• 산업기술연구
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• 제23권A호
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• pp.149-156
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• 2003

The development and maintenance of a sound bond are essential requirements of concrete repair and replacement. The bond property of a overlay to its substrate concrete during the lifetime is one of the most important performance requirements which should be quantified. A standard or a verified bond strength measurement method is required at field for screening, selecting materials and quality control for overlay or repair materials, but no test method has been adopted as a standard. In this study, a concrete pull off bond strength measurement method for field application is proposed and evaluated. This study compares the splitting tensile test, slant shear test, nipple pipe direct tensile test, flexural adhesion test, briquette tensile test, jumbo nail pull-out test and core pull-off test with their test procedures. From these comparison and investigation, core pull-off test is selected as a main topic of this study because of it's suitability for in situ testing, simplicities in field application and clearness at interface boundary condition. Thus, the proposed core pull off test is evaluated to be the most appropriate method for field application in a simple manner. The fracture surface and fracture mode could be easily determined by visual observation of failure surface of the field specimen. The core pull off test was found to be sensitive to surface condition and latex contents at latex modified concrete.

• 한국레이저가공학회지
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• 제16권3호
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• pp.1-10
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• 2013

In this study, Al-Si coated boron steel(1.2 mm) were laser welded by $CO_2$ laser and hot-stamping was applied to the laser joints. Tensile properties and microstructures of the joints were investigated before and after hot-stamping. Tensile and yield strengths of the as welded specimen similar with base metal and fracture occurred base metal of boron steel. Although, in case of heat treated specimen, fracture occurred fusion zone that Al segregated zone near the bond line. These could be explained by the existence of ferrite, in the Al segregated zone near the bond line and base metal of boron steel. Before hot-stamping, hardness of base metal is lower than fusion zone and heat affected zone in spite of exist Al segregation zone($Fe_3$(Al,Si)). So fracture occurred base metal. Although, after hot-stamping, microstructure of base metal and welds zone transformed to martensite and bainite except in Al segregation zone near the bond line that $Fe_3$(Al,Si) transformed to a-ferrite. So fracture occurred Al segregation zone near the bond line.

• 비파괴검사학회지
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• 제22권5호
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• pp.474-482
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• 2002

필름을 사용하지 않는 방사선투과검사 시스템인 1차원 Radiometric scanning system을 개발하여 부식 및 침적물이 있는 배관의 두께평가에 적용해 보았다. 개발된 시스템은 단일 방사성 동위원소에서 나오는 방사선을 선형으로 접속하여 시험체를 투과시킨 방사선을 한개의 섬광형 검출기언 BGO를 사용하여 검출하는 single source-single detector alignment system을 제어하는 기계주사 시스템과 제어 프로그램을 개발하였다. 개발된 시스템의 성능을 GEMANT4 프로그램을 사용하여 예측하여 보았다. 그리고, 인공결함을 제작하여 넣은 시편과 두께 변화를 준 시편에 적용하여 실제 성능을 평가하였다. 이 시스템은 방사성 동위원소를 이용하여 배관의 부식과 침적물에 의한 두께 변화에 대하여 실시간으로 필름을 사용하지 않고 평가할 수 있는 가능성을 알 수 있었다.

• 한국구조물진단유지관리공학회 논문집
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• 제25권4호
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• pp.75-82
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• 2021

이 연구의 목적은 강관과 강봉을 이용하여 프리스트레스력의 도입이 가능하도록 개발된 프리스트레싱(prestressing reinforcing units using steel bar and pipe, 이하 SP) 보강재의 응력손실을 확인하는데에 있다. 주요변수는 SP 보강재의 종류, 프리스트레스력의 크기 및 도입방법이다. 실험결과 SP 보강재의 응력손실은 프리스트레스력이 직접 도입하는 초기단계에서 가장 크게 있었는데, 그 크기는 압축도입형 보다 인장도입형에서 더 크게 있었다. SP 보강재의 응력손실은 프리스트레스력이 항복강도의 80%로 도입된 P800 강종인 압축도입형 실험체에서 1.6%로 가장 낮았다. 한편 시간경과에 따른 SP 보강재의 릴랙세이션은 압축도입형의 경우 SP 보강재의 종류, 프리스트레스력의 크기에 관계없이 0.4~1.9%로 평가되었는데, 이는 설계기준들에서 제시하고 있는 릴랙세이션 2.5% 이하를 만족하는 수준이었다. 결과적으로 프리스트레스력 도입 즉시 발생하는 응력손실을 감안할 때에 개발된 SP 보강재의 재질과 프리스트레스력 도입방식 및 크기는 각각 P800, 압축도입형 및 항복강도의 80%로 추천된다.

• 대한기계학회논문집A
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• 제21권3호
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• pp.519-527
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• 1997

AISI 316 steel has been used extensively for heater and boiler tube of the structural plants such as power, chemical and petroleum plants under severe operating conditions. Usually, material degradation due to microcrack or precipitation of carbides and segregation of impurity elements, is occured by damage accumulated for long-term service at high temperature in this material. In this study, the effect of aging time on fracture toughness was investigated to evaluate the measurement of material degradation. The elastic-plastic fracture toughness behaviour of AISI 316 steel pipe aged at $550^{\circ}C$for 1h-10000h (the aged material) was characterized using the single specimen J-R curve technique and eletric potential drop method at normal loading rate(load-line displacement speed of 0.2mm/min) in room temperature and air environment. The fracture toughness data from above experiments is compared with the $J_{in}$ obtained from predicted values of crack initiation point using potential drop method.

