Al-brass is usually used as the tube material of vessel's heat exchanger for seawater cooling system because it has high thermal conductivity and good mechanical properties and high corrosion resistance due to cuprous oxide (Cu20) layer against seawater. However, Al-brass tubes of heat exchanger for vessel at the actual environment is reported that local corrosion such as stress corrosion cracking occurred by synergism effect between mechanical factor and corrosion environment In this paper, the effect of corrosion environment on the stress corrosion cracking of Al-brass in various NH4OH of 3.5% NaCl solution, under flow by constant displacement tester. Based on the test results, the behavior of polarization, stress corrosion crack propagation and dezincification phenomenon of Al-brass are investigated. The main results are as follows：(1) Increasing range of potential from open circuit potential to repassivation gets lower, as the contain rate of NH4OH gets higher. (2) As contain rate of NH4OH gets higher, SCC of Al-brass is become activation but the protection film(Cu20) of Al-brass is created in 3.5% NaCl solution. (3) According as content of NH4OH increases in 3.5% NaCl solution, the dezincifiction area is spread. It is concluded that dezincification occurred by localized preferential anodic dissolution at stress focusing region.

해양환경의 비저항 변화에 따른 모재, Ni도금 및 Cr도금의 분극저항, 부식전류밀도, 부식억제율 및 분극지배기구에 관하여 연구한 결과 다음과 같은 결론을 얻었다. 1) Cr도금 및 Ni도금의 분극저항은 모재의 분극저항보다 더 높게 나타나고, 이들 재료의 분극저항은 비저항이 감소함에 따라 낮아진다. 2) 비저항이 낮아질수록 Cr도금 및 Ni도금의 부식전류밀도는 모재의 부식전류보다 더 억제됨에 따라 Ni 및 Cr도금의 부식억제율은 더 높게 된다. 3) 해양환경의 비정항에 따른 모재, Ni도금 및 Cr 도금의 부식반응은 음극지배로 판단된다.(이 논문의 결론부분임)

Most Recently, with rapid development in marine industries such as marine structures and ship, there occurs much interest in the study of corrosion characteristics which play an important role in design of cooling water system like heat-exchanger. Especially, as operating environment of fresh cooling water system in vessels is acidified, this system is seriously corroded. In this study, to study on the corrosion characteristics of Al-alloy shell for cooler, the electrochemical polarization test of materials for the marine fresh water cooler such as Al-alloy, Cu and naval brass was carried out in fresh water. And thus the polarization resistance and anodic polarization behavior of Al-alloy, Cu and naval brass are investigated. Also, galvanic corrosion characteristics of Al-alloy coupled with Cu and naval brass is considered. The main results obtained are as follows ; (1) The current density of corrosion is high in order of Al-alloy > naval brass > Cu (2) As anodic potential increases, the corrosion resistance of naval brass is better than that of Cu. (3) The galvanic corrosion of Al-alloy coupled with Cu and naval brass is activated than corrosion of Al-alloy.

증류수 및 수도수 중에서 방열기로 사용되는 알루미늄합금재의 온도 변화, 탈기에 의한 개로전위, 부식전류밀도에 관하여 연구한 결과 다음과 같은 결론을 얻었다. 1. 청수 중에서 개로전위는 온도가 높아짐에 따라 비전위화 되고, 또한 탈기 후의 개로전위는 탈기 전의 개로전위보다 비전위화 된다. 2. 증류수 중에서의 부식전류밀도는 수도수 중에서의 부식전류밀도보다 더 억제된다. 3. 탈기 후의 부식전류밀도는 탈기 전의 부식전류밀도보다 크게 억제된다

본 연구에서는 수도수 중에서 Mg합금유전양극에 의한 연강재 온수보일러의 음극방식특성을 연구한 결과 다음과 같은 결론을 얻었다. 1) 온수보일러 관체의 개로전위에서나 전위가 높은 구간에서 모재의 부식전류밀도가 용접부위의 부식전류밀도보다 더 적게 배류된다. 2) 주조된 표면 그대로의 Mg합금 유전양극의 전류밀도는 주조된 표면을 연마한 상태의 Mg합금 유전양극의 전류밀도보다 더 많이 배류된다. 3) Mg합금 유전양극으로부터 거리가 멀어질수록 연강재 온수보일러의 음극방식전위는 높게 나타나고, 음극방식시간이 경과하면서 방식전위는 높게 나타나다가 6-10일 이후부터 방식전위는 안정되고 있다.

