• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.11
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• pp.1009-1014
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• 2007

A detailed study on aged sleeves for old transmission lines was carried out to clarify the deterioration of sleeves and the condition of installation. A lot of removed aged sleeves from transmission lines were investigated. Many biased installed cases and corrosion of steel sleeve part were found. These defects can cause a serious accident such as blackout during operating. The temperature distribution within sleeve of ACSR conductor was precisely measured and examined, conducted as part of series of studies on large currents in transmission lines. According to measurements of the conductor temperature near a joint(sleeve and clamp), the electrical resistance of joint is lower than that of the same length conductor. The detailed results were presented in the text.

• Nuclear Engineering and Technology
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• v.53 no.8
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• pp.2591-2599
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• 2021

The effect of thermal aging at 475 ℃ and 750 ℃ of Z3CN20.09M cast duplex stainless steel (CDSS) on microstructure, mechanical and intergranular corrosion properties were investigated by transmission electron microscope (TEM), nano indenter, scanning electron microscope (SEM) and corrosion fatigue test system. The result indicated that the spinodal decomposition and G precipitated were occurred after aged at 475 ℃, as well as sigma precipitated at 750 ℃. The microstructure degeneration of ferrite was saturated after aged for 2000h and 200 h at 475 ℃ and 750 ℃ respectively. The mechanical properties, intergranular corrosion resistance and corrosion fatigue lives were continuing deteriorated with increasing the aging time at both temperatures. The difference of the degeneration mechanisms of Z3CN20.09M CDSS aged at 475 ℃ and 750 ℃ was analyzed.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.118-123
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• 2004

Cast austenitic stainless steel have been widely used for primary coolant piping in light water reactors. This material is subject to thermal embrittlement at reactor operating temperature. CF-8M and CF-8A cast austenitic stainless steel is used for several components, such as primary coolant piping, elbow, pump casing, and valve bodies in light water reactors. Thermal embrittlement results in spinodal decomposition of delta-ferrite leading to decreased fracture toughness. In this study, the specimens were prepared using an accelerated aging method. The measurement of ferrite content, Charpy impact test and J-R test were performed to verify the predicting equation for aged material properties. In case of above 25% ferrite content, predicted result of J-R curve might be non-conservative.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.104-105
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• 2008

According to previous report, aged sleeves of old transmission line showed several defaulted installation patterns, which is biased or corrosive-fractured of steel sleeve installed cases. The latter case occupied almost 25 percent of investigated aged sleeves. These defects can cause serious accidents such as rapid increasing of sag or falling out of overhead conductor from sleeves. This paper studies thermal properties and tension for ACSR conductor in case of fractured steel sleeve model. The detailed results were presented in the text.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.7
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• pp.1332-1339
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• 2002

This research was undertaken to clarify effects of thermal aging on electrochemical and mechanical properties of superaustenitic stainless steel and to detect the material degradation nondestructively. The steel was artificially aged at $300{\sim}650^{\circ}C$ for $240{\sim}10,000h$ and the mechanical properties were investigated at $-196{\sim}650^{\circ}C$ using small punch(SP) test. Also, the change in electrochemical properties caused by effects of thermal aging on superaustenitic stainless steel was investigated using electrochemical anodic polarization test in a KOH electrolyte. Carbides and ${\eta}-phase(Fe_2Mo)$ precipitated in the grain boundaries seem to deteriorate the mechanical properties by decreasing cohesive strength in the grain boundaries and to promote the current density observed in electrochemical polarization curves, The electrochemical and mechanical properties of superaustenitic stainless steel decreased significantly in the specimen aged at $650^{\circ}C$ corresponding to the sensitization temperature for conventional austenitic stainless steels.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.11
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• pp.2860-2870
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• 1994

When crack are detected in aged turbine rotors of power plants, information on fracture resistance of the aged material at operating temperature is needed for determination of critical loading condition and residual life of the turbine. In this study, fracture toughness (J$_lc$) and tearing modulus(T$_mat$) of virgin and thermally degraded 1Cr-1Mo-0.25V steel, which is one of the most widely used rotor steels, were measured at 538.deg. C according to ASTM E813 and ASTM E1152, respectively. Five kinds of specimen with different degradation levels were prepared by isothermal aging heat treatment at $630^{\circ}C.$ It was observed that J$_lc$ and T$_mat$ value decreased as the degradation level increased. Analysis of microstructures using a scanning electron microscope showed that the decrement of J$_lc$ is related to segregation of impurities at grain boundaries. It was also verified that the DC electric potential drop method is accurate and reliable for crack length monitoring at elevated temperature.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10b
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• pp.1031-1036
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• 2000

