Time to paint a water tower 4

[wojton]

I've got a 2,000,000 gal. double toroid water tower that needs to be painted.The exterior and interior coating systems have failed. My consultant is recommending to abrasive blast all of the surfaces and then apply a three layer Polyamide Epoxy systen on the interior and a three layer epoxy primer, followed by two coats of Epoxy Siloxane system on the exterior. No lead or site condition issues. My consultant is telling me that the construction period will be 180 days. Any comments on the time period?

 

[bimr]

You might check your paint spec again as not many people are using a 5 coat paint system.

You can probably build the water tank in 180 days. The paint should be appliedin 60-90 days depending upon the weather.

 

[cub3bead]

Check with Carboline or Tnemec for their recommendations.

NACE recommends a white metal blast for immersion service. I have also found that specifing a 2 mil anchor pattern gives you something for the prime coat to grip.

Watch you temperature and humidity during the blasting. Flash rusting can happen if it is cold and damp.

A white metal blast is expensive but your coating life and remaining tank life will be maximized.

 

[Valvecrazy]

How are you going to continue the supply of water to the system while the tower is off line for so long?

 

[semo]

I agree with both Bimr & Cub3bead. 60 to 90 days should take care of it. Depending on the weather/temp. the interior epoxy will take approximately 7+ days to cure before water can be introduced.

The 3 coat epoxy primer on the exterior looks a bit much. 1 coat of epoxy primer should be sufficient at the correct millage. A common exterior coating is 1 coat of zinc-rich primer, 1 coat of epoxy, and one coat of polyurethane to maintain the gloss.

The siloxane has a higher material cost; but, it is also said to have a longer gloss retention and longer life span. A big part of the cost to repaint is the labor. If you use this high solids coating, do as Cub3bead says and check with the coating manufacturer as to the undercoat system. One of their selling points is that this is a single or 2 coat system and saves on labor costs.

 

[corrosionman]

wojton This is a big tank - - with surface area 2500 sq mtrs inside and same again outside. If you have such doubts as to what your preferred contractor says, why not get alternative quotes including an itemised job program. Also, surely there is a coating manufacturer who will offer a single coat (high build) product rather than your several coats ( Talk to E Wood Ltd, Northallerton U.K.about their Copon Coating range) And if you have any doubts whatsoever about the integrity of a single coat , why not put in a cathodic protection system as "braces and a piece of string"
All this relates to the Inside - - - The outside can be done with the tank filled up and back in service so provided you are happy with the quote from your Contractor, does it matter how long he takes ?
( You probably guessed I am a Coating Contractor in U.k.)
REgards Corrosionman

 

[kervin520]

If you are blasting the interior and exterior of this tank, 180 days including weather is not out of the question. I am assuming you are using containment on the outside of the tank. There are not many places you can open blast these days.

As far as coatings, you can get a good life from a 2 coat interior epoxy system. I would recommend a 3-coat exterior, zinc-rich primer, epoxy, polyurethane finish coat.