Design Pressures for tank with internal floating cover and roof circulation vents

[sajk14]

Hi all,

I have been asked to carry out checks for roof frangibility and venting requirements on some existing tanks. However the tanks have had internal floating covers installed with half a dozen circulation vents fitted around the perimeter of the tank roof.

Am i therefore correct in saying that roof frangibility criteria no longer applies to the tank?
Also calculations for venting i.e. inbreathing, outbreathing and emergency relief would not be applicable?

API 650 clause 5.2.1.b states that if you have a tank fitted with circulation vents then you can use a design external pressure of 0kPa.
Is it correct to to say the design internal pressure is also 0kPa due to the presence of the circulation vents?

Thanks for your thoughts on the subject.

 

[Geoff13]

Correct. Clause 5.8.5.1 says that tanks with Annex H circulation vents meet the normal and emergency venting conditions. Use of a frangible junction or emergency vents is only required for other tanks needing to meet 5.8.5.3.

You can always use an internal design pressure of 0 kPa, which is why 5.2.1.c doesn't list a minimum like 5.2.1.b does for external.

 

[sajk14]

Thanks for your comments Geoff13.

Best Regards