API 650 Addenda and Unanchored Tanks

Please clarify API 650 Add 1 and Add 2 (11^th Edition) revision the equation is correct or wrong

5.11.2 Unanchored Tanks API 650 11^th Edition Add 2 Nov2009 Effective Date is May-2010

Unanchored tanks shall satisfy both of the following uplift criteria:

1. 0.6Mw + MPi < MDL /1.5

2. Mw + 0.4MPi < (MDL + MF)/2

where

MPi = moment about the shell-to-bottom joint from design internal pressure,.

Mw = overturning moment about the shell-to-bottom joint from horizontal plus vertical wind pressure,

MDL = moment about the shell-to-bottom joint from the weight of the shell and roof supported by the shell,

MF = moment about the shell-to-bottom joint from liquid weight.

The liquid weight (wL) is the weight of a band of liquid at the shell using a specific gravity of 0.7 and a height of one-half the design liquid height H. wL shall be the lesser of 0.90HD for USC units and 14.8HD for SI Units:.

In SI units:

WL = 59.tb x SQRT Fby.H (N/m)

But, Appendix E 6.2.1.1

Wa = 99.tb x SQRT. Fy.H Ge (N/m) < 201.1 HDGe in SI Units

based on the equations in appendix E i have calculated that for SI units it should be 141HD

Regards

Rajasekar