Investigation on Tendency of Stress in Local Thin Area of Shell Plate of Oil Storage Tank

The shell plate of oil storage tank is an important evaluating component in the Fitness-For Service Assessment (FFS), because it is required to have sufficient strength against static and dynamic pressures in both operating and earthquake conditions. This paper presents an investigation on the tendency of stress occurred in the local thin areas (LTAs) of shell plate subjected to an internal pressure by using a partial three-dimensional shell model. In the analyses, a LTA is assumed as a rectangular area or a ring area with a rectangular cross section, and its lengths in the longitudinal and circumferential directions are taken as study parameters. The tendency of stress ratio (the stress in LTA of shell plate to that without LTA) has been investigated and the analytical results show that there is a tendency for stress ratio to be going up when the longitudinal length of LTA lengthens gradually and the thickness of shell plate is decreased. But it is opposite for increasing the circumferential length, when the stress ratio is going down. The relation between the stress ratio and the shape of LTA with different combination of sizes are clarified by the analytical results.