Characteristic damage parameters were investigated for modified 9Cr-1Mo steel used in high efficiency fossil-fired power plants as hot section components. Microstructural observations and mechanical tests were carried out for base metal and welded joint after ageing, creep and fatigue tests at elevated temperatures. The precipitation of Laves phase caused the decrease in toughness. The creep damage in base metal corresponded to the decrease in hardness. Recovery of dislocation structure was related to decrease of hardness. The fatigue damage in base metal correlated to the maximum crack length among micro-cracks initiated during fatigue cycles. In the welded joint, the creep fracture occurred by the formation and growth of voids in the fine grained HAZ near base metal. The creep damage was associated with the increase in area fraction of voids.

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Creep ruptue and creep-fatigue interaction tests were coducted at 550°C for modified 316FR austenitic stainless steels in order to improve the creep-fatigue lives. Reducing the carbon contents from 0.01% to 0.002 or 0.003% and finning the grain size were effective for increasing the creep-fatigue lives and the creep rupture ductilities. From these results, an estimation method of the creep-fatigue lives by using the creep rupture ductilities in the modified 316FR steels was proposed.

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The double layered corrosion resistant alloy (CRA) pipe and tubing (C-II pipe), produced by thermal-hydraulic shrink fitting of the liner pipe made of CRA and outer pipe made of carbon steel, were developed, and features excellent corrosion resistance and strength.
The production processes of C-II pipe, which are composed of hydraulic expansion of liner pipe and thermal shrink fitting of both pipes, are relatively simple. The representative quality control index of product is the shrink fit stress caused by these processes. However, the mechanical phenomena to combine liner pipe and outer pipe are complicated, since two analyses, transient heat conduction analysis and elastic-plastic stress analysis, are required to clarify the phenomena and then to quantify the shrink fit stress.
In this paper, two finite element method analyses were performed using MARC code to clarify the behavior of shrink fit stress during production. In addition, an empirical formula of the shrink fit stress is conducted using regression analysis.
Following results are obtained.
(1) FEM can estimate the behavior of shrink fit stress during production, since the shrink fit stress calculated by FEM agrees fairly well with the measured value.
(2) The empirical formula for the shrink fit stress is practically applicable, since the values of the shrink fit stress estimated by the formula agree well with measured ones.

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This paper presents a study on the influences of layer structures upon the burst strength of FRP composite cylinders.
Six different types of reinforced layer structures were examined; (1) additional hoop winding at dome-cylinder boundary part, (2) increase in metallic liner thickness at dome part, (3) additional helical winding, (4) combination (1)+(3), and (5) combination (2)+(3). FEM analyses were conducted with special interests in the strain distribution at the dome-cylinder boundary parts. For each model, the strain distributions were examined for a set of deviated locations of hoop-winding ends. The discussions were directed to the control of burst pressure and fracture initiation sites by different reinforcing means in the design of composite cylinders.

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Temperature distribution in resistance seam welding is investigated to clarify the nugget formation in welding process.
Two-dimensional model describing the heat transfer and Joule's heating is developed, using the electric contact resistance of steel sheet and current path length in welding as a calculation parameter.
The calculation model is numerically solved by means of the finite-differential method.
The calculation results demonstrate that the steel sheet temperature is increasing in an increase of electric contact resistance and a decrease of current path length. Nugget form obtained from the calculation under the condition is that the current path length is changing periodically, with change of current, is similar to the welded nugget form.

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