Supposing the thermal shock which take place in the heat-exchanger due to misoperation of valves, thermal shock test of explosive plugged part is conducted under severer condition than that in service.
Microscopic inspection (×200) of the section of specimen after thermal shock test, ultrasonic inspection and observation of acoustic emission during testing are conducted to detect the peeling of bonded boundary and cracking in the material.
SUS 321 steel, 21/4 Cr-1 Mo steel and SUS 304 steel are used as testing materials, supposing the material of the super heater, and evaporator of F B R, and steam generater of P W R, respectively.
Low detonation velocity explosive and reverse detonation method are used for the plugging of specimen.
Range of temperature variation are also desided supposing the operating temperature of secondary cooling circuit of each type of reactor.
Reasults of testing are plotted against the number of heating and cooling cycles. However, peeling is seemed to take place in short period after beginning of the testing, considerable number of cycles are required to initiate the cracks and to propagate them to inside of plug or outside surface of tube plate.
Mechanism of fracture due to thermal shock are considered and it is concluded that there are three type of fracture depending on the result of welding.
Conclusions of these investigations are obtained as follows.
1. Failures of explosive welded part are divided into two types, peeling and cracking.
2. There are three type of crack initiation, i. e. crack initiation from peeling, crack initiation from unbonded zone near the surface of tube plate, and crack initiation from melting zone in bonded boundary.
3. It is possible to distinguish the peeling and cracking by AE, however, it is impossible to distinguish the above three type of crack initiation by AE.
4. Peeling occurs immediately after beginning of test but cracking occurs after 150-200 cycles in SH, 200-400 cycles in EV and 1000 cycles in SG.

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Details of the design and pressure calibration procedure are described for two compact clamp-type piston cylinder high pressure cells for use in low temperatures from 300K to 1.5K. One of the two cells has been used for electrical resistivity and a. c. magnetic susceptibility measurements at hydrostatic pressures up to 37 kbar. Another is made of nonmagnetic materials and has been used for magnetization measurement up to 17 kbar. The usefulness of the uniaxial stress technique to high pressure work is pointed out. Some typical experimental results obtained are shown as examples.

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A wire-wound type press frame capable of producing up to 30, 000ton forces was constructed. The press stand was wound with 390km of piano wire (6mm x 1.5mm) under a tension of approximately one ton. The pre-compressive force acquired by the frame from the wire winding was calculated to be 39, 000tons. The frame weighs 160tons which is quite light relative to conventional presses.

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The quality of steels generally degrades when the steels are used at elevated temperature. Such a degradation is called “embrittlement during service at elevated temerature” in a broad sense, which includes various problems such as isothermal embrittlement, temper embrittlement, creep embrittlement and hydrogen attack and so on.
Description in this paper is. concerned witch the experimental results about the embrittlement during service of low alloy steels which are extensively used for high temperature reactor vessels.
The results obtained are summarized as follows
1. C-1/2Mo steel and 11/4Cr-1 1/2Mo steel were embrittled by precipiation of fine carbides. The fracture surface was cleavage. HAZ embrittlement of 1 1/4Cr-1Mo steel, however, was temper embrittlement which showed intergranular fracture surface. The HAZ embrittlement was accelerated further under stress.
2. 2 1/4 Cr-1 Mo steel showed typical temper embrittlement. The degree of the embrittlement increased witch increasing the embrittlement factor X, carbon content and cooling rate at quenching.
3. Creep embrittlement of 11/4 Cr-1/2 Mo steel was observed only in HAZ. This embrittlement could be accelerated by impurities such as Sb, Cu and P. The degree of influence of impurity elements on creep embrittlement differed from that on temper embrittlement. The influence of Sb was severest.
4. The resistance to hydrogen attack of 21/4Cr-1 Mo steel decreased with increasing weld heat input because the amount of M7G3 in carbides dercreased.
5. The resistance to hydrogen attack of C-1/2Mo steel was markedly low when the steel was rapidly cooled from the austenitizing temperature above 105°C. The resistance of normalized specimen was fairly good except normalizing at 125°C Even if normalized at 125°C, the resistance was restored to high level by post weld heat treatment above 600°C.

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Estimation of residual life due to the fatigue crack growth is taken to account for design or inspection of structures. The residual life is estimated by integrating the fatigue crack growth rate which is a power function of the range of stress intensity factor. It is well known that the cyclic life mainly depends on slow fatigue crack growth rate near fatigue threshold, ΔK_th. This paper describes the relationships between fatigue crack growth rate, da/dn, and range of stress intensity factor, ΔK. The importance of welding residual stress induced around crack tip is pointed out based on experimental results which are obtained by using center cracked transverse butt welded specimens. These experimental results show that the relationships between da/dn and ΔK for welded joints are quite similar to each other in spite of the difference in welding conditions and materials. While the relationship for welded joints is inferior to that for base metal: ΔK_th for welded joints is about a quarter of that for base metal. The difference between welded joints and base metal is revealed to arise from the stress ratio effect due to the high tensile residual stress in welded joints, Finally a guide in applying the fatigue crack growth data in design or inspection of structures is furnished.

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