Recently, Stainless steels have been increasingly selected as the fitting or the valve materials of water pipes as the human health issue is getting higher and higher. Therefore, the connectors attached at pipes to deliver water are exposed to more severe environments than the pipes because crevice or galvanic corrosion is apt to occur at the fittings or the valves. Effects of the solid solution annealing, cooling rate after this heat treatment, and passivation on the corrosion properties of the shell mold casted SSC13 (STS304 alloy equivalent) were studied. The heating and quenching treatment more or less reduced hardness but effectively improved corrosion resistance. It was explained by the reduction of delta ferrite contents. Independent of heat treatment, the chemical passivation treatment also lowered corrosion rate but the improvement of corrosion resistance depended on temperature and time for passivation treatment indicating that the optimum conditions for passivation treatment were the bath temperature of 34 o C and operating time of 10 minutes. Therefore it is suggested that the corrosion resistance of SSC13 can be effectively improved with the heat treatment, where SSC13 is heated for 10 minutes at 1120 °C and quenched and passivation treatment, where SSC13 is passivated for at least 10 seconds at 34 °C nitric acid solution.
This study explains how to reduce the volume of radioactive wastes on the wires generated during the decommissioning process of nuclear facilities. The method involves spraying pressure treatment process to separate the aggregates from the wire; the latter of which contain the majority of the radioactive contaminants. The process acted to weaken the chemical bond between the wire and aggregate components on the wire. Optimal treatment conditions were determined to be as follows: pre-treatment for 1sec using round nozzle followed by flat nozzle horizontal to the wire for 1.5sec at room temperature. Such conditions were found to be effective at reducing the volume of the waste but could not remove the contaminants from the aggregates completely. Applying the additional process to remove the contaminants using dry ice, the clearance criteria could be attained for the aggregates separated. Therefore, the radioactive waste could be treated for clearance by the sequential treatment process, thus achieving an approximately 85% volume reduction of the radioactive waste and ultimately lowering the cost of decommissioning and waste disposal.
In this study, the measurement of FN (ferrite volume fraction) and the solution annealing ratio at a temperature of 1130 o C were determined with 15A elbow fittings of shell cast SSC13, and the corrosion resistance with and without austenitizing solution annealing were investigated in comparison with AISI304. The delta ferrite phase was observed in the material due to the slow cooling effect of the shell mold casting. However, the delta ferrite phase decreased gradually with the solution annealing at a temperature of 1130 o C. The hardness generally decreased with a heat treatment; however, its corrosion resistance was improved with the heat treatment. In addition, when a passivation treatment was applied, its corrosion ratio showed the lowest value. The pattern of general corrosion decreased due to the decrease in the delta ferrite phase with the solution annealing treatment. Consequently, it is suggested that the corrosion resistance of SSC13 elbow fittings can be improved by increasing the ratio of any solution annealing treatment used and by decreasing the ferrite phase. The relationship between the ratio of solution annealing and delta ferrite is expressed as follows: SA (solution annealing ratio,%) = 98 − FN (ferrite volume fraction, %).
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