Distributed fiber optic temperature sensing provides a robust and cost-effective tool that allows monitoring over several kilometers with the so-called Raman scattering; enabling high spatial resolution of 1 meter and a high measurement speed down to 10 seconds. Distributed sensors offer the unique ability to permanently measure temperature along the whole pipeline length. This capability allows the measurement of thousands of points using a single transducer. Distributed temperature sensing enables automatic leaks detection by identifying the characteristic temperature change associated with such leaks.
Comprehensive testing of the distributed fiber optic temperature sensing capabilities has been conducted at Ineris, France since 2013. Experiments consisted in simulating vertical and horizontal leaks of pressurized liquid ammonia. Leak rates of down to 50 grams liquid ammonia per second were detected in 20 seconds anywhere along the pipeline.
This detection principle extends to most of the pressurized liquefied gas pipelines; a given fluid requires specific sensing cable layout and detection algorithm settings. Average leak rates detected with this method ranges from a few grams to a few kilograms per second. After completing a learning period, the system is interfaced to the plant control system, enabling automatic activation of shut-down valve in case of leakage.
Distributed fiber optic temperature sensing system enables to meet demanding requirements of hazard and operability studies; such systems have been operated since more than 10 years as safety barriers in industrial facilities. Particularly distributed fiber optic temperature sensing is the preferred technology to be laid over long and insulated outdoor or buried lines of a few hundred meters to kilometers, with active detection in steady state and transient phases.