Buckling behavior of cylindrical steel tanks with concavity of vertical weld line imperfection

Shell structures are built using a number of welded curved panel parts. Hence, some geometrical imperfections emerge. These imperfections have a direct impact on structural behavior of shells during the external compressive loading. In this research, a field study was accomplished on the implementation of the storage tanks in a refinery site and then, the resulted imperfections were identified and categorized. The survey of imperfections revealed that the imperfection in form of concavity of vertical weld line is the most prevalent type of imperfection seen in the steel tanks. This imperfection experimentally modeled and the buckling behavior of these tanks was evaluated under uniform external pressure. Comparing obtained results of estimation, ASME code and experimental research represented a considerable difference in the amount of buckling load. Results show that the imperfections due to concavity of vertical weld line are very important in buckling of the tanks under uniform external pressure. This imperfection decreases initial, full and post buckling capacity of the tanks under uniform external pressure, significantly. Findings of this research show that for design of steel tanks under uniform external pressure load, 65% of the buckling load obtained from the ASME Code should be used.