한국부식방식학회

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다전극 탐상을 통한 토중 매설배관 피복결함 탐상 정확도의 개선
External corrosion of buried pipes can be controlled using both coating and cathodic protection. However, deterioration of the coating can occur due to several reasons. The detection reliabilty of coating flaw detection methods is affected by interference such as metal objects connected to rectifiers and copper grids. When performing parallel direct current voltage gradient (DCVG) inspection, a sine wave form without potential reversal in voltage gradient appears in the area where the interference exists. However, this area may be not identified using existing methods. The objective of this study was to determine the effect of analyzing direction on the reliability of coating flaw detection of pipes buried in soil using a multi-electrode detector. DCVG on the buried pipe was measured along the buried pipe. This measurement parallel to the pipe was repeated. Measured data were analyzed for parallel, vertical, and diagonal directions. The reliability of coating flaw detection was improved by up to 46.4% compared to the conventional method.
KEYWORDs : Buried pipe, Coating flaw detection, Multi-electrode detector, Interference, Reliability
AUTHORs : 김민기 ･ 임부택 ･ 김기태 ･ 장현영 ･ 박흥배 ･ 김영식†

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양극산화된 5083-H321 합금의 천연해수 내 전기화학적 부식 및 응력부식균열 특성에 관한 연구
Many studies have been conducted to improve the corrosion resistance and durability of various aluminum alloys through the anodizing technique. It is already used as a unique technique for enhancing the properties of aluminum alloys in various industries. This paper investigated the electrochemical corrosion and stress corrosion cracking characteristics of anodized aluminum 5083-H321 alloy in natural seawater. The corrosion characteristics were assessed by the electrochemical technique and potentiodynamic polarization test. The stress corrosion cracking characteristic was evaluated with a slow strain rate tensile test under 0.005 mm/min
rate, which showed that the hard anodizing film had a thickness of about 16.8 μm. Although no significant characteristics of stress corrosion cracking were observed in the slow strain rate test, the anodized specimen presented excellent corrosion resistance. The corrosion current density was measured to be approximately 4.2 times lower than that of the base material, and no surface damage was observed in the anodic polarization test.
KEYWORDs : 5083-H321, Corrosion, Stress corrosion cracking, Natural seawater, Slow strain rate test
AUTHORs : 황현규 ･ 신동호 ･ 정광후 ･ 김성종†

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해수 내 다양한 알루미늄 선박용 재료의 캐비테이션 진폭에 따른 캐비테이션-침식 손상 연구
Recently, 5000 series and 6000 series Al alloys have been used as hull materials for small and medium-sized ships because of their excellent weldability, corrosion resistance, and durability in marine environments. Al ships can navigate at high speed due to their light weight. However, cavitation-erosion problems cause reducing durability of Al ship at high speed. In this investigation, 5052-O, 5083-H321, and 6061-T6 Al alloy materials were used to evaluate the damage characteristics with amplitude (cavitation strength). As a result of the electrochemical experiments, the corrosion current density and corrosion potential of 6061-T6 in seawater were 8.52 × 10-7 A/cm2 and –0.771 V, respectively, presenting the best corrosion resistance. The cavitation-erosion experiment showed that 5052-O had the lowest hardness value and cavitation-erosion resistance. 5052-O also had a very short incubation period. As the experiment progressed for 5052-O, pitting formed and grew in a short time, and was observed as severe cavitation-erosion damage that surface detached. Among the three specimens, 5083-H321 presented the highest hardness value and the damage rate was the smallest after the initiation of pitting.
KEYWORDs : Hull materials, Cavitation-erosion, Amplitude, Seawater, Aluminum alloy
AUTHORs : 양예진 ･ 김성종†

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선박용 5052-O 알루미늄 합금의 해수 내 진폭 변수에 따른 캐비테이션-침식 손상 특성
The characteristics of cavitation-erosion damage with changes in the amplitude of 5052-O aluminum alloy for ships were investigated in a seawater environment. In the cavitation-erosion experiment, the cavitation environment was created using a vibration-generating device with a piezo-electric effect. The amplitudes of 5 μm, 10 μm, and 30 μm were created by changing the geometric shape of the cavitation horn. The resistance characteristics of cavitation-erosion damage were evaluated by weight loss and pitting area. The damaged surface was analyzed using scanning electron microscopy (SEM) and 3D optical microscopy. As the amplitude increased, the amount of damage and the area of the damaged surface increased, and the
damage was concentrated at the center and edge of the specimen. The pit was created after the initial incubation period with increasing experimental time, and then the pits were merged to grow and propagate into craters, and eventually, the surface was detached and damaged. The cavitation-erosion damage after 30 minutes with amplitude of 10 μm and 30 μm was 1.48 and 2.21 times compared to 5 μm, respectively.
KEYWORDs : Al ship, 5052-O Al alloy, Cavitation-erosion, Amplitude, Seawater
AUTHORs : 양예진 ･ 김성종†

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Comparison of Quantitative Analysis of Radioactive Corrosion Products Using an EPMA and X-ray Image Mapping
Radioactive corrosion product specimens were analyzed using an electron probe microanalyzer (EPMA) and X-ray image mapping. It is difficult to analyze the composition of radioactive corrosion products using an EPMA due to the size and rough shape of the surfaces. It is particularly challenging to analyze the composition of radioactive corrosion products in the form of piled up, small grains. However, useful results can be derived by applying a semi-quantitative analysis method using an EPMA with X-ray images. A standard-less, semi-quantitative method for wavelength dispersive spectrometry. EPMA analysis was developed with the objective of simplifying the analytical procedure required. In this study, we verified the reasonable theory of semi-quantitative analysis and observed the semi-quantitative results using a sample with a good surface condition. Based on the validated results, we analyzed highly rough-surface radioactive corrosion products and assessed their composition. Finally, the usefulness of the semi-quantitative analysis was reviewed by verifying the results of the analysis of radioactive corrosion products collected from spent nuclear fuel rods.
KEYWORDs : Semi-quantitative, X-ray image mapping, Shielded EPMA, Radioactive corrosion products
AUTHORs : Yang Hong Jung† and Yong Sun Choo

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