Seismic Use Group for API standard 650 special tank
The vent pipe mouth should be 4m or more above the ground. The nominal diameter of the API standard 650 special tank API 650 petroleum storage tank vent pipe should be no less than 50mm and a flame arrestor should be installed.
In this project, an elemental area of API 620 oil storage tank wall is constructed of ASTM A516 Grade 55 steel plate subjected to a meridional unit force, T1, of 2620 lbf/in. tension and a latitudinal unit force, T2, of 2880 lbf/in. compression. The meridional radius of curvature, R1, is 132 in., and the length of the normal from the surface to the axis of revolution, R2, is 409 in. The joints in the wall are spot-radiographed, double-welded butt joints, and no corrosion allowance is required.
The problem in this example is to graphically find the minimum thickness of tank wall required for the given conditions (see API 620 tank standard 5.10.3.3).
Solution: As determined from Table 5-1, the maximum, allowable tensile stress value, Sts, for ASTM A516 Grade 55 steel plate in simple tension is 16,500 lbf/in.2. Since the compressive stress is latitudinal, the governing value of R for this situation is R1, or 132 in.
Compared with the external floating roof API standard 650 special tank, the internal floating roof API standard 650 special tank 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.
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