descaling holding tank - how?

PaulR

PaulR

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we have a stainless steel holding tank which is not - as far as I can see removable whole - suspect was fitted before builders put the deck on and wont come out through small access hatch - the tank is gravity drained rather than having a deck pump out option so no easy access into it - certainly no access hatch .

had a blockage in system a season ago - not a nice job clearing and in doing so found some lumps of scale in the out pipe - have now renewed the pipes but suspect there may be scale in the holding tank itself and hence my question- how de we descale it?

hoping there is some wonderful liquid we can pump through from the heads into the closed tank which dissolves all the scale which we can then flush through.

boat currently ashore and this on our winter job list (once snow clears and we can get there)

be glad of guidance from any forumite who has succesfully descaled - thanks
 
We only use hydrochloric acid, which is cheap and easily available in Med countries. However, I wouldn't use it in a stainless steel tank. I read just the other day that Lee Sanitation sell some wonder stuff that will do this, but no experience.
 
Ariadne said:
Hydrochloric acid, is the only thing I can think of and its what we use when we have any lime-scale problems in the holding tank or in the pipework.

Not being chemist, what problems will its use cause to the stainless steel tank?
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I'm not a chemist either, but I am a metallurgist! Stainless steel and chlorides do not get on well together. Pitting is the most likely result of attack, something most definitely to be avoided in a thin-walled vessel.

A problem that affects many stainless steel tanks is sensitisation. Unless the steel used is a low carbon version (304L, 316L) and a corresponding filler rod, there is a likelihood that areas in and around the weld will be low in chromium, as this element preferentially forms carbides. The result is that weld regions are susceptible to rapid corrosion. Watching the requests for assistance here over many years I don't remember a single one where it was the tank walls that corroded as opposed to the welds. Putting HCl in there will increase the attack that is probably already taking place with the seawater. If you are fortunate enough to have a tank that has been well made by someone who knew what they were doing it should be safe, but unfortunately very many tanks are made using any old sheet stainless steel.
 
I recently spotted some old-fashioned "Spirit of Salts" in my local hardware shop, and used it on a lime-scale encrusted domestic installation. Highly effective, but with alarming gurgling noises and acrid fumes. Don't know what's in it but it's clearly acidic, so I should check on its ingredients in view of the preceeding warnings.
 
we had our holding tank block last Summer. Having worked for Thames Water and other organisations on many black water projects I am not fazed by having to deal with it but like most people it isn't at the top of my list so I looked in the cockpit locker for inspiration and found THIS left over from sorting out the potted water.

I threw the contents of the pot down the toilet and pumped it into the holding tank leaving it to work overnight, the next day when sailing well off the coast I opened the holding tank seacock and it emptied without any problem. The scale that was released at the same time was amazing and left a huge trail in the water and two further flushes of the tank released further scale.

Not saying for one minute this is the answer to all holding tank problems but it did save me getting my hands dirty!!
 
Did it work while the holding tank was full and blocked? Or did you notice the blockage and then attack it?

I've found sheets of lime scale about A4 in size and up to 10mm thick in my tank last time it blocked. Had to empty it by hand to get the stuff out.

I also increased the angle the tank sat at to stop the build up. Seems to have worked this last year as I have not any blockages.
 
Ariadne said:
Did it work while the holding tank was full and blocked? Or did you notice the blockage and then attack it?

I've found sheets of lime scale about A4 in size and up to 10mm thick in my tank last time it blocked. Had to empty it by hand to get the stuff out.

I also increased the angle the tank sat at to stop the build up. Seems to have worked this last year as I have not any blockages.
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I try not to get to the point where the holding tank is completely full before I empty it so the tank was about 3/4's full when I discovered it was blocked, I just tipped the Puriclean down the toilet and pumped it into the tank, I must admit I wasn't sure it would do anything at all as I suspected it was blocked by solids but overnight it must have done some good as it emptied the following day. As I said, I am not sure this is the answer to all holding tank problems and it may just have been luck, but it worked for me on this occasion.
 
Very interesting ,do you know what the Lee descaler is safe to use on and also how big a tank will it treat.The Puriclean already gives the info.
 
Sulphamic acid is an organic descaler which will not affect stainless steel, and is used in descaling nuclear power stations. You can buy it commercially....not it is NOT sulphuric acid!
 
footsoldier said:
I recently spotted some old-fashioned "Spirit of Salts" in my local hardware shop, and used it on a lime-scale encrusted domestic installation. Highly effective, but with alarming gurgling noises and acrid fumes. Don't know what's in it but it's clearly acidic, so I should check on its ingredients in view of the preceeding warnings.
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Sprits of salts is the old name for hydrochloric acid, just as oil of vitriol, for sulphuric acid.
 
pappaecho said:
Sulphamic acid is an organic descaler which will not affect stainless steel, and is used in descaling nuclear power stations. You can buy it commercially....not it is NOT sulphuric acid!
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Having quickly looked at a material data sheet for sulphamic acid HERE I couldn't help but notice it states it is "harmful in the aquatic environment".

I think the OP is currently ashore so he will need to consider how he drains and disposes of the waste but it appears that it certainly shouldn't be used if afloat.
 
P4Paul said:
Having quickly looked at a material data sheet for sulphamic acid HERE I couldn't help but notice it states it is "harmful in the aquatic environment".

I think the OP is currently ashore so he will need to consider how he drains and disposes of the waste but it appears that it certainly shouldn't be used if afloat.
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Virtually every de-scaler is harmful to the aquatic enviroment. As they are normally some sort of acid. AFAIK.
 
My father used to use spirit of salts in soldering ,if I remember, its as you say hydrochloric acid but he used to "kill" it by if I remember properly adding a certain amount of zinc to it.I remember it worked very good when soldering.
 
nedmin said:
My father used to use spirit of salts in soldering ,if I remember, its as you say hydrochloric acid but he used to "kill" it by if I remember properly adding a certain amount of zinc to it.I remember it worked very good when soldering.
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You are quite correct, "killed spirits" was and maybe still is used as a soft soldering flux.
But you have to make sure its all off the job afterwards or it corrodes. Not used for small electrical jobs, use resin flux instead.
 
P4Paul said:
Mind you the contents of the holding tank are not that friendly to aquatic life in the first place especially Bosun Higgs stella and vindaloo cocktail.
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Vindaloo alone, without passing through anybodies gut, is dangerous to any life!!
 
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