증기발생기 전열관의 입계부식에 대한 와전류검사 신호특성

최명식,허도행,이덕현,조세곤,임창재,한정호 한국비파괴검사학회 2002 한국비파괴검사학회지 Vol.22 No.2

가동중인 증기발생기 전열관에서 발생하는 결함 유형 중의 하나인 입계부식은 방진가공에 의한 모의 시편제작이 불가능하므로 입계부식에 대한 완전류검사 신호의 특성이 잘 알려져 있지 않다. 본 연구에서는 0.1 M sodium tetrathionate 용액에서 비확산 전열관에 입계부식을 형성시키고 와전류검사 신호를 수집하여 평가하였다. 이를 통하여 탐촉자의 종류와 주파수에 따른 신호특성 및 입계부식의 깊이 변화에 따른 검출등을 비교하였다. Because intergranular attack (IGA), one of the locallized corrosion forms occurring on steam generator tubes can not be fabricated by an electric discharge machining method, there are few data for the eddy current test (ECT) characteristics of IGA. In this paper, the characteristics of eddy current signals are evaluated using nonexpanded tubes with IGA defects formed in 0.1 M sodium tetrathionate solution at 40℃. The detectability and sizing accuracy of IGA were discussed in the coil type and frequency of the ECT probes.

전시 디자인용 스테인리스강의 부식 방지에 관한 연구

이정현(Lee, Jung Hyun),박재원(Park, Jae Won) 한국전시산업융합연구원 2014 한국과학예술융합학회 Vol.16 No.-

스테인리스강(stainless steel: STS) 구조 부재에 대한 고성능화, 고부가가치화, 경량화, 고기능화 등의 다양한 성능이 요구되면서 스테인리스강의 용접 적용에 대한 필요성이 점차 커지고 있는 추세이다. 최근에는 스테인리스강의 적용이 건물, 교량 등의 건축분야에까지 확대되면서 일반 구조용 탄소강과 스테인리스강의 용접기술도 활발히 연구되어지고 있다. 스테인리스강은 500~800℃사이의 온도에 노출되면, 탄소가 급속도로 입계(grain boundary)로 확산해 나간다. 그러나 확산속도가 느린 크롬은 자리를 지키고 있고, 입계로 확산해온 탄소는 입계 주변에 있는 크롬과 결합하여 크롬 카바이드를 형성하여 결정립계에서 석출한다. 결과적으로 입계 주위에 크롬이 고갈되어 부동태 현상을 잃게된다. 이러한 현상을 예민화(sensitization)라 한다. 본 연구에서는 STS 316L를 피복 아크 용접법(shielded metal arc welding: SMAW)으로 용접하여, 용접부에 대한 에너지 디스퍼시브 X-ray 스펙트로스코피(energy dispersive X-ray spectroscopy: EDS), 전기 화학부식, 미세조직 관찰을 통하여 현장에서 다층 및 보수 용접 등으로 야기될 수 있는 용접부의 입계부식(inter-granular corrosion: IGC)에 대한 검증을 규명하고자 하였다. 본 연구의 결과, 탄소함유량을 0.03%이하로 제한하여 탄화물 형성을 최소화하도록 하고, 크롬보다 탄소와 친화력이 더 강한 티타늄(Ti), 니오븀(Nb), 탈탄(Ta) 등을 사용하여 안정화 및 고용화 처리한 스테인리스강을 사용하면 부식 현상을 방지할 수 있다는 것을 알 수 있었다. With increase in the demand for diverse structural members with high performance, high added value, lighter weight and advanced functions, there is more need and demand for applying stainless steel to welding. Recently, as stainless steel is now used even in construction, such as buildings and bridges, welding of stainless steel and carbon steel for general structure has been active. When stainless steel is exposed to a temperature of 500 ~ 800 ℃, carbon rapidly diffuses to grain boundaries. However, chrome, with low diffusion speed, stays in its place. The carbon that is diffused to grain boundaries combines with chrome nearby to form chrome carbide, which is extracted from grain boundaries. In the end, the area around grain boundaries becomes depleted of chrome and loses its passive state. Such phenomenon is called sensitization. This study aims to verify the intergranular corrosion at welds due to multi-layered and repair welding in the field, through EDX on corrosion at welds for STS 316L, electrochemical corrosion and observation of structure. After conducting electrochemical corrosion test, elemental analysis and corrosion protection through biopsy on stainless steel at sensitization heat treatment temperature in this study, it was possible to reach the following conclusion. Corrosion could be prevented if carbon was limited to below 0.03% so as to minimize the formation of carbides, and if stainless steel was used after stabilization and solution treatment using titanium, niobium or tantalum, etc. that have stronger affinity with carbon than chrome.