• 한국지진공학회논문집
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• 제17권1호
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• pp.21-31
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• 2013

In this study, dynamic characteristics and seismic capacity of the nuclear power plant piping system are evaluated by model test results using multi-platform shake table. The model is 21.2 m long and consists of straight pipes, elbows, and reducers. The stainless steel pipe diameters are 60.3 mm (2 in.) and 88.9 mm (3 in.) and the system was assembled in accordance with ASME code criteria. The dynamic characteristics such as natural frequency, damping and acceleration responses of the piping system were estimated using the measured acceleration, displacement and strain data. The natural frequencies of the specimen were not changed significantly before and after the testing and the failure and leakage of the piping system was not observed until the final excitation. The damping ratio was estimated in the range of 3.13 ~ 4.98 % and it is found that the allowable stress(345 MPa) according to ASME criteria is 2.5 times larger than the measured maximum stress (138 MPa) of the piping system even under the maximum excitation level of this test.

• 센서학회지
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• 제23권1호
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• pp.58-65
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• 2014

We developed a low-cost automatic diagnosis system for water quality in cooling towers to measure the concentrations of key ingredients such as $Ca^{2+}$, $Cl^-$, $PO{_4}^{3-}$, and $Fe^{2+}$. $Ca^{2+}$, and $Cl^-$ are the main factors that cause the generation of scale, corrosion, and sludge in water pipes. $PO{_4}^{3-}$ prevents corrosion, sludge and scale by inhibiting the ions (i.e., $Ca^{2+}$, $Cl^-$) from sticking to the pipes. $Fe^{2+}$ is an indicator of pipe corrosion. The proposed system consists of a microprocessor, a specimen container and heater, a precision pump, relays and valves, LED optical sources, and photo detectors. It automatically collects water samples and carries out pretreatment for determining the concentration of each chemical, and then estimates the concentration of each ion using low-cost LED optical sources and detectors. Experimental results showed that the accuracy of the proposed system is sufficiently high for water quality diagnosis and management of cooling towers, demonstrating the possibility of the proposed system's wide usage in real environments.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.37-42
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• 2000

The boiler tubes and steam Pipes operating both at high temperature and pressure for a long period of time in a power plant are degraded by creep because of internal pressure. So, the remaining life of a component is evaluated by the creep rupture strength. Although the conventional method to evaluate the creep damage is widely used, it has some disadvantages such as requires large size specimen and long employed to evaluate the correlation between fracture toughness and evaluation time. Recently, new method so called "small lunch test' is used to evaluate degradation of creep. In this study, a conventional creep test and a small punch test are conducted using 2.25Cr-1Mo steel which is mainly used for the boiler tubes and steam pipes in power plant. The creep life, approximately 1,500 hrs, is determined by conventional method under a severe condition then specimens for a small Punch test are obtained after certain time intervals such as 1/4, 1/2 and 3/4 of final rupture time, respectively.

• 한국화재소방학회논문지
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• 제16권4호
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• pp.77-84
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• 2002

본 연구는 플라스틱재료 중 비드발포폴리스티렌폼, 압출발포폴리스티렌폼, 연질폴리우레탄폼, 경질폴리우레탄폼, 경질PVC파이프, 비닐장판, 폴리에틸렌폰(비난연), 폴리에틸렌폼(난연)를 대상으로 연소가스 독성평가를 위하여 NES 713 방법에 따라 발생되는 연소가스를 가스텍(GASTEC) 가스검지관을 이용하여 조사하였다. 연구결과 플라스틱재료의 연소시 발생되는 연소가스에 인간이 30분 동안 노출될 경우 사망에 이르는 독성지수 1 이상을 갖고 있었으며, 각 실험체의 독성지수 결과는 4.3∼179.2로 나타났으며 경질 PVC파이프가 179.2로 가장 높았다.

• Journal of Magnetics
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• 제21권1호
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• pp.57-60
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• 2016

Non Destructive Testing (NDT) methods that are capable of detecting the wall thinning and defects through insulation and cladding sheets are necessary. In this study we developed a Pulsed Eddy Current (PEC) system to detect wall thinning of ferro magnetic steel pipes covered with 95 mm thick fiber glass thermal insulator and shielded with aluminum plate of thickness 0.4 mm. In order to confirm the thickness change due to wall thinning, two different sensors, a hall sensor and a search coil sensor were used as a detecting element. In both the cases, the experimental data indicates a considerable change in the detected pulse corresponding to the change in sample thickness. The thickness of the tube was made to change such as 2.5 mm, 5 mm and 8 mm from the inner surface to simulate wall thinning. Fast Fourier Transform (FFT) was calculated using window approach and the results were summarized which shows a clear identification of thickness change in the test specimen by comparing the magnitude spectra.