• Plant Journal
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• v.14 no.2
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• pp.45-50
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• 2018

Nuclear safety law's amendment caused many problems to use radiography testing(RT). Phased array ultrasonic testing(PAUT) was adapted instead of RT for NDE of welding points in boiler tubes these days. Unfortunately, PAUT doesn't give us the discrimination characteristics about flaws distinction and flaws size clearly. In this thesis, the distinction characteristics of flaw types and the detection characteristics of flaw size using PAUT of welding points in boiler tubes were analyzed. It was concluded that PAUT can distinguish between planar flaws and rounded flaws, but it is hard to tell apart the types of flaw respectively. We paid attention to the discrimination of flaws size because PAUT tends to underestimate the flaw size of porosity and underestimate or overestimate the flaw size of porosity.

• Computational Structural Engineering
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• v.10 no.2
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• pp.213-223
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• 1997

Calculation of elastic wave fields has important applications in a variety of engineering fields including NDE (Non-destructive evaluation). Scattering problems have been investigated by numerous authors with different solution schemes. For simple geometries of the scatterers (e.g., cylinders or spheres), the analysis of steady-state elastic wave scattering has been carried out using analytical techniques. For arbitrary geometries and multiple inclusions, numerical methods have been developed. Special finite element methods, e.g., the infinite element method and a hybrid method called the Global-Local finite element method have also been developed for this purpose. Recently, the boundary integral equation method has been used successfully to solve scattering problems. In this paper, a volume integral equation method (VIEM) is proposed as a new numerical solution scheme for the solution of general elasto-dynamic problems in unbounded solids containing multiple inclusions and voids or cracks. A boundary integral equation method (BIEM) is also presented for elastic wave scattering problems. The relative advantage of the volume and boundary integral equation methods for solving scattering problems is discussed.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.6
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• pp.762-771
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• 2003

Statement of problem. In dentistry, the minimally prepared inlay resin-bonded fixed partial denture (FPD) made of new ceromer / fiber-reinforced composite (FRC) was recently introduced. However, the appropriate dimensions for the long-term success and subsequent failure strength are still unknown. Purpose. The aim of this study was to investigate the most fracture-resistible thickness combination of the ceromer / FRC using a universal testing machine and an AE analyzer. Material and Methods. A metal jig considering the dimensions of premolars and molars was milled and 56-epoxy resin dies, which had a similar elastic modulus to that of dentin, were duplicated. According to manufacturer's instructions, the FRC beams with various thicknesses (2 to 4 mm) were constructed and veneered with the 1 or 2 mm-thick ceromers. The fabricated FPDs were luted with resin cement on the resin dies and stored at room temperature for 72 hours. AE (acoustic emission) sensors were attached to both ends, the specimens were subjected to a compressive load until fracture at a crosshead speed of 0.5 mm/min. The AE and failure loads were recorded and analyzed statistically. Results. The results showed that the failure strength of the ceromer/FRC inlay FPDs was affected by the total thickness of the connectors rather than the ceromer to FRC ratio or the depth of the pulpal wall. Fracture was initiated from the interface and propagated into the ceromer layer regardless of the change in the ceromer / FRC ratio. Conclusion. Within the limitations of this study, the failure loads showed significant differences only in the case of different connector thicknesses, and no significant differences were found between the same connector thickness groups. The application of AE analysis method in a fiber-reinforced inlay FPD can be used to evaluate the fracture behavior and to analyze the precise fracture point.

• Journal of the Korean Institute of Gas
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• v.19 no.5
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• pp.29-35
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• 2015

Pipes, commonly used in energy and petrochemical facilities, have various types of defects induced by diverse factors and this is often issued in NDE society. Ultrasonic guided wave inspection method are normally adopted to insure the healthiness of industry pipes. Recently, ultrasonic guided wave inspection is shifted to adopt arrayed probes and system. And here we developed an array guided wave ultrasonic testing system can adapt arrayed probes and focusing methods. In this paper, an array guided wave ultrasonic testing system is presented including a transmitting focusing technique and flaw signal level enhancement.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.4
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• pp.111-119
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• 2016

Rebound hammer test, SonReb method and concrete core test are most useful testing methods for estimate the concrete compressive strength of deteriorated concrete structures. But the accuracy of the NDE results on the existing structures could be reduced by the effects of the uncertainty of nondestructive test methods, material effects by aging and carbonation, and mechanical damage by drilling of core. In this study, empirical procedure for verifying the in-situ compressive strength of concrete is suggested through the probabilistic analysis on the 268 data of rebound and ultra-pulse velocity and core strengths obtained from 106 bridges. To enhance the accuracy of predicted concrete strength, the coefficients of core strength, and surface hardness caused by ageing or carbonation was adopted. From the results, the proposed equation by KISTEC and the estimation procedures proposed by authors is reliable than previously suggested equation and correction coefficient.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.1
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• pp.38-44
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• 2002

