Effect of Household Bleach on Stainless Water Tanks

  • Thread starter Thread starter Deleted member 36384
  • Start date Start date
D

Deleted member 36384

Guest
Hello,

The water in my stainless tanks has become tainted. I have drained down, vacuumed out crud, sprayed and soaked the walls, floors and ceilings with 5ml per gallon of water / household bleach. I then vacuumed out agains and filled with 100 ml of bleach in each 60 gallon tank, and pumped through to taps. The water and bleach solution has been soaking since Thursday and today I will drain down and flush through with fresh water before filling again only with fresh water.

I noticed that the welds on the inside of the stainless tanks are slightly discoloured, rust like, but on the surface, not flaky like you would see on plain steel. The welds on the outside of the tank are stainless with no discolouration. Do you think that the household bleach solution will have an effect on the welds at this concentration and soak period, 4 days? I am aware that there could be a reaction due to the chlorine but no idea if it is vigorous at these concentrations. I don't think it is but all the Youtube / Google stuff suggests 12 hour soak periods. Is it possible that even with flushing out, that the welds could retain bleach and form pin holes over time, or is that just ridiculous over this time frame and the fact that 60 gallons of fresh water will likely dilute to the point of irrelevance.

Any information appreciated.

Thanks,

BlowingOldBoots
 
Pitting seems to be the most probable form of corrosion by bleach. See this Article: Selection of stainless steels for handling sodium hypochlorite (NaOCl) Several general articles found with Google suggest that some staining is likely.

It seems to me that the concentration you have used is very mild and unlikely to cause serious damage. Inspect for pits, which are the most dangerous damage, as they will keep driving over time.
 
I can't see the repeated dilution allowing even conc bleach to do much damage. And you are using very diluted solution.

For a strategic solution about clean potable water on board, have a look at the Endosan website.

EndoSan Silver Stabilised Hydrogen Peroxide | EndoSan Stabilised Hydrogen Peroxide

I am a pro user of the product for spraying in an agricultural context to keep algae and other nasties out of water tanks and pipes. Somehow a residual amount of the base liquid always finds its way to the boat. Result no moulds on galley or heads surfaces, and the tanks and pipes are clear, clear, clear.
 
BlowingOldBoots said:
Hello,

The water in my stainless tanks has become tainted. I have drained down, vacuumed out crud, sprayed and soaked the walls, floors and ceilings with 5ml per gallon of water / household bleach. I then vacuumed out agains and filled with 100 ml of bleach in each 60 gallon tank, and pumped through to taps. The water and bleach solution has been soaking since Thursday and today I will drain down and flush through with fresh water before filling again only with fresh water.

I noticed that the welds on the inside of the stainless tanks are slightly discoloured, rust like, but on the surface, not flaky like you would see on plain steel. The welds on the outside of the tank are stainless with no discolouration. Do you think that the household bleach solution will have an effect on the welds at this concentration and soak period, 4 days? I am aware that there could be a reaction due to the chlorine but no idea if it is vigorous at these concentrations. I don't think it is but all the Youtube / Google stuff suggests 12 hour soak periods. Is it possible that even with flushing out, that the welds could retain bleach and form pin holes over time, or is that just ridiculous over this time frame and the fact that 60 gallons of fresh water will likely dilute to the point of irrelevance.

Any information appreciated.

Thanks,

BlowingOldBoots
Click to expand...
Such long saturation with bleach not recommended, as you probably gather, but highly unlikely this concentration has damaged welds. Next time go for PL milton in grocers and use to their recommendations - half day at most should remove whatever can be removed this way.

PWG
 
Thanks for the comments, that's reassuring. I am assuming the taste was from the old cork floats and drilled softwood plugs used to supplement the old corks in the level gauges. They had broken up and gone slimy.
 
sarabande said:
I can't see the repeated dilution allowing even conc bleach to do much damage. And you are using very diluted solution.

For a strategic solution about clean potable water on board, have a look at the Endosan website.

EndoSan Silver Stabilised Hydrogen Peroxide | EndoSan Stabilised Hydrogen Peroxide

I am a pro user of the product for spraying in an agricultural context to keep algae and other nasties out of water tanks and pipes. Somehow a residual amount of the base liquid always finds its way to the boat. Result no moulds on galley or heads surfaces, and the tanks and pipes are clear, clear, clear.
Click to expand...
available on ebay
 
Given you and I have the same boat, I had to replace the water tanks in early 2012. They had sat in salt water on top of the ballast up to about an inch, result crevice corrosion and water leaks. On the plus side TekTanks should now have measurements for a Rival 41c ? & and all the joinery should come out for access
 
I had to get both my fresh water tanks out and have some of the welds re-welded, and was told that the probable cause of the pinhole leaks was that chlorine bleach had been used to sterilise them. I now empty the tanks when I leave the boat, and do not use any bleach.
 
