Bleaching Fresh Water Tanks / Bad Move ?

[dougshipl]

Our sailboat is 10 years old and we puta very small amount of clorox bleach in our stainless fresh water tanks then flushed with fresh water in attempt to clean them out. Months later we noticed, when inspecting interior of all 3 stainless tanks, that rust type bubbles are forming on the bottom seams of the tanks. Could the bleach have caused this corrosion? If they start to leak at the edges is there any caulk...etc that can be used to stop any leaks or are the tanks done for? All comments welcomed.

[sailaway21]

You should not have damaged the stainless steel in any event. You might discolor it, but even that is unlikely. I'd check those bubbles out a bit closer as there may be a coating on the inside that's breaking down. A photo wouldn't hurt if you can provide one.

[sailingdog]

Also, if the rust is at the seams, it may be due to the fact that welds are generally far more prone to corrosion than unwelded stainless. I seriously doubt that a small amount of chlorine bleach would bother stainless tanks much, especially if you flushed the system with fresh water shortly afterwards.

[camaraderie]

More likely is crevice corrosion in the stainless from being in an aneorobic environment and the welds are the first thing to fail. Diluted beach, properly washed out afterwards will not cause such a problem. Tanks will need to be pulled and re-welded. An interior coating of epoxy suitable for potable water should prevent a re-occurance otherwise you will have to contend with this again down the road.

[sailingdog]

BTW, one epoxy well suited for coating the interior of potable water tanks is CeramKote 54. It is designed specifically for potable water systems.

[brak]

MAS epoxy support told me that their low viscosity resin is suitable for potable water applications. For what it's worth. They do not have any NSF certifications though.

[peikenberry]

I agree with Camaraderie: Stainless Steel is very susceptible to crevice corrosion. That is probably what is occurring here. I has nothing to dowith the bleach.

[dougshipl]

Excellent - well that at least makes me feel better that we didnt screw it up as we used 8oz bleach per 10 gal h2o then flushed system. We had the same looking rust deposits on a leaky water heater we just removed - so it must have been devloping for 9 yrs 7 months (when new) then with our luck decided to leak months after we purchase boat.

Getting back to sailing dog and brak comments, i now know the right thing per cam is to rip them out to weld which we will do at some point but I do have pretty good access to the interior of the tanks through a 12" port and just plan to use for showering - thoughts on temp fix - after good cleaning and light sand can we apply epoxy to the seams and hold off on rewelding till later date? Or is that just compounding problem?

Thank you for all for your time and insight.

[sailaway21]

I'm not convinced that you necessarily have crevise corrosion as, unless you're running about with your tanks pressed up at all times, the environment is not anaeroebic. I'd investigate further as to what exactly is bubbling and, if it is crevise corrosion, I'd sand, treat with ospho, and seal with epoxy. It beats the joys of removal. The tank may well already have a coating and that may be what you're seeing fail at the welds-it's the most likely spot for any type of failure regardless.

[camaraderie]

doug...temp fixes are fine as long as they are working...just be sure your underlayment is dry and you don't have rot starting beneath the tanks.