Papers by Author: Jae Young Nam

Abstract: Even though an excavation is not under the direct control of the utility operators, it is the main cause of third-party damage on the underground natural gas pipelines. Since the damage due to third-party excavation may lead to horrible consequences, preventative techniques that can reduce the third-party damage are needed. The purpose of this paper is to introduce an on-line monitoring system using accelerometer to detect a propagating acoustic pressure pulse that is produced from the third-party damage. Also, in order to verify this system, the corresponding field tests were performed considering many third-party damage sources(breaker, hammer drilling, etc.) and signal transmission ratio of each source. From the tests, signals developed by the third-party damage sources were successfully detected with the digital filter, which can distinguish external noises at the distance of 13km. Therefore, it is expected that the system can be used as a useful tool for the third-party damage monitoring of underground natural gas pipelines

Abstract: The objective of this paper is to develop a fiber-optic acoustic emission(AE) sensor applicable to on-line monitoring systems which is suitable for long-distance signal transmission. An AE sensor was developed by use of a fiber-optic cantilever and an extrinsic Fabry-Perot interferometer(EFPI). The efficiency of signal processing was improved by driving the high frequency AE signals into the low frequency ones. In order to verify the developed sensor, the tensile and the pencil lead fracture(PLF) tests were performed including the experiment showing the Kaiser effect. From tests, AE signals were successfully detected in the elastic-plastic deformation range, especially higher signals at the crack propagation. The developed sensor is expected to be used for an on-line monitoring of crack propagation in mechanical systems.