• 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.

• Korean Journal of Materials Research
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• v.10 no.2
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• pp.138-143
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• 2000

화력발전설비의 주요 손상 요인 중의 하나인 응력부식 균열 성장에 대한 확률론적 잔존 수명평가에 대하여 연구하였으며, 손상해석 및 수명평가에 확률해석 기법을 도입한 확률론적 수명평가 프로그램을 개발하였다. 확률론적 수명평가는 재료물성치, 형상, 하중조건, 운전조건 등과 같은 불확실성과 변동 가능성을 고려하여 해석을 수행하며, 일정 시간 운전후 구조물의 손상이 일어날 확률을 예측하는 것이다. 응력부식 균열 성장에 대한 확률론적 잔존 수명평가 연구를 통하여 확률론적 수명평가 기술의 기반을 구축하였으며, 다른 손상기구에 대한 확률론적 수명평가를 수행하여 발전설비에 발생하는 모든 손상에 대하여 확률론적 수명평가가 가능하도록 확대할 계획이다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.6
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• pp.129-139
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• 2008

Due to uncertainty of numerous variables in durability model, a probalistic approach is increasing. Monte Carlo simulation (Level III method) is an easily accessible method, but requires a lot of repeated operations. This paper evaluated the effectiveness of First Order Second Moment method (Level II method), which is more convenient and time saving method than MCS, to predict the corrosion initiation in harbor concrete structure. Mean Value First Order Second Moment method (MV FOSM) and Advanced First Order Second Moment method (AFOSM) are applied to the error function solution of Fick's second law modeling chloride diffusion. Reliability index and failure probability based on MV FOSM and AFOSM are compared with the results by MCS. The comparison showed that AFOSM and MCS predict the similar reliability index and MV FOSM underestimates the probability of corrosion initiation by chloride attack. Also, the sensitivity of variables in durability model to corrosion initiation probability was evaluated on the basis of AFOSM. The results showed that AFOSM is a simple and efficient method to estimate the probability of corrosion initiation in harbor structures.

• Journal of the Korea Concrete Institute
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• v.22 no.4
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• pp.595-603
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• 2010

Monte-Carlo simulation technique is often used in order to predict service life of concrete structure subjected to chloride penetration in marine environment based on probability theory. Monte-Carlo simulation method, however, the method gives different results every time that the simulation is run. On the other hand, moment method, which is frequently used in reliability analysis, needs negligible computational cost compared with simulation technique and gives a constant result for the same problem. Thus, in this study, moment method was applied to the calculation of corrosion-initiation probability. For this purpose, computer programs to calculate failure probabilities are developed using first-order second moment (FOSM) and second-order second moment (SOSM) methods, respectively. From the analysis examples with the developed programs, SOSM was found to give a more accurate result than FOSM does. The sensitivity analysis has shown that the factor affecting the corrosion-initiation probability the most was the cover depth, and the corrosion-initiation probability was influenced more by its coefficient of variation than its mean value.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.4
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• pp.2401-2406
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• 2015

Pipelines are used by large heavy industries to deliver various types of fluids. Since this is important to maintain the performance of large systems, it is necessary to accurately predict remaining life of the corroded pipeline. However, predicting the remaining life is difficult due to uncertainties in the associated variables, such as geometries, material properties, corrosion rate, etc. In this paper, a statistical method for predicting corrosion remaining life is proposed using Bayesian inference. To accomplish this, pipeline failure probability was calculated using prior information about pipeline failure pressure according to elapsed time, and the given experimental data based on Bayes' rule. The corrosion remaining life was calculated as the elapsed time with 10 % failure probability. Using 10 and 50 samples generated from random variables affecting the corrosion of the pipe, the pipeline failure probability was estimated, after which the estimated remaining useful life was compared with the assumed true remaining useful life.

• Journal of the Korean Institute of Intelligent Systems
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• v.24 no.6
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• pp.651-656
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• 2014

Corrosion has a significant influence upon the reliability assessment and the maintenance planning of gas pipeline. Corrosion defects occurred on the underground pipeline can be obtained by conducting periodic in-line inspection (ILI). However, little study has been done for practical use of ILI data. This paper deals with remaining lifetime prediction of the gas pipeline in the presence of corrosion defects. Because a pipeline parameter includes uncertainty in its operation, a probabilistic approach is adopted in this paper. A pipeline fails when its operating pressure is larger than the pipe failure pressure. In order to estimate the failure probability, this paper uses First Order Reliability Method (FORM) which is popular in the field of structural engineering. A well-known Battelle code is chosen as the computational model for the pipe failure pressure. This paper develops a Matlab GUI for illustrating failure probability predictions Our result indicates that clustering of corrosion defects is helpful for improving a prediction accuracy and preventing an unnecessary maintenance.

• Journal of Navigation and Port Research
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• v.33 no.3
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• pp.235-240
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• 2009

Simulation method based on probability was developed to evaluate the durability of reinforced concrete structures about chloride attack. The effects of the probability parameters(surface chloride ion concentration, initial combined chloride ion concentration, the depth of cover thickness of concrete, and the chloride ion diffusion coefficient), probability distribution function and it's variation were calculated using the Monte Carlo method and Fick's 2nd law. From the durability design method proposed in this study, the following results were obtained. 1) The effects of the distance from the coast and the chloride ion diffusion coefficient to the corrosion probability were quite high. 2) The effect of the variation of each parameters was relatively low.

• Journal of the Society of Naval Architects of Korea
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• v.35 no.2
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• pp.83-93
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• 1998

The twin aims of the present study are to develop a PC program for the statistical analysis of the measured cohesion data and to suggest a probabilistic corrosion rate estimation model for longitudinal members of tanker structures. A data analysis for the corrosion rate statistics(i.e., mean, standard deviation) as a function of the corrosion parameters is established for various structural member categories/locations of interest. Development of the computer program is focused on possible operation together with future addition of more corrosion data as they become available. To investigate the influence of the corrosion protection scheme a series of the corrosion analysis varying the life of coating are carried out and several different corrosion models as a function of time are suggested depending on the coating life.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.873-876
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• 2002

This paper presents the effect of internal corrosion, external corrosion, material properties, operation condition, earthquake, traffic load and design thickness in pipeline on the failure prediction using a failure probability model. A nonlinear corrosion is used to represent the loss of pipe wall thickness with time. The effects of environmental, operational, and design random variables such as a pipe diameter, earthquake, fluid pressure, a corrosion rate, a material yield stress and a pipe thickness on the failure probability are systematically investigated using a failure probability model for the corrosion pipeline.

• Proceedings of the Korean Reliability Society Conference
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• 2002.06a
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• pp.403-410
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• 2002

This paper presents the effect of internal corrosion, external corrosion, material properties, operation condition, earthquake, traffic load and design thickness in pipeline on the failure prediction using a failure probability model. A nonlinear corrosion is used to represent the loss of pipe wall thickness with time. The effects of environmental, operational, and design random variables such as a pipe diameter, earthquake, fluid pressure, a corrosion rate, a material yield stress and a pipe thickness on the failure probability are systematically investigated using a failure probability model for the corrosion pipeline.