Aluminum Water Tank Contamination

[Steve Carpman22174]

After a particularly rough sail on our 1991 Hunter 37.5 last summer, the flow from our aluminum water tank was reduced by about 90%. We traced the problem to a whitish particulate substance that was blocking the flow at the tank's outlet valve. This contaminant probably broke loose during the rough sail. While we were able to restore most of the flow, I believe the contaminant that caused the initial problem is still lurking in the tank, just waiting for another opportunity to break loose and cause yet another blockage.

We are not able to inspect the tank and remove whatever resides there as there is no clean-out port. Also there is no access through the tanks outlet valve - space limitations prevent the removal of the valve. Is there a chemical treatment we can run through the tank to remove the remaining contaminant?

 

[sailingdog]

The whitish contaminant is probably corrosion byproduct of the aluminum tank corroding. Have you been using chlorinated water in your water tank. If so, that is probably what is causing the problem. I don't know of any treatment for this problem off hand.... and chances are good that the tank is probably going to need replacement fairly soon, since it sounds like there's a fair amount of the white corrosion byproduct. Aluminum tanks and heavily chlorinated water or chlorine bleach don't play nice with each other, and the tank always loses.

 

[cbsailor]

Some call it a corrosion salt.

The previous reply post is probably correct. Previous chlorinating of the aluminum tank is the culprit. The corrosion really attacks the weld joints and will usually result in pin holes developing there. Left untreated it will mean a tank replacement much sooner than normal. You see similar stuff grow in your coffee maker and using the same vinegar technique used to clean them may help some. Our 50 gal aluminum tank showed no outward signs of problem when we purchased the boat. There was no access port into the tank and and the strainer showed no signs of problems. When we filled the tank for our first long cruise, it didn't take long for the pressure to find all the weak spots and water just kept flowing from under the V-berth.

Tank removal followed and it was apparent that repair was not the answer. I got Ronco to build us a new poly tank and it was about the same price of a new aluminum tank. Removal and installing the new tank was a big project requiring tearing out the v-berth decking and installing new decking and glassing it back. I'd try neutralizing the corrosion first.

 

[Peggie Hall HeadMistress]

Most likely hard water mineral buildup

And maybe some corrosion "sluff" too, but However, it's not a "contaminant" that requires purification...it's just "sand" that needs to be flushed out.

If it is hard water minerals, distilled white vinegar will dissolve 'em without introducing any real contaminant into your water suply...however, using enough to do any good in a large water tank can be a challenge. And it's late in season where you are to leave a solution in the tank long enough to work.

So about all you can do now is flush as much of the loose material out as possible...most of it is on the bottom of the tank, so it'll be a PITA job, but not that hard. Disconnect the discharge line from the tank--if there's no access, you'll have to create it--and send lots of water into the bottom of the tank to stir it up and flush it out. Use a large kitchen strainer held under the discharge fitting will catch the sediment so it doesn't end up in your bilge pump to clog it up.

Use an air compressor to leave the tank dry for the winter...and deal with dissolving what's stuck to the sides next spring.

That's what I'd do anyway...someone else may have a better idea.

 

[Don S/V ILLusion]

Steve
the good news is the material you find, aluminum chloride hydrate, is not toxic. The bad news is there is nothing practical you can do to eliminate it. The chloride formation in aluminum tanks is common in formulation of numerous processes in the chemical industry and the only way it can be removed is by sublimation which typically involves mechanical methods not practical in boat tanks.
Flushing won't usually work except in the short-term - if you have sufficient access to the outlet, you can try high pressure hose capable of knocking some of the material off the walls which might help. Otherwise, frequent cleaning of the filter is all you can reasonably do once this starts inside a tank.

 

[sailingdog]

CBsailor-

one point, the white mineral buildup you find in a coffee maker is usually lime deposits, caused by using mineral laden water in it... and that dissolves in vinegar quite well... the stuff in the tank mentioned by the OP is probably not lime deposits but aluminum chloride hydrate and probably not affected much by a weak acidic solution like vinegar.

The reason I doubt that it is "hard water" mineral buildup is that lime deposits generally require hot water or heating of the water to really form to any significant degree. If no heat is involved, it would probably require vast amounts of evaporation, which is unlikely to occur in a relatively sealed fresh water system. I'd expect to see hard water lime deposits at the hot water heater, but if you're not seeing the white deposits clogging your hot water heater, chances are very good that it is aluminum corrosion byproduct instead.

 

[Rick D]

My Experience...

...on my Vision 32 1990 was that the tank failed, after seven years, in the seams. I glassed (polyester) the seams and got two years out of it before the bond failed (you might try epoxy to see if it works better for you altho I doubt it would in this application).

It,s just a maintenance item and would be better replaced when necessary with a Ronco tank if one fits or a custom made plastic one if needed. (See Triple-M Plastic for that option.)

 

[bobfnbw]

Anyone know if Ronco tanks have internal baffles like a aluminum tank has, or does the water just slosh around ?
When I cut out my foreward 75 gal. alum. tank on our Endeavour, it was covered inside with the deposits you are seeing. But there was very little floating around in there, most was stuck to the tank sides.

I opted to replace most of mine, and maybe all. But the original tanks are built in and impossible to replace with the same size tank, so I am going to split them up to allow for installation, removal and cleaning.