Risk Assessment and Damage Tolerance Study of LNG Storage Tanks with Cracks under Wind and Snow Loads

Objective: As critical energy infrastructure, the structural integrity of Liquefied Natural Gas (LNG) full containment tanks under extreme environmental loads is of paramount importance. Microscopic cracks initiated during manufacturing or in service may propagate under cyclic loads such as wind and snow, posing potential safety risks.Therefore, it is necessary to effectively evaluate the safety of storage tanks, especially the crack propagation of tanks with cracks, in industrial production. Methods: To quantitatively assess the safety of cracked storage tanks, this study establishes a numerical analysis framework integrating the Finite Element Method (FEM) and fracture mechanics. A 160,000m3 LNG storage tank is taken as the research object, with a semi-elliptical surface crack introduced in the weld region between the tank wall and the bottom plate. Multiple operational loads are considered, including design wind pressure, snow pressure, internal pressure, liquid hydrostatic pressure, and thermal stress. The stress intensity factor (KI) and J-integral at the crack tip are computed using the interaction integral method, enabling a static fracture assessment. In addition, Paris’ law is applied to predict the fatigue crack growth life under fluctuating wind loads. Results: Results demonstrate that under extreme wind and snow loads, the crack driving force parameters for the initial crack (depth=5mm) remain well below the fracture toughness of 9% nickel steel, indicating a sufficient structural safety margin. Parametric analysis identifies the critical crack depth in this region as approximately 16mm, providing a clear quantitative basis for non-destructive testing. Fatigue analysis reveals that the residual crack propagation life far exceeds the design service life of the structure. Nevertheless, the study underscores the necessity of establishing a periodic in-service inspection plan. Conclusion: This research confirms that the fracture mechanics methodology based on the damage tolerance concept can offer a scientific basis and key technical support for the lifecycle integrity management of LNG storage tanks, facilitating a transition from “defect-free design” to “defect-tolerant management”.