Safety Assessment of Double-Walled Crude Oil Storage Tanks Based on API 650 Standard

Double-walled crude oil storage tanks based on the API 650 standard adopt a composite structural design of inner tank + outer tank. The inner tank uses Q345R low-alloy steel (yield strength ≥345MPa), and the outer tank uses a carbon steel lining anti-corrosion layer. The wall thickness is distributed in a variable cross-section gradient (30mm at the bottom to 8mm at the top). A 0.5m annular detection channel is set between the double layers, equipped with fiber optic strain sensors to monitor structural deformation in real time. The seismic design meets the requirements of seismic intensity 8, and the elastic connection nodes allow ±15° angular displacement. The floating roof adopts a double-deck aluminum alloy structure, equipped with a triple sealing system, and the evaporation loss rate is controlled below 0.1%.

The safety assessment focuses on verifying three core indicators: 1) Nozzle load check, calculating the stress impact of pipeline thrust and pull on the tank wall opening according to API 650 Appendix P, ensuring that the local stress does not exceed 85% of the allowable value; 2) Wind load stability, verifying through finite element analysis that the critical buckling moment Mw ≤ 0.6Mcr when the wind girder spacing is ≤3m; 3) Leakage monitoring effectiveness, the sensor sensitivity of the annular detection channel needs to reach 0.1mm crack identification accuracy, and the response time is ≤30 seconds. The outer tank cathodic protection system uses magnesium anodes (protection current density 10mA/m²), combined with a three-layer HDPE impermeable membrane (permeability coefficient <1×10^-12 cm/s) to achieve dual leakage prevention guarantees.

This design realizes full life cycle management through a digital operation and maintenance platform, integrating stress monitoring, corrosion rate prediction, and emergency shut-off functions, with a fault early warning accuracy rate of 92%. Modular prefabrication technology is used in the construction phase, and the defect rate of welds detected by phased array is less than 0.8%, reducing steel consumption by 15% compared with traditional single-layer tanks. Operation and maintenance costs are reduced by 20%, and the comprehensive safety performance meets the dual standards of API 650 and GB 50341.