• Corrosion Science and Technology
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• 제16권4호
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• pp.201-208
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• 2017

A finite element analysis is proposed to study the effect of specimen dimensions on lateral diffusion of hydrogen during hydrogen permeation flux measurements. The error of measurement on thick specimens because of 1D diffusion approximation may be as much as 70%. A critical condition for accurate measurements is to designate the area of hydrogen monitoring/exit surface smaller than the area of hydrogen charging/entry surface. For thin to medium thickness specimens (ratio of thickness to specimen radius of 5:10 and below), the charging surface should be maximized and the monitoring surface should be minimized. In case of relatively thick specimens (ratio of thickness to specimen radius above of 5:10), use of a hydrogen-diffusion barrier on the specimen boundaries is recommended. It would completely eliminate lateral losses of hydrogen, but cannot eliminate the deviation towards 2D diffusion near the side edges. In such a case, the charging surface should be maximized and the monitoring surface should be as closer in dimension as the charging surface. A regression analysis was carried out and an analytical relationship between the maximum measurement error and the specimen dimensions is proposed.

• 한국구조물진단유지관리공학회 논문집
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• 제21권3호
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• pp.19-26
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• 2017

콘크리트는 다공성 건설재료이며, 매립된 철근의 부식은 내구성 및 안전성에 큰 영향을 미친다. 본 연구는 비파괴 검사인 반전위측정값과 생성된 부식량과의 상관성을 피복두께, 물-시멘트비를 고려하여 도출하는 것이다. 이를 위해, 3가지 수준의 물-시멘트비와 4가지 수준의 피복두께를 가진 시멘트 모르타르 시편이 제조되었으며, 3가지 수준의 촉진부식기간을 고려하여 부식량 및 반전위를 측정하였다. 습윤상태에서는 반전위가 크게 증가하였으며, 부식량과 촉진기간은 선형적인 관계를 가지고 있었다. 부식량이 증가할수록, 피복두께가 감소할수록, 물-시멘트비가 증가할수록 반전위는 증가하였다. 전체의 반전위 측정값을 부식량과 비교할 경우 0.67의 낮은 결정계수를 가지고 있었으나 부식량(촉진기간)을 고려하여 3가지 수준을 고려할 경우 0.90이상의 높은 결정계수를 가지고 있었다. 실내조건과 같이 온도가 일정하고 포화상태일 경우, 측정된 반전위는 부식량과 선형적인 상관성을 가지고 있었으며, 피복두께, 물-시멘트비, 철근직경, HCP의 측정범위를 알 수 있다면, 매립된 철근의 부식량을 예측할 수 있다고 판단된다.

• 한국해양공학회지
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• 제15권1호
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• pp.57-66
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• 2001

In order to measure steel corrosion in mortar by a transient electro-magnetic (TEM) Method, the development of the sensors have been studied. The sensors were made of enamelled wire with diameter of 0.25mm and Acril. The sensor configuration was used as a coincident loop type. The secondary electro motive force(EMF) was measured with SIROTEM III. The accelerator was equipped with the SIROTEM III. The accelerator permits the transmitter to turn off approximately 10~15 times faster than normal. The high resolution time series used for very shallow or high resistivity investigation was selected. The steels were embedded in mortar which were made from sand : cement : water ratio of 2 : 1: 0.5. The mortar specimen was 50cm long, 20cm wide and 10cm thick. To investigate steel corrosion in mortar, the sensors used were with 2$\times$2$cm^2$(3, 6, 9$\Omega$), 3$\times$3$cm^2$(3, 6, 9$\Omega$) and 6$\times$6$cm^2$(3, 6, 9$\Omega$). The obtained result obtained showed that the sensor 8(6$\times$6$cm^2$, 6$\Omega$) was the proper sensor for the measurement of steel corrosion in mortar.

• 한국가스학회지
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• 제5권3호
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• pp.45-50
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• 2001

개방형 기화기는 해수를 이용하여 열교환을 수행함으로써 액체상태의 액화천연가스를 천연가스로 기화시키는 역할을 한다 86년부터 가동된 U-tyre 기화기는 천연가스생산과 관련된 중요설비 중 하나로서, 기화기 튜브는 항상 해수내에서 운전되고 있으며 기화기 튜브와 파이프사이의 용접부에서 해수로 인한 부식이 진행되고 있다. 본 연구에서는 용접부에서의 국부적인 부식원인을 찾기 위해 이종금속부식의 가능성을 평가해 보았으며 또한 비파괴적인 방법을 이용하여 부식피트의 깊이를 측정하고 유한요소를 통한 안전성 평가에 목적을 두었다. 이종금속부식가능성에 대하여 용접부 각 부위별로 시료를 채취하여 3.5$\%$(wt.) NaCl 용액내에서 모재와 용접부위의 부식전위를 측정하였으며, 비파괴 검사를 통한 잔류두께측정은 tangential radio-graphy 시험이 가장 신뢰성 있는 기법임이 확인되었다. 미세한 부식피트가 발생된 경우에는 표면형상 복제기법을 적용하였다. 비파괴적인 방법을 이용하여 산출된 부식피트의 깊이와 형상을 근거로 2차원 유한요소 해석을 수행함으로써 내압으로 인한 기화기 튜브의 안전성을 평가할 수 있었다.

