• Journal of the Korean Institute of Gas
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• v.2 no.1
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• pp.40-46
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• 1998

Mathematical modeling on the corrosion of the steel casing and main pipe due to the protection current resulting from a cathodic protection system was carried out using boundary element method. The model is consisted of Laplace's equation with non-linear boundary conditions(Tafel equations) and the iterative technique to determine the miexed potential of the steel casing. The model is applied to the normal steel casing section as well as abnormal one with defects such as metal touch and insulation defects. From the modeling procedure, we can calculate the potential distributions and current density distributions of the system. The theoretical results of the qualitatiive corrosion aspect along the steel casing and main pipe agree well with the experimental results within the experimental conditions studied.

• Journal of the Korean Magnetics Society
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• v.21 no.1
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• pp.23-31
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• 2011

From among the NDT (nondestructive testing) methods, the MFL (magnetic flux leakage) method is specially suitable for testing pipelines because pipeline has high magnetic permeability. The system applied to MFL method is called the MFL PIG. The previous MFL PIG showed high performance in detecting the metal loss and corrosions. However, MFL PIG is highly unlikely to detect the cracks which occur by exterior-interior pressure difference in pipelines and the shape of crack is long and very narrow. In MFL PIG, the magnetic field is performed axially and there is no changes of cross-sectional area at cracks that the magnetic field passes through. Cracks occur frequently in the pipelines and the risk of the accident from the cracks is higher than that from the metal loss and corrosions. Therefore, the new PIG is needed to be researched and developed for detecting the cracks. The circumferential MFL (CMFL) PIG performs magnetic fields circumferentially and can maximize the magnetic flux leakage at the cracks. In this paper, CMFL PIG is designed and the distribution of the magnetic fields is analyzed by using 3 dimensional nonlinear finite element method (FEM). In CMFL PIG, cracks, standards of NACE, are detectable. To estimate the shape of crack, the leakage of magnetic fields for many kinds of cracks is analyzed and the method is developed by signal processing.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.5
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• pp.649-655
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• 2013

During welding, the dissimilar metal butt welds of nuclear piping are typically subjected to repair welding in order to eliminate defects that are found during post-weld inspection. It has been found that the repair weld can significantly increase the tensile residual stress in the weldment, and therefore, accurate estimation of the weld residual stress due to repair weld, especially for dissimilar metal welds using Ni-based alloy 82/182 in nuclear components, is of great importance in order to assess susceptibility to primary water stress corrosion cracking. In the present study, the stress distributions of dissimilar metal butt welds in nuclear reactor piping subjected to repair weld were investigated based on detailed nonlinear finite element analyses. Particular emphasis was placed on the variation of the stress distribution in the dissimilar metal butt weld according to the finite element welding analysis sequence for the repair welding process.

• Journal of the Korean Applied Science and Technology
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• v.38 no.1
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• pp.19-28
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• 2021

Corrosion is the degradation of metals by reaction with the environment. It is difficult to completely remove. Corrosion proceeds rapidly after the protective barrier is destroyed, and several reactions occur that alter the composition and properties of the metal surface and local environments, such as diffusion of metal cations into the matrix, the formation of oxides, and local pH changes. The study of corrosion of steel and iron is of theoretical and practical interest and is receiving considerable attention. Acid solutions, which are widely used in industrial pickling, acid descaling, cleaning and acidification of oil wells, require the use of corrosion inhibitors to suppress corrosion attacks on metallic materials. Physical removal of rust requires expensive special equipment, and chemical removal of it can cause corrosion or shorten the life of the metal. In this study, an eco-friendly rust cleaner was developed using cosmetics and food materials by applying the concept of perm reducing agent and chelate, and applied to remove rust from industrial and hot water pipes and various industrial devices. As a result, it was found that rust cleaners remove rust more effectively and safely compared to conventional treatment methods. At the same time, the rust removal efficiency was 1.75 to 2.5 times better for industrial piping and 1.56 to 2.2 times better for boiler hot water than conventional methods.

• Journal of the Korean Magnetics Society
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• v.22 no.2
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• pp.49-57
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• 2012

From among the NDT (Non-Destructive Testing) methods, the MFL (Magnetic Flux Leakage) PIG (Pipeline Inspection Gauge) is especially suitable for testing pipelines because the pipeline has high magnetic permeability. MFL PIG showed high performance in detecting the metal loss and corrosions. However, MFL PIG is difficult to detect the crack which occured by exterior-interior pressure difference in pipelines and the shape of crack is very long and narrow. Therefore, the new PIG is needed to be researched and developed for detecting the cracks. The CMFL (Circumferential MF) PIG performs magnetic fields circumferentially and can maximize the magnetic flux leakage at the cracks. In this paper, CMFL PIG is designed and the distribution of the magnetic fields is analyzed by using 3 dimensional nonlinear finite element method (FEM). By Simulating and Measuring the magnetic leakage field, it is possible to detect of axial cracks in the pipeline.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.1
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• pp.39-45
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• 2024

Seismic safety of expansion joints for piping systems has been underscored by water pipe ruptures and leaks resulting from the Gyeongju and Pohang earthquakes. Metal bellows in piping systems are applied to prevent damage from earthquakes and road subsidence in soft ground. Designed with a series of corrugated segments called convolutions, metal bellows exhibit flexibility to accommodate displacements. Several studies have examined variations in convolution shapes and layers based on the intended performance to be evaluated. Nonetheless, the research on the seismic performance of complex bellows having multiple corrugation heights is limited. In this study, monotonic loading tests, cyclic loading tests, and fatigue tests were conducted to evaluate the shear performance in seismic conditions, of metal bellows with variable convolution heights. Single- and triple-layer bellows were considered for the experimentation. The results reveal that triple-layer bellows exhibit larger maximum deformation and fatigue life than single-layer bellows. However, the high stiffness of triple-layer bellows in resisting internal pressure poses certain disadvantages. The convolutions are less flexible at lower displacements and experience leakage at a rate related to the variable height of the convolutions in certain conditions. At lower deformation rates, the fatigue life is rated higher as the number of layers increase. It converges to a similar fatigue life at higher deformation rates.

