• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.2
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• pp.103-109
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• 2005

Fiber reinforced plastic material should be inspected in fabrication process in order to enhance quality by prevent defects such as delamination and void. Generally, ultrasonic technique is widely used to evaluate FRP. In conventional ultrasonic techniques, transducer should be contacted on FRP. However, conventional contacting method could not be applied in fabrication process and novel non-contact evaluating technique was required. Laser-based ultrasonic technique was tried to evaluate CFRP plate. Laser-based ultrasonic waves propagated on CFRP were received with various transducers such as accelerometer and AE sensor in order to evaluate the properties of waves due to the variation of frequency. Velocities of laser-based ultrasonic waves were evaluated for various fiber orientation. In addition, laser interferometry was used to receive ultrasonic wave in CFRP and frequency was analysed.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.5
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• pp.377-383
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• 2005

Because explosive fluid is used at high temperature or under high pressure in petrochemistry and refined oil equipment, the interest about safety of equipments is intensive. Specially, the safety of high pressure reactor vessel is required among them. The material selected in this study is 2.25Cr-1Mo steel that is widely used for high pressure reactor vessel material of petrochemical plant. Eight kinds of artificially aged specimens were prepared by differing from aging periods under three different temperatures. The material was iso-thermally heat treated at higher temperatures than $391^{\circ}C$ that is the operating temperature of high pressure reactor vessel. Vickers hardness properties and electrical resistivity properties about artificially aged material as well as un-aged material were measured, and master curves were made out from the correlation with larson-Miller parameter. And electrical resistivity properties as well as Victors hardness properties measured at high pressure reactor vessel of the field were compared with master curves made out in a laboratory. Degradation evaluation possibility in the field of high pressure reactor vessel by using electrical resistivity method was examined. Electrical resistivity property measured in the field is similar with that of artificially aged material in similar aging level.

• Nuclear Engineering and Technology
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• v.51 no.7
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• pp.1816-1821
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• 2019

This research investigates the feasibility of using the thermoelectric power to monitor the thermal embrittlement in 2507 super duplex stainless steel (SDSS) exposed to a temperature between $280^{\circ}C$ and $500^{\circ}C$. It is well known that the precipitation of Cr-rich ${\alpha}^{\prime}$ phase as a result of the spinodal decomposition is the major cause of the embrittlement and the loss of corrosion resistance in this material. The specimens are thermally aged at $475^{\circ}C$ for different holding times. A series of mechanical testing including the tensile test, Vickers microhardness measurement, and Charpy impact test are conducted to determine the property changes with holding time due to the embrittlement. The mechanical strengths and ferrite hardness exhibit very similar trends. Scanning electron microscopy images of impactfractured surfaces reveal a ductile to brittle transition in the fracture mode as direct evidence of the embrittlement. It is shown that the thermoelectric power is highly sensitive to the thermal embrittlement and has an excellent linear correlation with the ferrite hardness. This paper, therefore, demonstrates that the thermoelectric power is an excellent nondestructive evaluation technique for detecting and evaluating the $475^{\circ}C$ embrittlement of field 2507 SDSS structures.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.3
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• pp.267-274
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• 2002

This research is described on the applicability of a electrochemical techniques for evaluating nondestructive material degradation with various polarization characteristics for Cr-Mo-V steel. The applied electrochemical technique is anodic polarization test which are widely used to evaluate the corrosion rate and/or sensitization at depleted zone of strengthening elements mainly caused by thermal experience for stainless steels. The evaluation of material degradation is performed by small punch test which has been well known as micromechanics test method using specimen size of $10{\times}10{\times}0.5mm$. The 1,000hrs aged material at $630^{\circ}C$ shows the highest material degradation$({\Delta}[DBTT]_{SP})$, but the 2,000hrs and 3,000hrs aged materials show the decrease of ${\Delta}[DBTT]_{SP}$ as aging time increases. It is observed that the difference of current density $({\Delta}I_{FP}\;and\;{\Delta}I_{SP})$.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.2
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• pp.151-157
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• 2004

