Internal coating and maximum operating temperature.

[Syahar1975]

Dear Experts.

Our Crude Oil Tank has maximum operating temperature 62 degree C.

We have painted the internal surface of this tank with High Build Coaltar Epoxy 2 coat @ 200 micron DFT. Total 400 micron DFT. According to the paint data sheet the Immersion Temperature should not exceed 49 degree C.

I can see there is 13 degree C different.

What would be happen during operation of this Crude Oil Tank ? Is there any possibility melting of this Coaltar Epoxy ?

I know Coaltar Epoxy should not be applied for Crude Oil Tank. But this already happen.

 

[CoryPad]

The coating will not melt, but it will suffer damage from the elevated temperature crude oil and will debond from the steel.

 

[CoCoE]

I hope in datasheet, it may be the recommended temperture. I would suggest to get the softening point, as well as maximum temp it can withstand, from the manufacturer. This is just to defend your current problem, as the job is already done.
Also, I dont believe coal tar epoxy cannot be used for crude tanks, untill unless there are aggressive chemicals included. I am still using coal tar on crude oil tanks with little problem. Can you help to give any references for your claim?

Cococa

 

[Syahar1975]

Good afternoon Gents,

Thanks for the response.

CocoCa, the data sheet states "immersion temperature should not exceed 49 C".

I have asked my paint subcontractor to get a letter from paint vendor stating " this high build coaltar epoxy still OK for 60 C operating temperature". To be honest I am very much doubt if the paint vendor will issue this letter.

I have called 2 paint vendor and they are not recommend coaltar epoxy for Crude Oil Tank due "causing cancer" issue more over this would be done in confined space.

The other vendor agree to use Coaltar Epoxy for Crude Oil tank but the operating temperature shall be below 49 C.

I have only 2 choices i.e. get letter from paint vendor or let us wait and see during operation.

 

[tbuelna]

Fully cured epoxy will not "melt", but if the Tg temp of the cured epoxy coating is exceeded it does become soft and pliable. Brief exposure to a temperature 11degC above the continuous limit the manufacturer guarantees the epoxy coating for would not seem to present a problem.

To be sure you can conduct a test by heating a small section of the coated tank surface to the temperature expected for the amount of time required, and see if the coating degrades.

Lastly, I find it hard to believe an epoxy tank coating would not be good for temps in excess of 49degC (120degF). A steel tank exterior surface exposed to direct sun during summer in many parts of the world would easily get hotter than 49degC. In fact, the painted steel roof, hood and trunk surfaces of my car regularly get far hotter than 49degC when the car is parked in the sun on a summer day. The car's paint is polyurethane, and not epoxy based. But it probably gets up to 150degF without melting or peeling off the steel substrate.

 

[Syahar1975]

Good morning Tbuelna,

Thanks for your comments. I like your idea about experiment heating small part of the painted surface and see what the impact on the painting.

Yes I have the same expectation like you i.e. practically still OK till 62 deg C.

But we have make sure from now before the real product came into the tank. It would be BIG BIG problem if something happen during the operation.

Also contractually we are not meet the client specs.

1. Use coaltar epoxy for crude oil tank with operating temperature till 70 deg C

2. Phenolic Epoxy shall be applied for tank with hydrocarbon product where operating up to 80 deg C.

My subcontractor use high build coaltar epoxy with maximum immersion temperature 49 deg. C. which is not meet to the above 2 specs.

I believe coaltar epoxy for operating temperature till 62 deg C is very very rare. But there is for Phenolic or Novolac.

 

[tbuelna]

Good luck to you. But if you determine the coating to be unacceptable, it seems like it will be a huge amount of work to remove the deficient coating. So I'd imagine you would want to do everything possible to show the existing coating is acceptable for this application.

 

[Syahar1975]

TBuelna,

You are correct. Re-blast and re-paint with the correct material is the best way but it would be big issue as well.

Asking the paint vendor to issue the guarantee letter is impossible.

Leave it as is and see what would be happen during operation is gambling. Maybe nothing will happen or maybe something happen.

"So I'd imagine you would want to do everything possible to show the existing coating is acceptable for this application" may the only option.