• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2006.11a
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• pp.230-232
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• 2006

Failure behaviors of thin cylinder with corrosion are very important for the integrity of boiler and pressure vessel system. In this study, FEM with internal pressure are conducted on 1000 mm diameter (length 3000 mm and thickness, 5.9 mm) SS400 carbon steel. Failure behaviors of locally wall thinned cylinders were calculated by elasto-plastic analysis using finite element method. The elasto-plastic analysis was performed by FE code ANSYS. We simulated various types of local wall thinning that can be occurred at cylinder surface due to corrosion. Locally wall thinned shapes were machined to be different in size along the circumferential or axial direction of straight cylinder. In case of local wall thinned length 30 mm, internal pressure, when the crack initiation and the plastic collapse occur, didn't decrease dramatically even though local wall thinned depth was deep. In 400 mm, the more local wall thinned depth is deep, the more internal pressure decreased dramatically. In degraded materials, crack is easily initiation but plastic collapse was difficult.

• Corrosion Science and Technology
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• v.3 no.1
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• pp.34-38
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• 2004

The corrosion of reinforcement is a very important factor on the serviceability and safety of reinforced concrete structures. The corrosion rate influences directly the cover failure time of reinforced concrete structures because the corrosion rate is used to estimate the amount of corrosion and thus expansive pressure due to corrosion. In this study, several series of experiments are performed considering the chloride concentration in artificial pore solution. The potentials are measured according to the applied current density and then corrosion current densities are obtained from the Tafel plot for various chloride concentrations. The measured corrosion rates show good correlation with those of other researchers.

• Corrosion Science and Technology
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• v.16 no.3
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• pp.100-108
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• 2017

In this investigation corrosion behavior of newly developed high-pressure die cast Al-Ni (N15) and Al-Ni-Ca (NX1503) alloys was studied in 3.5% NaCl solution. The electrochemical corrosion behavior was evaluated using open circuit potential (OCP) measurement, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. Potentiodynamic polarization results validated that NX1503 alloy exhibited lower corrosion current density ($i_{corr}$) value ($5.969{\mu}A/cm^2$) compared to N15 ($7.387{\mu}A/cm^2$). EIS-Bode plots revealed a higher impedance (${\mid}Z{\mid}$) value and maximum phase angle value for NX1503 than N15 alloy. Equivalent circuit curve fitting analysis revealed that surface layer ($R_1$) and charge transfer resistance ($R_{ct}$) values of NX1503 alloy was higher compared to N15 alloy. Immersion corrosion studies were also conducted for alloys using fishing line specimen arrangement to simultaneously measure corrosion rates from weight loss ($P_W$) and hydrogen volume ($P_H$) after 72 hours and NX1503 alloy had lower corrosion rate compared to N15 alloy. The addition of Ca to N15 alloy significantly reduced the Al3Ni intermetallic phase and further grain refinement may be attributed for reduction in the corrosion rate.

• Corrosion Science and Technology
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• v.7 no.2
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• pp.85-91
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• 2008

By operation in aqueous environment at high temperature and pressure, the structural materials from Primary Heat Transport System (PHTS) cover with protective oxide films, which maintain the corrosion rate in admissible limits. A lot of potential factors exist, which conduct to degradation of the protective films and consequently to intensification of the corrosion processes. The existing experience of different nuclear reactors shows that the water chemistry has an important role in integrity maintaining of the protective oxide films. To investigate the influence of water chemistry (pH, O2 dissolved, $Cl^-$, $F^-$) on corrosion of some structural materials (carbon and martensitic steel, Zr and Ni alloys) and to establish the maximum permissible values, corrosion experiments by static autoclaving and electrochemical methods were performed. The experimental results allowed us to establish the contribution of the water chemistry in initiation and evolution of some accelerated corrosion processes.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.221-228
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• 2003

The stress corrosion index of Kumamoto andesite are evaluated by two types of testing method. One is the uniaxial compression test under various water vapor pressures, and the other is the double torsion (DT) test under a constant water vapor pressure. For the uniaxial compression tests, the uniaxial compressive strength increases linearly with decreasing water vapor pressure on the double logarithmic coordinates. As the results, the stress corrosion index obtained is estimated 44. On the other hand, in the DT test, the relaxation (RLX) test and the constant displacement rate (CDR) test were conducted. For the CDR test, as the displacement rate of loading point increases, the crack velocity increases. However, the fracture toughness is constant regardless of the change in displacement rate and the average fracture toughness is evaluated $2.07MN/m^{3/2}$. For the RLX test, the crack velocity-stress intensity factor curves are smooth and linear. The stress corrosion index estimated from the curves is 37. Comparing stress corrosion indexes in the uniaxial compression test and the DT test, there is no significant difference in these values, and they are considered to be in coincident each other regardless of testing methods. Therefore, it is concluded that stress corrosion is one of material constants of rock.