Ultrasonic testing is a kind of nondestructive test to detect a crack or discontinuity in materials or on material surfaces by sending ultrasound to it. This conventional ultrasonic technique has some limitations in reliably detecting crack or accurately assessing materials in the case of complex-shaped power plant components such as a turbine blade root. An alternative method for such a difficult inspection is highly needed. In this study, application of a phased array ultrasonic testing (UT) system to a turbine blade, one of the critical power plant components, has been considered, and the particular incident angle has been determined so that the greatest track detectability and the most accurate crack length evaluation nay be achieved. The response of ultrasonic phased array was also analyzed to establish a special method to determine the track )ength without moving the transducer. The result showed that the developed method for crack length assessment is a more accurate and effective method, compared with the conventional method.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.2
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• pp.144-149
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• 2011

The lock-in thermography was employed to evaluate the integrity of railway bogies. Prior to the actual application on railway bogies, in order to assess the detectability of known flaws, the calibration reference panel was prepared with various dimensions of artificial flaws. The panel was composed of structural steel, which was the same material with actual bogies. Through lock-in thermography evaluation, the optimal frequency of heat source was determined for the best flaw detection. Based on the defects information, the actual defect assessments on railway bogie were conducted with different types of railway bogies, which were used for the current operation. In summary, the defect assessment results with thermography method showed a good agreement as compared with the conventional inspection techniques. Moreover, it was found that the novel infrared thermography technique could be an effective way for the inspection and the detection of surface defects on bogies since the infrared thermography method provided rapid and non-contact mode for the investigation of railway bogies.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.1
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• pp.1-10
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• 2011

Recently harbor remodeling projects are seriously considered to enhance the loading and unloading capability of old container terminals and to make decrepit ports as eco-friendly harbor and waterfront spaces in many countries. In such a case, quantitative and qualitative evaluations on concrete harbor facilities are mandatory to determine the current structural integrity condition of aged materials. Once the remodeling project is determined to be carried out, the reusability of individual structural members and facilities including caissons, cell-blocks, and tetra-pods need to be decided based on the simple and economic visual inspection and/or nondestructive testing. In this study, the systematic quantitative evaluation procedure for determining the structural integrity condition and the reusability is studied based the nondestructive testing and evaluation methods. Conventional methods including Schmidt hammer test and ultrasonicpulse velocity methods and elastic wave based methods including impact echo test and surface wave test are applied to the old harbor facilities in five different sites. The compressive tests are also carried out to determine the elastic modulus and compressive strength of concrete materials.

• Journal of the Korean Society for Nondestructive Testing
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• v.18 no.1
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• pp.10-16
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• 1998

Remaining life of turbine rotors with a crack can be assessed by the fracture toughness of the aged rotors at service temperature. DC potential drop measurement system was constructed in order to evaluate material toughness nondestructively. Test material was 1Cr-1Mo-0.25V steel used widely for turbine rotor material. Seven kinds of specimen with different degradation levels were prepared according to isothermal aging heat treatment at $630^{\circ}C$. Electrical resistivity of test material was measured at room temperature. It was observed that material toughness and electrical resistivity decreased with the increase of degradation. The relationship between fracture toughness and electrical resistivity was investigated. Fracture toughness of a test material may be determined nondestructively by electrical resistivity.

• Journal of the Korean Society for Nondestructive Testing
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• v.5 no.2
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• pp.12-21
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• 1986

Generally, butt welds with plate thickness $30{\sim}40mm$ are welded with groove angle $40^{\circ},\;60^{\circ},\;70^{\circ}$, etc. In the detection of internal weld defects, oblique testing with single probe has been mainly used. But, recently, in acccordance with enlargement of welded structure, thick plate with 100-200mm are frequently required. Thus I-groove welding method was lately developed and often used. In this case, most frequently generated defects are the lack of weld penetration and incomplete fusion between base metal and welding material. If we would detect by oblique testing with single probe, detecting flaw is occassionally impossible or very underestimated. In this study, the limit for applying tandem method was studied in dise and band type flaws. The estimation of flaw size could be within 10% error compared to real flaws.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.5
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• pp.497-519
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• 2003

Science and technology is an essential ingredient of the progress in modern society. Measurements enable action and actions enable results. Non-Destructive Evaluation (NDE) - the science and technology of measurements without affecting the Properties and performance of the test object is an interdisciplinary domain area of high significance far ensuring quality, productivity and safety thus enabling better qualify of lift to the inhabitants on this planet. The test object can be material, component, plant, earth, environment etc. Total qualify management, total productivity management, concurrent engineering and many other essential ingredients of success in plant engineering and manufacturing industry are dependent on NDE far success and good returns on investments.