In this study, a numerical simulation that can effectively predict the strengthening effect of repaired aged RC structures is developed using the axial deformation link elements. In repaired structures, concrete and interface are modeled as quasi-brittle materials. An elastic-perfectly plastic constitutive relationship is introduced for reinforcing bars. Also, a linear-elastic relationship for repair materials such as FRP or CFS. Structural deterioration in terms of corrosion of steel rebar is considered. The interfacial property between steel and concrete which is reduced by corrosion of steel rebar is obtained by comparing numerical results with experimental results of pull out tests. Obtained values are used in repaired reinforced concrete structures under flexural loading conditions. To investigate strengthening effect of the structures repaired with carbon fiber sheet(CFS), repaired and unrepaired RC structures are analyzed numerically. From analysis, rip-off, debonding and rupture failure mechanisms of interface between substrate and CFS can be determined. Finally, strengthening effect according to the variation of interfacial material properties is investigated, and it is shown that interfacial material properties have influence on the mechanical behavior of repaired structure systems Therefore, the developed numerical method using axial deformation link elements can use for determining the strengthening effects and failure mechanism of repaired aged RC structure.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.143-148
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• 2001

This research was undertaken to clarify effects of thermal aging on electrochemical and mechanical properties of superaustenitic stainless steel. The steel was artificially aged at $300{\sim}650^{\circ}C$ for $240{\sim}10,000hrs$. and investigated at $-196{\sim}650^{\circ}C$ using small punch(SP) test. Also, the change in electrochemical properties caused by effects of thermal aging was investigated using electrochemical anodic polarization test in a KOH electrolyte. Carbides and ${\eta}-phase(Fe_2Mo)$ precipitated in the grain bounderies seem to deteriorate the mechanical properties by decreasing cohesive strength in the grain bounderies and promote the current density observed in electrochemical polarization curves. The electrochemical and mechanical properties of superaustenitic stainless steel was drastically decreased in the specimen aged at $650^{\circ}C$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.11
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• pp.1036-1041
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• 2008

According to previous report, aged sleeves of old transmission line showed several defaulted installation patterns, which was biased or corrosive-fractured of steel sleeve installed cases. These defects can cause serious accidents such as rapid increasing of sag or falling out of overhead conductor from sleeves. Consequently, the defects lead to the major power outage. Corrosion of steel sleeve is a typical defect by aging of sleeves. And it occupied almost 25 percent of investigated aged sleeves. This paper studied thermal properties and tension for ACSR conductor in case of fractured steel sleeve model by corrosion. The temperature distribution within overhead conductor has a specific gradient. Thermal properties of splice connectors(sleeve and clamp) showed normal behavior. However, mechanical properties were worse than normal sleeves. The detailed results were presented in the text.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.1
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• pp.56-65
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• 2022

The electrochemical corrosion properties of austenitic AISI 304 steel subjected to a long-term-aging heat treatment were investigated. AISI 304 steel was aged at 700 ℃ for up to 10,000 h. The variation in the microstructure of the aged specimens was observed by optical microscopy and scanning electron microscopy. Electrochemical polarization experiments were performed to obtain the corrosion current density (Icorr) and corrosion potential (Ecorr). Analyses indicated that the metastable intermetallic carbide M₂₃C₆ formed near the γ/γ grain boundary and coarsened with increasing aging time; meanwhile, the δ-ferrite decomposed into the σ phase and into M₂₃C₆ carbide. As the aging time increased, the current density increased, but the corrosion potential of the austenitic specimen remained high (at least 0.04 ㎛/cm²). Because intergranular carbide was absent, the austenitic annealed specimen exhibited the highest pitting resistance. Consequently, the corrosion resistance of austenitic AISI 304 steel decreased as the aging heat treatment time increased.