# Application of FBG Based Sensor in Pipeline Safety Monitoring
## 1 Introduction  
Pipeline is an important means to transport oil and gas through long distance [1; 2]. However, due to the effect of the inner fluids and the harsh environmental conditions, these pipelines are particularly prone to be corroded [3]. Once the pipes are subjected to corrosion, it may probably cause leakage or breakages [4]. Thus, a number of pipeline detection technologies have been developed to ensure pipeline safety. Pole climbing robots that perform periodical inspections with non-destructive testing probes are widely used for assessing the progression of material degradation and detecting welding defects [5]. In order to inspect 80-100 mm pipelines in an indoor pipeline environment, [PERSON] et al. design a motion planning algorithm of a caterpillar-based pipeline robot [6]. An ultrasonic inspection robot equipped with an electromagnetic acoustic transducer was developed for inspection of a steel pipeline in service [7]. However, inspection techniques cannot provide real-time monitoring of the pipelines. Therefore, leakage or pipeline defects may not be detected in time and may cause much larger economic loss and environmental pollution [8]. Consequently, it is more significant to perform permanent and real-time integrity monitoring. Generally, oil and gas pipelines are buried underground and extend hundreds of kilometers. These working conditions mean that many traditional structural monitoring technologies are not applicable for pipeline structure. A fiber optic sensor, with its superior immunity to electromagnetic interference, long distance transmission, good embeddability and reliability [9], is an ideal approach for pipeline safety monitoring. Optical fiber based innovative distributed temperature monitoring techniques haveproven to be an efficient way to detect and localize leakages along pipelines [10]. Since leakages from the pipeline lead to regional temperature anomalies in the vicinity of the pipeline, Brillouin-based distributed temperature monitoring systems have been developed and equipped with a 55 km pipeline for the leakage localization [11]. [PERSON] et al. developed a Brillouin-scattering-based fiber optic distributed strain sensor and applied it to measure the longitudinal and hoop strain in a steel pipe model with wall thinning defects. According to the strain distribution, the locations of structural defects were found [12]. To detect the internal corrosion of pipeline, a novel distributed sensor, employing metal coated polymer-clad fiber optic cables, was studied and developed theoretically by [PERSON] et al. [13]. However, the widely applied distributed optic fiber sensor has its own advantages and limitations. For example, optical time-domain reflectometer (OTDR) based technique has distributed measurement over a long distance due to its larger dynamic range, while its spatial resolution is usually on the order of meters to tens of meters [14], and its measurement accuracy is not high. Generally, the distributed sensors are more suitable for localizing damage or leakage instead of measuring the degree of damage or corrosion. An FBG sensor, with the special advantages of high measurement accuracy [15], is also suitable for pipeline monitoring [16]. To monitor pipeline leakage, [PERSON] et al. applied FBG sensors to measure hoop strain at regular points along the pipeline [17]. [PERSON] et al. presented FBG accelerometers for detecting fuel theft from pipelines [18]. [PERSON] et al. applied the FBG sensors in the monitoring of the dynamic response of a submarine pipeline model under a variety of dynamic loading conditions [19]. [PERSON] et al. proposed a method to monitor the damage of pipeline using FBG sensors to measure guided wave responses [20]. In order to detect and localize pipeline leakage, [PERSON] et al. utilized an FBG strain sensor in the natural gas pipeline model to detect a negative pressure wave (NPW) caused by leakage [21]. It can be concluded that the current study based on FBG sensors mainly focus on the pipeline damage detection and leakage monitoring.