API Std 650 unanchored flat-bottom tank EN specifications plates

The manufacturing requirements of bottom plate of vertical metal tank, API Std 650 unanchored flat-bottom tank are as follows: 1. In order to compensate welding shrinkage, the layout diameter of tank bottom is 5-2mm than the design diameter; 2. The butt joint of edge plate of tank bottom shall be machined automatically or semi-automatically; 3. The distance between any two adjacent welding joints on the tank bottom plate and the distance between the butt joint of edge plate and the longitudinal weld of bottom ring wall plate shall not be greater than 200 mm.

Shell Stiffening Rings for Tanks That Contain Liquid
Internal or external shell stiffening rings may be required to maintain roundness when the tank is subjected to wind, vacuum, or other specified loads. When API Std 650 unanchored flat-bottom tank stiffening rings are required, the stiffener-to-shell weld details shall be in accordance with Figure Q-1 and Q.3.5.2 through Q.3.5.5.
Three-plate laps or butt-weld junctions in tank bottoms shall be not closer than 12 in. from each other or from the butt-welds of the annular plates.
Bottom plates, other than annular bottom plates for a 9% or 5% nickel steel or stainless steel tank that contains liquid, may have a minimum thickness of 3/16 in. exclusive of any specified corrosion allowance.

The internal floating plate of internal floating roof tank of API 650 tank is different from that of open floating plate of API Std 650 unanchored flat-bottom tank External floating roof tank of API 650 tank, so it is impossible to have rain and snow load.