Pipe segment with applied optical fiber
Source: BAM
Pipelines belong to the key elements of world’s material and energy supply infrastructure. They can be found in numerous applications ranging from very local industrial piping systems to global pipelines traversing continents. Degradation and damaging of the pipelines represent a critical concern with regard to the system operation cost and safety. Nevertheless, implementation of a robust and reliable leak detection system remains one of the core open issues of pipeline condition monitoring. In the recent years, distributed fiber-optic sensors (DFOS) have become increasingly attractive for pipeline monitoring tasks. The key asset of DFOS for pipeline monitoring is their ability to provide spatially-distributed measurement of local temperature or strain along the fiber up to hundreds of kilometers. Using DFOS as external pipeline monitoring systems is, therefore, very attractive, since a single interrogation unit can provide spatially- and temporally-continuous monitoring of extended pipeline lengths.
Fiber-optic distributed acoustic sensing (DAS) belongs to the most recent developments in the field of fiber optic sensors. DAS systems allow distributed measurement of highly-dynamic strain (vibration) signals up to the kHz range along the sensing fiber. The high potential of DAS has been recognized in the pipeline industry and the systems are being considered for various pipeline monitoring tasks including detection of third-party intrusion, maintenance pig tracking, flow monitoring and leak detection.
In BAM’s project AGIFAMOR, new technical approaches to extend the application field of DAS in pipeline condition monitoring were investigated. While larger leaks might be readily detectable by available monitoring systems, detection of small leaks (<1% of nominal volume flow) still poses a technological challenge. In the presented paper, potential of DAS for detection of small gas pipeline leaks was assessed. Fiber application approach relying on direct fiber wrapping around the pipe was used to increase system sensitivity for weak vibration signals. The results revealed that, using direct fiber application approach, DAS system was able to measure leak induced pipeline natural vibrations with acceleration values down to single μg. The approach was shown to be capable of detection and localization of gas pipeline leaks with leak rates well below 1% of the pipeline flow volume and might be of interest for short- to medium-length gas pipeline systems.
Schematic illustration of pipeline leak experiment highlighting monitored pipe zones and leak position (a). Detail of a pipe segment with applied optical fiber (b). Leak-induced vibrations detected by the DAS system (c).
Source: BAM, Division Fibre Optic Sensors
Detection of leak-induced pipeline vibrations using fiber-optic distributed acoustic sensing
Pavol Stajanca, Sebastian Chruscicki, Tobias Homann, Stefan Seifert, Dirk Schmidt, Abdel Karim Habib
Sensors. 2018 Sept; 18(9): 2841.
BAM Department Non-destructive testing