3 replies to this topic

[benoyjohn]

Hello,

The API STANDARD 2000 SIXTH EDITION, NOVEMBER 2009 indicates method for calculation of thermal inbreathing by formula.

Vit = C * Vtk ^0.7 * Ri (Sec 4.3.2.3.3)

For a case where volume of tank is 300 m3, located @ latitude 23 deg, operating at 30 deg C, the C factor for hexane fluid is 6.5.

Thus the thermal inbreathing requirement for a uninsulated tank works out to be 352 Nm3/hr.

However Annexure A which gives an alternative calculation method gives 50.4 Nm3/hr as the inbreathing requirement based on Table A.3.

Appreciate if someone could clarify this huge apparent discrepancy in the standard.

Thanks and regards,

Benoy

[ankur2061]

Benoy,

I would recommend that you go throught the following link carefully. The last post has a comparison between the old and the new API in the form of a powerpoint presentation where the importance of Annex A of the latest API 2000 is also discussed.Here is the link:

http://www.cheresour...g-requirements/

Regards,
Ankur.

[proinwv]

Ankur's suggestion is very good.

Also, I can add that I attended a presentation on the 6th edition before its publication and this was mentioned by the presenter.

We were told that the new values were established based upon good science and testing. I cannot validate that statement. However, I have always believed that it was better to err on the side of larger vents than to undersize which can lead to an accident.

Further, to protect the tank from sudden drops in pressure due to a large vent opening under a small demand, the engineer should use multiple vents, staged to open at slightly different set points.

[fallah]

benoyjohn,

My response in brief:

For normal tank venting;
Tanks that meet the criteria in Annex A (section A. 1. 2) can have tank vents designed using the method shown in Annex A.
Tanks that don’t meet the Annex A criteria, then the general method in 4.3.2 should be used.

Thus you should check the conditions as per mentioned criteria and then use one of above methods accordingly.

Fallah

Edited by fallah, 19 September 2011 - 03:59 AM.