Coating Solution for demineralized water storage tank

[Raghav]

Dear Members,

Could your suggest an arc spray coating for the internal of a tank storing demineralized water ? The PH value is 7. What should be the coating thickness and your recommendation of sealant ? What life can be expected of the coating ?

Thanks & Regards,

Raghav

[Gordon]

Hi Raghav

I would consider zinc or aluminium ~ 0.25 mm thick. Unsealed this could give in excess of 20 years life.

[Raghav]

Hi Raghav

I would consider zinc or aluminium ~ 0.25 mm thick. Unsealed this should give in excess of 20 years life.

Thanks for your reply, however on the below mentioned link it states that the corrosion rate of zinc coating in demineralized water is 137 microns per year. Is that correct ? Any hands on experience ?

(link dead)

Thanks Regards,

Raghav

[Gordon]

Hi Raghav

Interesting site you linked to

First apologies for my rather rash statement

Unsealed this should give in excess of 20 years life.

and will edit it to say could instead of should Estimating/predicting life is difficult due to the number of variable factors like temperature, agitation, composition, dissolve gases, pH etc. along with the fact that in real life cases we have to wait so long for results.

That said I can't help feeling a corrosion rate of 0.137 mm/yr sounds excessive, which would predict 0.250 mm zinc coating lasting only 2 years Without knowing the exact conditions of testing it is difficult to comment.

I know some of the information we use to predict corrosion rates is from galvanised steel, but generally corrosion rates are based on the amount of zinc and whether applied by hot dip, plating or thermal spray seems to make little difference. One advantage of thermal spray coatings is the ability to use thicker coatings.

Some intersting links which may generate more discussion than answers
(links dead)

[meshahan]

Dear Members,

Could your suggest an arc spray coating for the internal of a tank storing demineralized water ? The PH value is 7. What should be the coating thickness and your recommendation of sealant ? What life can be expected of the coating ?

Thanks & Regards,

Raghav

Do u have design calculation for demineralized water storage tank.

[LEN WOOD]

I don't think that Thermal Spray has a solution for this scenario.

Polyurea (elastomeric) coatings are currently the only viable and long lasting solution. They faciliate the longest lasting ptotection of any Carbon steel tank lining against the leaching nature of Demineralised water and VOCs (Volatile Organic Contaminants).

The only other option is to make the tank out of Stainless Steel tank - way more expense!

cheers

GlenB

[SimonH]

Hi,

I've recently been working with the water regulation authority for the approval for coating potable water containers with Zinc for anticorrosion - and it turns out to be a bit of a minefield.

The approvals body are there to approve organic coatings and therefore won't approve a metal coating - although it's a catch 22 because a metal coating doesn't require an approval....... It's like taking your bicycle for an MOT test. However of course the local water authorities won't let you apply anything without WRAS approval...Aaarg! Even more annoying is that Zinga (basically a heavily zinc loaded paint) is approved!

There is a US standard for zinc lining potable water tanks.

However you just said de-mineralised, so I'm guessing not for drinking water anyway?

Based on previous testing (kure beach etc) and textbook application of a zinc coating I would have thought that 20years is perfectly achievable for a thermally sprayed zinc coating?