API Std 650 unanchored liquid-storage tanks convective spectral acceleration parameter

In this project a cylindrical tank 75 ft in diameter is designed for an internal pressure of 0.5 lbf/in.2 gauge in the vapor space. The plate material is ASTM A131 Grade B steel for thicknesses of 1/2 in. and less.
The top course of the butt-welded cylindrical sidewall is 1/4 in. thick. The tank API Std 650 unanchored liquid-storage tanks roof is a conical shape with a 2:12 slope and a 1/4 in. thickness with single full-fillet welded lap joints. The maximum design liquid level is 6 in. below the plane of juncture of the roof and sidewall.

Corrosion allowance, if specified, shall be added to calculated API 650 tanks shell and self-supporting roof thicknesses; to minimum nominal thicknesses of bottom and supported API Std 650 unanchored liquid-storage tanks roof plates; to nozzles and manholes; and to all exposed surfaces of internal structural members and non-removable internals.

Compared with the external floating roof API Std 650 unanchored liquid-storage tanks, the internal floating roof API Std 650 unanchored liquid-storage tanks has the advantages of protecting the floating roof from wind and rain and ensuring the quality of liquid storage under the floating roof. At the same time, because the inner floating plate is in the tank, there is no rain and snow load, so the central drainage pipe and escalator and other accessories on the floating plate can be omitted. In addition, under the same sealing conditions, the internal floating roof tank can further reduce the evaporation loss compared with the External floating roof tank.