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열시효가 Mod.9Cr-1Mo강의 재료강도 및 파괴 거동에 미치는 영향
이형연,김우곤,손석권,홍석우,석창성,Lee, Hyeong-Yeon,Kim, Woo-Gon,Son, Seok-Kwon,Hong, Suk Woo,Seok, Chang Sung 대한기계학회 2016 대한기계학회 논문집. Transactions of the KSME. C, 산업기술과 혁신 Vol.4 No.2
발전소 내열강의 물성치는 고온 가동시간이 누적됨에 따라 열시효의 영향을 받는다. 본 연구에서는 제 4 세대 원자력시스템의 재료로 널리 채택되고 있는 Mod.9Cr-1Mo (ASME Grade 91)강을 대상으로 항복강도, 인장강도 및 파괴거동에 열시효가 미치는 영향에 대해 조사 및 분석하였다. 국내에서 가동 중인 초초임계(USC) 화력발전소의 배관계통에서 채취한, 73,716 시간의 가동 이력을 겪은 Gr.91 강 재료가 재료 실험을 위해 사용되었고, 동 시험결과와 가동 이력을 겪지 않은 신재의 시험결과를 비교 분석하였다. 또한 ASME 코드의 물성치와 RCC-MRx 의 물성치와 비교 분석하였고, 이들 설계기술기준 물성치의 보수성은 신재 및 가동 이력을 겪은 재료의 시험결과와 비교 분석을 통해 정량화하였다. The material properties of heat resistant materials at power plants are affected by thermal aging as operating time is accumulated. In this study, the influence of thermal aging on yield strength, tensile strength and fracture behavior for Mod.9Cr-1Mo (ASME Grade 91) steel which is a material widely adopted for Generation IV nuclear energy system has been investigated and analyzed. Service exposed Gr.91 steel materials sampled from a piping system of an ultra-supercritical (USC) plant in Korea with accumulated operation time of 73,716 hours were used for material testing. The test results of the service exposed material specimens were compared with those of the virgin Gr.91 steel specimens. Those test data were compared with the material properties of ASME code and RCC-MRx code. Conservatisms of the material properties in the design codes have been quantified based on the comparisons of those from virgin and service exposed material specimens.
Single-Layer 포텐셜과 가중함수를 이용한 응력강도계수의 계산
이형연,홍창선 대한기계학회 1995 대한기계학회논문집 Vol.19 No.4
A new weight function approach to determine SIF(stress intensity factor) using single-layer potential has been presented. The crack surface displacement field was represented by one boundary integral term whose kernel was modified from Kelvin's fundamental solution. The proposed method enables the calculation of SIF using only one SIF solution without any modification for the crack geometries symmetric in two-dimensional plane such as a center crack in a plate with or without an internal hole, double edge cracks, circumferential crack or radial cracks in a pipe. The application procedure to those crack problems is very simple and straightforward with only one SIF solution. The necessary information in the analysis is two reference SIFs. The analysis results using present closed-form solution were in good agreement with those of the literature.
초임계압 화력 과열기 구조의 고신뢰도 건전성 평가 방법
이형연,주용선,최현선,원민구,허남수 한국압력기기공학회 2020 한국압력기기공학회 논문집 Vol.16 No.1
Integrity evaluations on a platen superheater were conducted as per ASME Section VIII Division 2(hereafter ‘ASME VIII(2)’) which was originally used for design with implicit consideration of creep effects. A platen superheater subjected to severe loading conditions of high pressure and high temperature at creep regime in a supercritical thermal plant in Korea was chosen for present study. Additional evaluations were conducted as per nuclear-grade high-temperature design rule of RCC-MRx that takes creep effects into account explicitly. Comparisons of the two results from ASME VIII(2) and RCC-MRx were conducted to quantify the conservatism of ASME VIII(2). From present analyses, it was shown that the design evaluation results exceeded allowable limits of RCC-MRx for the plant design conditions although limits of ASME VIII(2) were satisfied regardless of operation time, which means that design as per ASME VIII(2) might be potentially non-conservative in case of operation in creep range. A high-temperature design evaluation program as per RCC-MRx, called ‘HITEP_RCC-MRx’ has been used and it was shown that pressure boundary components can be designed reliably with the program especially for the loading conditions of long-term creep conditions.
