Study Of Failure Analysis And Maintenance Methods Of Residual Oil Tank

Dome roof tank is a common large storage tank and its main failure mode is dome roof instability. According to 405tanks's roof instability in North China Petrochemical Corporation, this paper utilized the external pressure instability theory to analyze and get the reason is that the tank negative pressure exceeded the first order critical load to cause the dome roof's deformation. A comprehensive comparison has been made between repairing method and positive pressure method to select the water injection positive pressure method to restore 405tank according to the real situation of the tank. ANSYS software has been explicated to establish the dome roof tank's mechanical model to check the instability and analyze the intensity under inner pressure. The finite element model of the instable tank has been established using node method to analyze the stress during the restoring process, pointing out that positive pressure method is feasible to restore the instable tank in case of less serious deformation. During the repairing process, external temperature change should be paid more attention to prevent the change of tank's inner pressure. Water injection should not be too fast, and when the inner pressure is greater than 0.5 times of the first order instability critical load, water injection speed should be reduced. To prevent the seam fracturing, partial strengthening should be carried out before the restoration. Uplift force and dome roof hoop stress should be checked to ensure a safe restoration. This paper presents a method to improve the critical load and safety repair measures which is an important guiding significance to actual production.