바다모래에 의해 뒷채움된 지하연료저장탱크용 연강재의 부식전류밀도, 개로전위, 전식거동 및 연간부식률에 관하여 연구한 결과 다음과 같은 결론을 얻었다. 1) 습바다모래 중에서 비저항이 감소할수록 개로전위는 비전위화되고, 부식전류밀도는 높게 배류된다. 2) 습바다모래의 비저항이 감소할수록 인가전위 부가에 의한 부식전류밀도는 자연전위에서의 부식전류밀도보다 급격히 증가한다. 3) 습바다모래 중에서 비저항이 감소할수록 연간부식률은 선형적으로 증가함으로 지하연료저장탱크에 바다모래로 뒷채움하는 경우 습기가 유입하면 지하연료저장탱크의 부식성은 민감할 것으로 판단된다.

Cavitation can occur in pipes when liquid is moving at high velocity, especially at pittings where the smooth bore of the pipe is interrupted. The effect is usually to produce pitting on the downstream side of the turbulence. However, stress corrosion cracking behavior under cavitation erosion-corrosion was neatly unknown. In this study, therefore, some were investigated of stress corrosion cracking behavior, others were stress corrosion cracking behavior under cavitation erosion-corrosion of water injection. And datas obtained as the results of experiment were compared between the two. Mainresult obtained are as follows: 1) Stress corrosion cracking growth rate of heat affected zone under cavitation erosion-corrosion becomes most rapid, and stress intensity factor K1becomes most high. 2) Stress corrosion cracking growth mechanism by cavitation erosion-corrosion is judgement on the strength of the film rupture model and the tunnel model. 3) The range of potential as passivation of heat affected zone is less noble than that of base metal, and that value is smaller. 4) Corrosion potential under cavitation erosion-corrosion in loaded stress is less noble than that of stress corrosion, and corrosion current density is higher.

The effect of fluid flow on corrosion and erosion-corrosion of metal is a well-recognized phenomenon in pipelines and machinery equipment, and so on. Not only are fluid hydrodynamics important, but also the corrosiveness of the process or production stream affects the corrosion system. Recent research demonstrates that it is possible to erosion-corrosion(E/C) phenomena in terms of hydrodynamics, electrochemical corrosion kinetics and film growth/removal phenomena. Stress corrosion cracking behavior under cavitation erosion-corrosion of mild steel(SS41) was investigated of base metal and weldment under loaded stress. Main result obtained are as follows : 1) The cavitation erosion sensitivity of base metal affected weight loss is more susceptive than heat affected zone, 2) The corrosion sensitivity affected weight loss of welding heat cycle is less susceptive on stress corrosion under cavitation erosion-corrosion than stress corrosion.

본 연구에서는 오스테나이트계 스테인리스 강재(STS 304)에 대해 NaCl 환경 중에서 틈부식 특성을 연구하기 위해, 정전압 분극장치에 의해 분극특성시험을 실시하여 NaCl 용액의 농도에 따른 STS 304 강재의 틈부식에 의한 분극 거동에 대해 연구한 결과는 다음과 같은 결론을 얻었다. 1) 틈부위는 심하게 부식되고 틈의 인접한 외부 표면은 부동태화된다. 2) 오스테나이트계 스테인리스강재인 STS 304 강재는 분극거동에 있어서 부식 전위는 3.5% NaCl까지 농도가 증가할수록 귀전위화되다가 농도가 3.5%이상으로 증가할수록 오히려 비전위화된다. 3) 부식 전위하에 전류밀도는 NaCl 농도가 3.5%까지 증가할수록 더 많이 배류되다가 3.5% 이상으로 증가할수록 오히려 더 적게 배류된다.(이 논문의 결론(요약) 부분임)

In the case that erosion and corrosion occurs in machinery and structure at the same time, the synergy effect by erosion-corrosion affects fatal effect to durability of machinery and structure. Therefore, in machinery and structure which use corrosion liquid, the study of the synergy effect of erosion-corrosion which affects metal material is requested. In this paper. the flow corrosion experiment about the effect of temperature change and liquid velocity change in sea water was carried out to study the characteristics of erosion-corrosion for tube material Cu heat exchanger The main results obtained are as follows. (1) Damage appearance of tube outside by erosion-corrosion becomes dull because electrode potentials of Cu tube is higher than electrode potential of STPG38 shell. (2) In the cooling system by sea water, the weight loss rate of Cu at tube outside liquid temperature of 70℃ is higher than that of temperature of 20℃. (3) In cooling system by sea water, the weight loss rate of Cu at liquid velocity of 5.1m/s is higher than that of velocity of 1.47m/s. But as the testing time passed, the weight loss rate of Cu at velocity of 5.1m/s is almost steady and becomes dull at velocity of 1.47m/s.

