• Corrosion Science and Technology
• /
• 제14권1호
• /
• pp.33-39
• /
• 2015

Pipe wall-thinning by flow-accelerated corrosion and various types of erosion is significant damage in secondary system piping of nuclear power plants(NPPs). All NPPs in Korea have management programs to ensure pipe integrity from degradation mechanisms. Ultrasonic test(UT) is widely used for pipe wall thickness measurement. Numerous UT measurements have been performed during scheduled outages. Wall-thinning rates are determined conservatively according to several evaluation methods developed by Electric Power Research Institute(EPRI). The issue of reliability caused by measurement error should be considered in the process of evaluation. The reliability analysis method was developed for single and multiple measurement data in the previous researches. This paper describes the application results of reliability analysis method to real measurement data during scheduled outage and proved its benefits.

• Journal of Mechanical Science and Technology
• /
• 제14권2호
• /
• pp.207-214
• /
• 2000

Fracture phenomenon has been reported on blades, rotors, connections and rotor discs of LP turbines of nuclear power plants, which is caused by fatigue, stress corrosion and erosion. In this study, as a tool of reliability evaluation, a number of stress and fracture analyses were performed on the defected area under various operating conditions using the finite element method. Possible defects on key-way and rotor disc were assumed to be two-dimensional cracks and centrifugal force, temperature distribution and shrink-fit effect were included as external loads. From stress analysis results, stress intensity factors were obtained and these values can be utilized to evaluate reliability and predict remaining lifetime of the turbine discs.

• 비파괴검사학회지
• /
• 제17권4호
• /
• pp.262-269
• /
• 1997

발전 설비중 열교환기 튜브와 같이 단면 형상이 원형인 부품의 원주 방향으로 마모, 침식 등에 의해 발생할 수 있는 단면 형상 변화를 검사(profilometry)하기 위한 와전류 탐촉자를 임피던스 등가회로이론을 적용하여 개발하였다. 본 연구에서는 외경 9.68mm, 벽두께 0.47mm인 SS304 튜브 외부에 발생할 수 있는 마모, denting 등의 결함을 모의한 시편을 제작하여 실험을 통해 검출 감도와 S/N비가 최적인 탐촉자의 코일치수, 전기적 특성, 적용 시험 주파수 등을 설정하였다. 이 결과에 따라 단면 형상 검사용 $8{\times}1$ 다중표면 탐촉자를 설계 제작하여 모의시편의 각 결함별 마모율을 검사한 결과 튜브 외부 발생 단면 형상 변화를 튜브외경의 ${\pm}0.2%$ (0.022mm) 측정 오차 범위로 측정이 가능함을 확인하였다.

• 한국재료학회지
• /
• 제9권10호
• /
• pp.1032-1036
• /
• 1999

Pb($\textrm{Zr}_{0.5}\textrm{Ti}_{0.5}$)$\textrm{O}_3$ 강유전체의 상부 전극 크기를 변화시키며 펄스 전기장에 의한 전자 방출 특성 및 열화에 대하여 연구하였다. 상부 전극 크기 감소에 따라 상부 전극 모서리 부근에서 분극 반전에 기여하는 강유전체 분율이 증가되어 분극이 높아졌으며, ANSYS 5.3에 의한 전기장 시뮬레이션을 통하여 비대칭 전극 구조에서의 상부 전극 모서리 부근의 전기장이 증가한다는 것을 알 수 있었다. 분극 증가에 기여하는 상부 전극 모서리 주변의 강유전체의 부피 및 전극크기당 전자 방출량은 상부 전극 크기에 무관하였다. 전자 방출 횟수에 따라 상부 전극이 침식되어 분극 및 유전 상수는 감소하였으나 전극 복구에 의해 재생되었으며, 강유전체의 표면 손상에 의해 항전계 및 유전 손실은 증가되었다.

• 대한치과보철학회지
• /
• 제39권1호
• /
• pp.1-13
• /
• 2001

An absolutely passive fit at the interface with the superstructure and the abutment cylinders is need for implant longevity. In this study, a method of cast framework correction using spark erosion technology was evaluated. Electric discharge machining(EDM) is a process that uses electrical discharges, or sparks, to machine metal, The surface being machined is bombared with high-intensity electrical energy pulses that gradually melt away the stock until the desired configuration is obtained. Master model was fabricated by using metal block impression analogue, which fired 5 Branemark squared impression coping in an arc shaped metal block. Then framework using 4mm standard gold cylinder and type IV gold alloy was fabricated. In order to measure the fit of the framework we used both contact and noncontact coordinate measurement machine and data was processed by computer program. After superimposition of gold framework and master model numeric image data the distances between gold cylinder bearing surfaces and abutment replica bearing surfaces, and the angle deviations between gold cylinder and abutment replica centroid points were calculated. The results were as follows 1 The total mean distance (p<0.01) and standard deviation (p<0.001) between the gold cylinders and abutment bearing surfaces were significantly decreased after EDM 2. The total mean of maximum distances was significantly decreased after EDM (p<0.05). 3. After EDM, the mean angle deviation between centroid points was decreased.

