The Tokachi-oki Earthquake (M8. 0) caused the sever damage of oil storage tanks at Tomakomai such as fires and sinkage of floating roofs. The cause of damage is liquid sloshing of oil storage tanks excited by the long-period strong ground motions. It is thought that the pontoons of oil storage tanks of 40m-diameter were damaged by the first sloshing mode and tanks of 80m-diameter suffered damage to the intersection parts between the deck and the pontoons.
After the earthquake, the technical standard of the Fire Service Act regarding the sloshing of floating roof tanks were revised in consideration of the circumstances of damage of the floating roof tanks.
However, it is difficult to say that dynamical behavior of sloshing of a floating roof due to liquid sloshing was not verified thoroughly with a real-scale storage tank. Especially, there were not so many researches about sloshing behavior considering real floating roof, which is not rigid but elastic.
There is more need to examine the formulations of the sloshing with large wave height and the effect of the second sloshing mode when floating roofs are involved
In this study, in order to examine the formulations of the behavior of non-linear liquid sloshing with floating roof and the deflection of a deck plate by the second sloshing mode of oil storage tanks defined in the Fire Service Act, we conducted a shaking experiment by using a large shaking table and a small-scale floating roof tank of 7. 6m-diameter, which is comparatively large tank however.
We concluded that the formulations of the behavior of non-linear liquid sloshing and the deflection of a deck when floating roofs are involved are adequate in considering the results obtained from the experiments.

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In a previous paper¹⁾, the authors investigated the elastic plastic behavior of dissimilar material flanges with a metal ring joint gasket operated at elevated temperature using FEA. Case studies were performed to study the effects of load path, material combination and flange size on the contact pressure and the plastic strain distribution in the ring joint gasket. In that paper, the authors concluded that the load path has a large impact on both, the contact pressure and the plastic strain, and, on the other hand, the material combination of the flanges and their size have small effects.
In this paper, the authors present further FEA-based investigation on this mechanism. The first issue is the effects of meteorological changes, such as wind velocity, ambient temperature and rain, as is often the case with real energy and process plants. These meteorological changes result in the temperature change of bolts and flanges. The bolt temperature change causes different thermal expansion in the ring joint gasket and the bolts. This may affect the sealing performance. In this paper, the wind velocities were changed to investigate meteorological changes as a typical such change.
The second issue is the behavior of the metal ring joint gasket after the second operation cycle. The metal ring joint gaskets are usually replaced after the first operation cycle, i. e. , from start-up to shut-down. However, it is said that all ring joint gaskets are not replaced. In the previous paper, the behavior of the ring joint gasket during the first operation cycle was investigated. Increase of plastic strain in the sequential operation cycles is an important issue in terms of sealing performance. Therefore the behavior of the ring joint gasket in the second operation cycle was investigated.
Finally the sealing mechanism and characteristics of this dissimilar material flanges under elevated temperature operation cycles were made clear.

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High-temperature fatigue properties for austenitic heat-resisting materials A286, Alloy718 and 304L were investigated in region between 10³ and 10⁷ cycles. A286 and Alloy718 are precipitation hardening type-austenitic alloys, and 304L is a solid-solution hardening type-austenitic steel.
The fatigue strengths for A286 and Alloy718 in high-cycle region over 10⁴ cycles showed a grain size effect. The fatigue strengths for the coarse-grain alloys are lower than those for the fine-grain alloys. Initiation sites of the fracture were the facets corresponding to the austenitic grain size. On the other hand, the fatigue strengths under10⁴ cycles showed no the grain size effect. Initiation sites of the fracture were the surface of the specimens.
Therefore, the high-cycle fatigue strengths for the precipitation hardening type-austenitic alloys depend on their austenitic grain size. The ratio (σ_W⁄σ_B) of the fatigue limit (σ_W) normalized by the tensile strength (σ_B) decrease to below 0.5 for the alloys with coarse grain.

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The 2003 Tokachi-Oki earthquake caused severe damage to oil storage tanks due to liquid sloshing. Six single-deck floating roofs had experienced structural problems as evidenced by sinking failure in large diameter tanks at the refinery at Tomakomai, Japan. The pontoon of floating roof might be buckled due to circumferential bending moment during the sloshing. The content in the tank was spilled on the floating roof from small failures which were caused in the welding joints of pontoon bottom plate by the buckling. Then the floating roof began to lose buoyancy and submerged into the content slowly. The failure of the roof expanded gradually in the sinking process. It is presumed that the initial small failures were caused by the elastic buckling of the pontoon due to circumferential bending moment. This paper presents the buckling strength of the pontoon using axisymmetric shell finite element analysis. Linear elastic bifurcation buckling analysis is carried out and the buckling characteristics of the pontoon with ring stiffeners are investigated.

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Situation of the RBM (risk-based maintenance) application to power plants in Japan is presented. Results of RBM assessment on a utility boiler and an industrial boiler are described in this paper. For decision making of the strategy on optimized maintenance program, RBM is an effective tool. “Flexible”risk assessment techniques are proposed under conditions of lacking in quantitative data or various aims or goal of plant owner. For aged power plants in Japan, the life extension beyond the original design lifetime with retaining the safety and the cost-effectiveness is required. Therefore it is important to minimise the risk and maintenance cost to keep operating the plants. The Life Cycle Maintenance (LCM) concept is proposed for optimized maintenance planning with reliability in the life of the plants.

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