• Journal of Welding and Joining
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• v.25 no.5
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• pp.36-44
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• 2007

This paper is the first part of the study on the accuracy improvement of numerical analysis of steel welds. The aim of this paper is to raise the accuracy of thermal analysis results, such as the shape and size of the weld cross section and the hardness distribution in HAZ(Heat-Affected Zone). It is known that the factors affecting on the accuracy are thermal properties, metallurgical properties and welding heat source model. It was found that the arbitrary distributed heat source model should be used to predict practical weld cross section shape and size. Also, in order to improve the prediction accuracy of HAZ hardness distribution, it was essential to consider 2 CCT(Continuous Cooling Transformation) diagrams in calculating volume fraction of transformed phases. One is the peak temperature being around melting temperature. The other is the peak temperature being around metallurgical transformation temperature.

• Corrosion Science and Technology
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• v.19 no.4
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• pp.224-230
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• 2020

Stainless steel has excellent corrosion resistance. The drawback is that pitting occurs easily due to the concentration of chloride. In addition, corrosion of socket weld, which is structurally and chemically weaker than the other components of the pipe, occurs rapidly. Since these two phenomena overlap, pinhole leakage occurs frequently in the seawater pipe socket welds made of stainless steel at the power plants. To analyze this specific corrosion, a metallurgical analysis of the stainless steel socket welds, where the actual corrosion occurred during the power plant operation, was performed. The micro-structure and chemical composition of each socket weld were analyzed. In addition, selective corrosion of the specific micro-structure in a mixed dendrite structure comprising γ-austenite (gamma-phase iron) and δ-ferrite (iron at high temperature) was investigated based on the characteristic micro-morphology and chemical composition of the corroded area. Finally, the different corrosion stages and characteristics of socket weld corrosion are summarized.

• Nuclear Engineering and Technology
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• v.50 no.6
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• pp.890-898
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• 2018

Nondestructive inspection (NDI) is an integral part of structural integrity analyses of dry storage casks that house spent nuclear fuel. One significant concern for the structural integrity is stress corrosion cracking in the heat-affected zone of welds in the stainless steel canister that confines the spent fuel. In situ NDI methodology for detection of stress corrosion cracking is investigated, where the inspection uses a delivery robot because of the presence of the harsh environment and geometric constrains inside the cask protecting the canister. Shear horizontal (SH) guided waves that are sensitive to cracks oriented either perpendicular or parallel to the wave vector are used to locate welds and to detect cracks. SH waves are excited and received by electromagnetic acoustic transducers (EMATs) using noncontact ultrasonic transduction and pulse-echo mode. A laboratory-scale canister mock-up is fabricated and inspected using the proposed methodology to evaluate the ability of EMATs to excite and receive SH waves and to locate welds. The EMAT's capability to detect notches from various distances is evaluated on a plate containing 25%-through-thickness surface-breaking notches. Based on the results of the distances at which notch reflections are detectable, NDI coverage for spent nuclear fuel storage canisters is determined.

• Transactions of Materials Processing
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• v.13 no.6 s.70
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• pp.484-489
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• 2004

This paper employed a systematic analysis using a 2-D hybrid special finite element containing an edge crack in order to describe the fracture behavior of spot-welds in automotive structures. The 2-D hybrid special finite element is derived form a mixed formulation with a complex potential function with the description of the singularity of a stress field. The hybrid special finite element containing an edge crack can give a better description of its singularity with only one hybrid element surrounding one crack. The advantage of this special element is that it can greatly simplify the numerical modeling of the spot welds. Some numerical examples demonstrate the validity and versatility of the present analysis method. The lap-shear, lap-tension and angle-clip specimens are analyzed and some useful fracture parameters such as the stress intensity factor and the initial direction of crack growth are obtained simultaneously.

• Journal of Welding and Joining
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• v.16 no.1
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• pp.52-62
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• 1998

Laser beam welding of zinc-coated steel, especially lap joints, has a problem of zinc vapor produced during welding which has a low vaporization temperature of 906.deg. C. It is lower than the melting temperature of steel (1500.deg. C). The high pressure formed by vaporization of zinc during laser welding splatters the molten pool and creates porosities in weld. During laser lap welds of zinc-coated steel sheets with CW CO$_{2}$ laser the gap size has been analyzed and simulated using a FEM. The simulation has been carried out in the range of gap aetween 0 and 0.16 mm. The vaporized zinc gas has effected to prevent heat from conducting toward the bottom of sheets. In vaporized zinc gas has effected to prevent heat from conducting toward the bottom of sheets. In the case of too small gap size, zinc gas has not ejected and existed between two sheets. Therefore heat was difficult to conduct from the upper sheet to lower sheet and the upper sheet could over-melted. In the case of large gap size the zinc gas has been prefectly ejected but only a part of lower sheet has melted. The optimum range of gap size in the lap welds of zinc-coated steel sheets has been calculated to be between 0.08 and 0.12 mm. According to the comparison of experiment, the simulation is proved to be acceptable and applicable to laser lap welds.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.5 no.5
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• pp.462-465
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• 2004