입계부식시험에 영향을 주는 시험변수에 관한 연구

백승세,나성훈,이해무,유효선,Baek, Seung-Se,Na, Seong-Hun,Lee, Hae-Mu,Yu, Hyo-Seon 대한기계학회 2001 大韓機械學會論文集A Vol.25 No.12

Recently the non-destructive test technique which uses the grain boundary etching characteristics owing to the variation of material structures has been proposed. However, during in-serviced GEM test there are a lot of variables such as the changes of temperature and concentration of etching solution, the roughness condition of surface polished etc.. The purpose of this paper is to investigate the influences of these test variables on GEM test results in order to establish a reliable and sensitive of GEM evaluation technique. The experiments are conducted in various solution temperatures, 10$\^{C}$, 15$\^{C}$, 20$\^{C}$, and 25$\^{C}$ and in 70% and 100% concentrations of that, and in various surface roughnesses polished by #800, #2000, and 0.3㎛ alumina powder. Through the test with variables, it is verified that the decrease of temperature and concentration of etching solution and the coarsened surface roughness by not using polishing cloth and powder induce some badly and/or greatly influences on GEM test results like grain boundary etching width(W$\_$GB) and intersecting point ratio(N$\_$i/N$\_$0/). Therefore, to get reliable and good GEM test results, it must be prepared the surface of specimen polished by polishing cloth and 0.3㎛ alumina powder and the saturated picric acid solution having 25$\^{C}$ and be maintained the constant temperature(25$\^{C}$) during GEM test.

보일러 管材料의 크리프破斷特性에 미치는 고온부식의 影響

오세욱,박인석,강상훈 대한기계학회 1989 대한기계학회논문집 Vol.13 No.2

본 연구에서는 주로 보일러의 과열기 및 재열기등의 관재료로 널리 사용되고 있는 304 스테인레스강에 대하여 실제 고온부식현상을 재현한 부식환경하인 630.deg. C, 690.deg. C 및 750.deg. C 3가지 온도범위에서 크리프시험을 실시하고 고온부식이 크리프파단 특성에 미치는 영향을 부식조건이 없는 고온대기중의 실험결과와 비교 검토하였다. In order to investigate the effects of hot corrosion on the creep rupture properties and creep life of 304 stainless steel being used as tube materials of heavy oil fired boiler, the creep rupture tests were carried out at temperature 630.deg.C, 690.deg.C and 750.deg.C in static air for the specimens with or without coating of double layer corrosives according to the new hot corrosion test method simulating the situation commonly observed on superheater tubes of the actual boiler. The double layer corrosives are 85% V$_{2}$O$_{5}$ + 10% Na$_{2}$So$_{4}$ + 5% Fe$_{2}$O$_{3}$ as the inner layer corrosive being once melted at 900.deg. C and crushed to powder, and 10% V$_{2}$O$_{5}$ + 85% Na$_{2}$SO$_{4}$ +5% Fe$_{2}$O$_{3}$ as the outer layer corrosive. As results, in the specimen coated with the double layer corrosives, the rupture strength was extremely lowered and showed a large difference each other. The rupture ductility also lowered remarkably as a result of the brittle fracture mode due to hot corrosion. These results indicate that hot corrosion could essentially alter the creep fracture mechanism. From the metallographic observation, it was clarified that the rupture life of 304 stainless steel subjected to hot corrosion was chiefly determined by the behavior of the aggressive intergranular penetration of sulfides.des.

