Leak monitoring is used not only for pipelines and tube systems transporting gas and liquids, but also at storage locations for tank and reservoir monitoring. In addition to protecting against the loss of transported materials, distributed fiber-optic sensing is used to reduce environmental hazards and spill-risks for example explosion-protection with LNG tanks and pipelines.
Distributed fiber-optic leak detection systems are found not only in the oil & gas industry, but also in monitoring district heating and water supply- and treatment facilities. Depending on the exact application, measurements are based on three different principles.
For systems with an adequate temperature difference between the transported material and the surrounding environment, or those with a high pressure differential where the Joules-Thompson law can be applied, leaks are effectively detected and localized with a temperature sensing cable.
For applications where this does not work, but for which there is adequate pressure in the transportation system, leaks are detected based on sound and vibration utilizing acoustic sensing cables.
Strain sensitive cables can also be used to detect leaks in specific cases where the transported liquid changes the strain in the cable or surrounding material. In cases where external mounting of the sensing cable on the transport system is not possible, a strain cable can be floated in the pipe and fixed the inner wall to detect leaks through pressure drops.
In order to detect the tiniest leak, acoustic and vibration sensitive sensor cables are installed directly on the piping. Acoustic sensing enables protection against “tapping” and dangers from construction equipment. For leak detection through temperature sensing, cables can be installed at a specific stand-off from the pipeline. This is an advantage for pipelines in use.
Tank monitoring is often used for explosive goods storage (e.g. LNG). Leaks are detected with acoustic and vibration monitoring – the corresponding pressure difference is used for measurement, as well as also humidity differences. In contrast to reservoir monitoring, heatable cables can not be used because of the risk of eplosion.