the sparks tried to ignite.
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