Under-bottom connections for API 650 floating-roof tanks

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When the API 650 floating-roof tanks is welded, the weldment should be fixed rigidly. After welding, when the weldment is cooled to normal temperature, the rigid fixation can be removed, which can effectively prevent angular deformation and wave deformation. Although some measures have been taken, the welding deformation of API 650 floating-roof tanks is still unavoidable, so it is necessary to take corrective measures to compensate the deformation. Mechanical correction is to make the parts easy to deform in the welding process by mechanical or other rigid materials to produce simple deformation, so as to restore the state before welding.

The pressed-steel, round manhole with a 20-in. inside diameter shown in Figure F-8 is located in API 620 crude oil tank solid plate in spherical portion of a torispherical roof on a cylindrical storage tank 72 ft in diameter. The internal pressure, Pg, on the underside of the roof is 15 lbf/in.2 gauge. The thickness, t, of the roof plate required by 5.10.3 for the spherical portion of the roof is 1/2 in., which is exactly the thickness provided. No corrosion allowance is required. The materials in the oil tank roof plates and manhole frame conform to ASTM A283 Grade C steel; the main joints in the roof are double-welded butt joints, spot radiographed in accordance with 7.16 and 7.17.