• 해양환경안전학회지
• /
• 제10권1호
• /
• pp.51-54
• /
• 2004

최근 양어 양식장은 증가하고 있으며 이러한 곳에 사용할 가열장치는 경울 수온 조절을 위해 사용된다. 해수 가열장치는 부식성이 높고 압력이 높은 곳에 사용하기 위하여 고강도와 내식성이 요구된다. 만약 저강도와 저내식성을 갖게 되면 결국 누설 또는 파손되어 해수오염을 일으킬 수 있다. 대부분의 부식은 정체된 액과 틈이 형성된 부위에서 부식의 발생이 일어난다. 이 연구에서는 430 스테인레스재를 크기 $15{\times}20{\times}3mmt$에 대하여 1N H2SO4 + 0.05N NaCl용액을 사용하여 틈부식을 시험하였다. 틈의 크기는 $0.24{\times}3{\times}15mmL$로 하였으며 외부에 300mV전위를 인가하였다. 실험 결과 틈 부식 유기 시간은 750초로 나타나고, 틈 전위 강화는 -320에서 -399mV로 나타나 부식의 주 원인이 전위강화 기구에 의해 발생하였다.

• Journal of Advanced Marine Engineering and Technology
• /
• 제27권7호
• /
• pp.872-878
• /
• 2003

As the results of recent industrial development, many industrial plants and marine structures are exposed to severe corrosion environment than before. Especially, under the wet environment, crevice corrosion damage problems necessarily occur and encourage many interests to prevent them. In this study, the electrochemical polarization test was carried out to study characteristics of crevice corrosion for AISI 304 stainless steel in various solution temperatures. The results are as follows ; 1) as the solution temperature increased in IN $\textrm{H}_2\textrm{SO}_4$, the passive current density and critical current density were increased, whereas corrosion potential and break down potential were nearly constant, 2) as the solution temperature increased. the induced time for initiation of crevice corrosion was shortened. 3) The potential range in the crevice was -220mV/SCE to -380mV/SCE according to the distance from the crevice opening, which is lower than that of external surface of -200mV/SCE.

• 한국표면공학회지
• /
• 제36권4호
• /
• pp.324-328
• /
• 2003

This study was made on the crevice corrosion behavior of chromium plating in fresh water. Under the various crevice, the electrochemical polarization test of chromium plating was carried out. Results are discussed In terms of corrosion potential, polarization resistance, corrosion current density and cathodic control of chromium plating.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 춘계학술대회논문집D
• /
• pp.884-889
• /
• 2001

Combustion chamber crevices in SI engines are identified as the largest contributor to the engine-out hydrocarbon emissions. The largest of crevice region is the piston ring pack crevice. To predict and understand the oxidation process of piston crevice hydrocarbons, a 3-dimensional numerical simulation method was developed. A engine shaped computational mesh with moving grid for piston and valve motions was constructed. And a 4-step oxidation model involving 7 species was used and the 16 coefficients in the rate expressions were optimized based on the results from a detailed chemical kinetic mechanism for the oxidation condition of engine combustion chamber. Propane was used as a fuel in order to eliminate oil layer absorption and liquid fuel effect.

• Bulletin of the Korean Chemical Society
• /
• 제26권11호
• /
• pp.1783-1789
• /
• 2005

Modeling of a steam generator crevice in a nuclear power system needs to take into account both thermalhydraulic and chemical phenomena. As a first step towards developing a reliable model, a chemical equilibrium model was developed to predict chemical speciation in a magnetite-packed crevice by adopting the “tableau” method. The model was benchmarked with the available experimental data and the maximum deviation did not exceed two orders of magnitude. The developed model was applied to predict the chemical speciation in a magnetite-packed crevice. It was predicted that caustic environment was developed by the concentration of NaOH and the dissolution of magnetite. The model indicated that the dominant aqueous species of iron in the caustic crevice was $FeO_2\;^-$. The increase of electrochemical corrosion potential observed in the experiment was rationalized by the decrease of dissolved hydrogen concentration due to a boiling process. It was predicted that under the deaerated condition magnetite was oxidized to hematite.

• Corrosion Science and Technology
• /
• 제14권6호
• /
• pp.288-295
• /
• 2015

The present work addresses crevice and galvanic corrosion processes occurring at the cylinder head gasket/cylinder head interface and cylinder head gasket/cylinder liner interface of four-stroke medium-speed diesel engines for marine applications. The contact between these systems and the marine environment can promote formation of demanding corrosion conditions, therefore influencing the lifetime of the engine components. The electrochemical behavior of various metals and alloys used as head gasket materials (both ferrous alloys and copper alloys) was investigated. The efficacy of corrosion inhibitors was determined by comparing electrochemical behavior with and without inhibitors. In particular, crevice corrosion has been investigated by electrochemical tests using an experimental set-up developed starting from the requirements of the ASTM G-192-08, with adaptation of the test to the conditions peculiar to this application. In addition to the crevice corrosion resistance, the possible problems of galvanic coupling, as well as corrosive reactivity, were evaluated using electrochemical tests, such as potentiodynamic measurements. It was possible to quantify, in several cases, the corrosion resistance of the various coupled materials, and in particular the resistance to crevice corrosion, providing a basis for the selection of materials for this specific application.

