Papers by Author: Sang J. Lee

Abstract: To monitor the wear and degradation on a pipe by corrosion during a plant operation, the vibration signals were measured by an accelerometer and analyzed by several analysis techniques. From the conventional methods, it was difficult to identify the wear and degradation on the pipe. And hence, the time-frequency distribution (TFD) and the adaptive cone-kernel distribution (ACKD) devised for reducing the interfering cross-terms are applied to the acquired data. They can provide the distinguishing peak patterns between the normal and corrosion signals.

Abstract: This study was aimed at developing a new method for detecting the sodium-water reaction as a result of a water leakage into the liquid sodium boundary for the liquid metal reactor. In the case of a passive acoustic method, to develop the leak detection algorithm, several signal processing methods have been evaluated. When the acoustic emission signal has a relatively high signal-to-noise ratio for the acoustic noises the spectral estimation method could be used to detect the sodium water reaction. In the case of a low signal-to-noise ratio within -5 dB to -15 dB, the system modeling and the identification methods using an autoregressive and an adaptive algorithm could be used to detect the sodium-water reaction. Regarding the active acoustic method, the basic attenuation factors of the ultrasonic beam were evaluated in the case of normal and abnormal plant conditions.

Abstract: There are several efforts for an advanced on-line health monitoring of a piping system by using a chemical condition monitoring, a X-ray radiography and a ultrasonic techniques. In order to increase the confidence of the understanding on the health condition of the underlying piping system, an integrated and multi-disciplinary approach has been adopted in this paper. Flow-Accelerated Corrosion (FAC) under an undesirable combination of the water chemistry, flow velocity and material composition has usually caused a pipe wall thinning. The condition monitoring tests on a piping elbow of a piping system have been conducted by using several advanced sensors such as an accelerometer, ultrasonic device, and chemical sensors.

Abstract: The mechanochemical reaction of hematite with graphite by mechanical alloying (MA) has been investigated at room temperature. The solid state reduction of hematite to Fe₃O₄ and FeO has been observed after 120 hours of MA by a planetary ball mill. Saturation magnetization is gradually increased with milling time up to 80 h, and then deceased after 120 h of MA, indicating the transformation of Fe₃O₄ into nonmagnetic FeO through further reduction. Neither the solid state reduction of Fe₂O₃ by graphite nor a sizable grain refinement is observed in the MA process using a horizontal ball mill.

Abstract: This paper investigates the effect of bubble on the primary Si size in Al-18wt.%Si alloy. The primary Si size observed was varied with bubble size and bubbling time in bubble process. The effect of the holding temperature of the melt in bubbling process was also investigated. In water model, as the injecting bubble size decreases, the residual bubble size in the water decreases and the residual bubble conservation time in the water increases. Also in the experiment of Al melt, the primary Si size decreases, as the injecting bubble size decreases and as the bubble processing time increases. Pore was observed at the center of primary Si. This pore was observed at many Si phases. So, this experiment suggests that the bubble can be used as nucleation sites of primary Si.