API 2000 - Inbreathing flow: which one? 1

[boerngen]

For sure another person already did this question before, but I couldn't find any!
If one have a (for example) ethanol 5000 m3 tank, on Santos, Brazil, and would like to know the venting required for thermal inbreathing (for filling and emptying there are no problems), three situations arise:
By item 4.3.2.3.3 the venting required would be 2524 Nm3/hr;
By Annex A, table A.3, it will be 787 Nm3/hr;
By Annex F, depending on instrumentation level, it woul be: 252 Nm3/hr, 504 Nm3/hr and 1262 Nm3/hr.
Which one is the correct?
The conditions are the same: horizontal vessel, uninsulated, maximum temperature 48,9 degrees C, etc..
How could it be so different?
I appreciate any tip showing me where I am making the mistake!
Thank you!

 

[don1980]

I haven't checked your math, but you probably haven't made an error. The new version of API 2000 has a 3-4X increase in inbreathing. That was done to bring it into alignment with the equivalent European standard (EN 14015). It also recognizes a need to be more conservative. The old API 2000 is found in the annex. So you're results are exactly what I'd expect to see.

 

[boerngen]

Don, this is exactly the question: how could one standard give me two different values? I knew that Annex A is on the standard just to keep the values of the 5th edition, but how could this be possible? The user is supposed to choose any one?
My customer is looking at me in a strange way, as I'm a complete stupid!
I've discussed this with a Protego guy here in Brazil and he said they are choosing valves based on item 4.3.2.3.3.
I misunderstood the question of nitrogen venting: API is only suggesting a value, depending on the level of safety one have on each tank.
Anyway, thanks again.
Boerngen

 

[CMA010]

For new tanks 4.3.2.3.3 should always be used. For existing tanks (designed and installed before the Sixth edition was effective) the annex or 4.3.2.3.3 can be used. Protego can provide more background as they were involved in the sixth edition.