Recent news headline came to remind the dangers associated with gas transportation. Due to its asset size, pipelines are often the facilities the more difficult to protect in cases of an explosive gas leakage.
The objectives of the Fibre Optic Leak Detection (FOLD) project were to assess the capability of fibre optic sensing to detect a small gaseous leakage on a buried pipe, to give guidelines regarding the best deployment positions of the fibre along the pipe, to compare the performance of several methodologies and to assess the impact of the fibre optic length on the detection performance.
The strength of this project is to propose a representative test bench to help the industry to mature the detection methodologies: Gaseous leakages were performed from the external surface of a steel pipe with an internal diameter of 390 mm and a length of 30 m. These leakages were of methane, hydrogen or nitrogen and took place through different orifices (from 1 to 7 mm) and at varying released pressure (between 20 and 100 bar). This pipe and the optical cable were buried in a granular type soil compacted to a known level. Several types of interrogator (DTS - Distributed Temperature Sensor) from different suppliers were tested during the FOLD project.
The paper will present the experimental bench and the main results. Based on these results, it will be possible to conclude on the overall performance of the DTS technologies to detect a small gaseous leakage on a buried pipe, to give guidelines to optimise several parameters for improved detection performances: fibre optic position or deployment architecture along the pipe (directly buried or into a polyethylene tube), detection range assessment, equipment choice... Five different instrument suppliers took part in the initiative and delivered comprehensive data.
To make sure that detection will occur whatever the gaseous leakage flow rate on a buried pipe, it could be interesting to use both internal detection means (pressure or flowrate transducers placed at both ends) and external ones. Among the technologies available for external sensing, the optical fibre seems to be a promising candidate. This paper will present brand new data, collected in very controlled conditions, to assess the performance of such technology.
We will present the proportion of instruments capable of detecting leaks and the possible configurations presently recommended to pipeline designs in project phase.