• KEPCO Journal on Electric Power and Energy
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• v.4 no.1
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• pp.25-31
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• 2018

A boiler system transforms water to pressured supercritical steam which drives the running of the turbine to rotate in the generator to produce electricity in power plants. Materials for building the tube system face challenges from high temperature creep damage, thermal fatigue/expansion, fireside and steam corrosion, etc. A database on the creep resistance strength and steam oxidation of the materials is important to the long-term reliable operation of the boiler system. Generally, the ferritic steels, i.e., grade 1, grade 2, grade 9, and X20, are extensively used as the superheater (SH) and reheater (RH) in supercritical (SC) and ultra supercritcal (USC) power plants. Currently, advanced austenitic steel, such as TP347H (FG), Super304H and HR3C, are beginning to replace the traditional ferritic steels as they allow an increase in steam temperature to meet the demands for increased plant efficiency. The purpose of this paper is to provide the state-of-the-art knowledge on boiler tube materials, including the strengthening, metallurgy, property/microstructural degradation, oxidation, and oxidation property improvement and then describe the modern microstructural characterization methods to assess and control the properties of these alloys. The paper covers the limited experience and experiment results with the alloys and presents important information on microstructural strengthening, degradation, and oxidation mechanisms.

• Structural Engineering and Mechanics
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• v.81 no.5
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• pp.565-574
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• 2022

The infrastructures such as offshore, bridges, power plant, oil and gas piping and aircraft operate in a harsh environment during their service life. Structural integrity of engineering components used in these industries is paramount for the reliability and economics of operation. Two regression models based on the concept of Gaussian process regression (GPR) and Minimax probability machine regression (MPMR) were developed to predict stress intensity factor range (𝚫K). Both GPR and MPMR are in the frame work of probability distribution. Models were developed by using the fatigue crack growth data in MATLAB by appropriately modifying the tools. Fatigue crack growth experiments were carried out on Eccentrically-loaded Single Edge notch Tension (ESE(T)) specimens made of API 5L X65 Grade steel in inert and corrosive environments (2.0% and 3.5% NaCl). The experiments were carried out under constant amplitude cyclic loading with a stress ratio of 0.1 and 5.0 Hz frequency (inert environment), 0.5 Hz frequency (corrosive environment). Crack growth rate (da/dN) and stress intensity factor range (𝚫K) values were evaluated at incremental values of loading cycle and crack length. About 70 to 75% of the data has been used for training and the remaining for validation of the models. It is observed that the predicted SIF range is in good agreement with the corresponding experimental observations. Further, the performance of the models was assessed with several statistical parameters, namely, Root Mean Square Error (RMSE), Mean Absolute Error (MAE), Coefficient of Efficiency (E), Root Mean Square Error to Observation's Standard Deviation Ratio (RSR), Normalized Mean Bias Error (NMBE), Performance Index (ρ) and Variance Account Factor (VAF).

• The Journal of the Korea Contents Association
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• v.10 no.9
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• pp.309-317
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• 2010

The stainless steel wire is extensively used for the orthodontic treatment. But, the stainless steel wire that has commonly superior corrosion resistance has caused hypersensitive reaction or allergy as side effects because of corrosion in the oral environment. For improving the problem of corrosion, we was evaluated the suitability of the duplex stainless steel(DSS) as orthodontic wire through this study. The DSS wire was evaluated the mechanical strength and bio-stability for suitability and bio-compatibility as orthodontic wire. In this work, the DSS and stainless steel(SS) as common use of medical grade were prepared for the tensile strength test. The DSS wire were treated by heat. and Temperature conditions of the heat treatment were $28^{\circ}C$, $500^{\circ}C$, $600^{\circ}C$, $700^{\circ}C$, $800^{\circ}C$, $900^{\circ}C$, respectively. And the DSS wires that treated by heat on the optimum temperature condition were conducted the bending moment test and calculated the S-Max value and the modulus of elasticity. For evaluating the bio stability, each materials were conducted in vitro test for measuring the cell survival rate. The most interesting results was that the tensile strength test of SS wire($8.17\times10^4\;N/mm^2$) and DSS wire($8.05\times10^4\;N/mm^2$) that treated at $500^{\circ}C$ by heat were similar in mechanical strength. In the bio-stability study, the DSS has no cytotoxicity (p=0.05) Thus, we could make a conclusion that the duplex stainless steel wire has vastly superior corrosion resistance was suitable as orthodontic wire.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.04a
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• pp.243-248
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• 1994

The purpose of this study is to develop Deterioration Diagnosis System for the Reinforced Concrete Structure which can be used preliminary in determining the factors causing deterioration by simple inspection and mapping of the indicators of deterioration. Total 29 items compromising material, structural and constructional factors causing deterioration were considered in this system. Also the indicators of deterioration were subdivided into 54 items such as concrete crack pattern and steel corrosion etc. Each indicator of deterioration was quantatified by allocating and giving grade to each item which has extra weight according to its conscquence. Satisfactory results were obtatined by applying this Diagnosis system to the indicators of deterioration in ref. [3]. Further research was required on the indicators of deterioration in construction site to enhance the field applicability of this system.