• 방사성폐기물학회지
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• 제8권3호
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• pp.247-260
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• 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.

• Corrosion Science and Technology
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• 제16권6호
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• pp.273-277
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• 2017

Atmospheric corrosion is clearly the most noticeable of all corrosion processes. A tremendous amount of economic losses are caused by atmospheric corrosion. Thus, it is imperative to know the level of atmosphere's aggressiveness or in other words "corrosivity", before designing or planning any corrosion prevention strategy. In Singapore, corrosivity values were not recorded earlier though the process of measurement and recording was prevalent in other countries. With an aim of filling this gap, three test sites were setup at three locations in Singapore to represent marine, industrial and urban atmospheres or their mixtures. Subsequently, corrosivity readings were measured and recorded according to ISO 9223:2012 for the first time in Singapore. Salient atmospheric constituents or parameters like time of wetness (TOW), $Cl^-$, $SO_2$, $NO_2$, $O_3$, and $HNO_3$ were measured at all sites over a period of time to categorize corrosivity of particular atmosphere. The effect of the atmosphere on corrosion of steel, Cu, Al, and Zn has also been investigated and quantified. "Estimated" and "determined" corrosivities were quantified and compared according to ISO 9223 standard. The study data along with final corrosivity measurements will be presented and discussed in the present work.

• Corrosion Science and Technology
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• 제19권3호
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• pp.156-162
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• 2020

The objective of this study was to investigate delayed oxygen evolution and localized corrosion resistance of titanium alloys by performing potentiodynamic polarization, potentiostatic polarization, and Mott-Schottky measurements. Delayed oxygen evolution was compared among titanium alloys, 316 stainless steel, and platinum. Difference in delayed oxygen evolution between titanium alloys and other metals was attributed to specific surface characteristic of each metal. Delayed oxygen evolution of titanium alloys resulted from the predominant process of ionic conduction over electronic conduction. The effect of oxygen evolution on localized corrosion of titanium alloys was investigated using electrochemical critical localized corrosion temperature (E-CLCT) technique. Mott-Schottky measurement was performed to clarify the difference in film properties between titanium alloys and stainless steels. Titanium alloys were found to have much lower donor density than stainless steels by 1/28. These results indicate that delayed oxygen evolution has little influence on the concreteness of passive film and the resistance to localized corrosion of titanium alloys.

• Structural Engineering and Mechanics
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• 제56권2호
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• pp.257-273
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• 2015

Numerical value of correlation between effective parameters in the strength of a structure is as important as its stochastic properties in determining the safety of the structure. In this article investigation is made about the variation of coefficient of correlation between effective parameters in corrosion initiation time of reinforcement and the time of concrete cover cracking in reinforced concrete (RC) structures. Presence of many parameters and also error in measurement of these parameters results in uncertainty in determination of corrosion initiation and the time to crack initiation. In this paper, assuming diffusion process as chloride ingress mechanism in RC structures and considering random properties of effective parameters in this model, correlation between input parameters and predicted time to corrosion is calculated using the Monte Carlo (MC) random sampling. Results show the linear correlation between corrosion initiation time and effective input parameters increases with increasing uncertainty in the input parameters. Diffusion coefficient, concrete cover, surface chloride concentration and threshold chloride concentration have the highest correlation coefficient respectively. Also the uncertainty in the concrete cover has the greatest impact on the coefficient of correlation of corrosion initiation time and the time of crack initiation due to the corrosion phenomenon.

• Corrosion Science and Technology
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• 제12권5호
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• pp.220-226
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• 2013

The uncertainty in statistical noise resistance measurement was evaluated for a type 316 stainless steel in NaCl solutions at room temperature. Sensitivity coefficients were determined for measurands or variables such as NaCl concentration, pH, solution temperature, surface roughness, inert gas flow rate and bias potential amplitude. The coefficients were larger for the variables such as NaCl concentration, pH, inert gas flow rate and solution temperature, and they were the major factors increasing the combined standard uncertainty of noise resistance. However, the contribution to the uncertainty in noise resistance measurement from the above variables was remarkably low compared to that from repeated measurements of noise resistance, and thus, it is difficult to lower the uncertainty in noise resistance measurement significantly by lowering the uncertainties related with NaCl concentration, pH, inert gas flow rate and solution temperature. In addition, the uncertainty in noise resistance measurement was high amounting to 17.3 % of the mean, indicating that the reliability in measurement of noise resistance is low.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• 제2권2호
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• pp.91-98
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• 1998

In this study, we carried out the experiments for measuring the variations of corrosion potential and current density for polarization curves with polyvinylchloride. The results exhibited especially the influence affecting the corrosion potential and various conditions (temperature, day, pH, bacteria, and added salt). The second anodic current density peak and the minimum passive current density are designated $I_P/I_0,$ respectively. The value of $I_P/I_O$ is used as a measurement for the extent of degradation of the polyvinylchloride. The potentiodpnamics parameters of the corrosion were obtained using Tafel equation.