Seismic Freeboard

[JoseAcevedo]

Could anybody answer me the following question about freeboard?:

1.- What is consider like a secundary containment?.
2.- Could the external dike area be consider like a secundary containment?
3.- Is Freeboard required in tank with internal or external floating roof?

 

[khardy]

1. Please clairify this question.

2. The external dyke area is secondary containment. The foundation should also supply secondary containment under the bottom.

3. Some amount of freeboard is required on a tank that has a floating roof. If it is an internal floating roof, you need enough freeboard to prevent the internal floating roof from hitting the underside of the fixed roof structure. External floating roof tanks need enough freeboard to prevent the floating roof from going over the top of the shell or hitting some other obstruction like a foam chamber. Freeboard may also be required on a tank with out a floating roof for several reasons. For example, foam chambers. Also, freeboard is often added to provide a safty margin against overflow. See API recomended practice 2350.

 

[JoseAcevedo]

Thank Khardy.

1. I am talking about secundary containment as is indicated in API 650 table E-7 (b.1 & c.1).
3. I undersetand all what you said but I am asking about freeboard for seismic sloshing wave. Is it required a freeboard according API 650 App. E, par. E.7.2 in tanks with internal or external floating roof?. I think that for tank with internal or external floating roof the height of the sloshing wave is smaller than in tank without floating roof. Am I right or not?. If it is smaller, How can calculate it.

 

[khardy]

1. I believe the exepmtions provided in tamble E-7 refers to a dyked in containment as defined in NFPA-30.

3. I do not believe E-7 allows you to reduce the amount of freeboard required if you have a floating roof. However, a floating roof will require freeboard and you could take credit for that freeboard when satisfying E-7.

 

[JoeTank]

Seismic freeboard is not considered to be secondary containment.

Joe Tank