Vibration of a floating roof due to nonlinear sloshing is investigated theoretically in this paper. First, a variational principle is introduced based on the equality between the liquid pressure and the Lagrangian density of the liquid. The floating roof is modeled by a finite element approach. A weighted-residual form of the governing equations is transformed into time-domain nonlinear ordinary differential equations to be solved by the Galerkin method. Numerical results show that stress responses obtained by the nonlinear analysis are larger than those obtained by the linear analysis. This is due to the fact that internal resonance occurs because the natural frequency of a mode with circumferential wave number 2 is twice the natural frequency of the radial first mode with circumferential wave number 1. Examination of the mode shapes of the floating roof shows that although the vibration amplitude is large over the deck and is small at the pontoon in most of the modes, a mode with significantly large vibration amplitude at the pontoon exists for the circumferential wave number 2. When this type of mode undergoes the internal resonance, stresses become very large in magnitude and exceed the levels that are predicted by the linear analysis.

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The 2003 Tokachi-Oki earthquake caused severe damage to oil storage tanks due to liquid sloshing. Seven single-deck floating roofs had experienced structural problems as evidenced by sinking failure in large diameter tanks at the refinery in Tomakomai, Japan. The pontoons of the floating roofs 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 authors had reported the buckling strength of the pontoons subjected to circumferential bending load in the previous paper. This paper presents the buckling strength of the pontoons subjected to both circumferential and radial bending load. The axisymmetric shell finite element method is used in the 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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Neutron diffraction method is used to be applied to measure micro-structure for material physics and chemicals. Recently neutron diffraction has been used for non-destructive testing, such as radiography, prompt gamma analysis and residual stress. In the industrial applications residual stresses and textures in the engineering materials are measured using neutron diffraction. In this paper the present techniques for measurements of residual stress and texture are mainly reviewed.

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A guide draft of “Risk Based Inspection for oil storage tanks”was proposed by the TSM committee in the HPI, under the sponsorship by JOGMEC, at March 2007. A risk in the RBI is defined as multiplication of probability of failure (PoF) and consequence of failure (CoF) . In this RBI for oil storage tank, failure means a leakage of internal fluid, namely oil. Failures are caused by damage on structural materials, which is mainly corrosion. The purpose of this RBI guide is to propose an optimum inspection program in order to keep the lower risk and to reduce the higher risk of oil storage tank as a result of estimation of risk. This paper presents the outline of the guide which was completed to keep safe operation against long term material deterioration and⁄or disaster such as corrosion and earthquake.

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