Recently, with the rapid development in the industries such as mechanical plants, automobiles, ships and marine structures, it is enlarged by the use of the SS 41 steel. This mechanical plants and marine structures are exposed m corrosion because of Cl-under marine environments. To protect their accidents, mainly applied anti-corrosion epoxy coating and various protective its structures. In this study, corrosion control characteristics on the epoxy coating were investigated by the galvanic corrosion of impressed voltage tester under marine environments The main results obtained are as follows; 1. Corrosion current density of amine-epoxy coating becomes more increased than that of other epoxy coating and the time area rate of pin hole and pit until 5% becomes most rapid. 2. The potential of SUS 304 stainless steel(cathode) for Al-epoxy coating is nearly zero potential. 3. Corrosion current density of Amine-epoxy by shot blast becomes more decreased than that of not shot blast and cathodic potential becomes more noble. 4. As distance of anode and cathode is more decreased, corrosion current density of epoxy coating is more increased and cathodic potential becomes less noble.

Recently, with rapid increase of gas demand, there occurs much interest their security of safety in the gas storage tanks and pressure vessels etc. In order to solve the problems, the occurrence of corrosion fatigue crack and the propagation behavior must be investigated. Especially the occurrence of corrosion fatigue crack and the propagation behavior in the part which has concentrated stress or defects, must be studied more carefully. In this paper, the high-tensile steel of SPV 50 which is much used for building the LPG storage tanks was tested by the use of a plane bending corrosion fatigue tester under the various marine environments and in the air. These experiments were done to investigate the corrosion fatigue crack propagation behavior, the variation of aspect ratio for part through crack and electro-chemical characteristics of the metal. The main results obtained are as follows ; 1. Comparing the same surface crack length with the crack depth, the crack depth toward the thickness of specimen in air propagated faster than that in corrosion environment. 2. The aspect variation of the half elliptical crack can be estimated as following equation; b/a=i-jb/t where a : surface crack length, b : crack depth, t : specimen thickness, i,j : experimental constants but the slope j is decreased as specific resistance decreases. 3. As the specific resistance of corrosion environment decrease or the corrosion fatigue crack propagates, the corrosion potential become less noble.

The component materials threatened by cavitation include ship propellers as well as turbine runners, pump impellers, pipe lines and radiators. Today it is known that cavitation damage takes place on many other components including on the coding water side of the cylinder liners of diesel engines. Cavitation erosion - corrosion implies damage to materials due to the shock pressure or shock wave that results when bubbles form and collapse at a metal surface within a liquid. To suppress cavitation erosion as well as cavitation erosion - corrosion to hydraulic equipment, innovations such as the improvement in the geometric design of the equipment or the selection of suitably resistant construction materials are necessary. In this study, we investigated that the cavitation erosion - corrosion damage under vibratory cavitation can be reduced by adding of side now velocity to the cavitation bubble group in order to eliminate bubbles formed in sea water environment.

Recently with the rapid development in the industries such as an iron mill and chemical plants, these are enlarged by the use of the piping. This piping was encountered the stress corrosion cracking(SCC) because of stress by water pressure and residual stress of welding etc. under industrial water. In this paper, the behaviour of stress corrosion cracking on the weld zone of steel pipe piping water(SPPW) were investigated according to pre-heat before welding in natural seawater(specific resistance : 25Ω-cm). The main results obtained are as follows :1) The stress corrosion cracking for SPPW and SB 41 is most ready to propagate in heat affected zone of weldment. 2) The SCC sensitivity of SPPW on weldment is more susceptible than that of SB 41. 3) The stress corrosion cracking growth of heat affected zone is delayed by the preheat and dry of base metal and electrode before welding.

