API 650 welded steel storage tanks roof configuration

For open top and fixed roof API 650 tanks, the net working capacity is the liquid volume contained between the minimum operating level (top of API 650 tanks API 650 welded steel storage tanks outlet connection) and the maximum operating level [limited to the bottom of overflow connection, 75 mm below foam chamber connection, or 150 mm below rim, whichever is greater.

Welders participating in the construction of API 650 welded steel storage tanks must pass the examination and perform welding within the validity period of the qualified items. Special operators such as on-site maintenance electricians, cranes, and shelf workers must hold job certificates. All oil pipelines need to use arc welding for bottoming and electric welding to ensure the welding quality. Oil tanks and process pipelines must be tested for non-destructive flaws in accordance with the flaw detection ratios and methods required by the design and acceptance specifications. The flaw detectors must be certified.

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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.