• 한국항공우주학회지
• /
• 제37권5호
• /
• pp.496-501
• /
• 2009

소형 인공위성에 적합한 300 W 급 원통형 홀 추력기의 추력부를 개발하였다. 추력부채널 내부에서의 자기장 분포는 추력 성능을 좌우하는 주요한 변수이다. 자기장 구조가 다른 두 종류의 추력부를 설계하고 제작하여 추력 및 효율에 대한 비교 측정 시험을 수행하였다. 또한 내구성 시험을 수행하여 추력부의 안정된 작동 시간과 작동 후 발생하는 문제점에 대한 결과를 얻었다.

• 동의신경정신과학회지
• /
• 제4권1호
• /
• pp.77-97
• /
• 1993

Human and animals are living by acclimation to environmental changes like high and cold temperature, nose, confinement, etc. If the above changes reach a defined levels, some physiological abnormal state could appear, which we call them as stress state. Catecholamines are excreted by the sympathetic-adrenomedullary system in free from in urine. Catecholamines are derived from the adrenal medulla and urinary epinephrine can be taken as a rough estemation of the activity of this gland. Many scientist reported the endocrinological change, excretion of catecholamine and its metabolites, stomach ulcer formation, etc. under the condition of the confinement and high temperature. In this study author gave restraint, electric shock and immersion stress to rats by administrating by HPLC and got the following results. 1. In the restriant experiment, epinephrine contents in control rat was 194.7 ng, but in Bohyulanshintang administered rat urine 198.9 ng of epinephrine was found. 2. In the electrical shock experiment, 199.5 ng of epinephrine was found in the control rat urine, but in Bohyulanshintang administered rat urine epinephrine content was 142.4 ng. 3. Dopamine contents in control rat urine the immersion environment was 118.9 ng, but in Bohyulanshintang administered rat urine only 55.2 ng of dopamine was found. 4. Incontrol rat stomach there appeared focal erosion and inflamatory exudate, but in experimental group these symptom were turned to mild condition.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2003년도 춘계학술대회 논문집
• /
• pp.1865-1868
• /
• 2003

This paper provides a new method for hybrid machining, particularly suited to micro fabrication applications such as micro point, micro line, micro structure, micro partition and so on. Developed micro fabrication process by electrical discharge machining (EDM) and electrical discharge deposition (EDD) with metal powder (Ti, Fe) has been studied to build TiC or FeC structure. Titanium powder or iron powder is supplied from working fluid (kerosene or de-ionized water with powder) and adheres on a workpiece by the heat and electric power caused by the electrical discharge. The use of a tool electrode is expected to keep powder concentration high in the gap between a workpiece and a tool electrode and to accrete powder material on the workpiece. The deposition is tried under various electrical conditions (workpiece. tool electrode, working fluid, discharge current, voltage and powder etc.). On the other hand. using electrical discharge machining (EDM) with the same tool electrode, it can be used as a removal process (cutting) by electro erosion at the same time. Therefore. this new method can do a hybrid machining to build up and down a structure with the workpiece.

• Nuclear Engineering and Technology
• /
• 제48권3호
• /
• pp.820-830
• /
• 2016

Pipe wall thinning by flow-accelerated corrosion and various types of erosion is a significant and costly damage phenomenon in secondary piping systems of nuclear power plants (NPPs). Most NPPs have management programs to ensure pipe integrity due to wall thinning that includes periodic measurements for pipe wall thicknesses using nondestructive evaluation techniques. Numerous measurements using ultrasonic tests (UTs; one of the nondestructive evaluation technologies) have been performed during scheduled outages in NPPs. Using the thickness measurement data, wall thinning rates of each component are determined conservatively according to several evaluation methods developed by the United States Electric Power Research Institute. However, little is known about the conservativeness or reliability of the evaluation methods because of a lack of understanding of the measurement error. In this study, quantitative models for UT thickness measurement deviations of nuclear pipes and fittings were developed as the first step for establishing an optimized thinning evaluation procedure considering measurement error. In order to understand the characteristics of UT thickness measurement errors of nuclear pipes and fittings, round robin test results, which were obtained by previous researchers under laboratory conditions, were analyzed. Then, based on a large dataset of actual plant data from four NPPs, a quantitative model for UT thickness measurement deviation is proposed for plant conditions.

• 한국전기전자재료학회논문지
• /
• 제29권10호
• /
• pp.647-651
• /
• 2016

The power relay can easily control high voltage and high current through metallic contacts. In addition, it has the advantage in reasonable price. So it has been used in many applications. But the power relay has a weak point by mechanical movements. These mechanical movements cause the bouncing phenomenon. Arc and bouncing phenomenon are the main causes of electric abrasion and material erosion. In this study, mechanical repetitive experiments and repetitive experiments in electrically connected state are conducted. Then these two experimental results in terms of bouncing phenomenon and changes in the contact surface are compared. In all number of repetitions, contacts in an electrically connected state cause smaller number of bounce. Also, It has lower contents of silver on eroded surface than the other. The experimental results would be helpful to the further study of contacts life span.