Oil storage tanks are usually constructed directly on tank foundations without anchors. In such a flat-bottom cylindrical tank subject to seismic horizontal force, a part of the bottom plate adjacent to the shell will be lifted off the tank foundation by the overturning moment, and excessive plastic strain cyclically occurs at the toe of the inside fillet weld of the shell-to-bottom joint¹⁾.
Previously, expanding the basic theory of Elastic-Plastic Hinge Method (E.P.H.M.) to uplift behavior of flat-bottom of cylindrical tank, the authors proposed the analytical method to evaluate the integrity of annular plate adjacent to the shell from the viewpoint of seismic design⁵⁾⁶⁾. Then, the equilibrium equations of 2 elastic-plastic hinges model of uplifted bottom plate were formulated for the elastic sidewall tank, considering nonlinear M～ϕ relationship based on elastic-plastic beam theory and the effect of large deflection of uplifted bottom plate⁷⁾⁸⁾⁹⁾.
Furthermore, in this paper, the effects of reyielding of bottom plate under unloading path is taken into consideration, and the method (E.P.H.M.) is expanded for the analysis on uplift behavior of flat-bottom of cylindrical tank subject to cyclic loading.　Then, calculations are carried out for a 9,900kl oil storage tank made of mild steel SS400, and the effectiveness of this method was shown by comparing it with results of FEM non-linear axisymmetric analysis.

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A model to describe the carbide precipitation resulting in the sensitization in the weld heat affected zone (HAZ) of the austenitic stainless steel has been proposed on the basis of the metallurgical principle. The purpose of that is to provide a practically convenient way to predict the sensitization risk in the HAZ. In the HAZ, especially heated to between 500 to 800 degree C in austenitic stainless steel, the chromium carbide precipitation can be caused resulting in high sensitivity to intergranular corrosion.
The proposed model to predict the progress of sensitization in the HAZ is as a function of cooling rate or weld heat input. That model formula consists of the constants determined by the C content in the stainless steel. The validity of predicted results was confirmed by the good fit between the results calculated with the proposed formula and the experimental data referred in the reported papers.

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The recommended practice, API RP 581, “Risk-based Inspection Methodology” was revised and published at January 2025 for fourth edition. The RBM (Risk-Based Maintenance)/RBI standard has been widely applied as a reasonable management system of maintenance and inspection planning for various facility or equipment.
In this explanation, documents for the fourth edition are compared with the third edition published in 2016. Though basic concept of risk calculation and analysis is not changed, updates to thinning and cracking modules are focused for damage factor determination. Improvement of inspection planning methodology, handling of clad/weld overlay, coating and others are concentrated. At the same time, document composition as standard was maintained understandably.

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