After 6 month of using, cracking of gas exhaustion bag cage of Type 304 stainless steel wire for Al melting reverberatory furnace was founded in welds. Analysis of crack causes in the wire were tested by electrochemical method, SEM images of structure and analysis of composition. Resulted from the test, it could be observed that cracks in the welds were a accelerated by formed polythionic acid on surface of bag cage in sensitized region of HAZ, tensile stress and using environment.

• Nuclear Engineering and Technology
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• v.49 no.5
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• pp.1109-1112
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• 2017

The precise prediction of radiation embrittlement of aged reactor pressure vessels (RPVs) is a prerequisite for the long-term operation of nuclear power plants beyond their original design life. The expiration of the operation licenses for Korean reactors the RPVs of which are made from SA533B-1 plates and welds is imminent. Korean regulatory rules have adopted the US Nuclear Regulatory Commission's transition temperature shift (TTS) models to the prediction of the embrittlement of Korean reactor pressure vessels. The applicability of the TTS model to predict the embrittlement of Korean RPVs made of SA533B-1 plates and welds was investigated in this study. It was concluded that the TTS model of 10 CFR 50.61a matched the trends of the radiation embrittlement in the SA533B-1 plates and welds better than did that of Regulatory Guide (RG) 1.99 Rev. 2. This is attributed to the fact that the prediction performance of 10 CFR 50.61a was enhanced by considering the difference in radiation embrittlement sensitivity among the different types of RPV materials.

• International Journal of Korean Welding Society
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• v.1 no.2
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• pp.30-35
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• 2001

Nowadays, repair welding on in-service natural gas pipeline is a matter of primary concern of gas company. The main purpose of this study is to investigate the effects of welding conditions on the allowable heat input for crack-free welds and welds without burn-through onto in-service natural gas pipeline. First of all, single pass weld bead on plates of the various thickness was deposited to evaluate the penetration of weld metal, the depth of heat affected zone and the hardness of repair weld under various welding conditions. Also, finite element analysis has been conducted to validate experimental results of bead-on plate welds and to develop appropriate model for repair welding. The welding experiments of bead-on-plate weld confirmed the influence of plate thickness, heat input and welding process on safety. And, the finite element model was demonstrated by comparing experimental results. The agreement between the computed and measured values was shown to be generally good. Therefore, It is possible to predict the safety of repair welding under various welding conditions with experimental results and finite element analysis model.

• Nuclear Engineering and Technology
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• v.56 no.1
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• pp.317-327
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• 2024

This study investigated the chloride-induced stress corrosion cracking (CISCC) behavior expected to occur in welds of austenitic stainless steel, which are considered candidate materials for dry storage containers for spent nuclear fuel. The behavior was studied by varying temperature, relative humidity (RH), and chloride concentration. 304L-ER308L welded plates were processed into U-bend specimens and exposed to a cyclic corrosion chamber for 12 weeks. The CISCC behavior was then analyzed using electron microscopy. A previous study by the authors confirmed that CISCC occurred in ER308L at 60 ℃, 30% RH, and 0.6 M NaCl via selective corrosion of δ-ferrite. When the temperature was lowered from 60 ℃ to 50 ℃, CISCC still occurred. However, when the humidity was reduced to 20% RH, CISCC did not happen. This can be attributed to the retardation of the deliquescence of NaCl at lower humidity, which was insufficient to promote CISCC. Furthermore, increased chloride concentration to 1.0 M resulted in the absence of CISCC and widespread surface corrosion with severe pitting corrosion because of the increase in thin film thickness.

• Transactions of Materials Processing
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• v.33 no.3
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• pp.193-199
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• 2024

The friction welding characteristics of stainless steels, mainly used in energy and chemical plant industries due to its excellent corrosion resistance and high strength, was evaluated in this study. Friction welding was introduced and conducted at a rotation speed of 2,000 RPM, friction pressure of 30 MPa, burn-off length of 5 mm and upset pressure of 110 ~ 200 MPa on rod typed specimens. The grain boundary characteristics distributions such a grain size, shape, misorientation angle and kernel average misorientation of the welds were clarified by electron backscattering diffraction method. The application of friction welding on SUS304 alloy resulted in a significant refinement of the grain size in the weld zone (5.11 mm) compared to that of the base material (48.09 mm). The mechanical properties of the welds, on the other hand, appeared to be relatively low or similar to those of the base material, which were mainly caused by dislocation density in the initial material and grain refinement in the welds.