• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.3
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• pp.248-255
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• 2009

After several damages by PWSCC were found in the world, USNRC and PNNL(Pacific Northwest National Laboratory) started the research on PWSCC under the project name of PINC. The aim of the project was 1) to fabricate representative NDE mock-ups with flaws to simulate PWSCCs, 2) to identify and quantitatively assess NDE methods for accurately detecting, sizing and characterizing PWSCCs, 3) to document the range of locations and morphologies of PWSCCs and 4) to incorporate results with other results of ongoing PWSCC research programs, as appropriate. Korea nuclear industries have also been participating in the project. Thermally and mechanically cracked-four mockups were prepared and phased array and manual ultrasonic testing(UT) techniques were applied. The results and lessons learned from the preliminary RRT are summarized as follows: 1) Korea RRT teams performed the RRT successfully. 2) Crack detection probability of the participating organizations was an average 87%, 80% and 80% respectively. 3) RMS error of the crack sizing showed comparatively good results. 4) The lessons learned may be helpful to perform the PINC RRT and PSI /ISI in Korea in the future.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.185-188
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• 2008

Fiber reinforced polymer(FRP) bars are proving to be a valuable solution in the corrosion problem of steel reinforced concrete structures. As such, a number of guidelines for their use have been developed. These guidelines are primarily based on modifications to existing codes of practice for steel reinforced concrete structures. These guidelines are also similar in that though the design equations are presented in the partial factor formats that are often used in probability based design, they are not true probabilistic codes. Instead, they typically make use of already existing design factors for loads and resistances. Thus, when concrete structures reinforced FRP bars are designed, the structural reliability levels are not known. This paper investigates uncertainties of concrete beams reinforced with GFRP bars. Also, the structural reliability levels are evaluated for the flexural failure mode.

• 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.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.420-420
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• 2021

상수도관은 시간이 경과됨에 따라 부식이 발생하고 이로 인해 관의 두께 및 강도가 감소하여 점차 상수도관의 기능을 상실하게 된다. 이러한 노후 상수도관은 누수, 적수 등 수자원에 막대한 경제적인 손실을 발생시키고 사람들에게 많은 불편을 끼친다. 현재 우리나라도 전체 상수도관 중 노후 상수도관이 많은 부분을 차지하고 있기 때문에 교체나 개선이 시급한 실정이다. 하지만 전체 상수도관을 교체하는 것은 막대한 예산이 필요하기 때문에 현실적으로 어려운 문제이다. 따라서 상수도관의 노후도 분석을 통하여 상수관망의 최적 교체 우선순위를 판단하고 교체를 실시하는 것이 필요하다. 본 연구에서는 노후도 분석에 중요한 관의 부식깊이와 잔존수명을 예측하고 신뢰성해석을 통해 파괴확률을 산정하였다. 이를 위해 Romanoff(1957)와 환경부(2002)에서 실측한 상수관의 관종에 따른 관두께 변화를 적용하여 해석하였다. 실측 자료를 통해 부식깊이, 잔존수명 예측 모델을 수립하였으며 이에 따른 관의 파괴확률을 산정하였다. Romanoff(1957)의 혼합강관과 주철관에 대한 실측 자료를 사용하여 상수관의 사용연수가 10년, 20년, 30년 경과됨에 따른 부식깊이와 관파괴확률을 산정하였다. 혼합강관의 경우 사용연수에 따른 부식깊이는 0.57mm, 0.92mm, 1.21mm으로 산정되었으며, 주철관의 경우 0.16mm, 0.24mm, 0.31mm으로 산정되었다. 또한 신뢰성모형을 직경 300mm관에 적용한 결과 최대 상수도압 15kg/cm²에서 혼합강관의 사용연수에 따른 파괴확률은 3.36%, 4.65%, 6.18%로 나타났으며 주철관은 1.36%, 2.50%, 2.68%로 나타났다. 환경부(2002)의 주철관에 대한 부식 실측 자료를 통해 상수관의 사용연수 10년, 20년, 30년 경과에 따른 부식깊이와 관파괴확률을 산정하였으며 초기 관두께 측정 자료를 통해 잔존수명도 예측하였다. 부식깊이는 1.02mm, 1.25mm, 1.41mm으로 산정되었으며, 파괴확률은 5.15%, 6.30%, 7.35%로 산정되었다. 그리고 잔존수명의 경우 부식률이 20%일 때, 잔존수명은 약 30년으로 산정되었다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.5
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• pp.148-160
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• 2012

This study proposed more reasonable prediction models on compressive strength and carbonation of concrete structure and developed a more effective tunnel safety diagnosis and maintenance method through field application of the proposed prediction models. For this study, the Seoul Metro's Line 1 through Line 4 were selected as target structures because they were built more than 30 years ago and have accumulated numerous diagnosis and maintenance data for about 15 years. As a result of the analysis of compressive strength and carbonation, we were able to draw prediction models with accuracy of more than 80% and confirmed the prediction model's reliability by comparing it with the existing models. We've also confirmed field suitability of the prediction models by applying field, the average error of an estimate on compressive strength and carbonation depth was about 20%, which showed an accuracy of more than 80%. We developed a more effective maintenance method using durability prediction Map before field inspection. With the durability prediction Map, diagnostic engineers and structure managers can easily detect the vulnerable points, which might have failed to reach the standard of designed strength or have a high probability of corrosion due to carbonation, therefore, it is expected to make it possible for them to diagnose and maintain tunnels more effectively and efficiently.

• Fire Science and Engineering
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• v.26 no.4
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• pp.31-41
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• 2012

This study collected 5,100 cases of gas accident occurred in Korea for 14 years from 1995 to 2008, established Database and based on it, analyzed them by detailed forms and reasons. As the result of analyzing the whole city gas accidents with Poisson analysis, the item of "Careless work-Explosion-Pipeline' showed the highest rate of accidents for the next 5 years. And, "Joint Losening and corrosion-Release-Pipeline" showed the lowest rate of accident. In addition, for the result of analyzing only accidents related to LPG vaporizer, "LPG-Vaporizer-Fire" showed the highest rate of accident and "LPG-Vaporizer-Products Faults" showed the lowest rate of accident. Also, as the result of comparing and analyzing foreign LPG accident accompanied by Jet fire, facility's defect which is liquid outflow cut-off device and heat exchanger's defect were analyzed as the main reason causing jet fire, like the case of Korea, but the number of accidents for the next 5 years was the highest in "LPG-Mechanical-Jet fire" and "LPG-Mechanical-Vapor Cloud" showed the highest rate of accidents. By grafting Poisson distribution theory onto gas accident expecting program of the future, it's expected to suggest consistent standard and be used as the scale which can be used in actual field.