Problem in Crude Tank

[KazakhJeff]

We run a refinery, which shares its crude storage with an export crude terminal. Our largest floating roof tank has developed a leak in the roof, as well as about 10% of the pontoons. Oil covers about 80% of the roof now. We cannot sit the tank on the floor due to waxy deposits, and management do not want to take the tank out for repair yet, due to needing the tank to manage export obligations. Our crude is light and contains about 1% LPG. What advice would you give? Take the time to shut down and repair for safety reasons, whatever? Is there a serious risk from the volatiles? If so, how should we cope with this?
Thanks for the advice.

 

[aybee]

I think that you will have no option but to shutdown and repair as the roof will become unstable and tilt once the leak covers enough to get to the critical tip point...once it starts to tilt it will be an acellerated process. as the crude will run to the low point , the you wont be able to lift or lower the roof.... The you will get a gas bubble under the high side...more problems ... shut it down ..good luck

 

[IFRs]

Assuming you have a steel floating roof:
Lowering the product level will be tricky. When the roof legs contact the tank bottom and more liquid is drained out of the tank, the liquid on top of the roof may remain and overload the roof legs. The roof legs may buckle and collapse the roof onto the tank floor. Worse, the load on the roof legs may puncture the tank bottom.

You are in a very bad situation.

For environmental reasons, you may want to remove the crude oil and replace it at the same time with water so leaks will only be water.

What size is the tank?

 

[KazakhJeff]

The tank is 50,000 m3, about 60 metre diameter. We are keeping the tank out of operation at the moment, about 1/3 full, and stable. We do not think that water is an option at present, as we will probably need to circulate hot oil to remove the waxes, to allow us to drop the roof (a good idea though for when we have removed the waxes).
Our present concern is safety. Will the leak allow sufficient build-up of light hydrocarbons to have a potential for a Vapor Cloud Explosion, or other risk? This will probably dictate how and when we handle.