Weld cladding, which was made on the heavy section plate of 2 1/4 Cr-1 Mo steel using austenitic stainless steel strip, incurs rich hydrogen after prolonged exposure to high temperature and high pressure hydrogen gas. The resulting disbonding of the cladding was investigated. The obtained results are as follows;
1. Delayed cracking occurs when the specimen is rapidly cooled from hydrogen charging temperature to the room temperature.
2. This type of cracking takes place in grain boundaries of cladding adjacent to the fusion line.
3. Susceptibility to the cracking rises by increasing the temperature and holding time of post-weld heat treatment.
4. Susceptibility decreases by applying post heating (hydrogen degassing heating) or by reducing the rate of cooling after hydrgen charging.

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In Conventional pipe truss structures, large stress concentration occur at the welded joints, making it difficult to achieve weight reduction of the structures. Therefore, bulge formed joint pieces are usually interposed among the main pipe and the branch pipes in the welding of the structures.
The joint pieces can reduce the stress concentration since forces generated at the joints during welding flow smoothly throughout the joint pieces, and additionally make the welding procedure easy.
However, a bulge forming method has been applicable only to small sized parts not to large sized structure parts. We have developed the hydraulic bulge forming equipment which can be applied to large sized structure parts as well as small one and established the forming techniques. The equipment is very compact in size and low in cost due to our sophisticated designs.
This paper describes the hydraulic bulge forming equipment for large sized structure parts, forming conditions and the quality of the bulge formed joint pieces.

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An applicability of ceramic materials as pressure media for ultra high pressure experiment has been examined. Compressibility and the generated pressure for three kinds of ceramics, namely, semi fired-silica, -alumina and -magnesia, as well as raw and fired pyrophillite were compared to each other. The compressibility was measured at room temperature and at pressure level than 1.5GPa, with the use of uni-axial piston cylinder type apparatus. While ultra-high pressure generation was conducted by use of a hexahedral anvil type high-pressure apparatus.
High pressure experiment at elevated temperatures was carried out using alumina and fired pyrophilite pressure media. The highest pressure of about 5.5GPa was attained at room temperature in the case of alumina, magnesia and fired pyrophillite, while in the case of silica and unfired pyrophillite, generation of a pressure high than 5.5GPa was difficult. The compressibility of ceramic pressure media was considerably affected by its porosity. The compressibility of ceramic media increased with the order of alumina, magnesia and silica. In the case of pyrophillite, the efficiency for pressure generation decreased at high temperature and higher pressure level, while alumina ceramics did not show any appreciable decrease of the efficiency. When alumina ceramics was used as a pressure media, higher electric power supply was required for heating compared with fired pyrophillite. In conclusion, ceramic material is considered to be applicable as a pressure medium for ultra-high pressure generation.

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Guiding principles for generation of ultra high pressures, such as massive support of anvils, conditional intensification of pressure, elastic design of anvils, compressibility matching between pressure medium and gaskets, and mechanical property of compressible gaskets, are briefly discussed.
Applying these guiding principles to an MA8 type apparatus, the requirements for the mechenical property of compressible gaskets are derived. The use of single component gaskets is shown to be difficult to generate very high pressures, and the use of “composite metal gaskets” is proposed in order to satisfy all the requirements for the optimum designing of pressure generation. The newly devised composite metal gaskets are examined experimentally for pressure generation up to 15-18GPa in 0.05cm³.
Theoretical analysis of the experimental results is made by calculating the distribution of stress in anvils from the data of strength of metals used for the gaskets, and also the distribution of plastic strain in anvils from the data on plastic deformation of anvils. Combining the calculated stress and plastic strain in anvils, a safety limit of -4.5GPa in terms of allowable differential stress is derived for cemented tungsten carbide anvils used in the present work.
The problem concerning scaling-up of system is discussed; effects disturbing Wakatsuki's scaling law of compressible gaskets are analyzed. The correlation between probability of blowout and scale of system is also analyzed. Stable generations of 8GPa in 15cm³ and 15GPa in 1.8cm³ averelized by means of the metal gaskets with a special care on the blowout.

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