During the developing of next-generation type High-Pressure Natural Gas Strage System, we intended to store the gas in the rock cavern. In order to develop a steel-line rock cavern stroge system, we have designed and constructed a small scale model tank to carry out demonstration tests.
For assessment of adequacy and viability of design technology, the demonstration tests were consisted of Pressure Test, Air Tight Test and Repeated Long-term Loading Test at 20MPa and Pressure Test at 30MPa. Report #2 of this paper describes the outlines and test results of the demonstration test and the assessment results on the adequacy of design technology for the steel liner, which is a steel lining, and the viability of the system based upon the subsequent analysis.

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Under conditions of internal pressure, circumferential compressive stresses are developed in the knuckle plate of refrigerated storage tank. In “Recommended Practice for LNG Aboveground Storage” and “Recommended Practice for LNG Inground Storage”, the analogy between compressive stresses in knuckle plate and those in axially loaded cylinders is employed and the allowable compressive stresses for knuckle plate are given linking to the allowable tensile stresses. In the ASME Boiler and Pressure Vessel Code Sec. VIII Div. 1, the factor of safety on tensile strength has been reduced from 4. 0 to 3. 5 in establishing the allowable tensile stresses. According to the reduction in the ASME Code, the factor of safety in these Practices were reexamined. In the reexamination, the design margin of the allowable compressive stresses for knuckle plate was investigated.
The knuckle plate is equivalent to the torus region of torispherical shell and the investigation of the design margin was performed using the failure pressure of the shell. The failure modes of the shell are buckling and plastic collapse and the design equations for these modes were used to calculate the pressure. The materials of the shell studied were A5083-O, 9% Ni steel and SUS304 for which the allowable tensile stresses have been increased because of the reduction in the factor of safety. The failure stress was calculated using the failure pressure and the design margin was defined as the ratio of the failure stress to the allowable compressive stress. The tentative lower limit for the design margin was set to be 2. 0 and at least 1. 5. For A5083-O and 9% Ni steel, the minimum design margins were above 2. 0, and the value for SUS304 was 1. 79. This demonstrates the validity of the reduction in the factor of safety in establishing the allowable tensile stresses.

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The effects of overload on the ΔK_th of SUS316 were studied in this study. Tensile overload was applied to a compact tension (CT) specimen. Then, fatigue tests were carried out to determine the resultant ΔK_th. It was found that the value of ΔK_th increases as increasing the overload. The results were discussed from the viewpoint of fracture mechanics. The size of compressive residual stress is the key factor controlling the value of ΔK_th. Fractgraphic observation of fracture surface after fatigue tests were also carried out.

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There are known many expressions of correlation between various kinds of fracture measure such as fracture toughness and Charpy energy. The present paper presents a model which makes it possible to explain basis of these expressions on the Beremin model. It is suggested that the difference of the transition temperatures between static toughness and dynamic one decreases with increase in strength of steel as far as steels of high toughness are concerned, but has a tendency to decrease with rise of the static toughness transition temperature when viewed over all steels regardless of toughness.

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In order to rationalize the safety margin of the pressure equipments which have local metal loss, we apply the probabilistic reliability method to the assessment. The modeling of the local metal loss is based on API 579-1⁄ASME FFS-1 and we consider the safety margin of its assessment criterion. Moreover, we proposed the assessment curve based on the reliability. As a result of calculation, we showed that the reliability index of the assessment criterion of API 579-1⁄ASME FFS-1 depends on the dimension of local metal loss. Therefore, the assessment criterion of API 579-1⁄ASME FFS-1 can be rationalized from the reliability point of view. The proposed assessment curve based on the reliability can assess the local metal loss based on quantified safety margin and can expand the accepted area for the local metal loss compared with that by API 579-1⁄ASME FFS-1.

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