Turbine Blade재료의 부식민감성과 부식피로특성에 관한 연구

조선영,김철한,류승우,김효진,배동호,Jo, Seon-Yeong,Kim, Cheol-Han,Ryu, Seung-U,Kim, Hyo-Jin,Bae, Dong-Ho 대한기계학회 2000 大韓機械學會論文集A Vol.24 No.3

Corrosion characteristics on the 12Cr alloy steel of turbine blade was electro-chemically investigated in 3.5wt% NaCI and 12.7wt% Na2S04 solution, respectively. Electro-chemical polarization test, Huey test and Oxalic acid etching test were previously conducted to estimate corrosion susceptibility of the material. And, using the horizontal corrosion fatigue tester, corrosion fatigue characteristics of 12Cr alloy steel in distilled water, 3.5wt% NaCI solution, and 12.7wt%(1M) Na2S04 solution were also fracture-mechanically estimated and compared their results. Parameter considered was room temperature, 60'C and 90'C. Corrosion fatigue crack length was measured by DC potential difference method.Obtained results are as follows,1) 12Cr alloy steel showed high corrosion rate in 3.5wt% NaCI solution and Na2S04 solution at high tempratue.2) Intergranular corrosion sensitivity of 12 Cr alloy was smaller than austenitic stainless steel.3) Corrosion fatigue crack growth rate in 3.5wt% NaCI and 12.7wt%(IM) Na2S04 solution is entirely higher than in the distilled water, and also increased with the temperature increase.

입계부식법을 이용한 열화도 평가 프로그램 개발

유효선,백승세,나성훈,김정기,이해무,Yu, Hyo-Seon,Baek, Seung-Se,Na, Seong-Hun,Kim, Jeong-Gi,Lee, Hae-Mu 대한기계학회 2001 大韓機械學會論文集A Vol.25 No.7

It is very important to evaluate material degradation like temper and carbide embrittlements to secure the reliable and efficient operational conditions and to prevent brittle failure in service. The extent of material deterioration can be accurately evaluated by mechanical test such as impact test or creep test. But it is almost impossible to sample a large specimen from in-service plants. Thus, the material degradation evaluation by a non-destructive method is earnestly required. Recently the non-destructive test technique which uses the grain boundary etching characteristics owing to the variation of material structures has been proposed. However the program for material degradation evaluation using the grain boundary etching method(GEM) in Windows 98 domain doesnt be developed now. The aims of this paper are to develop the program and to complete the new master curve equations for the evaluation of material degradation on in-serviced high temperature components.

부식환경에 따른 SAE 5155의 부식거동 평가

안재필(Jae-Pil An),박경동(Keyung-Dong Park) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5

In this study, the influence of shot peening and corrosive condition for corrosion property was investigated on immersed in 3.5% NaCl, 10% HNO₃ + 3% HF, 6% FeCl₃. The immersion test was performed on two kind of specimen. The immersion periods was performed 30days. Corrosion potential, weight loss were investigated from experimental results. From test results, the effect of shot peening on the corrosion was evaluated.

입계부식법에 의한 사용중인 화력발전소 요소의 잔여수명평가

한상인,윤기봉,정세희,Han, Sang-In,Yoon, Kee-Bong,Chung, Se-Hi 대한기계학회 1997 大韓機械學會論文集A Vol.21 No.1

