Kazuma Kawano

A Study of Influence of Locally Reduced Thickness on Stress of Bottom Annular Plate of Oil Storage Tank During Uplifting by Seismic Loading

In 1978, Off-Miyagi Prefecture Earthquake in Japan caused damage to large oil storage tanks. Their annular plates had been greatly reduced in thickness due to local corrosion, and they were broken by uplifting due to the earthquake. In order to examine the stress tendency of annular plates with local metal loss during uplift by earthquakes, nonlinear static uplift analyses by three-dimensional shell FEM were carried out on a 110,000kl oil tank. The sizes of locally reduced parts, such as the circumferential and radial dimensions, were taken as the analytical parameters. Many useful results were obtained regarding the relationship between the range of local metal loss and the stress in annular plate. The “stress increase ratio” is defined in this study as the ratio of radial surface stress in an annular plate with metal loss to that without metal loss. The following results were obtained. As the radial width of metal loss part decreases, the annular plate radial stress increases. The stress increase ratio is 1.47 when the thickness of radial metal loss part of radial width 23mm is reduced to 18.4mm from an original thickness of 21mm. For a circumferential length of metal loss part of less than 2.1m that is calculated by multiplying the radius of tank with the tank central angle of three degrees, the stress increases proportionally to the length of metal loss part. On the other hand, when the length is more than 2.1m, the maximum stress has a tendency to saturate.Copyright

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.Copyright

Building a Real Time System for Evaluating Oil Storage Tank Damage Due to Earthquakes in Petroleum Stockpiling Bases

It will be difficult to prevent the damage of oil storage tanks caused by a large earthquake even if extreme care has been exercised. Therefore, rational emergency responses will be required for preventing expansion into secondary disaster. In this paper, we propose a system that can estimate ground motion distribution in a whole of petroleum stockpiling base using a seismic record and evaluate damage of oil storage tanks just after an earthquake in order to support rational emergency responses. Spectral ratios of horizontal and vertical component of microtremors were used for evaluation of relative surface soil amplification. The system can assess the hazard for circumferential shell stress, axial shell stress, seismic capacity and liquid sloshing wave height immediately using the ground motion at each tank site estimated from both the relative soil amplification factors and a seismic record at a petroleum stockpiling base just after a large earthquake.Copyright