3.5Ni-Cr-Mo steel forging is used as the pressure vessel material with high strength and toughness. The steel is well known to have high susceptibility to temper embrittlement due to its high Ni and Cr content. The effect of chemical compositions on temper embrittlement of the heavy wall 3.5Ni-Cr-Mo steel forging was investigated.
The susceptivility of the forging to temper embrittlement induced slow cooling from post-weld-heat-treatment temperature or step cooling treatment increased with increasing the contents of Si, Mn and impurity elements but was not influenced by C, Ni and V contents. The degree of embrittlement of weld heat-affected zone was larger than that of base material induced by slow cooling from PWHT temperature. The critical value of (2Si+Mn)⋅X, whereX=10P+5Sb+4Sn+As, ppm/100, is about 8.5 to satisfy the specification requirement of SA508 class 4 for the weld heat-affected zone after PWHT with cooling rate of 40°C/hr. The shift in FATT due to step cooling treatment was larger than that due to slow cooling from PWHT temperature. The critical value of (2Si+Mn)⋅X was about 4.5 to satisfy the specification requirement after step cooling treatment.

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Welding processes applied for the shell plates' construction of LPG storage tank have been mainly GTAW and SMAW, the heat input of which is less than about 50kj/cm. Then it's demanded that the high efficient welding process applied for the fabrication of LPG storage tank is developed. The success in developing the high efficient welding process depends upon both the development of high toughness steels and of high toughness welding materials even if large heat input is applied. And it was enabled by using high toughness welding material added Ti-B elements and high toughness steel, TMCP (Thermo Mechanical Control Process) steel.
In this paper, the TMCP steel with accelerating cooling and the electrogas arc welding are studied. The characteristics of welded joints with TMCP steel and electrogas arc welding checked in detail. For example, fracture strength, fracture toughness, sensibility of weld cracking and so on are studied. As the results, carbon equivalent, Ceq, of TMCP steel for LPG storage tank is low enough to prevent the weld cracking at 0°C. Even if large heat input e. q. 100kj/cm, of the electrogas arc welding was applied, it was remarkable that the fracture toughness, absorbed enerqy and COD value, were still high. It was confirmed that the electrogas arc welding with large heat input is able to apply the vertical welding of shell plates of LPG storage tank by using accelerate cooling TMCP steel.

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The fatigue life and fatigue crack growth rate analysis at the junction of small radial holes and main bore of the vessel, which is the most critical part of a high pressure polyethylene reactor, is presented. The repeated internal pressure tests using model cylinders containing a cross-bore were conducted to evaluate the effect of radial holes on the fatigue life and fatigue crack growth rate. The stress intensity factor expression at a cross-bore corner of the vessel was also developed successfully. Based on these results and the fracture toughness data, a fracture safe analysis diagram for the junction of the radial and main bores was constructed.

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A series of pipe rupture tests have been performed at the Japan Atomic Research Energy Institute to demonstrate the safety of the primary coolant circuits in the event of pipe rupture in nuclear power plants. Pipe whip tests and jet discharge tests have been conducted under the BWR and PWR LOCA conditions. The results of the pipe whip tests using 4, 6 and 8 inch test pipes under the BWR LOCA conditions were reported in the previous paper. The present paper describes the experimental and analytical results of the pipe whip tests performed under the PWR LOCA conditions using 4, 6 and 8 inch test pipes. The tests were carried out at an initial pressure and a temperature of 15.7MPa and 325°C.
Two different types of tests were performed. One was the cantilever type pipe whip test using the test pipe of 3000mm in length and U-shaped restraints. The other was the crossover leg pipe whip test using a 1/6 model of piping in the PWR nuclear power plants.
The cantilever type pipe whip tests were performed to investigate the influences of overhang length and pipe diameter on the pipe whip behavior. The movement of the test pipe is limited effectively by the restraints when the overhang length is short. The restraint force increases in proportion to the breaking area.
The crossover leg pipe whip test was performed to demonstrate the integrity of the restraints at the LOCA. Strain-gages, accelerometers and load cells were used to measure the dynamic response of the test pipe. Test results showed that the deformation of the restraints were within elastic limit, and the residual deformation at a free end was 6.7mm.
The dynamic structural analysis of pipe whip tests was carried out using the general purpose finite element program ADINA. Damping factor of the restraint was attached to the truss element to improve the transient response, of the restraint force. Analytical results using this finite element model were approximately coincident with the results of 6 inch pipe whip test.

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