API 12D vs 650 Tank Design- Anchorage Requirements

[Soln]

API 650 Tank in Colorado, 40'Dia X 24', with 3.5 oz/in^2 requires overturning anchorage. On the other hand, API 12D tank, equal size, equal pressure, same location- I don't see any 12D reference to wind design, seismic design, or anchorage requirements. Am I missing something? How is it justified- equal tanks, one 650 requires anchorage, one 12D no anchorage required?

 

[JStephen]

There's a couple of differences. The main one is in design philosophy. If you set a 55-gallon drum in a pasture, you don't hire a structural engineer to evaluate the stability of it, you just put it there and hope it doesn't blow over, and figure if it does, no big loss. That's generally the approach used in the API-12F and 12D tanks. It's not that the tank does or doesn't require anchorage, but rather that it's just not addressed.

On the pressurization, API-650 generally neglects the strength of the bottom plate and requires that the shell be anchored so that it doesn't uplift. The allowable pressures for API 12F and 12D assume that the bottom will resist some of the pressure. If the pressure is applied while the tank is completely empty, the shell will presumably lift up some distance.