Airtight and liquidtight sealing are the most fundamental function for underground storage system. In order to make clear that, we conducted in-stiu experiment at the small cavern (2.5m(W)×2.5m(H)×10m(L)) constructed in the bedrock of pure and homogeneous mud stone. The items of the experiment are selected as follows: (1)
Grasp the behavior of underground water around the cavern and simulate that with numerical analysis. (2) Prove the airtight sealing function at actual underground tank.
For these purpose, we conducted the test as follows: Changing the inner pressure of the cavern by degress between-0.5-+2.0kg/cm²G by pouring and drawing the water or directly compressing the air, we measured pore pressure inside bedrock surrounding the cavern (they are measured from the time of construction), air pressure, temperature, etc. inside the cavern. At the same time, we made numerical simulation to the measured value with three-dimensional groundwater flow analys is by method of images, Besides, we conducted proof test of limit inner pressure for airtight sealing.
Results of the experimental study mentioned above are summarized as follows: (1)
Numerical analysis of groundwater flow based on Darcy's law is applicable to the behavior of underground water surrounding the cavern. (2) The higher the inner pressure of the cavern, the higher the pore pressure inside bedrock surrounding the cavern, and the less the inflow water to the cavern. (3) The function of airtight sealing is retained even when the hydraulic gradient just around the cavern (at the plug of upper shaft) is nerly equal to zero.

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This paper describes the life prediction program system ‘the MiCRACK’ based on fatigue crack propagation analysis. The program system consists of material database handling, crack propagation analysis and graphic representation of the results.
The material database are converted from those of the Society of Materials Science in Japan, from which material data can be quickly retrieved and represented using tables and figures.
The crack propagation analysis deals with multiple surface planar cracks, in which the coalescence of adjacent cracks, the change of crack aspect ratio, the effect of residual stresses and so on are considered.
The data input is carried out interactively and the results are obtained as some kinds of figures.

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The maximum depth of pitting corrosion on bottom plates of oil storage tank was evaluated by extreme value statistics. The maximum pit depth of each sample fitted in with a doubly exponential distribution. But, the distribution of extreme values is affected by the original distribution which is exponential and therefore the estimated value X_max becomes small, when sample size is too small. In case of this tank, sample size 0.5m square or larger is desired.
Samples shall be removed from the region where pitting corrosion took place heavily, as much as possible.
The parameters of cumulative distribution function were calculated in accordance with some methods. It was suggested that the MVLUE method was available for N≤20 and the maximum likelihood method for N>20.
The life of storage tank was predicted by the growth speed of pitting corrosion. Time dependence of the estimated maximum pit depth was linear within the period of 12.8 years use.

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Two-criteria method was applied to a cylindrical shell of pressure vessel assuming a longitudinal surface flaw on the cylinder. The effects of flaw depth and fracture toughness were investigated under assumed various operating conditions. Critical flaw depths of a longitudinal surface flaw on the cylinder were estimated by Two-criteria method under assumed various operating conditions. No effect of thermal stresses on the critical flaw depths was found when internal pressure was the same.

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The results of the present experiments proved that pressures working on the inner wall of a vessel were reduced by the use of a rigid sleeve of sintered alumina. The pressure vessel consisted of tapered pistons and a cylinder with flat ends and a straight bore. The sleeve was tightly inserted in the bore. The pressures generated in the center of the sleeve reached the fixed point of Ba without any damage of the vessel. This assemblage was also shown to be useful to high temperature-pressure experiments such as a raphite-diamond conversion. Through these trials, it was found that the pressure at the contact surface between the sleeve and the cylinder was much lower compared to that in the cases of onventional cells without the sleeve and several advantages of this system were discovered.

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