Research on Inverted Construction Method and Circumferential Hoist Basket Technology for Extra-large-diameter Vertical Cylindrical Cold Storage Tanks

Large vertical chilled-water storage tanks are characterized by tall shells, large diameters, and stringent demands for air-tightness and thermal insulation. A strategic-reserve warehouse project included two such tanks of exceptionally large diameter; their size precluded shop fabrication and direct delivery to site. Erecting them by the conventional “bottom-up” (normal-sequence) method would have caused shell-plate distortion at the lower courses as height—and thus dead load—increased, while the risk to personnel would have risen with every lift. To meet the installation requirements of these oversized vertical tanks, we developed a “top-down” (reverse-sequence) erection procedure combined with a circular electric gondola system for insulation work. The shell was assembled in horizontal courses, starting with the roof and the top shell ring; each subsequent ring was lifted, positioned and welded in segments, followed by the bottom course, floor and ancillary items. The method proved suitable for large-diameter, high-capacity vertical tanks erected in restricted, complex environments. Compared with traditional bottom-up construction, direct costs were reduced by approximately 9 %. A self-propelled, rotating electric gondola, designed in-house, allowed polyurethane spray application on the external shell inside a confined workspace, eliminating the need for full scaffolding and cutting both exposure time and fall risk.