Summary of Key Design Points for Large Oil Tanks

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Key design considerations for large oil tanks: The key design considerations for large oil tanks are summarized as follows: 01 Design pressure – For oil tanks with fixed roofs and at atmospheric pressure, the design negative pressure should not exceed 0.25 kPa, and the lifting force generated by positive pressure should not exceed the total weight of the tank roof and the components it supports； When the requirements of Appendix A to this code are met, the maximum design pressure can be increased to 18 kPa; when the requirements of Appendix B to this code are met, the maximum design negative pressure can be increased to 6.9 kPa. The design pressure for floating roof oil tanks should be taken as atmospheric pressure. 02 Design temperature: The design temperature of the tank shall comply with the following requirements: (1) The design temperature of the oil tank shall not be lower than the highest metal temperature that the tank walls and stress-bearing components may reach under normal operating conditions, nor shall it be higher than the lowest metal temperature that these components may experience under the same conditions. (2) The maximum design temperature of the oil tank should not exceed 90°C. When the requirements of Appendix C to these specifications are met, the maximum design temperature for fixed-roof oil tanks can be increased to 250°C. (3) For oil tanks that have neither heating nor insulation, the minimum design temperature of the tank shall be the lowest daily average temperature in the area where the tank is constructed plus 3°C. 03 Seismic resistance: When constructing tanks in areas with a seismic design intensity of 6 degrees or higher, seismic design is mandatory. 04 Materials: The steel used for oil tanks should be produced by oxygen converter or electric furnace processes. For low-alloy steel sheets with a minimum standard yield strength of more than 390 MPa, as well as low-temperature steel sheets and forged parts designed for temperatures below -20°C, secondary refining processes must also be employed. 05 Allowable stress: The allowable stress values for steel plates not listed in Table 4.2.2 of this specification shall comply with the following provisions: (1) When carbon steel that meets the requirements of this specification, or low-alloy steel plates with a standard yield strength lower limit of 390 MPa or less, are selected, the value of 2/3 of the standard yield strength lower limit at the design temperature shall be used ； (2) When low-alloy steel plates with a standard yield strength lower limit greater than 390 MPa that meet the requirements of these specifications are selected, 60% of the standard yield strength lower limit at the design temperature shall be used. 06 Thickness: The thickness of the steel plates used for the tank walls shall comply with the provisions of this specification, and the nominal thickness of the steel plates shall not exceed 45 mm. 07 Condition of steel plates: When the design temperature of the oil tank is below -10°C, Q245R steel plates with a thickness of more than 20 mm and Q345R steel plates with a thickness of more than 30 mm should be used in the normalized state. 08 Edge plate thickness: The minimum thickness of the edge plate is as follows: Image. The thickness does not include corrosion allowance or negative thickness deviations. 09 Floor thickness: Minimum floor thickness: Image. The thickness does not include corrosion allowance or negative thickness deviations. 10 Bottom structure: When the inner diameter of the oil tank is less than 12.5 m, an annular edge plate is not required at the tank bottom ； When the inner diameter of the oil tank is 12.5 m or greater, an annular edge plate should be provided at the bottom of the tank.