There are 63 spherical tanks in the tank farm of the Olefin Plant of PetroChina Dushanzi Petrochemical Company. The minimum volume of single spherical tank is 400 cubic meters, and the maximum volume of single spherical tank is 5 000 cubic meters. Spherical tank belongs to pressure vessel, so periodical inspection must be carried out in accordance with TSG R7001 Pressure Vessel Periodical Inspection Regulation, and the inspection cycle depends on the safety grade, generally 1 to 6 years. To carry out pressure vessel inspection without shutdown of the ethylene plant, the inspection of the spherical tanks is performed separately within the inspection cycle while satisfying the production needs, i.e. 10 spherical tanks each year calculated by the longest cycle of 6 years. Pressure vessel inspection construction includes the erection of internal and external scaffolding, the weld grinding of storage tank, the inspection of spherical tank and the four levels of high-risk operation for spherical tank inspection. To keep the process safety under control, it is necessary to develop standards from the aspects of construction force arrangement, material entry into the plant, standardized erection of scaffolding and weld grinding quality, perform well the standardized actions and reduce the errors in optional actions.