Buried pipelines exist in large numbers in the urban environment — such as water conservancy pipelines, gas pipelines and heating pipelines — and are a core part of the normal operation of the whole city. Especially with the rapid development of the social economy, in urban construction, pipeline safety monitoring is receiving more and more attention from construction personnel and pipeline maintenance staff. Pipeline safety concerns people's livelihood and public property safety, and more and more pipeline users realize its necessity. Once a safety accident occurs in a pipeline, it will cause great asset losses and even casualties of heat-detecting fiber optic detection host personnel.
For the safety protection requirements of buried pipelines, traditional detection methods are mostly periodic personnel patrols, which inevitably lead to untimely safety monitoring or even omission of vibration sources. Secondly, in most scenarios, several pipelines converge, and multiple pipeline extension directions must be monitored at the same time. In addition, traditional detection methods identify vibration source modes through manual/artificial intelligence means, while in actual application fields the vibration source modes far exceed the preset items. In practice, end users only need to monitor the influence of the expected vibration sources on the pipeline to make corresponding decisions. For the above problems, a multi-channel long-distance pipeline network vibration early-warning monitoring method is urgently needed.
Distributed fiber optic sensors have various advantages such as low loss, small size, light weight, high sensitivity, strong corrosion resistance, anti-electromagnetic interference, no power supply requirement and low cost, filling the deficiencies of traditional electrical sensors in monitoring range and reliability indicators, and have developed rapidly in just a few decades. Using various fiber optic online monitoring systems, we have successfully completed the measurement of changing quantities such as temperature, concentration, pressure, vibration, displacement and refractive index. So far, various types of fiber optic sensors have been widely used in surrounding security, aerospace, pipeline monitoring, electric power engineering and biomedical engineering. Among them, the most significant is the distributed fiber optic sensing system.
The distributed fiber optic temperature/vibration instrument uses a narrow linewidth laser as the system light source, and uses the correlation fading effect between backward Rayleigh scattering signals (RBS) to complete distributed measurement of disturbance signals. When an external disturbance event acts on the cable, the core refractive index and cable length at the disturbance position change, causing changes in the frequency and phase of the RBS at that position. By analyzing the Rayleigh scattering curves before and after the disturbance event, detection of dynamic disturbance events can be achieved. This technology has high sensitivity and fast measurement response, and can achieve long-distance full-distributed blind-spot-free dynamic monitoring. Distributed fiber optic vibration monitoring systems have been widely used in tunnel and underground utility corridor security positioning, power cable monitoring, information pipeline online monitoring, railway security monitoring systems, gas pipeline safety monitoring, security around key equipment and other fields.
