Paint system for Aboveground Storage Tanks in Marine+Acidic environment

[shaafishaikh]

I am responsible for upgradation of the external paint system on a number of carbon steel aboveground storage tanks at a chemical plant.

The environment that the paint system will have to protect against is:
1. Marine conditions - we are a stones throw from the sea.
2. Moisture - Spray of chemical-dosed water from nearby cooling towers
3. Acid - There is some concentration of acetic acid and hydrochloric acid in the air.
4. Caustic - There is a caustic plant in the neighborhood, as well as Caustic storage/processing at our plant.
5. Chlorine and other chemicals - we are located in an industrial zone with a number of chemical plants nearby.
6. Temperatures in excess of 40 C/104 F for much of the year.
7. Smoke, unburnt hydrocarbons and other combustion products from next-door steel processing facility.

The original paint system was:
Primer: 2 pack epoxy zinc phosphate - 75 DFT
Intermediate: 2 pack high build epoxy - 125 DFT
Finish: Acrylic Urethane - 125 DFT
Minimum surface prepapration specified was SSPC-SP10.
The system failed with widespread blistering and through holes in the tank roofs which we have had to repair.

What paint system can I apply to achieve the most comprehensive protection with least amount of maintenance?

Thanks!
Shaafi

 

[SJones]

The usual selection for the most comprehensive protection with least amount of maintenance is thermal spray aluminium. If this is not financially appropriate, consult Table A.7 of ISO 12944-5 for a high durability coating system recommendation. Then, when dealing with paint suppliers, demand that they substantiate their paint system offerings with a NORSOK M-501 qualification testing report.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[moltenmetal]

Wow: if that paint system was applied properly on a near-white blasted surface (SP-10), and failed that rapidly, I don't know what will survive. I'm also quite concerned for anyone who has to breathe that air...

You could replace the epoxy with a polysiloxane- more expensive but definitely more resistant than either the polyurethane or the epoxy, but both of those are good finishes and quite acid/base/chloride resistant- and you had the organic zinc underneath too...

Thermal spray aluminum isn't going to survive the acid exposure unless you top-coat it with something, again unless I'm missing something which makes the coating more resistant than solid aluminum.

 

[Compositepro]

Aluminum certainly will not help resist acid. The film thicknesses seem very high, but if that is what the manufacturer says then stay with that. Thick films are more likely to blister because they apply more stress to the interface.

I suspect that poor surface preparation is the problem. Salt spray on the surface before painting will lead to blisters.

 

[SJones]

TSA works in pH 4 to 11 - it will require a sealer for sure in the quoted conditions; it's not cheap though.

JPCL,PCE, March 2005, pp 48 - 50

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[shaafishaikh]

Many thanks for your suggestions!
I am looking into polysiloxane and thermal spray aluminium. Im also going through ISO 12944 which has some useful info.

I will try to update this thread with some pictures of the failure mode of our original system.
I strongly suspect that the failure was related to improper application. Since we're dealing with large surface areas and a seaside location, perhaps flash rusting/condensation may have had a role to play.

Thanks again for your inputs.
Shaafi

 

[babouic]

"The system failed with widespread blistering and through holes in the tank roofs which we have had to repair"​

+​

" Since we're dealing with large surface areas and a seaside location"​

I suspect a salt contamination during application. If your surface has not been properly cleaned and checked for salt contamination (bresle, scm400...) before application of your epoxy zinc phosphate, you surely have a large amount of salt under your paint system.

 

[TomDOT]

I concur with babouic. Perform salt testing and see what the results are before dedicating yourself to a process. Salt remediation may be the cheapest way to extend the lifespan of the coating system.

 

[shaafishaikh]

Attached are some pictures of the failure we experienced on the roofs of our tanks.

Interestingly enough the paint on the tank shells did not deteriorate very much.

 

[shaafishaikh]

Sorry. Struggling with attaching the photos. Here are some more: