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API 650, 620

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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.

 

Bob

 

Robert M. Hanson, SE

Kappa Engineers

(310) 233-3800 x109