MFL method is a qualitative inspection tool and is a reliable, fast and economical NDT method. The application of MFL method to the inspection of storage tank floor plates has been shown to be a viable means. Examination of tank floors previously depended primarily upon ultrasonic test methods that required slow and painstaking application. Therefor most ultrasonic inspection of storage tank has been limited to spot testing only. Our NDE group have developed magnetic flux leakage system to overcome limitation of ultrasonic test. The developed system consists of magnetic yoke, array sensor, crawler and software. It is proved that the system is able to detect artificial flaw like 3.2mm diameter, 1.2mm depth in 6mm thick steel plate.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.3
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• pp.207-216
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• 1999

A phased array is a multi-element piezoelectric device whose elements are individually excited by electric pulses at programmed delay time. One of the advantages of using phased array in nondestructive evaluation (NDE) application over conventional ultrasonic transducers is their great maneuverability of ultrasonic beam. There are some parameters such as the number and the size of the piezoelectric elements and the inter-element spacing of the elements to design phased array transducer. In this study, the characteristic of ultrasonic beam for phased array transducer due to the variation of the number of elements has been simulated for ultrasonic SH-wave on the basis of Huygen's principle. Ultrasonic beam directivity and focusing due to the change of time delay of each element were discussed due to the change of the number of piezoelectric elements. It was found that ultrasonic beam was much more spreaded and hence its sound pressure was decreased as steering angle of ultrasonic beam was increased. In addition, the ability of ultrasonic bean focusing decreased gradually with the increase of focal length at the same piezoelectric elements. However, the ability of beam focusing was improved as the number of consisting elements was increased.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.2
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• pp.40-48
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• 2012

Steel corrosion in concrete is a main cause of deterioration and early failure of concrete structures. A novel integration of electromagnetic heat induction and infrared (IR) thermography is proposed for nondestructive detection of steel corrosion in concrete, by taking advantage of the difference in thermal characteristics of corroded and non-corroded steel. This paper focuses on experimental investigation of the concept. An inductive heater is developed to remotely heat the embedded steel from concrete surface, which is integrated with an IR camera. Concrete samples with different cover depths are prepared. Each sample is embedded with a single rebar in the middle, resulting an identical cover depth from the front and the back surfaces, which enable heat induction from one surface and IR imaging from the other simultaneously. The impressed current (IC) method is adopted to induce accelerated corrosion on the rebar. IR video images are recorded during the entire heating and cooling periods. The test results demonstrate a clear difference in thermal characteristics between corroded and non-corroded samples. The corroded sample shows higher rates of heating and cooling than those of the non-corroded sample. This study demonstrates a potential for nondestructive detection of rebar corrosion in concrete.

• Journal of Magnetics
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• v.16 no.1
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• pp.36-41
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• 2011

If gas is leaking out of gas pipelines, it could cause a huge explosion. Accordingly, it is important to ensure the integrity of gas pipelines. Traditionally, over the years, gas-operating companies have used the ILI system, which is based on axial magnetic flux leakage (MFL), to inspect the gas pipelines. Relatively, there is a low probability of detection (POD) for the axial defects with the axial MFL-based ILI. To prevent the buried pipeline from corrosion, it requires a protective coating. In addition to the potential damage to the coating by environmental factors and external forces, there could be defects on the damaged coating area. Thus, it is essential that nondestructive evaluation methods for detecting axial defects (axial cracks, axial groove) and damaged coating be developed. In this study, an electromagnetic acoustic transducer (EMAT) sensor was designed and fabricated for detecting axial defects and coating disbondment. In order to validate the performances of the developed EMAT sensor, experiments were performed with specimens from axial cracks, axial grooves, and coating disbondment. The experimental results showed that the developed EMAT sensor could detect not only the axial cracks (minimum 5% depth of wall thickness) and axial grooves (minimum 10% depth of wall thickness), but also the coating disbondment.

• Nuclear Engineering and Technology
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• v.53 no.9
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• pp.2982-2989
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• 2021

One of the consequences of the 475 ℃ embrittlement of duplex stainless steels is the reduction of the resistance to localized corrosion. Therefore, the detection of this type of embrittlement before the material exhibits significant loss in toughness, and corrosion resistance is important to ensure the structural integrity of critical components under corrosion threats. In this research, conductivity measurements are performed using the alternating current potential drop (ACPD) technique with using a portable four-point probe as a nondestructive evaluation (NDE) method for detecting the embrittlement in a 2507 (UNS S32750) super duplex stainless steel (SDSS) aged at 475 ℃ from as-received condition to 300 h. The electric conductivity results were compared against two electrochemical tests namely double loop electrochemical potentiokinetic reactivation (DL-EPR) and critical pitting temperature (CPT). Mechanical tests and the microstructure characterized using scanning electron microscopy (SEM) imaging are conducted to track the progress of embrittlement. It is shown that the electric conductivity correlates with the changes in impact energy, microhardness, and CPT corrosion tests result demonstrating the feasibility of the four-point probe as a possible field-deployable method for evaluating the 475 ℃ embrittlement of 2507 SDSS.