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post #1 of 7 Old 06-07-2010 Thread Starter
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Repair Corroded Aluminium water tank

I have a 60' Sea Ranger with a floor tank about 4 m long and 0.5 wide and 0.5 deep. It has surge baffles that divide it into about 6 compartments. It sprung a leak so I undid an inspection cap in the end compartment and it had a lot of white chalk lumps all over the bottom and sides of the tank with slight pitting underneath. Removing the tank would be very difficult.
Has anybody had a similar problem and if so any suggestions on how to resolve the problem?
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post #2 of 7 Old 06-12-2010
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JC Whitney has an inner liner that I have used very satisfactorily in repairing pitted and corroded gas tanks on antique vehicles. Get the literature and find out if its satisfactory for potable water. Difficulty is that the tank must be removed and if you've got it out you may as well either weld a new bottom on it or replace it.

Another alternative (preferred IMO) would be to install a plastic bladder in the existing tank. The baffles will present some engineering challenges but there are several advertisers (Good Old Boats Magazine) that can custom build plastic tank liners.

I replaced mine with an off the shelf 80 gal plastic and after a fun afternoon dealing with epoxies and fiberglass while standing on my head had it both securely mounted, and easily removeable.

Be careful, You can get a cheap(?) high from the various solvents etc. found in dealing with epoxies or polyesters. This may not be conducive to becoming an old sailor!

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post #3 of 7 Old 06-12-2010
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If can remove the tank from the boat, cut large access holes into the top, cut the entire bottom off and do a major repair/replacement of the bottom, then (through the large cuts of access) apply a FDA/NSP "for potable water service " rated epoxy liner. Lining epoxies are 'rolled-on' and are special formulations that emit very low amine content when cured.

The large access holes can 'studded' using common 18-8 bolts to which to apply large plates (drilled to accept the studs added to the tank), and sealed with thick Silicone caulk (which is rated for 'potable water service'.

This will result in a cost of approximately 1/2 the cost of a new tank and if 'lined' with a FDA type potable water epoxy will last indefinitly. This is the way that potable water tanks aare repaired by airlines, railroads, commercial shipping.

Aluminum tanks that are charged with water that is chlorinated will always 'rot out' due to the formation of aluminum chloride. The chlorine in the 'chlorinated water' aggressively attacks the aluminum. There is no economical way to sanitize an aluminum water tank. Epoxy coatings ("Lining" epoxies NOT structural epoxies) are the solution for aluminum tanks.

Most 'commercial divisions' of marine coatings manufacturers have "potable water" lining epoxies. The best supplier for small quantities (quart quanties) Ive found is: NSP 120 - NSF 61 Potable water approved Epoxy Adduct

Last edited by RichH; 07-06-2010 at 08:30 AM.
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post #4 of 7 Old 06-12-2010
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Sounds like a good way to go to me.

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post #5 of 7 Old 06-17-2010
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The 55gallon aluminum water tank in my San Juan 34 began weaping and within a couple of months got to the point that it would drain itself in about an hour. I cut a 12"x18" access port in the top and discovered that the entire interior of the tank was covered with aluminum oxide pox. After cleaning the tank I found a couple of sizable holes in the areas where loose oxide had piled up in the low spot. I epoxied aluminum patches in place with thickened non-aliphatic (sp?) epoxy and after cure I coated the entire interior. This fix is a year old and is working great.

Everybody (even the pros) advised I yank the tank but there is no way to do that without major deconstruction.
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post #6 of 7 Old 07-06-2010
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SJ34 what did you use to coat the interior?
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post #7 of 7 Old 07-07-2010
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Quote:
Originally Posted by RichH View Post
....Aluminum tanks that are charged with water that is chlorinated will always 'rot out' due to the formation of aluminum chloride. The chlorine in the 'chlorinated water' aggressively attacks the aluminum. ....
Take care, you and all that have old aluminum tanks. Aluminum degrades with age and result in potential severe hamrful effects to your health.

"Some patients on long-term hemodialysis develop speech disorders, dementia, or convulsions. This syndrome is associated with increased concentration of aluminum in serum, brain, muscle, and bone [Amdur et al. 1991; Hathaway et al. 1991]. There is some evidence that Alzheimer's disease may be linked to aluminum content in the body [Amdur et al. 1991]. Analysis of the aluminum content in the brains of persons dying from Alzheimer's have shown increased levels, although brain aluminum levels vary greatly."
Aluminum


Health effects of aluminum

Aluminum is one of the most widely used metals and also one of the most frequently found compounds in the earth's crust. Due to these facts, aluminum is commonly known as an innocent compound. But still, when one is exposed to high concentrations, it can cause health problems. The water-soluble form of aluminum causes the harmful effects, these particles are called ions. They are usually found in a solution of aluminum in combination with other ions, for instance as aluminum chlorine.

The uptake of aluminum can take place through food, through breathing and by skin contact. Long lasting uptakes of significant concentrations of aluminum can lead to serious health effects, such as:

- Damage to the central nervous system
- Dementia
- Loss of memory
- Listlessness
- Severe trembling



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Last edited by PCP; 07-07-2010 at 08:39 AM.
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