이형연,Jae-Hyuk Eoh,이용범 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.9
A high temperature design and creep-fatigue damage evaluation for a helical type sodium-to-air heat exchanger (AHX) in a 600MWe sodium-cooled fast reactor (SFR) has been conducted. The AHX is a safety-grade component in a passive decay heat removal (DHR)system. Safe and reliable decay heat removal is one of the most important tasks in the successful design of a sodium-cooled fast reactor. Therefore, independent, diverse and redundant DHR systems incorporating both passive and active mechanisms have been employed in the demonstration SFR developed by Korea Atomic Energy Research Institute (KAERI). One of the key DHR components is sodium-toair heat exchanger, which has a helically coiled tube arrangements. A creep-fatigue damage evaluation has been performed according to the elevated temperature design codes of ASME Subsection NH and RCC-MRx based on a full 3D finite element analysis. The integrity of the heat exchangers under creep-fatigue loading was confirmed and code comparisons were made as well.
이형연,이제환,최현선 한국압력기기공학회 2020 한국압력기기공학회 논문집 Vol.16 No.1
A number of so-called ‘Type IV’ cracking was reported to occur at the welded joints of the P91 steel or P92 steel reheat steam piping systems in Korean supercritical thermal power plants. The reheat steam piping systems are subjected to severe thermal and pressure loading conditions of coolant higher than 570C and 4MPa, respectively. In this study, piping analyses and design evaluations were conducted for the piping system of a specific thermal plant in Korea and suggestions were made how structural integrity could be improved so that type IV cracks at the welded joints could be prevented. Integrity evaluations were conducted as per ASME B31.1 code with implicit consideration of creep effects which was used in original design of the piping system and as per nuclear-grade RCC-MRx code with explicit consideration of creep effects. Comparisons were made between the evaluation results from the two design rules. Another approach with modification or reduction of the redundant supports in the piping systems was investigated as a tool to mitigate thermal stresses which should essentially contribute to prevention of Type IV cracking without major modification of the existing piping systems. In addition, a post weld heat treatment method and repair weld method which could improve integrity of the welded joint of P91 steel were investigated.
아스피린 유발성 기관지 천식 환자에서의 아스피린 탈감작 치료 2예
이형연,윤형진,김성철 동국대학교 경주대학 1993 東國論集 Vol.12 No.-
Some asthma patients are intolerant to aspinin.In these patients ingestion of aspirin causesymptoms of rhinitis, and/or urticaria, bronchospasm whthin 1 to 2 hours, which may be fatal. We conducted oral aspirin test and desensitization in two patients with aspirin induced asthma. One of these patients was admitted due to acute asthmatic attack which develop after ingestion of one tablet(500mg) of aspirin, which followed by acute repiratory failure with cyanosis and severe hypoxia which needed intubation and ventilatory care. And the other was occasionally experienced rhinorrhea, generalized itching and dyspnea after the URI medications including aspirin. They were received increasing doses of aspirin in every two hours until a fall in FEV_1 of 20% and experience asthmatic episode. Asprin desensitization, defined as the ability of the patients to ingest 650mg of aspirin, was successfullly achieved with careful managements at third day of aspirin administration. After desensitization the patient can be tolerant 650mg aspirin of without experiencing respiratory symptoms or decreasing in lung function. These two patients could be successfully desensitized to aspirin with safety. Even though there is no exact mechanism about asprin intolerance, most likely to be related to the ability of aspirin to inhibit cyclooxygenase pathway. Therefore enhanced lipoxygenase metabolism perhaps plays a crucial role. Aspirin desensitization enable the aspirin sensitive patients to use aspirin or other NSAIDs with safety.