In line with the expected increase of natural gas demand and for establishment of its efficient supply infrastructure including pipelines, the introduction of a new storing technology is anxiously needed. To meet such need, we have developed a “Steel Lined Rock Cavern System”, a next-generation type technology for storing natural gas in the bedrock. The development of new steel liner and design technology for rock has become essential for this system. For assessment of their adequacy and viability, we have carried out fundamental research by means of indoor model test and a demonstration test by means of test cavern. Report #1 of this paper describes the outlines of steel-lined rock cavern storage system and technical problems in designing steel lining (steel liner) in the plastic region together with their design countermeasures.

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For the practical use of Lined Rock Cavern (LRC) gas storage system called ANGAS (Advanced Natural GAs Storage) , one of the important technical issues is the confirmation of the design procedure for steel liner. The steel liner plate should be designed to keep the integral structure with the backfilled concrete and surrounding rock mass, as the cavern expands and contracts by cyclic pressure load. To satisfy this design concept, the steel liner is required to deform up to plastic region when the internal pressure is acting, so that the steel liner plate does not separate from the backfilled concrete due to residual displacement of the rock at the release of internal pressure. Based on this concept, the design procedure for the steel liner consists of following items as explained in the 1^streport.
(1) Check for strain accumulation due to cyclic pressure load during operation
(2) Stability check for local buckling at the release of internal pressure
(3) Stability check for overall buckling at the release of internal pressure
(4) Calculation of strain concentration due to concrete cracking and check for fatigue failure
(5) Calculation of strain concentration and check of fatigue failure for discontinuous structure between concrete layer and concrete plug
Especially, local buckling, which may occur in initial imperfection at the weld seam of steel liner due to compressive load at the release of internal pressure, is complex behavior includes material nonlinear problem and contact problem with surrounding materials. We have performed the laboratory experiment with model lining plates and the FEM analysis for the experiment model, in order to verify reasonability and reliability of the design procedure for local buckling behavior. As a result, the FEM analysis could simulate the local buckling behavior and it was shown that the design procedure could be applied for the actual storage system.

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Crack Growth Behavior and Redistribution of Residual Stress Caused by Crack Propagation from Residual Tensile Stress Field through Residual Compressive Stress Field of stress corrosion cracking (SCC) and Fatigue. At the beginning, re-distribution of Residual Stress Field boiled and depended on crack propagation was clarified. Based on analysis output, the crack propagation examination check by fatigue test was done. Comparison analyses of analysis output and a fatigue testing result were performed, and consideration was added.

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In this study, micro-hardness tests and AFM observations were performed on SUS316L low-carbon austenitic stainless steel pre-strained by cold rolling to investigate its deformation behavior. The following results were obtained. Despite the fact that the same plastic strain was applied, post-tensile test AFM showed narrower slip-band spacing in a reduction in area of 30% cold-rolled specimen than the unrolled specimen. Concentrated slip bands were observed near grain boundaries. These were presumably due to slip blocking at grain boundaries. SCC sensitivity increased at a hardness of 300 or higher, the frequency occurrence of a hardness of 300 or higher in the micro-hardness measurements was compared. The micro-hardness did not exceed 300both within grains and at grain boundaries in the unrolled and up to a reduction in area of 20% cold-rolled specimens of before and after the tensile tests. Micro-hardness exceeding 300 was found to occur frequently in after tensile test specimens with a reduction in area of 30% or more, particularly at grain boundaries. It is suggested that the nonuniformity of deformation at grain boundaries plays an important role of IGSCC crack propagation mechanism of low-carbon austenitic stainless steel.

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The present paper describes the behavior of plastic region tightening of a bolt in a downsized flange joint subjected to internal pressure. An API 4-inch flange joint is downsized for plastic region tightening. The nominal diameter of the bolt is reduced from M16 to M8, and the bolt pitch circle diameter and the outer diameter of the flange are decreased by 11%. The flange rigidity and the stresses of the compact flange joint are calculated and are superior to the original API flange joint. Internal pressure is applied to a compact flange joint, and the behavior of additional bolt force is demonstrated. Load factor depends on the type of gasket, such that the load factor is positive for a flexible graphite sheet gasket. The load factor is in agreement with the value calculated by the Load Factor Method (LFM) . When the external force is applied to the bolted joint under plastic region tightening, the allowable limit of the additional bolt force is approximately 10% of the bolt yield force. In the compact flange, the additional bolt force is as small as 1% of the bolt yield force. Therefore, the additional bolt force has sufficient margin for the allowable limit.

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The floating roofs are widely used to prevent evaporation of content in large aboveground oil storage tanks. This paper deals with the research trends on structural design of the floating roofs. The author summarized the researches due to accumulated rain water, sloshing and wind load condition.

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