• Proceedings of the Korean Society for Applied Microbiology Conference
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• 1986.12a
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• pp.510.2-511
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• 1986

The biotechnology including genetic engineering is expected to be applied to various fields of wastewater treatments in order to promote biological reaction rate, to grade up the effluent quality and to advance the stability of microorganisms against temperature, pH and toxic substances. The current topics in Japan on application of biotechnology to wastewater treatment will be reviewed at the beginning of the presentation. Next, the research of Biochemical Engineering Laboratory is to be presented, especially focused on the following subjects ; (1) Application of genetic engineering to the investiation of heavy metal uptake by the resistant bacteria of Hg Cd or Zn. (2) Relationship between sulfate reducing bacteria and wastewater treatment, offensive odor and corrosion of sewer tranks.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.40.1-40.1
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• 2010

Recently high strength steel sheets with high formability for automotive parts have been being developed to meet the demands for passenger safety and weight reduction of car body. Among these high strength steels, dual-phase steels are regarded as one of the attractive steels due to their excellent mechanical properties including high strength and ductility. However, to be successfully applied to automotive parts they should be corrosion resistant enough to satisfy the required quality of car maker. This also requires their feasibility for galvannealed production including hot dip galvanizability. In this study has been placed on understanding the effects of heat-treatment(austenizing and isothermal treatment) on the microstructures and mechanical properties of a 0.06C-0.03Si-2.0Mn high strength steel for cold forming. The microstructure and phase distribution were examined with eth aids of SEM, EBSD, TEM etc.. Through the study the production of 590MPa grade DP GA steels with good formability and galvaniability were shown to be possible.

• Journal of Welding and Joining
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• v.17 no.4
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• pp.46-52
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• 1999

Some of the pressurized reactor pressure vessels used in many chemical plants are made of low alloy carbon steel plates internally clad with an austenitic stainless steel for improved anti-corrosion properties. In this study, metallurgic structure of the weld interface of A 387 Grade12Class1 low alloy carbon steel claded with A182-F321 austenitic stainless steel after thermal exposure simulation heat treatment was investigated to display a characteristic behavior of dissimilar metal weld interface with thermal exposure during service at high temperature and pressure. EPMA, STEM, vickers-hardness test were performed and the results were correlated with the microstructure. To estimate the depth of the carburized/decarburized bands quantitatively, a model for carbon diffusion was proposed. The validity of the proposed theoretical relationships was confirmed by the directly measured data from the welded parts failed during service.

• Computers and Concrete
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• v.3 no.2_3
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• pp.145-161
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• 2006

This article involves architecting prototype-fuzzy expert system for designing the nominal cover thickness by means of fuzzy inference for quantitatively representing the environment affecting factor to reinforced concrete in chloride-induced corrosion environment. In this work, nominal cover thickness to reinforcement in concrete was determined by the sum of minimum cover thickness and tolerance to that defined from skill level, constructability and the significance of member. Several variables defining the quality of concrete and environment affecting factor (EAF) including relative humidity, temperature, cyclic wet and dry, and the distance from coast were treated as fuzzy variables. To qualify EAF the environment conditions of cycle degree of wet-dry, relative humidity, distance from coast and temperature were used as input variables. To determine the nominal cover thickness a qualified EAF, concrete grade, and watercement ratio were used. The membership functions of each fuzzy variable were generated from the engineering knowledge and intuition based on some references as well as some international codes of practice.

• Corrosion Science and Technology
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• v.3 no.2
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• pp.59-66
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• 2004

In construction of new ships and large steel bridges in Korea, pre-construction primers (PCP), also known as shop primer, are routinely used and retained as an integral part of the protective coating system. Retention of PCP's can significantly reduce building schedule and cost. Retaining PCP through the so-called "sweep blasting" procedure eliminates or minimizes the necessity of a second blast operation, thus shortening overall schedule as well as reducing labor cost and hazardous waste disposal cost. This study evaluates the feasibility of retaining PCP as the part of primer for high performance protective coating systems applied to ships' hull, bottom and ballast tanks. Upon proving that the retention of the PCP is a viable option, the process of coating application can he improved significantly in terms of cost and working schedule of new ships and large steel bridges. Results indicate that use of the PCP via sweeping blasting in conjunction with standard high performance protective coating systems does not degrade the overall performance of the coating systems. At the same time, it is also highly recommended that the secondary surface preparation should consist of grit blasting of weld burnt and other damaged areas to SSPC SP-IO grade (Sa 2.5 Gr.), Near White Blast Cleaning with proper application and attention to detail.

• Advances in concrete construction
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• v.9 no.2
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• pp.207-215
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• 2020

This paper describes the experimental studies carried out to determine the properties of fresh and hardened concrete with Recycled Plastic Waste (RPW) as a partial replacement material for fine aggregates. In the experimental study, RPW was used for replacing river sand and manufactured sand (M sand) aggregates in concrete. The replacement level of fine aggregates was ranging from 5% to 20% by volume with an increment of 5%. M40 grade of concrete with water cement ratio of 0.40 was used in this study. Two different types of RPW were used, and they are (i) un-activated RPW and (ii) activated RPW. The activated RPW was obtained by alkali activation of un-activated RPW using NaOH solution. The hardened properties of the concrete determined were dry density, compressive strength, split tensile strength, flexural strength and ultrasonic pulse velocity (UPV). The properties of the concrete with river sand, M sand, activated RPW and un-activated RPW were compared and inferences were drawn. The effect of activation using NaOH solution was investigated using FT-IR study. The micro structural examination of hardened concrete was carried out using Scanning Electron Microscopy (SEM). The test results show that the strength of concrete with activated RPW was more than that of un-activated RPW. From the results, it is evident that it is feasible to use 5% un-activated RPW and 15% activated RPW as fine aggregates for making concrete without affecting the strength properties.