The grain boundary etching method as a method for assessing degradation of structural materials has received much attention because it is simple, inexpensive and easy to apply to real components. In this study, the effectiveness of the method is verified by successfully applying the technique to in-service components of aged fossil power plants such as main steam pipes, boiler headers an turbine rotors. A new degradation parameter, intersecting number ratio (N$_{1}$/N$_{0}$), is employed. The intersecting number ratio (N$_{1}$/N$_{0}$) is defined as the ratio of intersection number (N$_{1}$) obtained from 5-minute picric acid etched surface to the number (N$_{0}$) obtained from nital etched surface. Two kinds of test materials, 2.25Cr-1Mo steel and 1Cr-1Mo-0.25V steel, were artificially thermal-aged at 630.deg. C in different levels of degradation., (N$_{1}$/N$_{0}$) were measured. And, correlations between the measured values and LMP values calculated from aging temperature and aging time were sought. To check the validity of the correlations obtained in laboratory, similar data were measured from service components in four old Korean fossil power plants. These on-site measurement data were in good correlation with those obtained in the laboratory.oratory.

용사 도막의 내식성에 관한 전기화학적 평가

문경만(Kyung-Man Moon),신중하(Joong-Ha Shin),이명훈(Myung-Hoon Lee),이성렬(Sung-Yul Lee),김윤해(Yun-Hae Kim) 한국마린엔지니어링학회 2010 한국마린엔지니어링학회지 Vol.34 No.4

가혹한 부식환경 하에 사용되어 지고 있는 다양한 강구조물에 대해서 많은 표면방식법이 있다. 그 중의 한방법인 용사는 다양한 강구조물의 표면방식을 위하여 비교적 최근에 개발된 유용한 방식법이다. 그러나 용사피막도 환경오염의 가속화에 따라 점차 더욱 좋은 내식성을 필요로 하고 있다. 본 연구에서는 아아크 용사에 의해서 도막두께 200㎛의 피막을 만들었으며, 피막의 종류는 순 아연,순 알류미늄, 합금피막(Al:Zn=85:15) 및 (Al:Zn=95:5)의 합금피막이었다. 그리고 이들 피막의 내식성을 해수용액에서 전기화학적인 방법으로 고찰 하였다. 순 알류미늄 피막은 다른 피막에 비해서 비교적 상당히 좋은 내식성을 보였다. 그리고 합금피막도 역시 순 아연피막에 비해서 좋은 내식성을 보였다. 특히 순 알류미늄 피막은 갈바륨 용사라고 알려진 합금피막(Al:Zn=85:15)보다 해수용액에서 내식성이 상대적으로 좋았음이 관찰되었다. 순 아연의 부식된 표면양상은 입게부식의 형태를 나타내었으나 순 알류미늄과 합금피막은 균일부식의 형태를 나타내었다. There are many surface protection methods for numerous steel structures being used under severely corrosive environment, one of them, metallizing(thermal spray) is a available protection method which is comparatively and recently developed for surrface protection of various steel structures. However coating film obtained by spraying is to be needed increasingly more good corrosion resistance due to accelerating of environmental contamination. In this study, coating films(DFT:200㎛) are performed with arc spray by wire metal and their types of films are pure zinc, pure aluminum, alloy film(Al:Zn=85:15) and alloy film(Al:Zn=95:5). And corrosion resistance of their films was investigated with electrochemical methods in seawater solution. Pure aluminum film showed a relatively somewhat good corrosion resistance compared to among those of other films and alloy films also showed a good corrosion resistance compared to pure zinc film. Especially it was observed that pure aluminum film showed a comparatively good corrosion resistance than that of alloy film named as galvarium spray(Al:Zn=85:15) in seawater solution. Morphology of corroded surface of pure zinc film appeared the pattern like intergranlar corrosion, however films of pure aluminum and alloy metal showed a general corrosion pattern.

304 스테인리스강의 내식성에 미치는 붕소의 영향

안병국,원태연,이윤용,윤정모,최병길,황선효 대한용접접합학회 1995 대한용접·접합학회지 Vol.13 No.3

Effect of boron on corrosion resistance of Type 304 stainless steel has been studied. Boron tends to segregate at the grain boundaries during cooling after solution treatment, and so boron treated steel usually exhibits a ditch structure under the 10% oxalic acid test. However, it was found that the addition of 25 ppm boron in Type 304 steel has no effect on the general and pitting corrosion resistance while it has a little effect on the intergranular corrosion resistance.