Norman_E how was the probable cause arrived at, did you or a previous owner use bleach regularly in the season or annually to clean? Any facts to help frame the conditions that caused the pin holes would be useful.
 
I use Tesco Thin Bleach, difficult to but during Covid crisis, but now back in their stores. About 50p for a couple of litres. Mix in circa 2% solution. Leave to stand in pipeworks, taps etc, then rinse through at least twice.

In teh basence of thin bleach this year I tried thick bleach, but it appears to have some sort of soap in it as it came out of the tap foamy, but rinsing through at least twice solved that problem.
 
Tell me about the soap. Filling tank after first cleaning so that the bleach can soak over a few days, looked down from deck washing to see a 3’ tall by 9” diameter foam sausage rising out the tank hatch and falling onto the sole. ?. The cockpit locker where the tank air vent is also had foam on the floor.

Thanks Rafiki about the double flushing. I’ll need to rig up the electric bilge pump to a hose into the tank as it takes the faucet pump about 3 hours to empty the fresh water tanks.
 
BlowingOldBoots said:
Norman_E how was the probable cause arrived at, did you or a previous owner use bleach regularly in the season or annually to clean? Any facts to help frame the conditions that caused the pin holes would be useful.
Click to expand...
I don't know what was put into the tanks to clean them before I had the boat. I used to run the levels down and add Milton to them before leaving the boat and it was thought that the chlorine in it may have been the cause. Since the welding job I have always left the tanks as empty as I can get them, and have had no further problems. The boat and its tanks date from 1998, and the welding jobs were done about 2013.
 
The bleach didn't do anything bad that fast. You concentrations are not far outside the range of industry standards.

(Steel Institute)
Chlorine is very aggressive to stainless steels. The Nickel Institute guidelines for continuous exposure at ambient temperatures (~20˚C) and neutral pH (~ pH7), are that 304 can cope with 2ppm chlorine and 316 ~5ppm chlorine. In alkaline solutions (pH>7) higher concentrations are possible but this does not help much in swimming pools or drinking water. Chlorine frequently causes corrosion problems. Chlorine attack can occur with bleach laden washdown water if pools form in drains which are usually empty. Chlorine concentrations in droplets or water films immediately above a still pool or water tank can be higher than the chlorine level in the bulk water. When dosing concentrated chlorine into pipes or tanks, it must be well mixed otherwise concentrated streams will eat out downstream elbows or tank walls near the chlorine inlet.


Much higher concentrations can be used for short periods as the attack on the stainless steel must initiate and form a stable pit for failure to occur. The American Water and Wastewater Association permits 25ppm for 24 hours in cases of emergency disinfection. The food industry can use up to 100ppm in hot water for minutes followed by rinsing and/or passivation. It is an effective biocide because the kill rate depends on (exposure time) * (concentration of biocide) but the stainless steel is resistant to the chlorine for the relatively short, high concentration exposure.

That said, it sounds like the welds need repassivating (stain removed, iron leached from surface) by using citric acid (ASTM A967) according to one of these methods. Gelling the CA with fumed silica can help hold it in place:

Citric 1: 4-10 w% Citric Acid, 140-160F, 4 minutes minimum
Citric 2: 4-10 w% Citric Acid, 120-140F, 10 minutes minimum
Citric 3: 4-10 w% Citric Acid, 70-120F, 20 minutes minimum. (This is the basis of the commercial products we are testing in this review.)
Citric 4: Other combinations of temperature time and concentration of citric acid with or without chemicals to enhance cleaning, accelerants or inhibitors capable of producing parts that pass the specified test requirements.
Citric 5: Other combinations of temperature time and concentration of citric acid with or without chemicals to enhance cleaning, accelerants or inhibitors capable of producing parts that pass the specified test requirements. Immersion bath to be controlled at pH of 1.8-2.2.

Basically, this is about as strong as lemon juice. You cannot soak it too long, so an hour is better. Heat helps, but more time at temperatures above 75F works. Piece of cake.
 
We had nasty -smelling water coming out of the galley tap - it was OK once a few litres had been pumped through, so the tank was OK, but there was something nasty in the pipework or pump. I used sulphamic acid (like this: Cleanline 037450 Sulphamic Acid Toilet Cleaner, 5 L Pack of 2: Amazon.co.uk: Business, Industry & Science ). I pumped the tank empty, put the stuff in and pumped it through the pipework, left it a couple of hours (as far as recall) then pumped it out and flushed with clean water. It's all been fine since; about a year ago.
 
Maybe best to add nothing as tap water has a little chlorine in it .
http://dwi.defra.gov.uk/consumers/advice-leaflets/chlorine.pdf
I took to flushing with fresh water only a few years ago in the spring after leaving the water system as empty as possible over the winter.
Our usual turnover of water in the warmer months is a tank every couple of weeks at most , although no so much , so far this year .
 
You must log in or register to reply here.

Share this page

Top