Owing to protect the inside bottom steel plate in the oil strage tank, coating tank by resin increase.
The non-destractive inspection system on the coating film has been developed,
1. Measurement method of bottom steel plate thickness by ultrasonic thickness gage.
2. Detecting method of the surface flaw on the weld parts by creeping wave ultrasonic testing, eddy current testing, and magnetic flux leakage testing.

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Underground oil storage is a system of storing oil in rock caverns excavated underground under water seal mechanism.
Since 1976, the possibility of underground oil storage in Japan had been studied by the Agency of Natural Resources and Energy. Since 1979, practical investigation data had been collected through the construction and operation of Kikuma test plant. These data suggested that the construction of large-scale underground facilities for crude oil was technically possible. On the other hand, feasibility studies on the possibilities at Kuji, Kikuma and Kushikino areas were performed.
In 1987, construction of first crude oil storage facilities in underground rock caverns were started at three areas by Japan Underground Oie Storage Co., Ltd.. Now, the construction of three plants are in full swing.
In this paper, principle of underground oil storage under water seal system, rock excavation of storage facilities and outlines of Kuji, Kikuma and Kushikino plants are reported.

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Inground storage tanks are essentially safe structures and this is one of their foremost advantages. Convinced of the excellent properties of inground storage tanks, Tokyo Gas built the world's first 10, 000kl membrane-lined inground storage tank at the firm's Negishi Terminal in 1970. Since then, 46 inground tanks have been built altogether, from a minimum capacity of 650kl to a maximum capacity of 140, 000kl per unit. In the meantime, we have addressed wide-ranging technologies related to inground storage tanks. The research and development efforts have been reflected in the construction of large-capacity inground tanks. This paper focuses on the LNG inground storage tanks with the latest technologies, centering on our latest 140, 000kl inground tank, and then discusses the current state of the technology in this area. It also refers to the future trends such as the development of extra-large tanks.

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Since LNG introduction to Japan in 1969, it has been increasingly demanded as a clean energy source, with more than 170 LNG storage tanks constructed so far.
80 or more double-shelled, flat-bottom, cylindrical storage tanks with ranging from 25, 000kl to 140, 000kl have been installed at the LNG receiving terminals, and 40 or more vertical or horizontal cylindrical above-ground storage tanks have been installed in the LNG satellite bases. It is anticipated that more such storage tanks will be constructed as LNG demand grows.
The LNG storage tank, which stores liquefied natural gas at -160°C, has a doubleshelled structure with an insulation layer. The inner tank is made of 9%Ni steel, Al alloy or austenitic stainless steel, which provides high cryogenic toughness. The storage tank is constructed according to the standard specified by the Gas Utility Industry Law, the Electric Utility Industry Law, or the High Pressure Gas Control Law, depending on the purpose.
In Japan, with limited available land and soaring land prices, the effctive utilization of site area is an essential requirment.
Accordingly, the industry's developmental efforts are directed toward PC aboveground LNG storage tanks and larger storage tanks.
PC aboveground LNG storage tank is realised by installing a prestressed concrete dike extremely or infinitely close to the conventional aboveground storage tank, so that it is essentially integral with the tank. Commissioned by the Ministry of International Trade and Industry, the Center for Promotion of Natural Gas conducted verification tests, analyses and investigation of the storage tank for safety and reliability, and presented “Report on Technical Developement and Investigation for PC Aboveground LNG Storage” in March, 1990.
As well, recent radical advances in steelmaking, welding and non-destructive examination techniques have made it possible to realize larger storage tank, which offers economic advantages and is more favorable inlight of effective site utilization.
Now, PC aboveground LNG storage tank with a capacity of 140, 000kl is under construction at Senboku Works II of Osaka Gas.
Meanwhile, maintenance and inspection techniques have also seen remarkable development.
“Low Temperature Line Sensors” and “Storage Interior Monitoring Equipment” have been developed, with the aim of improving the reliability of LNG storage tanks.

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Strage test of crude oil in underground rock cavern has been accomplished, and commercial rock cavern is under constructing.
On the otherhand, strage test of LPG in underground rock cavern is now investigating.

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Refrigerated LPG storage tanks in Japan increased both in their number and capacity since their first construction in end 1961, and now have reached to 140 units, 3.4 million tonnes in total.
Japan LP-Gas Association, in 1989, made an inquiry among its member firms on their records of inside inspection of storage tanks and it was found that, during a period from December 1961 to December 1988, such inspections have voluntarily been carried out 29 times in total with 21 units.
The results of these inspections were generally satisfactory with no problematic findings.

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The PS-type Cryogenic Storage Tank is designed to provide double safety against leakage. The tank consists of an inner tank and an outer enclosure. The inner tank contains the low temperature and ultra-low temperature liquefied gases, such as Liquefied Petroleum Gas (LPG) and Liquefied Natural Gas (LNG). Even in the event of an accidental leakage occurring on the inner tank, the outer enclosure of prestressed concrete will serve as an integral secondary barrier to keep the gas from flowing out.
Several ethylene storage tanks with storage capacity of 3, 000 to 7, 000 ton and two 40, 000 ton LPG storage tanks have been constructed as the results of our research and davelopment efforts and these tanks have been enjoying a high reputation as the storage facilities with the highest safety and integrity.

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