I'm specifying an elevated tank repainting. Right now, I'm going with AWWA Interior Coating System #5 (ICS-5) for the interior wet area of the tank. ICS-5 consists of a zinc-rich primer and epoxy intermediate and finish coats. All paints must be ANSI/NSF Standard 61 approved for immersion in potable water.

Honestly, I know very little about paint. The ICS-5 was initially chosen based on a recommendation from a paint manufacturer. However, I just talked to a different manufacturer who said that they did not make a zinc primer that's NSF 61 approved. She said the reason for this wasn't because they weren't capable of doing so - they have a zinc primer for exterior use - but rather, they do not support the use of zinc as a primer for potable water immersion systems. This manufacturer is concerned that subsequent coats could be compromised and leave the zinc primer exposed to potable water, and in the future zinc will become the "new lead".

Just wondering if anyone shares or has heard this viewpoint.

Thanks in advance for your help.

I see it as a potential issue. With our wastewater discharge permit (Indiana) we are working to a zinc level of 2.61ppm. I don't know what the level for potable water is, but we have had issues exceeding out discharge limits due to residual zinc compounds in the plastic piping for a spray system on a phosphating line. So, it is one of those issues where you can't quantify the risk.

Zinc is an essential nutrient for human life and galvanized pipe is commonly used for water pipes.

Too much of ANYTHING can be bad. Zinc would be no exception:
http://www.nlm.nih.gov/medlineplus/ency/article/00...
http://en.wikipedia.org/wiki/Zinc_toxicity

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OK. Just heard back from the sales rep. She misunderstood (or maybe I did) the company's reason for not providing zinc primers for immersion environments. It actually has nothing to do with health risks. She sent me a copy of a technical bulletin explaining their stance.

Basically, they say that specifying topcoated zinc underwater is poor practice. Eventually, the topcoat will be compromised and the zinc primer will be exposed to water. When it is exposed to water, it reacts and forms blisters, causing the system to fail.

This is the complete opposite stance I've heard from other manufacturers, who claim that a three coat system with a zinc primer is the "Cadillac" of paint systems, and should definitely be specified for tank interiors.

Thoughts?

Compositepro,
And in the older galvanized pipe had lead in the zinc coating.

Three coat systems are the "Cadillac" of atmospheric exposure coating systems. Many zinc primers are susceptible to problems under immersion conditions. Others seem to work. In particular the high-ratio inorganic zinc coatings are supposed to work well underwater.

TomDOT,
This is a repainting, so you wouldn't use an inorganic zinc primer.

I suggest that the coatings supplier who rubbished the idea of a zinc rich primer was simply trying to push her product.
This is the one I would research and probably use:
https://www.tnemec.com/product/view/Series-94-H2O-...

hokie66, while IOZ is most often restricted to shop painting a competent crew working on a relatively simple structure can successfully apply it in the field. I agree that it's easier to just restrict it to shop application rather than make a judgement call each time for field painting.

There are some concerns about using any solventborne coating inside potable water tanks due to water odor/taste problems - with your suggested material, the PCBTF solvent has a particularly pungent odor. The first time I had a paint with that solvent sprayed out at the steel fab, the paint crew commented on that several times.

Again, a competent crew (no over-thick application, no thinning, forced ventilation in the tank during cure) can overcome that challenge.

It is a repainting, but the interior is to be blasted to SSPC SP-10. Should this be treated differently than a new tank?

In my experience, the problem with blasting a big thing like a tank is keeping the surface pristine until the coating is applied. Flash rusting is the issue. With inorganic zinc, it really needs a white metal surface, while the organic coatings are more forgiving.

Here are two products that maybe allow you to blast without the flash rust forming. You will need to see if this product is cleared for Potable water and is compatible with your choice of coating.
It is a little strange, but we have one water tank that is still coated with Anhydrous Lanolin


http://www.targetproducts.com/prod-detail.aspx?id=...

http://www.google.com/url?sa=t&rct=j&q=coa...

Grease/wax works great for a lot of corrosion protection applications. It even self-heals to some extent. It's messy and not "high tech" though :)

I've painted a number of immersion service steel items on freshwater navigation locks and dams. I used 2 coats of epoxy over SSPC-SP 10/NACE No. 2 Near White Blast Cleaning. SSPC books and talking to manufacturer's reps recommended against zinc for immersion service. Splash zone it's cadillac; just not for immersion.