Device and method for maintaining and replacing vertical crude oil pipe of offshore platform

The invention provides a novel device for maintaining and replacing a vertical crude oil pipe of an offshore platform. The device comprises a water partition cabin and a plurality of connecting assemblies for connecting the water partition cabin with pile legs of the offshore platform. A through hole for the vertical crude oil pipe to penetrate through is formed in the bottom of the water partition cabin. The device further comprises a sealing piece. The sealing piece comprises a rubber sealing cylinder and a rubber sealing frustum which are sequentially arranged. The diameter of the upper bottom face of the rubber sealing frustum is smaller than that of the lower bottom face of the rubber sealing frustum. The rubber sealing cylinder is connected with the upper bottom face, with the small diameter, of the rubber sealing frustum. The sealing piece is provided with an inner cavity penetrating through the two axial end faces. The lower bottom face of the rubber sealing frustum is connected with the through hole. The invention further provides a method for maintaining and replacing the vertical crude oil pipe of the offshore platform. By means of the novel device for maintaining and replacing the vertical crude oil pipe of the offshore platform, the interior of the water partition cabin can be separated from seawater, and water can be prevented from entering the water partition cabin; when the lower portion of the water partition cabin is fixedly installed, operation is convenient, and the construction safety of workers can be guaranteed.