Cavitation erosion-corrosion implies damage to materials due to the shock pressure or shock wave that results when bubbles form and collapse at a metal surface within a liquid. If the liquids corrosive to the material, a condition typically encountered in industry, the component materials may suffer serious damage by a combination of mechanical and electrochemical attack. To suppress cavitation erosion as well as cavitation erosion-corrosion to hydraulic equipments, innovations such as the improvement in the geometric design of the equipment or the selection of suitably resistant construction materials are necessary. This study was tested by using the piezoelectric vibrator with 20kHz, 24μm for cavitation generation. And also, the vibratory cavitation erosion-corrosion tests on commercial mild steel SS41were carried out. We carefully observed the erosion pattern and surface photography. The geometrical mechanism of pit growth, which is to be likely these processing; shallow typelongrightarrowundercut typelongrightarrowwide shallow type.

To improve the corrosion resistance of stainless steel and Fe, the adherence between fIlm and substarte and the corrosion resistance to ceramic fIlm (TiO2 and ZrO2), coated by RF magnetron sputtering, were studied. The adherence index (X) was determined by the measure of micro - hardness test. Also, the corrosion resistance on oxide coatings was studied using electrochemical measurement. The main results obtained are as the following: 1) In the micro - hardness test, with 1J.UI1 thickness fIlm, it has only one the value of X. Above 2J.UI1 thickness fIlm, however, get another value ofX as the cracks in fIlm. 2) The adhensivity of titania (TiO2) coated fIlm is superior to that of zirconia (ZrO2) coated fIlm. 3) All oxide fIlm used adhere well on the mild materials such as pure steel than high intensity materials like stainless steel. 4) The corrosion resistance of zirconia coated materials was improved compared to titania coated materials.

To ceramic mm, SiO2 and Al2O3, coated on pure Fe and stainless steel(SUS41O) by RF magnetron sputtering, the adherence between mm and substarte was studied. The adherence index (χ) was determined by the measure of micro hardness test. Also, the corrosion resistance on oxide coatings was studied using electrochemical measurement. The main results obtained are as the following: 1) In the micro-hardness test, with 1μm thickness mm, it has only one the value of χ. Above 2μthickness fIlm, however, get another value of χas the cracks in fIlm. 2) The oxide fIlm adhere well on the mild materials such as pure steel than high intensity materials like stainless. 3) Alumina(Al2O3) coated materials have better corrosion resistance than silica(SiO2)coated materialsterials

각종 환경 조건에서 진동 캐비테이션 침식-부식 시험 장치에 의해 연강(SS41)의 캐비테이션 침식-부식 손상 거동에 관한 연구를 한 결과 다음과 같은 결론을 얻었다. 1) 해수 중에서 캐비테이션 침식-부식 손상 거동은 중앙부와 테두리 부에서 거의 비슷한 정도로 발생하여 성장되지만, 증류수 중에서는 테두리부에서 손상이 먼저 발생한 다음 중앙부에도 손상이 점차 일어난다. 2) 비저항이 낮은 수도수 중의 캐비테이션 침식-부식 손상은 초기에는 비저항이 높은 증류수중에서의 것보다 증가하지만 시간이 경과하면서 CaCO 하(3)의 피막 형성에 의해 둔화된다. 3) 케비테이션 침식-부식 손상 특성은 잠복기, 증가기, 감소기 및 안정기의 4단계로 구분된다.

Recently. with the rapid development in large sea water systems. there occurs much interest in the study of erosion-corrosion. In this study. the mild steel(SB41) was tested by using of a erosion-corrosion test apparatus with fountain-jet and was investigated under the environments of liquid, air-liquid 2 phase flow and solid particle-liquid 2 phase flow. Main results obtained are as follows : 1. The weight loss by corrosion-erosion in air-liquid 2 phase flow are more increased than that in only liquid solution. 2. Effect of air-liquid 2 phase flow on corrosion-erosion sensitivity becomes more sensitive in natural seawater than that in distilled water. 3. The corrosion potential by corrosion-erosion in air-liquid and solid particle-liquid 2 phase flow becomes noble than that of only liquid solution.

The corrosion rate, behavior of corrosion fatigue and characteristic of cathodic protection for SB41 were investigated by corrosion and corrosion control tests in seawater at laboratory and coast. The main result obtained are as the following; 1) The corrosion rate of base metal (BM) is about 28-37 mg/dm super(2) day in seawater of coast. 2) The correlation between the stress intensity factor range δK and crack propagation rate da/dN for weldment follows paris' rule in seawater : da/dN=C(δK) super(m) where m is the slope of the correlation, and is 2.02 for BM and 1.75 for heat affected zone (HAZ) respectively. 3) The corrosion sensitivity of HAZ is more sensitive than that of BM under the low region of δK. 4) With increase of bared surace area of cathode, cathodic protection potential is increased sharply.