• Journal of the Korean Society of Safety
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• v.30 no.4
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• pp.168-173
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• 2015

A steam generator tubing is one of the main pressure boundary of the reactor coolant system in the nuclear power plants. Structural integrity refers to maintaining adequate margins against failure of the tubing. Burst pressure of a tube at tube support plate can be higher than that for a free-span tube because failure behaviors could be interfered from the tube support plate. Alternative repair criteria for out-diameter stress corrosion cracking indications in tubes to the drilled type tube support plate were developed, however, there are very limited information to the eggcrate type tube support plate. This paper discussed reinforcement effect of steam generator tube burst pressure with axial out-diameter stress corrosion cracking within an eggcrate type tube support plate. A series of tube burst tests were performed under the room temperature and it was found out that there is no significant but marginal effects.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.05a
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• pp.232-233
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• 2014

Recently, water treatment facility is usually eastablished in underground, and waterproofing and anti-corrosion materials for concrete structures applied water treatment tank is developing in various ways. However, as the limit of research focused on durability improvement of top coating material, it is insufficient to study on the adhesion strength between the concrete surface and primer. Therefore, there is to confirm the adhesion of between concrete surface and the three primers used as anti-corrosion waterproofing materials, and to investigate the properties of adhesion strength according to the condition such as wet codition and water pressure condition of the concrete surface in this study.

• Structural Engineering and Mechanics
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• v.16 no.6
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• pp.749-769
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• 2003

The structural deterioration of concrete structures due to reinforcement corrosion is a major worldwide problem. Service life of the age-degraded concrete structures is governed by the protective action provided by the cover concrete against the susceptibility of the reinforcement to the corrosive environment. The corrosion of steel would result in the various corrosion products, which depending on the level of the oxidation may have much greater volume than the original iron that gets consumed by the process of corrosion. This volume expansion would be responsible for exerting the expansive radial pressure at the steel-concrete interface resulting in the development of hoop tensile stresses in the surrounding cover concrete. Once the maximum hoop tensile stress exceeds the tensile strength of the concrete, cracking of cover concrete would take place. The cracking begins at the steel-concrete interface and propagates outwards and eventually resulting in the through cracking of the cover concrete. The cover cracking would indicate the loss of the service life for the corrosion-affected structures. In the present paper, analytical models have been developed considering the residual strength of the cracked concrete and the stiffness provided by the combination of the reinforcement and expansive corrosion products. The problem is modeled as a boundary value problem and the governing equations are expressed in terms of the radial displacement. The analytical solutions are presented considering a simple 2-zone model for the cover concrete viz. cracked or uncracked. A sensitivity analysis has also been carried out to show the influence of the various parameters of the proposed models. The time to cover cracking is found to be function of initial material properties of the cover concrete and reinforcement plus corrosion products combine, type of rust products, rate of corrosion and the residual strength of the cover concrete. The calculated cracking times are correlated against the published experimental and analytical reference data.

• Tribology and Lubricants
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• v.18 no.4
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• pp.299-304
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• 2002

This paper reports the studies on the wear-corrosion behavior of ductile cast iron in the acidic environment. In atmosphere and variety of pH solution, specific wear rate and wear-corrosion characteristics of GCD 60 with various sliding speed and distance were investigated. And electrochemical polarization test of GCD 60 was examined in the environment of various pH values. The main results are as following : As the contact pressure increases, the critical velocity of specific wear rate becomes transient at low sliding speed. As pH value becomes low, wear-corrosion loss increases in the aqueous solution. As the corrosion environment is acidified, corrosion potential of GCD 60 becomes noble and corrosion current density increases.

• Journal of the Korean institute of surface engineering
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• v.37 no.5
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• pp.296-300
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• 2004

The defects of partial denture frameworks are mainly shrinkage porosity, inclusions, micro-crack, particles from investment, and dendritic structure. In order to investigate a good casting condition of partial denture frameworks, the three casting alloys and casting methods were used and detected casting defects were analyzed by using electrochemical methods. Three casting alloys (63Co-27Cr-5.5Mo, 63Ni-16Cr, 63Co-30Cr-5Mo) were prepared for fabricating partial denture frameworks with various casting methods; centrifugal casting (Kerr, USA), high frequency induction casting (Jelenko Eagle, USA), vacuum pressure casting (Bego, Germany). The casting temperature was $1,380^{\circ}C$ (63Co-27Cr-5.5Mo and 63Ni-16Cr) and $1,420^{\circ}C$ (63Co-30Cr-5Mo). The casting morphologies were analyzed using FE-SEM and EDX. The corrosion test of the dendritic structure was performed through potentiodynamic method in 0.9% NaCl solutions at $36.5^{\circ}C$ and corrosion surface was observed using SEM. The defects of partial denture frameworks improved in the order of centrifugal casting, high frequency induction casting, and vacuum pressure casting method, especially, pore defects were found at part of clasp in the case of centrifugal casting method. The structure of casting showed dendritic structure for three casting alloys. In the 63Co-27Cr-5.5Mo and 63Co-30Cr-5Mo, $\alpha$-Co and $\varepsilon$-Co phases were identified at matrix and $${\gamma}$-Ni_2$Cr second phase were shown in 63Ni-16Cr. Also, the corrosion resistance of cast structure increased in the order of vacuum pressure casting, high frequency induction casting, and centrifugal casting method.