抄録
A fracture mechanics-based integrity assessment was conducted on the T-joint of a large-scale liquid storage tank under major seismic events, utilizing three-dimensional finite element analysis (3D-FEA) and multiple Fitness-for-Service (FFS) codes. The 3D-FEA, considering only external forces from site-specific seismic motion and internal pressure, determined that the fracture driving force (J-integral) for an assumed initial flaw was low, approximately 10 kJ/m², indicating a limited risk of ductile fracture from these loads alone. However, an analysis using the WES2805 code revealed that welding residual stress is the dominant factor, contributing an additional 28.5 kJ/m² for a total estimated driving force of 40 kJ/m². In contrast, assessments using international standards BS7910 and API/ASME FFS yielded a significantly lower total driving force of less than 15 kJ/m². This discrepancy highlights the conservative nature of the WES2805 approach to residual stress and underscores the need for more precise quantification methods, such as direct measurement or thermo-elasto-plastic analysis. Collectively, the findings also suggest that the fracture toughness requirements specified in ASME Sec. VIII for cryogenic service (below 77K) are considerably conservative.