• Congress of the korean instutite of fire investigation
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• 2010.12a
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• pp.147-171
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• 2010

도장작업은 기계 기구, 금속, 자동차, 전기 전자, 선박, 가구제조업 등 각종 사업장에서 많이 취급되고 있는 작업으로서 취급물질이 대부분 합성수지 유기용매 등 인화성 또는 가연성 액체이거나 가연성 분체로서 용매 또는 분진으로 인한 폭발 화재의 위험성이 아주 높은 실정이다. 보통 4류 위험물의 유증기는 공기보다 무겁다 라는 생각으로 발생된 모든 유증기는 위험물 인근에 체류할 것이라는 생각을 하지만 상온에서 증발한 유증기 대부분은 인근의 대기와의 밀도차에 의해 주변으로 흩어지거나 연소하고 중량(重量)의 유증기만이 남아 화재조사에서 중요한 단서로 역할을 한다. 대부분분의 페인트 제품이 가열과 동시에 끊기 시작해서 비등점 측정이 어려웠고 발화점이 비슷한 다른 페인트에 비해 중량(重量)유증기 발생이 단시간 동안 낮은 온도에서 많이 발생한 것은 페인트의 안료가 유증기 발생을 방해해서 시너의 유증기 발생량과 동일한 양의 페인트 유증기 발생시간이 더 걸린 것 같다. 대부분의 유증기는 집진시설을 통해 A/C타워의 활성탄에 흡착되어 제거된다. 하지만 슬러지에 남아있는 희석제는 A/C타워를 정지하고 집진시설등의 배관에 있는 슬러지 청소 과정에서 주위 열원에 의해 많은 유증기를 발생하여 화재의 위험성이 존재함으로 작업자의 각별한 주의가 필요하다.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.8
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• pp.877-885
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• 2013

A seawater pipe of the engine room in the ships is being surrounded with severely corrosive environments caused by fast flowing of the seawater, containing aggressive chloride ion and high conductivity etc.. Therefore, the leakage of the seawater from its pipe have been often occurred due to its local corrosion by aggressive chloride ions. Subsequently, its leakage area is usually welded by AC shielded metal arc welding with various electrodes. In this study, when the sea water pipe is welded with several types of electrodes such as E4301, E4311, E4313 and E4316, a difference of the corrosion resistance on the welding metal zones was investigated using an electrochemical method, observing microstructure, measuring polarization behaviors and hardness. The weld metal zone welded with E4313 electrode exhibited the lowest value of hardness compared to other weld metal zones. In addition, its zone indicated also the best corrosion resistance than those of other weld metal zones. Furthermore, all of the weld metal zones revealed a relatively better corrosion resistance than those of the base metal zones. and also showed higher hardness than the base metal zones.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.496-496
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• 2023

상수도관의 노후화 등으로 발생하는 누수는 안정적인 급수운영을 저해하고 경제적 손실을 발생시킬 뿐만 아니라 지반 침하 등 2차 피해가 발생할 수 있다. 상수도관 누수는 배관 내·외부 부식으로 발생하는 핀홀(Pin Hole)로 인한 관통누수, 강관 용접 시 발생하는 시공불량, 볼트 및 고무패킹 등 부자재의 노후화, 굴착 등 작업에서 발생하는 물리적 충격 등 여러 원인으로 발생할 수 있다. 상수도관에서 누수가 발생할 경우, 관 내부수가 관 밖으로 유출되어 발생하는 파열음, 유출수와 지반과의 마찰로 인한 진동 및 소음 등이 발생할 수 있다. 청음식, 상관식 누수탐사와 같은 기존 누수탐사 방식은 전문가의 경험에 대한 의존도가 매우 높으며, 기존 장비의 특성상 비금속관 및 대구경관 등 특정 환경에서는 적용이 어려우며, 효율적인 탐사가 쉽지 않은 실정이다. 이에 대한 해결책으로 본 논문에서는 상수도 누수가 의심되는 구간을 대상으로 실시간 누수음 데이터 수집 및 인공지능(Artificial Intelligence) 분석을 실시하여 기존 조사방법보다 효율적이고 신뢰성 있는 누수탐사를 수행한 사례를 분석하고자 한다.

• Journal of the Korean Institute of Gas
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• v.22 no.6
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• pp.76-89
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• 2018

The distribution of the combined heat and power system is active as a solution to the instability of energy supply and environmental pollution caused by continuous industrial development. In Korea, the safety standards for combined heat and power system using a gas engine are insufficient therefore the study on this is needed. In this study, the safety performance and structural/material assessment items of domestic and international standards applied to the combined heat and power system were analyzed to carry out a standardization study on safety performance applicable to 20 kW gas engine combined heat and power system. In addition, the safety performance assessment (plan) of the gas engine combined heat and power system was derived by performing risk analysis and risk assessment using HAZOP. Assessment items include engine ignition systems related to safety performance, piping tight performance, watering and temperature rise performance, combustion performance, electrical efficiency, thermal efficiency, overall efficiency and humidity performance. Gas and water pipes, gas control and shut-off valves, durability, heat resistance, and cold resistance of metal or non-metallic materials related to the structure and materials of the gas engine combined heat and power systems.