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RE: API 650, 620

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For tank with unknown age , use API-653.
Buckling is addressed in API 650, E.5.3
I don't see how API 620 will address this tank.

I recall that UBC and possibly IBC allow use of tank codes for seismic
analysis.  I understand that the 100mph wind (per API) was determined for
coastal areas and is used every where.  Wind pressures of 30, 18 & 15 psf
are very high for most code wind values.

I don't think reducing roof live load is advisable.  Notice it is a
projected area value and you can reduce the loads on the dome near the edge.

Ronald A. Hill, P.E.
HILL Consulting Engineering
PO BOX 26525
Birmingham, Alabama 35260 USA
Phone: 205-823-4784
FAX: 205-823-4145
email: ronhill(--nospam--at)
-----Original Message-----
From: Robert M. Hanson [mailto:Bob(--nospam--at)] 
Sent: Friday, January 17, 2003 9:02 AM
To: seaint list
Subject: API 650, 620


I have been asked to do a quick study on a 117 foot dia., 42 tall steel
petroleum tank with floating roof. Age unknown and plate thickness at
construction known but no thickness reading yet for actual. The code I have
been asked to use is the API 650, 620 and appendix E. Does any one know when
appendix E came into use and what the criteria was prior to that for
seismic? The seismic has the sloshing effect and you end up with a
reasonable base shear overall but the formula is pretty old and does not
account for the near fault and soil interaction as is done now. The only
wind I can find is in sections 9.9 and 3.11 and does not vary with height.
The pressures seem low. In reading these documents I sense that only API 620
addresses shell buckling due to stresses in the vertical direction between
the wind girder and the base. The roof live load is 25 psf and seems ok for
a steel roof but with a aluminum dome seems high and improbable. Also no
reductions for a dome seems inconsistent with building codes. 

The client want no surprises when he adds a dome so I am also looking at
Appendix G. 

My opinion right now if I also inspect using California Building code is to
use a R of 2.9 for seismic.   

I am really concerned with the wind and maybe when seismic came into play as
first run on shell the tank wall at base seems to thin for seismic case.
Thanks for any information and opinions.


Robert M. Hanson, SE
Kappa Engineers
(310) 233-3800 x109

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