• Corrosion Science and Technology
• /
• 제3권6호
• /
• pp.227-232
• /
• 2004

The carboxylates as a corrosion inhibitor has been studied by many researchers because of its environmental safety and low depletion rate. However, conventional test methods of inhibitor such as weight loss measurements, linear polarization resistance and corrosion potential monitoring etc., evaluate uniform corrosion of metals. These methods are unable to evaluate crevice-related corrosions, which are encountered in most of heat exchanging facilities. In order to choose the optimum corrosion inhibitor, the appropriate test methods are required to evaluate their performances in service environment. From this point of view, polarization technique was used to evaluate the characteristics of sodium heptanoate on corrosion behavior for carbon steel. Especially a thin film crevice sensor technique were applied to simulate the crevice corrosion in this study. From these experiments, we found that oxygen as an oxidizing agent was required to obtain stable passive film on the metal. Presence of oxygen, however, accelerated crevice corrosion. Potential shift by oxygen depletion and weakened inhibitive film inside the crevice were responsible for such accelerated feature. It is shown that film for corrosion inhibition is a mixture of sodium heptanoate and iron (II) heptanoate as reaction product of iron surface and sodium heptanoate. The iron (II) heptanoate which has been synthesized by reaction of heptanoic acid and ferrous chloride in methanol solution forms bidentate complex.

• 방사성폐기물학회지
• /
• 제8권3호
• /
• pp.247-260
• /
• 2010

한국원자력연구원 처분시스템개발과제에서는 처분용기 재료로 개발중인 저온분사코팅 구리에 대한 틈새부식(Crevice Corrosion) 시험을 실시하였다. 본 시험을 통하여 틈새에서의 부식의 발생여부와 발생되는 시점인 재부동태 전위(Repassivation Potential)를 측정하고자 하였다. 틈새부식 시험 방법으로 (1) ASTM G61-86 : Cyclic Potentiodynamic Polarization Measurements, (2) SWRI의 Potentiodynamic Polarization plus intermediate Potentiostatic Hold method, 그리고 (3) ASTM G192-08 (THE method) :Potentiodynamic- Galvanostatic -Potentiostatic Method 등의 3가지 방법을 소개하였다. 실제 저온분사 코팅구리의 부식시험에서는 ASTM G61-86에 따라서 틈새부식장치를 설치하고, 저온분사코팅구리가 KURT 지하수를 모사한 용액에서 어떻게 틈새부식이 일어나는지 살펴보았다. 전기적 부식조건으로는 Cyclic Polarization Test, Potentiostatic Polarization Test, 및 Electrochemical Impedance Spectroscopy 등을 사용하였다. 그리고 부식이 된 시편에 대해 Profilometer Measurement를 통해 실제 부식표면의 높낮이를 조사하여 틈새부식 유무를 관찰하였다. 최종적인 결론에서는 저온분사코팅구리는 틈새부식을 나타나지 않는다는 것을 확인할 수 있었다. 그리고 시험에 사용된 세종류의 구리에 대한 상대적인 부식평가를 한 결과, 부식전위를 나타내는 개방회로(Open Cell)에서의 전위는 구리의 제조방식과 상관없이 구리의 순도가 높을수록 높은 값을 보이는 것을 확인할 수 있었다. 결론적으로 KURT 심층지하수 조건에서는 구리는 틈새부식이 발생되지 않는다고 결론지었다.

• 대한기계학회논문집B
• /
• 제20권4호
• /
• pp.1481-1490
• /
• 1996

This study is intend to improve flow pattern within evaporator, which is low quality and low mass flux, by installing narrow horizontal annular crevice so that enhance heat transfer coefficient. The motive, which made to study heat transfer enhancement by using narrow annular crevice, came from capillary phenomena and pumping force of generating vapor on refrigerant boiling. Tests were run about 5 models of turbulence promoter with CFC-12, in the range of evaporating temperature (15.deg. C), mass flux (50 to 100 kg/m$\^$2/s), heat flux (3.4 to 6.7 kW/m$\^$2/), quality (0.1 to O.5). It is observed that flow pattern within evaporator is changed closely to semi-annular flow or annular flow, of which refrigerant liquid is reached to the upper side of tube by using narrow annular crevice. When the narrow annular crevice is installed in the evaporator tube, local heat transfer coefficient is generally more improved than that of smooth tube. That fact is according to observed result of flow pattern. It is learned that narrow annular crevice has more efficiency at a low mass flux. At the TP-5, enhancement of heat transfer rate is about 170% compare to that of smooth tube on a low mass flux (50 kg/m$\^$2/s), and it is about 134% on a high mass flux (100 kg/M$\^$2/S), so that we know that it is on a very high condition.

• Nuclear Engineering and Technology
• /
• 제52권11호
• /
• pp.2552-2564
• /
• 2020

The crevice stress corrosion cracking (SCC) susceptibility of austenitic stainless steels was evaluated in simulated pressurized water reactor (PWR) environments. To simulate the abnormal condition in temporary clamping devices on leaking small bore pipes, crevice bent beam (CBB) tests were performed in the oxygenated as well as hydrogenated conditions. No SCC cracks were found for SS316 in both conditions. SS304 also showed good resistance in the hydrogenated condition. However, all SS304 specimens showed SCC cracks in the oxygenated condition, indicating poor crevice SCC resistance. It was found that residual ferrites were selectively dissolved because of the galvanic corrosion coupled with the neigh-bouring austenite phase, resulting in SCC initiation in SS304. Crack morphologies were mostly transgranular assisted by the damaged δ-ferrite and deformation-induced slip bands.